Sonderheft 283

Special Issue

st
Proceedings of the 1 Sino-German Workshop
on Aspects of Sulfur Nutrition of Plants
23 - 27 May 2004 in Shenyang, China

edited by
Luit J. De Kok and Ewald Schnug
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2005

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Table of contents

Aspects of sulfur nutrition of plants; evaluation of China's current, future and available resources
to correct plant nutrient sulfur deficiencies – report of the first Sino-German Sulfur Workshop
Ewald Schnug, Lanzhu Ji and Jianming Zhou 1
Pathways of plant sulfur uptake and metabolism – an overview
Luit J. De Kok, Ana Castro, Mark Durenkamp, Aleksandra Koralewska, Freek S. Posthumus,
C. Elisabeth E. Stuiver, Liping Yang and Ineke Stulen 5
Advances in sulfur fertilizer requirement and research for Chinese agriculture: Summary of field
trial data from TSI's China project from 1997 to 2003
Ming Xian Fan and Donald L. Messick 15
Sulfur and baking-quality of bread making wheat
Ingo Hagel 23
Relationship between sulfur deficiency in oilseed rape (Brassica napus L.) and its attractiveness
for honeybees
Silvia Haneklaus, Anja Brauer, Elke Bloem and Ewald Schnug 37
Influence of drought and flooding on sulfur nutrition of deciduous trees at the whole plant level
Cornelia Herschbach 45
Chemical behavior of soil sulfur in the rhizospere and its ecological significance
Zhengyi Hu, Silvia Haneklaus, Zhihong Cao and Ewald Schnug 53
Measuring fluxes of reduced sulfur gases
Beate Huber and Werner Haunold 61
The global sulfur cycle and China's contribution to atmospheric sulfur loads
Jürgen Kesselmeier 67
Sulfur-rich proteins and their agrobiotechnological potential for resistance to plant pathogens
Cordula Kruse, Ricarda Jost, Helke Hillebrand and Rüdiger Hell 73
Crop response to sulfur fertilizers and soil sulfur status in some provinces of China
Shutian Li, Bao Lin and Wei Zhou 81
The sulfur cycle in the agro-ecosystems in southern China
Chongqun Liu and Xiaohui Fan 85
An Agricultural Sulfur Information System for China
Youhua Ma, Hongxiang Hu, Qiang Wang, Xiaoli Liu, Yanping Zhao, Hongxia Liang and Zhaoming Zhu 91
Global sulfur requirement and sulfur fertilizers
Donald L. Messick, Ming Xian Fan and C. de Brey 97
Sulfur in organic farming
Hans Marten Paulsen 105
Sulfur nutrition and its significance for crop resistance – a case study from Scotland
Ioana Salac, Silvia Haneklaus, Elke Bloem, Elaine J. Booth, Karene G. Sutherland, Kerr C. Walker and
Ewald Schnug 111
Metabolic background of H2S release from plants
Ahlert Schmidt 121
The role of sulfur in sustainable agriculture
Ewald Schnug and Silvia Haneklaus 131
Metabolism and catabolism of glucosinolates
Dirk Selmar 137
Regulation of glutathione (GSH) synthesis in plants: Novel insight from Arabidopsis
Andreas Wachter and Thomas Rausch 149
Ecological significance of H2S emissions by plants – a literature review
Pia Wickenhäuser, Elke Bloem, Silvia Haneklaus and Ewald Schnug 157
Sulfur status of Chinese soils and response of Chinese cabbage to sulfur fertilization in the Beijing
area
Liping Yang, Ineke Stulen and Luit J. De Kok 163
The role of sulfur fertilizers in balanced fertlization
Yiming Zhou, Defang Wang, Jinghua Zhu, Qingshan Liu and Ming Xian Fan 171
Landbauforschung Völkenrode, Special Issue 283, 2005 1

Aspects of sulfur nutrition of plants; evaluation of China’s current, future and available
resources to correct plant nutrient sulfur deficiencies - report of the first Sino-German
Sulfur Workshop

Ewald Schnug1, Lanzhu Ji2 and Jianming Zhou3

Abstract 1 pathogenesis related (PR) proteins of the thionin-

type, and H2S released from Cys. As activated sul-
Sulfur is an essential plant nutrient that must be sup- fate (APS) and Cys are also basic components of
plemented through fertilizer application when primary metabolism and structural compounds (sul-
quantities in the soil are insufficient or when other folipids, proteins), plants had to develop strategies
natural inputs are not available. Besides just being to reconcile S availability and S demand during
involved in producing yield, sulfur-containing com- plant development with the requirements of different
pounds are responsible for numerous aspects of crop stress responses. A major goal of the recent research
quality and the natural resistance of plants. As a carried out by a DFG research group in Germany is
result of increasing crop yields and removal, grow- to develop a model for the coordination of S assimi-
ing use of sulfur-free fertilizers and increased atten- lation with the synthesis of GSH, glucosinolates, S-
tion to air quality standards leading to continuing rich defense proteins and H2S, using an integrated
reductions in atmospheric sulfur contributions, the approach based on the tools of molecular physiology
need for the application of plant nutrient sulfur is and cell biology. The comparative approach with
accelerating in China. In order to stimulate network- plants of different physiotype (Arabidopsis thaliana,
ing between plant sulfur-related research initiatives Brassica napus/juncea, Populus tremula/alba) will
in China and Germany, the first Sino-German allow to address general and species-specific
Workshop on "Aspects of sulfur nutrition of plants; mechanisms, in particular the role of a luxuriant
evaluation of China’s current, future and available secondary metabolism (glucosinolates) and the im-
resources to correct plant nutrient sulfur deficien- pact of different growth patterns (herbaceous versus
cies", was held on May 24-29, 2004 in the Institute non-herbaceous). The use of transgenic plants with
of Applied Ecology, Shenyang, China. During the changed expression of single genes will allow to
workshop the China’s current, future, and available assess their contribution to the overall stress re-
resources to correct plant nutrient sulfur deficiencies sponse. The integration of field experiments will
were evaluated. help to evaluate the relevance of S nutrition-
mediated defense reactions for resistance under field
Keywords: Crop yield, crop quality, food quality, conditions.
Sulfur deficiency, sulfur fertilization, sulfur metabo- China accounts for one-fifth of the world popula-
lism, sulfur nutrition tion, but has only 7% of the world’s agricultural
land mass. Thus, the country faces a significant
challenge to meet food demands for its 1.3 billion
Introduction inhabitants. China’s economic and agricultural
policies have changed dramatically over the last 20
Sulfur is one of the mineral elements essential for years. Seeking to expand its agricultural sector,
plant life. Starting from the amino acid cysteine China has increased importation of fertilizers as well
(Cys), higher plants synthesize a complex spectrum as increased domestic production. Chinese con-
of S compounds with diverse physiological func- sumption of the three major nutrients nitrogen (N),
tions. Among these are the tripeptide glutathione phosphorus (P), and potassium (K) has expanded
(GSH), which is central to the response against significantly at annual growth rates averaging 4, 7,
abiotic stressors (reactive oxygen species, heavy and 10 percent, respectively. Concurrently, agricul-
metals). In addition, there are several sulfur- tural production has made considerable gains. As
containing pathogen-directed defense compounds: N, P, and K demands have been increasingly met,
Glucosinolates as secondary S metabolites, rich deficiencies of other nutrients have arisen and sulfur
has become of increasing interest since it is typically
1
required in quantities ranking fourth behind N, P,
Institute of Plant Nutrition and Soil Science, Federal and K.
Agricultural Research Center (FAL), Braunschweig, This paper reports on the objectives, presentations
Germany
2 and topics of the first Sino-German Workshop on
Institute of Applied Ecology, Chinese Academy of
Science, Shenyang, China "Aspects of sulfur nutrition of plants; evaluation of
3
Institute of Soil Science, Chinese Academy of Science, China’s current, future and available resources to
Nanjing, China correct plant nutrient sulfur deficiencies", May 24-
2 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

29, 2004, Institute of Applied Ecology, Shenyang, Speakers from the German DFG-Research Group
China. 383 (Sulfur metabolism in plants):
Prof. Dr. Ruediger Hell, University, Heidelberg, E-
mail: r.hell@bot.uni-hd.de
Objectives of the workshop Dr. Cornelia Herschbach, University, Freiburg,
E-mail: cornelia.herschbach@ctp.uni-freiburg.de
The goals of this workshop were: Prof. Dr. Thomas Rausch: University, Heidelberg,
x To discuss fundamental, agronomic and environ- E-mail: trausch@bot.uni-hd.de
mental aspects of sulfur in higher plants, to promote Dipl.-Chem. Joana Salac, FAL-PB, Braunschweig,
and better coordinate sulfur-related research in E-mail: ioana.salac@fal.de
plants. Prof. Dr. Ahlert Schmidt, University, Hannover,
x To stimulate networking between plant sulfur- E-mail: ahlert.Schmidt@botanik.uni-hannover.de
related research initiatives in China and Germany. Dipl.-Ing. Agr. Pia Wickenhäuser, FAL-PB, Braun-
x To provide optimal training of young scientists schweig, E-mail: pia.wickenhaeuser@fal.de
(PhD students, post docs, junior group leaders) in a
complex research field with state-of-the-art ap- Foreign speakers
proaches in physiology, biochemistry and molecular
biology of plants. Dr. Ming Xian Fan, TSI, Washington, E-mail: ag-
markt@sulphurinstitute.org
x To evaluate China’s current, future, and available
Dr. Luit J. De Kok, Chairman of the European
resources to correct plant nutrient sulfur deficiencies
COST Action 829 “Fundamental, agronomical
through the next 10 years.
and ecological aspects of sulfur in plants”, Univer-
sity, Groningen, E-mail: l.j.de.kok@rug.nl
Mr. Donald Messick, TSI, Washington, E-mail:
List of speakers and participants (within groups
DMessick@sulphurinstitute.org
alphabetical order):
Speakers from China:
The delegates came from German universities in
Braunschweig, Frankfurt, Hanover, Hamburg, Former holders of German research fellowships
Mainz and Groningen, The Netherlands. Scientists granted by the Max Planck Society
from the Max Plank Institute and the German Agri- Dr. Fan Xiaohui, ISSAS, Nanjing, E-mail:
cultural Research Centre participated. The Chinese xhfan@issas.ac.ch
delegates came from the Institute of Applied Ecol- Dr. Hu Zhengyi, ISSAS, Nanjng, E-mail:
ogy, CAS, the Institute of Soil Sciences, CAS, the zhyhu@ns.issas.ac.ch
Chinese Academy of Agricultural Sciences, Jiangxi
Academy of Agricultural Sciences, Tianjin Academy Former holder of a DAAD fellowship:
of Agricultural Sciences and Anhui Agricultural Dr. Ma Youhua, University, Anhui, E-mail: mayou-
University. Scientists from The Sulfur Institute, hua@mail.hf.ah.cn
Washington, DC, also participated in the workshop.
Former holder of several fellowships granted by
Speakers from Germany: NFSC and the bilateral cooperation programmes
between MoAs:
Dipl.-Geoecol. Anja Brauer, FAL-PB, Braun-
schweig, E-mail: anja.brauer@fal.de Dr. Wang Shiping, IB-CAS, Beijing, E-mail: ship-
Dr. Ingo Hagel, FAL-PB Braunschweig, E-mail: ing.wang@95777.com
ingo.hagel@t-online.de
Dr. Beate Huber, GSF, Munich, E-mail: beate- Other speakers from China:
huber@aol.com Prof. Lin Bao, ISSAS, Nanjing, E-mail:
Prof. Dr. Juergen Kesselmeier, MPI & University, blin@caas.ac.cn
Mainz, E-mail: jks@mpch-mainz.mpg.de Prof. Liu Chongqun, ISSAS, Nanjing, E-mail:
Dr. Hans-Marten Paulsen, FAL-OEL, Trenthorst, E- qzfan@issas.ac.cn
mail: hans.paulsen@fal.de Prof. Luo Qixiang, Academy of Agricultural Sci-
Prof. Dr. Dr. Ewald Schnug, FAL-PB, Braun- ences, Jiangxi,
schweig, E-mail: ewald.schnug@fal.de Dr. Zhou Yiming, Soil and Fertilizer Institute, Tian-
Prof. Dr. Dirk Selmar, University, Braunschweig, E- jing, E-mail: ymzhou@public.tpt.tj.cn
mail: d.selmar@tu-bs.de
Landbauforschung Völkenrode, Special Issue 283, 2005 3

Synopsis of the scientific contributions key role as an important redox-system and precursor
for many other S containing metabolites.
Kesselmeier presented the auditorium a view to Glucosinolates are a special metabolic pathway
the global sulfur cycle and China's contribution to for S in a number of plant families like for instance
atmospheric sulfur loads. On Wednesday, March 20, cruciferous crops. Selmar explained in his lecture
2002 “Peoples Daily” published a headline “China the metabolism and catabolism of glucosinolates.
Fighting Acid Rain, Sulfur Dioxide”. The article The significance of glucosinolates for the subject of
revealed that China has decreased the release of the workshop have to be seen in their role as an ac-
sulfur dioxide by 1.86 million tons over the past two tive principle in chemical plant defense, which
years as a result of its efforts to combat acid rain and stimulation either by altered genetics or environ-
sulfur dioxide control. In 1998, the State Council ment bears challenges for improving plant health
designated 11.4 percent of China's land, covering without pesticides.
175 cities in 27 provinces, autonomous regions and “Sulfur-rich Proteins” are also involved in stress
municipalities as acid rain and sulfur dioxide control resistance and supposed to be an important part of
regions. The sulfur dioxide release in these regions SIR. Hell demonstrated that thionins and defensins
accounted for 60 percent of China's total. Over the are ubiquitous elements of innate defense in plants,
past two years, the number of Chinese cities that which are encoded by large gene families and are
have met the national standards has increased from differentially expressed. The inducibility of at least
81 to 98, and the amount of sulfur dioxide has de- some Thi and Def genes by pathogens depends on
creased from 14.08 million tons to 11.14 million optimal sulfur supply. Membrane damage by sulfur-
tons. Beijing and Shanghai have taken the lead to set rich proteins can be exploited to enhance resistance
up areas without coal burning. By the end of last to pathogenic fungi using transgenic approaches and
year, the output of high sulfur coal decreased by 32 possibly also breeding.
million tons. Some 250 thermoelectric generating Not only agricultural crop plants but also forests
sets were shut down. China plans to shut down an- may suffer from S deficiency. Herschbach ex-
other 4,000 high sulfur coalmines, 135 thermoelec- plained their view to the sulfur nutrition of decidu-
tric generating sets and 1,300 small-sized cement ous trees at the whole plant level during stress.
and glass production lines this year. The annual A new field for extended plant S research are as-
Chinese emissions projected for 2020 are 40-45 Tg pects of so-called sulfur-induced resistance (SIR),
yr-1 S by 2020. However, there are already trends which were brought to the attention of the audito-
towards a lower figure for emissions observed, rium by Salac. Because of a number of evidences on
which is due a reduction in industrial coal use and a the interaction of S with plant health, research has
slow-down of the Chinese economy and a closure of been stimulated in this field in order to understand
small and inefficient plants. the relationship between the S status of plants and
Lu made a downscaling of the global to the Chi- resistance mechanisms. The significance of S fertili-
nese S situation. This contribution revealed that the zation for crop resistance has coined the term Sulfur
total S content in soils of China ranges from 100- Induced Resistance, abbreviated SIR. The fungicidal
500 mg kg-1 S. The organic S in soils of southern effect of elemental S on pests and diseases is long
China accounts for 86-94% of the total S. The inor- known while the significance of soil-applied S for
ganic sulfur is mostly the easily soluble and the ad- crop resistance became evident a century later. Nev-
sorbed sulfur. The content of the total S, organic S ertheless, the fungicidal effect of foliar applied S has
and available S in the cultivated soils of southern to be distinguished strictly from the health promot-
China is 299, 266 and 34 mg kg-1 S respectively. In ing effect of soil-applied S. Therefore, in what fol-
southern China the sulfur input into the soil comes lows the significance soil-applied S fertilization on
mainly from sulfur fertilizers (28.2 kg ha-1 S), rain- plant health will be highlighted. These recent find-
fall (13.4 kg ha-1 S), and irrigation water (9.2 kg ha-1 ings clearly indicate that S supply has a strong influ-
S), with a total input of 50.6 kg ha-1 S. Balanced ence on plant resistance by stimulating directly the
with sulfur removed from the soil by crop uptake biochemical processes in the primary and secondary
(25.3 kg ha-1 S), sulfur leaching (19.9 kg ha-1 S) and metabolism. Nevertheless, future research is neces-
runoff. sary in order to understand the efficacy of individual
As a general introduction to the biology of S com- S metabolites involved in the activation and
pounds De Kok refreshed the knowledge of the strengthening of plant defenses by S fertilization.
auditorium concerning the basic facts of plants' S As representatives of the S fertilizer industry
metabolism and the main steps in the regulation of Messick and Fan stressed the increasing demand for
uptake, transport and storage of S compounds. In S fertilizers and their use in Chinese agriculture, a
addition, the significance of S in physiological func- fact which provides significant benefits to both fer-
tioning of plants was reviewed. For instance, S- tilizer manufacturers and farmers. The estimated
containing metabolites as glutathione (GSH) plays a annual need of S for plant nutrition in China is 1.7
4 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

million tons S. It has been estimated that 30% of cation and soil S balance of input and output in Chi-
Chinese farmland, mainly in the counties Ji and nese different regions could be directly queried.
Baodi are responding to S fertilization. Yield losses With increasingly maturation and popularization of
in rice, wheat and corn caused by S deficiency are the internet technology, attention is paid to WebGis
6% - 24%, particularly S demanding crops like Chi- (World-Wide-Web Geography Information System).
nese cabbage, garlic, turnips and scallion responded It not only solves the problem of expensive price for
to S fertilization of 60 kg ha-1 S with yield increased GIS software, but also reduces the cost of collecting
around 20%. Messick and Fan expect a deficit in S geography spatial data and improves the sharing
supply from 2011 on. Assuming that 20% of the degree and extension of the geography information.
market is captured (340,000 tons S) and a price of t Organic farming has its special requirements to the
180 US$ per ton S for fertilizer this corresponds to a quality of fertilizers: no soluble P sources are al-
financial volume of 61.2 Million US$. The average lowed in fertilization. Fan demonstrated a technol-
yield increase potential in Chinese crop production ogy where available P could be produced from com-
by sulfur fertilization is estimated to 10% on 40 mil- pounds of elemental S and rock phosphate fertilizers
lion ha of S deficient land. The additional yield is in soils directly.
estimated to a total of 24 million tons for which the Finally Schnug highlighted the significance of S
additional sulfur fertilizer demand amounts to 1.2 fertilization as a part of sustainable development of
million tons of S. At the same time with yield in- agriculture. Understanding “sustainable develop-
creases an improved efficiency for nitrogen fertiliz- ment” as development that meets the needs of the
ers of at least 2% is expected which saves a mini- present without compromising the ability of future
mum of 5.5 million tons of N from being lost to the generations to meet their own needs (The
environment. Brundtland Commission, 1997) sulfur fertilization
Despite its distinctive effects of crop yield S fer- contributes to sustainability because it, improves
tilization also improves the quality of plant prod- production performance, reduces the environmental
ucts. Hagel demonstrated this by the example of the impact of nitrogen and pesticides, improves the effi-
baking-quality of bread-making wheat. He carried ciency of non renewable resources (P), improves
out that in modern breeding (unconsciously) varie- crop quality.
ties with a higher demand of vitalizing sulfur were
selected. This affects primarily the content of high
molecular weight (HMW-)glutenin. This not only General conclusions and further actions
affects the technological features of the dough pre-
pared from S deficient wheat grain, but also the di- All participants addressed the workshop as a great
gestibility of the wheat bread in the human intestine. success. Both German and Chinese scientists dis-
Paulsen stressed the special role of S nutrition cussed the content of future cooperative projects to
and S application in organic farming. Besides a introduce advanced research technologies and meth-
plant nutrient, S in elemental form may have a nega- ods, genetic research on sulfur-induced crop resis-
tive impact on rice roots, which are sensitive to low tance to stresses, aspects of sulfur fertilizer use in
levels of sulfide. H2S can derive from superfluous S conventional and environmentally-sound agricul-
in rice soils due to the nocturnal decline in the de- ture, GIS technology and its use in diagnosis of sul-
gree of oxidation in the rhizosphere, since the sto- fur deficiency and sulfur fertilizer recommendations
mata of the rice plants are closed at night. in different regions.
Under severe S starvation plants develop more or Further actions will be the proposal of two work-
less characteristically deficiency symptoms. Brauer shops to the Center, addressing the specific interests
et al. demonstrated the symptomatology of visual of science and society in organic farming and ge-
symptoms of S-deficiency. They showed that symp- netic engineering. Individual research collaborations
toms of S deficiency can occur in all crops and in all between partners have been initiated already and
growth stages and they concluded that the identifica- seeking for funding will also involve approaches to
tion of such symptoms are an important tool in crop the Center.
management. S deficiency symptoms can be diag-
nosed comparatively reliable in oilseed rape, while Acknowledgements
in cereals (including corn) and sugar beet this is
only possible together with hydrological and other The workshop was organized by Institute of Ap-
site parameters. plied Ecology, CAS, China, Institute of Plant Nutri-
Ma demonstrated that a combination of informa- tion and Soil Science, FAL, Germany, Institute of
tion technology, soil-fertilizer and plant-nutrition Soil Science, CAS, China and sponsored by Sino-
technology can be used as a tool for managing S German Center for Research Promotion of DFG and
fertilizers throughout larger regions. By this system, NSFC.
soil S-deficiency status, effects of S fertilizer appli-
Landbauforschung Völkenrode, Special Issue 283, 2005 5

Pathways of plant sulfur uptake and metabolism - an overview

Luit J. De Kok1, Ana Castro1, Mark Durenkamp1, Aleksandra Koralewska1, Freek S. Posthumus1, C. Elisabeth
E. Stuiver1, Liping Yang2 and Ineke Stulen1

Abstract 1 2 tion and function of proteins. Plants contain a large

variety of other organic sulfur compounds, as thiols
The sulfur requirement of plants varies strongly (glutathione), sulfolipids and secondary sulfur com-
between species and can be defined as relative pounds (alliins, glucosinolates, phytochelatins),
growth rate times the plants' sulfur content. In gen- which play an important role in physiology and pro-
eral sulfate taken up by the roots is the major sulfur tection against environmental stress and pests (De
source for growth, which has to be reduced to sul- Kok et al., 2002a). Sulfur compounds are also of
fide prior to its metabolism into essential sulfur great importance for food quality and for the
compounds. Plants are also able to metabolize fo- production of phyto-pharmaceutics. Sulfur defi-
liarly absorbed sulfur gases as sulfur source for ciency will result in the loss of plant production,
growth. The reduction of sulfur takes predominantly fitness and resistance to environmental stress and
place in the shoot in the chloroplast. Cysteine is the pests. Plants may have to deal with temporary or
precursor or sulfur donor for most other organic prolonged periods of excessive sulfur or sulfur
sulfur compounds in plants. Sulfur amino acids cys- deficiency. Excessive sulfur from both pedospheric
teine and methionine are of great significance in the and atmospheric origin may be utilized as sulfur
structure, conformation and function of proteins and source for plants (De Kok et al., 2002a, b). On the
enzymes. Cysteine is the precursor of glutathione, a other hand, it may cause physiological imbalances
water-soluble thiol compound which functions in and negatively affect plant growth.
the protection of plants against oxidative stress,
heavy metals and xenobiotics.
Plants' sulfur requirement for growth
Key words: sulfate uptake, sulfate reduction, sulfate
assimilation, cysteine, methionine, sulfate assimila- The uptake of sulfate by the roots and its
tion, sulfolipids, proteins, phytochelatins, secondary reduction and further assimilation in the shoots, is
sulfur compounds under normal conditions highly regulated on ''a
whole plant level" and it will be in tune with the
actual sulfur requirement of a plant species for
Introduction biomass production (De Kok et al., 2002a). The
sulfur requirement strongly varies between species
Sulfur is an essential element for growth and and it may strongly vary at different developmental
physiological functioning of plants, however, its stages of the plant (vegetative growth, seed
content strongly varies between species and it production). The overall plants' sulfur requirement
ranges from 0.1 to 6 % of the dry weight (0.03 to 2 (Srequirement) can be estimated as follows (De Kok et
mmol g-1 dry weight; De Kok et al., 2002a). Sulfate al., 2002a; Durenkamp and De Kok, 2004):
taken up by the roots is the major sulfur source for
growth, though it has to be reduced to sulfide before Srequirement (Pmol g-1 plant day-1) =
it is further metabolized. Root plastids contain all RGR (% day-1) x Scontent (Pmol g-1 plant)
sulfate reduction enzymes, however, the reduction
of sulfate to sulfide and its subsequent incorporation where RGR represent the relative growth rate and
into cysteine takes predominantly place in the shoot Scontent the total plant tissue sulfur content. The RGR
in the chloroplast (Figure 1). Cysteine is the precur- can be estimated as follows:
sor or reduced sulfur donor of most other organic
sulfur compounds in plants. The predominant pro- RGR = (lnW2 - lnW1)/(t2 - t1)
portion of the organic sulfur is present in the protein
fraction (up to 70 % of total S), as cysteine and me- where W1 and W2 represent the total weight (g) at
thionine residues. In proteins cysteine and methion- time t1 and t2, respectively, and t2 - t1 the time inter-
ine are highly significant in the structure, conforma- val (days) between harvests. The rate of sulfate up-
take by the roots necessary to meet the plants' sulfur
1
Laboratory of Plant Physiology, University of Gronin- requirement for growth can be estimated as follows:
gen, P.O. Box 14, 9750 AA Haren, The Netherlands
2
Soil and Fertilizer Institute, Chinese Academy of Agri- Sulfateuptake (Pmol g-1 root day-1) =
cultural Sciences (CAAS), Beijing, 100081, China Srequirement (Pmol g-1 plant day-1) x (S/Rratio + 1)
6 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

where S/Rratio represents the shoot (S) to root (R) whereas the function of Group 5 sulfate transporters
biomass partitioning of the plant. is not known yet (Buchner et al., 2004).
At optimal growth conditions the sulfur require-
ment (equivalent to sulfur flux) of different crop
species ranges from 2 to 10 Pmol g-1 plant fresh
weight day-1 (0.08 to 0.4 Pmol g-1 plant fresh weight
h-1, Figure 1). Generally the major proportion of the
sulfate taken up is reduced and metabolized into
organic compounds essential for structural growth.
However, seedlings of some plant species, e.g.
Brassica oleracea, may contain relatively high sul-
fate contents and here the organic sulfur content
might be used for the estimation of the sulfur re-
quirement needed for structural growth (Castro et
al., 2003).

Uptake and assimilation of sulfate

Sulfate is taken up by the roots with high affinity

and the maximal sulfate uptake rate is generally
already reached at pedospheric sulfate levels of 0.1
mM and lower (Hawkesford, 2000; Hawkesford and
Wray, 2000; Hawkesford et al., 2003a, b). The up-
take of sulfate by the roots and its transport to the
shoot is strictly controlled and it appears to be one
of the primary regulatory sites of sulfur assimilation
(Figure 1).
Sulfate is actively taken up across the plasma
membrane of the root cells, subsequently loaded
into the xylem vessels and transported to the shoot
by the transpiration stream. The uptake and trans-
port of sulfate is energy dependent (driven by a pro-
ton gradient generated by ATPases) through a pro-
ton/sulfate (presumably 3H+/SO42-) co-transport
(Clarkson et al., 1993). In the shoot the sulfate is
unloaded and transported to the chloroplasts where
it is reduced. The remaining sulfate in plant tissue is
predominantly present in the vacuole, since the cy- Figure 1:
An overview of sulfate reduction and assimilation in
toplasmatic concentrations of sulfate are kept rather
plants (APS, adenosine 5'-phosphosulfate; Fdred, Fdox,
constant. reduced and oxidized ferredoxin; RSH, RSSR, reduced
Distinct sulfate transporter proteins mediate the and oxidized glutathione) and the rates of sulfate uptake
uptake, transport and subcellular distribution of sul- by the roots and its reduction and assimilation in the
fate. According to their cellular and subcellular ex- shoots of a variety of plant species grown under optimal
pression, and possible functioning the sulfate trans- sulfur supply (adapted from De Kok et al., 2002a).
porters gene family has been classified in up to 5
different groups (Davidian et al., 2000; Hawkesford
2000; Hawkesford et al. 2003a, b; Buchner et al., Regulation and expression of the majority of sul-
2004). Some groups are expressed exclusively in the fate transporters are controlled by the sulfur nutri-
roots or shoots or expressed both in the roots and tional status of the plants. Upon sulfate deprivation,
shoots. Group 1 are 'high affinity sulfate transport- the rapid decrease in root sulfate is regularly accom-
ers', which are involved in the uptake of sulfate by panied by a strongly enhanced expression of most
the roots (Figure 2). Group 2 are vascular transport- sulfate transporter genes (up to 100-fold), accompa-
ers and are 'low affinity sulfate transporters'. Group nied by a substantially enhanced sulfate uptake ca-
3 is the so-called 'leaf group', however, still little is pacity (Hawkesford, 2000; Hawkesford and Wray,
known about the characteristics of this group. Group 2000; Hawkesford et al., 2003a, b; Buchner et al.,
4 transporters may be involved in the transport of 2004). It is still unresolved, whether sulfate itself or
sulfate into the plastids prior to its reduction, metabolic products of the sulfur assimilation (viz.
Landbauforschung Völkenrode, Special Issue 283, 2005 7

O-acetyl-serine, cysteine, glutathione) act as signals sions, where the annual average SO2 concentrations
in the regulation of sulfate uptake by the root and its may exceed 0.1 Pl l-1. However, the impact of sul-
transport to the shoot, and in the expression of the furous air pollutants on plant functioning is para-
sulfate tranporters involved (Davidian et al., 2000; doxical, since they may both act as toxin and nutri-
Hawkesford, 2000; Hawkesford et al., 2003a, b; ent (De Kok, 1990; De Kok et al., 1998, 2000,
Buchner et al., 2004). 2002a, b; De Kok and Tausz, 2001). Plants even
Even though root plastids contain all sulfate re- may benefit from elevated levels of atmospheric
duction enzymes, sulfate reduction takes predomi- sulfur gases, since they contribute to plants' sulfur
nantly place in the leaf chloroplasts. The reduction nutrition and exposure may result in enhanced
of sulfate to sulfide occurs in three steps (Figure 1). yields, especially when sulfate is deprived in the
Sulfate needs to be activated to adenosine 5'- root environment (Ernst, 1993; Van Der Kooij et al.,
phosphosulfate (APS) prior to its reduction to sul- 1997; De Kok et al., 1997, 2000).
fite. The activation of sulfate is catalyzed by ATP
sulfurylase, which affinity for sulfate is rather low
(Km approximately 1 mM) and the in situ sulfate
concentration in the chloroplast is most likely one of
the limiting/regulatory steps in sulfur reduction
(Stulen and De Kok, 1993). Subsequently APS is
reduced to sulfite, catalyzed by APS reductase with
likely glutathione as reductant (Leustek and Saito,
1999; Kopriva and Koprivova, 2003). The latter
reaction is assumed to be one of the primary regula-
tion points in the sulfate reduction, since the activity
of APS reductase is the lowest of the enzymes of the
sulfate reduction pathway and it has a fast turnover
rate (Brunold, 1990, 1993; Leustek and Saito, 1999;
Kopriva and Koprivova, 2003; Saito, 2003). Sulfite
is with high affinity reduced by sulfite reductase
with ferredoxin as a reductant and the formed sul-
fide is incorporated into cysteine, catalyzed by O-
acetylserine(thiol)lyase, with O-acetylserine as sub-
strate (Figure 1). The synthesis of O-acetylserine is
catalyzed by serine acetyltransferase and together
with O-acetylserine(thiol)lyase it is associated as
enzyme complex named cysteine synthase (Droux et
al., 1998; Hell, 2003). The formation of cysteine is
the direct coupling step between sulfur and nitrogen
assimilation in plants (Brunold, 1990, 1993;
Brunold et al., 2003)
The remaining sulfate in plant tissue is transferred
into the vacuole. The remobilization and redistribu- Figure 2:
tion of the vacuolar sulfate reserves appear to be Metabolism of SO2 and H2S in plant shoots and possible
rather slow and sulfur-deficient plants may still con- sites of feedback inhibition of sulfate uptake (adapted
tain detectable levels of sulfate (Cram 1990; David- from De Kok et al. 2002a).
ian et al., 2000; Hawkesford, 2000; Buchner et al.,
2004).
Plant shoots form a sink for atmospheric sulfur
gases, which can directly be taken up by the foliage.
Metabolism of atmospheric sulfur gases The foliar uptake of SO2 is generally directly de-
pendent on the degree of opening of the stomates,
The rapid economic growth, industrialization and since the internal resistance to gas is low. SO2 is
urbanization are associated with a strong increase in highly soluble in the apoplastic water of the meso-
energy demand and emissions of gaseous pollutants phyll, where it dissociates under formation of bisul-
including SO2 (Shen et al., 1995; Feng et al., 2000; fite (HSO3-) and sulfite (SO32-). Sulfite may directly
Emberson et al., 2001; Yang et al., 2002). As a con- enter the sulfur reduction pathway and be reduced to
sequence agricultural crop yields are at most risk sulfide, incorporated into cysteine, and subsequently
from current levels of sulfurous air pollutants, viz. into other sulfur compounds (Figure 3). Sulfite may
SO2, since they are grown close to sources of emis- also be oxidized to sulfate, extra- and intracellularly
8 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

by peroxidases or non-enzymatically catalyzed by precursor for the formation of the sulfoquinovose

metal ions or superoxide radicals and subsequently group of this lipid (Harwood and Okanenko, 2003).
reduced and assimilated again. Excessive sulfate is Glutathione (JGlu-Cys-Gly; GSH) or its homo-
transferred into the vacuole; enhanced foliar sulfate logues, e.g. homoglutathione (JGlu-Cys-EAla) in
levels are characteristic for SO2-exposed plants. The Fabaceae; hydroxymethylglutathione (JGlu-Cys-
foliar uptake of H2S appears to be directly depend- ESer) in Poaceae are the major water-soluble non-
ent on the rate of H2S metabolism into cysteine and protein thiol compounds present in plant tissue and
subsequently into other sulfur compounds (De Kok account for 1-2 % of the total sulfur (De Kok and
et al., 1998, 2000, 2002a.b; Figure 2). There is Stulen, 1993; Rennenberg, 1997; Grill et al., 2001).
strong evidence that O-acetyl-serine (thiol)lyase is The content of glutathione in plant tissue ranges
directly responsible for the active fixation of atmos- from 0.1 - 3 mM. Cysteine is the direct precursor for
pheric H2S by plants. Plants are able to transfer from the synthesis of glutathione (and its homologues).
sulfate to foliar absorbed SO2 or H2S as sulfur First, J-glutamylcysteine is synthesized from cys-
source (De Kok, 1990, De Kok et al., 1998, 2000, teine and glutamate catalyzed by J-glutamylcysteine
2002a,b, Yang et al., 2003) and levels of 0.06 Pl l-1 synthetase. Second, glutathione is synthesized from
appear to be sufficient to cover the sulfur require- J-glutamylcysteine and glycine (in glutathione
ment of plants (Yang et al., 2003; Buchner et al.,
homologues, E-alanine or serine) catalyzed by glu-
2004). There is an interaction between atmospheric
tathione synthetase (2). Both steps of the synthesis
and pedospheric sulfur utilization. For instance, H2S
of glutathione are ATP dependent reactions:
exposure resulted in a decreased activity of APS
reductase and a depressed sulfate uptake in Brassica cysteine +glutamate +ATP Ÿ J-glutamylcysteine +ADP + Pi (1)
oleracea (Westerman et al., 2000, 2001; De Kok et J-glutamylcysteine synthetase
al., 2002b). However, H2S solely affected the ex-
pression of the different sulfate transporters in the J-glutamylcysteine + glycine + ATP Ÿ GSH + ADP + P (2)
glutathione synthetase
shoot, but not in the roots (Buchner et al., 2004).
NADPH + H+ + GSSG Ÿ 2GSH + NADP+ (3)
glutathione reductase
Synthesis and physiological functions of sulfur
metabolites Glutathione is maintained in the reduced form by an
NADPH-dependent glutathione reductase (3) and
Cysteine is sulfur donor for the synthesis of me- the ratio of reduced glutathione (GSH) to oxidized
thionine, the major other sulfur-containing amino glutathione (GSSG) generally exceeds a value of 7
acid present in plants (Giovanelli, 1990; Noji and (Rennenberg, 1997; Foyer and Noctor, 2001; Tausz,
Saito, 2003). Both sulfur-containing amino acids are 2001).
of great significance in the structure, conformation Glutathione fulfils various roles in plant function-
and function of proteins and enzymes, but high lev- ing. In sulfur metabolism it functions as reductant in
els of these amino acids may also be present in seed the reduction of APS to sulfite (Figure 1). It is also
storage proteins (Tabatabai, 1986). The thiol groups the major transport form of reduced sulfur in plants.
of the cysteine residues in proteins can be oxidized Roots likely largely depend for their reduced sulfur
resulting in disulfide bridges with other cysteine supply on shoot/root transfer of glutathione via the
side chains (and form cystine) and/or linkage of phloem, since the reduction of sulfur occurs pre-
polypeptides. Disulfide bridges make an important dominantly in the chloroplast (De Kok et al., 1993;
contribution to the structure of proteins. The thiol Rennenberg, 1997; Grill et al., 2001). Glutathione is
groups are also of great importance in substrate directly involved in the reduction and assimilation
binding of enzymes, in metal-sulfur clusters in pro- of selenite into selenocysteine (Andersen and
teins (e.g. ferredoxins) and in regulatory proteins McMahon, 2001). Furthermore glutathione is of
(e.g. thioredoxins). great significance in the protection of plants against
Sulfoquinovosyl diacylglycerol is the predomi- oxidative and environmental stress and it de-
nant sulfur-containing lipid present in plants. In presses/scavenges the formation of toxic reactive
leaves its content comprises up to 3 - 6 % of the oxygen species, e.g. superoxide, H2O2 and lipid hy-
total sulfur present (Heinz, 1993; Benning, 1998; droperoxides (Grill et al., 2001; Tausz et al., 2003).
Harwood and Okanenko, 2003). This sulfolipid is Glutathione functions as reductant in the enzymatic
present in plastid membranes and likely is involved detoxification of reactive oxygen species in the glu-
in chloroplast functioning. The route of biosynthesis tathione-ascorbate cycle and as thiol buffer in the
and physiological function of sulfoquinovosyl dia- protection of proteins via direct reaction with reac-
cylglycerol is still under investigation. From recent tive oxygen species or by the formation of mixed
studies it is evident that sulfite it the likely sulfur disulfides. The potential of glutathione as protectant
is related to the pool size of glutathione, its redox
Landbauforschung Völkenrode, Special Issue 283, 2005 9

state (GSH/GSSG ratio) and the activity of glu- (Schnug, 1990, 1993; Ernst, 1993). However, when
tathione reductase. Glutathione is the precursor for Brassica was exposed to H2S (Westerman et al.,
the synthesis of phytochelatins ((JGlu-Cys)nGly), 2001) and Arabidopsis to SO2 (Van der Kooij et al.,
which are synthesized enzymatically by a constitu- 1997), the sink capacity of the glucosinolate fraction
tive phytochelatin synthase. The number of J- seemed to be rather limited. Upon tissue disruption
glutamyl-cysteine residues (JGlu-Cys)n in the phy- glucosinolates are enzymatically degraded by my-
tochelatins may range from 2 - 5, sometimes up to rosinase and may yield a variety of biologically ac-
11. Despite the fact that the phytochelatins form tive products such as isothiocyanates, thiocyanates,
complexes which a few heavy metals, viz. cadmium, nitriles and oxazolidine-2-thiones (Rosa, 1997,
it is assumed that these compounds play a role in 1999; Kushad et al., 1999; Graser et al., 2001; Peter-
heavy metal homeostasis and detoxification by buff- sen et al., 2002; Reichelt et al., 2002; Wittstock and
ering of the cytoplasmatic concentration of essential Halkier, 2002). The glucosinolate-myrosinase sys-
heavy metals (Rauser, 1993, 2000, 2001; Verkleij et tem is assumed to play a role in plant-herbivore and
al., 2003). Glutathione is also involved in the detoxi- plant-pathogen interactions. Furthermore, glucosi-
fication of xenobiotics, compounds without direct nolates are responsible for the flavor properties of
nutritional value or significance in metabolism, Brassicaceae and recently have received attention in
which at too high levels may negatively affect plant view of their potential anticarcinogenic properties
functioning. Xenobiotics may be detoxified in con- (Kushad et al., 1999; Graser et al., 2001; Petersen et
jugation reactions with glutathione catalyzed by al., 2002; Reichelt et al., 2002).
glutathione S-transferase, which activity is constitu- The content of Ȗ-glutamyl peptides and alliins in
tive; different xenobiotics may induce distinct iso- Allium species strongly depends on stage of devel-
forms of the enzyme (Schröder, 1998, 2001; Gullner opment of the plant, temperature, water availability
and Kömives, 2001). Glutathione S-transferases and the level of nitrogen and sulfur nutrition
have great significance in herbicide detoxification (Randle et al., 1993, 1995; Randle, 2000; Randle
and tolerance in agriculture and their induction by and Lancaster, 2002; Coolong and Randle, 2003a, b;
herbicide antidotes (safeners) is the decisive step for Durenkamp and De Kok, 2002, 2003, 2004). In on-
the induction of herbicide tolerance in many crop ion bulbs their content may account for up to 80 %
plants. Under natural conditions glutathione S- of the organic sulfur fraction (Schnug, 1993). Less
transferases are assumed to have significance in the is known about the content of secondary sulfur
detoxification of lipid hydroperoxides, in the conju- compounds in the seedling stage of the plant. It is
gation of endogenous metabolites, hormones and assumed that alliins are predominantly synthesized
DNA degradation products, and in the transport of in the leaves, from where they are subsequently
flavonoids. transferred to the attached bulb scale (Lancaster et
Some plant species contain so-called secondary al., 1986). The biosynthetic pathways of synthesis of
sulfur compounds, viz. glucosinolates in Brassica Ȗ-glutamylpeptides and alliins are still ambiguous.
(Schnug, 1990, 1993; Rosa, 1997; Graser et al., Ȗ-Glutamylpeptides can be formed from cysteine
2001, Glawisching et al., 2003) and Ȗ-glutamyl pep- (via Ȗ-glutamylcysteine or glutathione) and can be
tides and alliins (S-alk(en)yl cysteine sulfoxides) in metabolized into the corresponding alliins via oxida-
Allium (Randle et al., 1993, 1995; Randle, 2000; tion and subsequent hydrolyzation by Ȗ-glutamyl
Randle and Lancaster, 2002; Coolong and Randle, transpeptidases (Lancaster and Boland, 1990;
2003a, b). In shoot and roots of Brassica the glu- Randle and Lancaster 2002). However, other possi-
cosinolate content accounted for 1 - 2 % of the total ble routes of the synthesis of Ȗ-glutamylpeptides and
sulfur, however, there is a great diversity in glucosi- alliins may not be excluded (Granroth, 1970; Lan-
nolates between cultivars based on differences in caster and Boland, 1990; Edwards et al., 1994;
amino acid derived side chains and their elongated Randle and Lancaster, 2002). Alliins and Ȗ-
derivatives (Castro et al., 2004). Glucosinolates are glutamylpeptides are known to have therapeutic
composed of a ß-thioglucose moiety, a sulfonated utility and might have potential value as phytophar-
oxime and a side chain. The synthesis of glucosi- maceutics (Haq and Ali, 2003). The alliins and their
nolates starts with the oxidation of the parent amino breakdown products (e.g. allicin) are the flavor pre-
acid to an aldoxime, followed by the addition of a cursors for the odor and taste of species. Flavor is
thiol group (through conjugation with cysteine) to only released when plant cells are disrupted and the
produce thiohydroximate. The transfer of a glucose enzyme alliinase from the vacuole is able to degrade
and a sulfate moiety completes the formation of the the alliins, yielding a wide variety of volatile and
glucosinolates (Schnug, 1990; Rosa, 1997, 1999; non-volatile sulfur-containing compounds (Lancas-
Graser et al., 2001). ter and Collin, 1981; Block, 1992). The physiologi-
The physiological significance of glucosinolates is cal function of Ȗ-glutamylpeptides and alliins is
still ambiguous, though they are considered to func- rather unclear (Schnug, 1993).
tion as sink compounds in situations of sulfur excess
10 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

Various other sulfur metabolites, e.g. alliins, glu- Clarkson DT, Hawkesford MJ, Davidian, J-C (1993)
cosinolates, phytoalexins, the release of volatile Membrane and long-distance transport of sulfate. In: De
sulfur compounds as H2S, the production of sulfur- Kok LJ, Stulen I, Rennenberg H, Brunold C, Rauser W
rich proteins (thionins) and localized deposition of (eds) Sulfur Nutrition and Sulfur Assimilation in Higher
Plants: Regulatory, Agricultural and Environmental As-
elemental sulfur are assumed to have significance in pects. SPB Academic Publishing, The Hague, pp 3-19,
the resistance of plants against stress and pests ISBN 90-5103-084-3
(Schnug, 1997; Glawishnig et al., 2003; Haneklaus Coolong, TW, Randle, WM (2003a) Ammonium nitrate
et al., 2003; Haq and Ali, 2003). Several aspects of fertility levels influence flavor development in hydro-
sulfur metabolism and its possible significance in ponically grown ‘Granex 33’ onion. J Sci Food Agric
"sulfur-induced-resistance" need further evaluation 83:477-482
(Schnug, 1997; Haneklaus et al., 2003). Coolong TW, Randle WM (2003b) Temperature influ-
ences flavor intensity and quality in ‘Granex 33’ onion.
J Am Soc Hort Sci 128:176-181
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Westerman S, Stulen I, Suter M, Brunold C, De Kok LJ
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14 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants
 Landbauforschung Völkenrode, Special Issue 283, 2005 15

Advances in sulfur fertilizer requirement and research for Chinese agriculture:

Summary of field trial data from TSI’s China project from 1997 to 2003
Ming Xian Fan1 and Donald L. Messick1

Abstract1 Key words: sulfur deficiency, sulfur fertilizer, sulfur

requirement, Chinese agriculture, crop production
Sulfur deficiency is increasingly becoming one of the
limiting factors to further sustainable increases in agri-
cultural production. The Sulphur Institute collaborated Introduction
with 15 institutions throughout China to evaluate soil
sulfur deficiency and sulfur fertilizer requirements from In China, the rapid agricultural production growth
1997 to 2003. A total of 535 field trials have been com- during the last two decades (1980 to 2000) was
pleted in 14 provinces, evaluating direct effects of sulfur closely linked with the increased use of mineral
fertilizer on major agricultural crops, over the six-year fertilizers, which was increased from 12.6 million
period. The data generated from field trials showed that tons to 41.5 million tons, averaged at about 300 kg
sulfur fertilizer significantly increased crop yields in 468 ha-1. It is estimated that 50 percent of farmer
trials, 87% of the total trials completed. Average yield production costs in China go to fertilizer; and
increases achieved with sulfur fertilization varied from fertilizer also contributed about 45 to 50% increase
7% to 30%, among different crops. About 30% of soils in modern agricultural production (Chen Shoulun,
in China, equivalent to about 40 million hectares, are 2002). In the high yield provinces of China the
sulfur-deficient, especially in Anhui, Fujian, Heilongji- level of fertilizer use is over 400 to 500 kg ha-1
ang, Henan, Hunan, Guangdong, Guangxi, Jiangxi, (China Agriculture Yearbook, 2000). According to
Shaanxi, and Yunnan Provinces. Based on the results of Chinese governmental forecasts, China’s population
field trials, an average 30 kg ha-1 sulfur fertilizer is and grain production are expected to reach 1.4
needed to maximize both crop yield and economic return billion and 560 million tons in 2010, respectively,
in sulfur deficient soils. Therefore, a total of 1.2 million based on the assumption of 400 kg grain
tons of sulfur is currently needed in Chinese agriculture. consumption per capita per year. To meet the
This sulfur deficit will increase to 2.4 million tons annu- increasing demand of food and fiber for the
ally by 2013 unless correct measures are taken with in- increasing population and living standard, fertilizer
clusion of sulfur into fertilizer recommendation pro- use is projected to increase to 50 million tons in
grams. With effective sulfur fertilizer strategies, China 2010 (Xiao Yunlai, 2001). However, with this high
can increase by an average of 10% the yield in sulfur volume of fertilizer consumption improving
deficient soils (approximately 0.6 ton per hectare), add- fertilizer knowledge and technology is becoming
ing about 24 million tons of grain in Chinese agricultural even more important for optimizing its use for both
production every year. It will also improve crop quality economic and environmental considerations, like
and fertilizer efficiency through interaction of sulfur balanced fertilization, i.e. tailor fertilizer program
with other fertilizer nutrients and increase the economic based on crop demand and soil fertility status for
return to farmers by approximately 36 billion yuan. The both higher yield and economic returns. This
results generated from the six years’ field trials provide requires increasing use of all essential plant
further solid evidence that sulfur fertilizer is playing an nutrients in addition to traditional nitrogen, phos-
important role in the sustainable development of Chi- phate and potassium to achieve the maximum bene-
nese agriculture through balanced fertilization, we en- fit possible from fertilizers through improved man-
courage the Chinese government to recognize sulfur as agement practices that include all sources of nutri-
an essential fertilizer nutrient like nitrogen, phosphorus, ents and innovative technologies, while maintaining
and potassium; to adopt favorable policies associated or improving soil fertility without harmful impacts
with sulfur fertilizer production, distribution and use; onLike
the environment.
nitrogen, phosphorus, and potassium, sulfur
and to allow farmers to capitalize on the economic bene- is one of the major essential plant nutrients, and it
fit with a relatively small input. contributes to an increase in crop yields in three
different ways: 1) it provides a direct nutritive value,
2) it provides indirect nutritive value as soil
amendments, especially for calcareous and saline
1 alkali soils, 3) it improves the use efficiency of other
The Sulphur Institute, Washington, DC. USA
 16 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

20
Average Yield Increase, %
15 14
15 13 13 13 13 13
12 13
11 11
10 10
9 9
8
7
5

E( )
A AT 3)
T AN 2)

PE N )

C IS )

W LIC )
R (3)
SW GA EA 5)*

R TE (2)

IC (46

B RN )
G 6)

L( )
U )

SE 20)
IO (8

T O AT )

8)
D 3

R (30
7

TA (34
A (10

E (4
SC OT (2
EE C N(6

11

46
H
B (2

T
R T(
LL O

ED

(
(
O
E

G E
A
SO US

O
R

A
A
R

H
A
R
C
A

B
PE
SU Y
IT

R
P
C

A
C

Figure 1:
Average crop yield responses from sulfur fertilization within China during 1997 to 2003 (values in the parentheses represent the
total number of field trials).

essential plant nutrients, particularly nitrogen and phos- ating direct effects of sulfur fertilizer on major agri-
phorus. However, its importance as a fertilizer nutrient cultural crops, over the six-year period. The data
and its requirements in agriculture were unrecognized in generated from field trials showed that sulfur fertil-
the past. Sulfur deficiencies were masked by the deple- izer significantly increased crop yields in 468 trials,
tion of soil sulfur and sulfur input through precipitation, 87% of the total trials completed. Average yield
irrigation water, manures, and sulfur-containing fertiliz- increases achieved with sulfur fertilization varied
ers, such as ammonium sulfate and single superphos- from 7% to 30%, among different crops (Figure 1).
phate (SSP). According to The Sulphur Institute’s model Among the crops tested, chili, tomato, citrus, sugar-
analysis on plant nutrient sulfur demand in the world, cane, sweet potato, soybean, cauliflower, scallion,
Asia is the most sulfur deficient region in the world, rapeseed, and peanut had the highest yield response
with an annual 5.8 million ton sulfur fertilizer deficit at 10% or greater. Eighteen field trials were con-
predicted by 2011(The Sulphur Institute 2003). China ducted to examine the residual effect of sulfur fertil-
and India represent the largest sulfur demand countries izer. Crop yields were increased by sulfur fertilizers
in the region, with annual sulfur deficits of 2.3 and 1.9 applied in the preceding crops in15 field trials, rang-
million tons, respectively. Sulfur deficiency is increas- ing from 4% to 7%.
ingly becoming one of the limiting factors to further Crop yield responses to sulfur fertilizer were also
sustainable increases in agricultural production in China, different among the tested provinces. Differences
as agricultural production intensifies and high-analysis were observed due to soil sulfur fertility status,
fertilizers, containing little or no sulfur, are increasingly cropping system and fertilizer use history. Gener-
used. ally, better crop responses to sulfur fertilization
were obtained in the southern provinces. The aver-
age yield increases over the six-year time period,
Sulfur fertilizer effect on crop yield 1997 to 2002, in the tested provinces are presented
in Figure 2.
From 1997 through 2003, The Sulphur Institute (TSI) Over sixty field trials were conducted to evaluate
collaborated with 15 institutions throughout China as a crop responses to different sulfur fertilizers, includ-
cooperative network to evaluate soil sulfur fertility ing ammonium sulfate, elemental sulfur, gypsum,
status and sulfur fertilizer requirements. A total of 535 phosphogypsum and SSP in all fourteen provinces.
field trials have been completed in 14 provinces, evalu- No significant difference was obtained in crop yield
 Landbauforschung Völkenrode, Special Issue 283, 2005 17

16
Average Yield Increase, % 15
15 13
12 12 12
11 11
10 10
9
10 8 8 8
7

0
)
YU U 0)

G EI 9)

)
H G )
AN XI )
FU U I )

LO EJ N ( )

AN G )
JI NA )*

R XI )
ER SH GX 3)

TO ON 0)
U HU N )

L 7)
N IAN 52

40
H (37

AN 41
G (7

H ZH JIA (57

G ON (21

M AAN (24
N (44
N (47
G (2

AN B (5

(3

G (3
TA IA (
(4
JI G(
AN N
AN IN

I
A
JI N J

U
A

D
TI

O
EI

N
IN

Figure 2:
Average sulfur fertilization effect on crop yield in different provinces of China from 1997 to 2002 (Yunnan, Tianjin and Jiangsu
are the mean of three year’s data).

due to sulfur sources, though in some field trials,

y = -0.2091x + 23.152x + 6235.4
2 higher yield increases were found with ammonium
8000
Wheat 2
R = 0.9902 sulfate and SSP fertilizers in northeastern China, as
Corn
7000 compared to elemental sulfur.
Yield, kg/ha

Crop yield increased significantly with increasing

6000 sulfur rates to 60 kg sulfur ha-1 for cereal crops, and
2
y = -0.1396x + 14.693x + 5855.4 to 90 kg sulfur ha-1 for oil, sugar and vegetable
2
5000 R = 0.8731 crops in over 200 field trials conducted in 14 prov-
inces with different soils and fertilizer manage-
4000 ments. The optimum sulfur fertilizer rates for
0 30
Sulphur Rate, kg/ha
60 90 maximum yield ranged from 40 to 60 kg ha-1 for
cereal crops; and from 60 to 90 kg ha-1 for oil, sugar,
vegetable and cash crops (Figure 3).
5000 Soybean(22) 2
y = -0.0394x + 10.912x + 3384.3
Peanut(19) 2
R = 0.9999
Rapeseed(28)
4000 Sulfur fertilizer effect on crop quality
Yield, kg/ha

2
y = -0.0461x + 8.2833x + 2411
2
R =1
3000 Sulfur is a constitute of three essential amino ac-
y = 4.9482x + 1428.7 ids, vital to protein production and enzyme activity,
2
2000 R = 0.9387 and participates in the synthesis of many secondary
compound in plants. Sulfur fertilization has a deci-
1000 sive role in improving crop quality and increasing
0 30 60 90 its market value, particularly in the case of wheat,
Sulphur Rate, kg/ha rapeseed, sugarcane, fruits, vegetables and tea. Ac-
cording to the results of field trials, sulfur fertilizer
Figure 3:
Average yield responses of cereal (123 field trials) and oil
increased crude protein content in rice and wheat by
crops (69 field trials) to sulfur fertilizer rates in China from 10% to 27% in Anhui and Jiangsu provinces; oil
1997 to 2002.
 18 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

Table 1:
Sulfur fertilizer effect on tea leaf quality and orange quality in Southern China Provinces in 2002.
Tea (average of four field trials)

Yield Phenols Amino Acid Caffeine Water extract

(kg ha-1) (%) (%) (%) (%)
Control 1691 21.1 2.14 2.76 35.7
-1
ES 60 kg ha 1842 21.9 2.27 2.92 36.1
(8.9%) (3.8%) (6.2%) (5.6%) (1.2%)
Orange (average of six field trials)
Yield Vitamin C Sugar Acidity Soluble Solid
(t ha-1) (mg 100 ml-1) (g 100 ml-1) (g 100 ml-1) (%)
Control 33.2 34.2 8.0 0.89 10.1
ES 60 kg ha-1 38.5 35.7 8.3 0.95 10.2
(16%) (4.4%) (3.8%) (6.7%) (1.0%)

content of peanut by 6.5% and methionine content in creased nutrient uptake and nutrient use efficiency,
peanut by 40% in Fujian and Jiangxi Provinces; sugar such as nitrogen, which resulted in less likelihood of
content in sugarcane and banana by 10% to 23% in nutrient loss to the environment due to leaching
Guangdong, Guangxi, and Jiangxi provinces. Amino and/or runoff. This effect has been demonstrated by
acid and polyphenol contents in tea leaves and Vitamin large number of data generated from sulfur interac-
C and sugar content in orange juice are important in- tion with nitrogen field trials on different crops in
dexes in evaluating tea leaf and orange quality and mar- China. Total nitrogen uptake by rice was increased
ket value. The results from three years’ field trials con- by 13 kg ha-1 and 19 kg ha-1 by applying 30 and 60
ducted in Hunan, Zjhejiang and Anhui Provinces from kg sulfur ha-1 with 120 kg nitrogen ha-1 in one rice
1999 to 2002, sulfur fertilizer increased amino acid con- field trial in Jiangxi, which resulted in a 7 % and
tent of tea leaves by 6.6% and Vitamin C content in or- 10% increase in nitrogen use efficiency. In most
ange juice by 4.4% (Table 1), thereby greatly improving field trials studying the interaction of sulfur with
green tea and orange quality. Sulfur fertilization also nitrogen on rice, adding 30 kg sulfur ha-1 with the
reduced nitrate concentration in various leaf vegetables low rate of nitrogen (120 kg ha-1) resulted in higher
by 10% to 50% in Anhui, Fujian and Guangdong Prov- yield than the high rate of nitrogen (180 kg ha-1)
inces. without sulfur (Figure 5). With the increasing con-
cerns about nitrogen fertilizer cost and the potential
impact on environment, the beneficial effect of sul-
Economic benefits of sulfur fertilization fur fertilizer on nitrogen uptake and utilization by
plant is critical in precise farming and fertilizer
Sulfur fertilizer increased crop yield, improved crop management.
quality, and also significantly increased economic return
to the producers. According to the Value Increase: Input
Cost Ratio (VCR) calculated from the field trial results Soil sulfur deficiency in China
for the seven years (Figure 4), for high yield cash crops
like banana, vegetables, citrus, sugarcane, sweet potato Combining with the field trials evaluating crop
and tea, the economic returns from sulfur fertilizer in- response to sulfur fertilizers, over 20,000 soil sam-
vestment (VCR) were very high, ranging from 18 to 40. ples have been taken from major agricultural soils to
The average VCRs for oil and grain crops were from 10 determine the soil sulfur fertility status. The results
to 15. Considering that a VCR of 2 to 2.5 is generally show that about 30% of soils in China, equivalent to
accepted as profitable and conducive to fertilizer appli- about 40 million hectares, are sulfur-deficient, espe-
cation, sulfur fertilization is viewed as highly profitable cially in Anhui, Fujian, Guangdong, Guangxi,
in soils having inadequate sulfur due to its lower cost as Heilongjiang, Henan, Hunan, Jiangxi, Shaanxi, and
compared to that of other fertilizer nutrients, like nitro- Yunnan Provinces (Figure 6). Based on the results
gen, phosphorus and potassium. of several years’ field trials, an average 40 kg ha-1
Sulfur fertilizer increased crop yield, and also in- sulfur fertilizer is needed to maximize both crop
 Landbauforschung Völkenrode, Special Issue 283, 2005 19

50
40
Value : Cost Ratio
40 35 34
29 29
30
24
20 23
20 18
15
15 14
10 11 11 10

0
C N E 2)

T AG 10)

8)
L( )
SW A LIO 20)

SO AD ( 8)
S )

PE AN 3)
)

UT )
AP IC 43)
A EA )

E E 17)

R 6)

TO A T )
TA (34
RU (23

TA (30

2
SC T (25

H (87

46
(

A (6
E (

C D(4
CA NA

YB ISH
(
(

R TO

(
ES E( 1
PO E

W N
N
AR A

E
N

O
G AN

EE B B

R
IT

L
SU B

Figure 4:
Average economic profit obtained from crop response to sulfur fertilizer in the field trials from 1997 to 2003 (values in the paren-
theses represent the total number of field trials).

izer use in balanced fertilization in China, more than

10 large-scale demonstration projects were estab-
7000
lished in sulfur deficient, intensively cultivated re-
gions in Anhui, Fujian, Guangdong, Guangxi, He-
Yield, kg/ha

6000
nan, Jiangxi, Tianjing, and Zhejiang Provinces on
major agricultural crops such as rice, corn, peanut,
5000
soybean, sugarcane, tea, vegetables. These demon-
S0 S30 S60 stration projects showed sulfur fertilizer increased
4000
both crop yield and economic returns. For example,
0 120 180
Jiangxi Academy of Agricultural Sciences, collabo-
N Rate, kg/ha
rating with TSI, established two large scale demon-
Figure 5: stration projects in Xia Jiang County, located in the
Average rice yield responses to interactions of three sulfur southern Jiangxi province with >60% of sulfur defi-
rates and three nitrogen rates in ten field trials in southern cient soils, equivalent to 20,000 ha; and Xing Guo
China (1999 to 2002). County, located in the center of Jiangxi province
with 46% of sulfur deficient soils, equivalent to
15,000 ha in 2001. Each demonstration project in-
yield and economic return, while maintaining soil fertil- cludes 750 ha demonstration area, and three simple
ity in sulfur deficient soils. Therefore, a total of 1.6 mil- comparison fields. The site-measured yield in the
lion tons sulfur fertilizer is needed in Chinese agricul- “Harvest Day” showed sulfur fertilizer increased
ture. rice yield by 10.6%, compared with the rice yield in
the plots without sulfur fertilizer; and 15.4% in-
crease, compared with the previous three years’ av-
Demonstration and Extension Activities in China erage yield. Meanwhile, combined with these dem-
onstration projects, numerous regional site-
To further increase the awareness of the importance of workshops and extension activities, such as field
sulfur in balanced fertilization and promote sulfur fertil- tours and “Harvest Day” events have been organized
 20 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

in these regions to show sulfur’s beneficial effects on Conclusions

crop production and promote sulfur use through bal-
anced fertilization. Through these extension activities The results generated from the six years’ field
and other education publication materials, the latest re- trials conducted in the major agricultural provinces
search achievements and sulfur fertilizer technology of China provide further solid evidence that sulfur
were disseminated to a large number of Chinese farmers, deficiency is limiting crop production, affecting
agricultural extension workers as well as government crop yield and quality as well as economic return.
officials, who are responsible for conversion of research Sulfur fertilization is playing an important role in
achievements to farmers’ practices within their province, the sustainable development of Chinese agriculture,
which greatly increased their awareness of the impor- given the now extensive database of information
tance of sulfur in agriculture, and helped to accelerate demonstrating sulfur fertilization benefits.
the interest in sulfur fertilization in China.

Figure 6:
Soil sulfur deficiency distribution and the location of The Sulphur Institute and PRISM Sulphur Corporation’s research projects
within China.
 Landbauforschung Völkenrode, Special Issue 283, 2005 21

To increase agricultural production, efficiency and

farmer’s income, the Chinese government has been ad-
justing agricultural production structures by increasing
cash crop production, such as oil, sugar, vegetables, tea
and fruits; and by encouraging production of high qual-
ity products (Li Tianshen, 2003). Most cash crops and
high crop quality production have higher demand for
sulfur and balanced fertilizer technology for realization
of their high quality and market values. Therefore, due
to the well-demonstrated important role of sulfur in Chi-
nese agricultural production, we encourage the Chinese
government to recognize sulfur as an essential fertilizer
nutrient like nitrogen, phosphorus, and potassium; to
adopt favorable policies associated with sulfur fertilizer
production, distribution and use; and to allow farmers to
capitalize on the economic benefit with a relatively
small input. With the development of effective sulfur
fertilizer policy and strategy, it is expected that sulfur
fertilizer use in China will increase significantly over the
coming decade and make a greater contribution to in-
creasing Chinese agricultural production through bal-
anced fertilization, including sulfur.

References

China Agriculture Yearbook (2000) Ministry of Agriculture,

People’s Republic of China. China Agricultural Publisher,
Beijing
Chen S (2002) The Role of Fertilizer and Plant-Nutrient in
Sustainable Development of Chinese Agriculture. IFA
Technical Conference, Quebec, Canada
Li T (2003) The Impact of Chinese Economic Growth on Ag-
riculture. The Sulphur Institute’s 19th Sulphur Phosphate
Symposium, Beijing, China
The Sulphur Institute (2003) Sulphur Update. Washington,
DC. USA
Xiao Y (2001) Implication of China’s Accession to WTO to Its
Fertilizer Market. IFA Regional Conference for Asia and
The Pacific. Hanoi, Vietnam
22 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants
Landbauforschung Völkenrode, Special Issue 283, 2005 23

Sulfur and baking-quality of bread making wheat

Ingo Hagel1,21

Abstract1 break of the Second World War, many cultivars

existed with low performance (Klemt, 1934) and
It is well known in biological science that all fac- very soft glutens. Some of them were like glue
tors applied to living organisms (light, water, from a tube, so one could write one’s name with it
warmth, fertilizers etc.) show an optimum, when on the work surface (Kosmin,1934). And even at
their input is increased. Healthy organisms and sus- the beginning of the 60’s German grown wheat had
tainable systems are, on the long run, only achieved to be blended with 25-28% Canadian or American
when care is taken not to destroy this equilibrium of high quality wheat (Bolling, 1989).
factors producing an optimum. With regard to the So it is understandable, that especially after the
baking quality of wheat breeders and cereal scien- Second World War cereal chemists provided innu-
tists obviously failed to achieve this aim by breed- merable contributions on wheat and its quality.
ing their cultivars on the background of ample S Breeders successfully selected wheat cultivars with
depositions in the ecosystems. They (involuntarily) ever firmer and elastic glutens, a process that is still
selected plants showing definite characteristics of S in progress. So the question may arise if this devel-
deficiency (higher proportions of HMW-glutenin, opment only shifted the protein quality of the staple
stronger gluten and dough) even under conditions food wheat from one extreme to the other. One has
of ample S supply. I suppose they also selected to keep in mind that the word “quality” with regard
plants with a high warmth susceptibility as this also to wheat almost exclusively means “technological
delivers firm protein structure. When this environ- quality”, and this in fact means “baking quality”,
mental pollution was stopped and S supplies re- not “nutritional quality”. The mediation of all life
turned to natural conditions, even with a non S processes are closely linked to proteins. As an in-
craving plant like wheat, problems arose with the creasing number of people nowadays suffer from
gluten structure as doughs turned out so strong that wheat incompatibility, one may ask whether we
the baking volume decreased. So one may ask, par- have lost sight of the nutritional needs of human
ticularly with regard to S, if the plant constitutions beings through the changing of wheat protein for
of our modern wheat cultivars are still harmonious merely technological reasons.
and in balance. And as a consequence ot that also
the nutritional quality of these cultivars is rather
questionable.

Key words: wheat, sulfur, baking quality, gluten,

maximum resistance, temperature influence, nutri-
tional quality

Introduction

When wheat is milled into flour and the dough is

baked into bread, the developing carbon dioxide
gas bubbles that develop through fermentation
(yeast or sour dough) are prevented from escaping
the dough by its protein or gluten matrix. By keep- Figure 1:
ing the gas bubbles in place, nice bread with attrac- Relation between the amount of acetic-acid-insoluble
glutenin and the baking volume per percent-unit of pro-
tive baking volume arises, not only delighting the
tein in the flour (Orth und Bushuk, 1972, from Bushuk,
bakers by lowering their flour-input costs, but also 1989)
appealing to the human senses. Yet baking quality
was not always as outstanding as it is today. For Today we will focus on the question whether the
example, in Germany until shortly before the out- firm protein structure and excellent baking quality
of modern wheat varieties comes from some sort of
1
a S deficiency syndrome induced involuntarily by
Dr. Ingo Hagel, Federal Agricultural Research Center, breeding (Hagel 2000a, 2002).
Institute of Plant Nutrition and Soil Science, Bundesallee
2
50, D-38116 Braunschweig Germany; Umkreis-Institut,
Martinstrasse 73, D-64285 Darmstadt, Germany
24 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

Sulfur and wheat proteins proportion of these two protein fractions greatly
influence the structure of gluten, the rheological
The crude protein of wheat can be separated into performance of the dough and therewith the techno-
several fractions (according to their solubility in logical quality of the wheat i.e. the baking volume.
different solvents), which also contribute quite dif- While gliadins contribute to viscosity and extensi-
ferently to baking quality. The salt soluble albu- bility, glutenins are regarded as the main factor for
mins and globulins are concentrated in the periph- elasticity and firmness (Wieser et al., 1994). Addi-
ery of the grain, directly under the bran (Hagel, tional gliadin leads to softer and more extensible
2000b). Therefore their content depends very much glutens (Kim et al., 1988). On the other hand, ac-
on thousand-kernel weight and flour quality (whole cording to the basic results of Orth and Bushuk
grain flour or flours with a lower ash content). With (1972, Figure 1), the strengthening effect of glu-
regard to a flour featuring a low ash content of tenin to gluten and dough (Seilmeier et al., 1992;
0.55% they account for approximately 11 – 22% of Wieser et al., 2000; Antes and Wieser, 2000; Wie-
protein, depending on the total protein content of ser and Kieffer, 2001) (and thus leading to higher
the grain and cultivar (Wieser and Seilmeier 1998; baking volume) has been consistently corroborated
Wieser et al., 1980a). So the vast majority of the (Field et al., 1983; Gupta et al., 1993; Kieffer et al.,
wheat proteins in such flour are gluten proteins, 1998).
comprising the gliadins and the glutenins. Type and

Figure 2:
Deviations (%, absolute) of protein fractions from the mean (regressions of the protein fractions versus N content) of all culti-
vars of wheat (whole grain, harvest 1994; Hagel et al., 1998a).

So it is understandable that in the course of the the modern cultivars Fregatt and Rektor had very
last 60 years the development from old to modern high proportions of glutenin above the mean, but
wheat cultivars has led to a drastic shift in the pro- also the modern cultivars Bussard and the older
portions of protein fractions (Hagel et al., 1998, cultivars Diplomat, Jubilar and Progress showed
Figure 2): The very old wheat type Weisser Am- glutenin proportions well above the mean and lower
mertaler (WAT), a cross of the older cultivar Jubi- gliadin, which led to very firm glutens (gluten indi-
lar with an old Hessischer Landweizen (JXHL) as ces of 84-99% (Hagel et al., 1998)). Parenthetically,
well as a cross of Jubilar with another Jubilar-cross from Figure 2 it can be seen that not only gliadin
(JXJHi) showed glutenin proportions far below the was replaced by glutenin, but also albumins and
average of all other variants of this trial, but with globulins, being the protein fractions with the high-
higher gliadin proportions and thus leading to ex- est S contents (see below and Table 1).
tremely soft glutens (gluten indices of 42-56%;
Hagel et al., 1998a). On the other hand, particularly
Landbauforschung Völkenrode, Special Issue 283, 2005 25

Table 1:
Contents (Mol-%) of cysteine, methionine and lysine of protein fractions of wheat (cultivars: KOLIBRI and REKTOR), (Wie-
ser et al., 1980 & 1991).
Cysteine +
Cysteine Methionine Lysine
Methionine
Albumins 3.3 1.6 4.9 3.1
Globulina 3.2 - 3.7 2.0 - 2.1 5.8 4.1
Gliadins (total) 1.8 - 2.2 1.1 - 1.4 2.9 - 3.6 0.8
Z5-Gliadins 0 0 0 0.4 - 0.5
Z1,2-Gliadins 0 0.0 - 0.3 0.0 - 0.3 0.3 – 0.6
Glutenins (total) 1.4 1.3 2.7 2.1
HMW-Glutenins 0.6 - 1.3 0.1 - 0.3 0.7 - 1.6 0.7 – 1.1
LMW-Glutenins 1.9 - 2.6 1.2 - 1.6 3.1 - 4.2 0.2 – 0.6

Glutenins can be separated into (high-molecular- sciously (by analyzing for HMW-glutenin) and
weight) HMW-glutenins (Mr = 80.000-120.000) involuntarily (by selecting wheat with firm and
and (low-molecular-weight) LMW-glutenins (Mr = elastic glutens, high sedimentation values, high
30.000 -52.000 (Wieser, 2000)). HMW-glutenins baking volumes etc.) developed their wheat culti-
are highly responsible for inducing firmer protein vars not only by increasing the glutenin content
structure i.e. higher resistances of the glutens (Wie- (Figure 2) but also by increasing the HMW:LMW
ser et al., 1994; Seilmeier et al. 1992; Schropp and ratio, though for the latter assumption no data is
Wieser, 2001) and therefore play a key-role in glu- available. Anyway, all these measures (including of
ten structure (Wieser and Zimmermann, 2000). The course replacing albumins and globulins by gluten
LMW-glutenin does not (or to a much lesser extent) proteins (Figure 2)) led to an increase of proteins
contribute to the firmness (resistance) of the gluten low (gliadins, glutenins) or very low (HMW-
(Antes and Wieser, 2000; Wieser and Kieffer, glutenins) in S compared to albumins and globu-
2001). So HMW-glutenin appeared to be such an lins. These salt soluble proteins are very rich not
interesting research topic for cereal chemists that only in essential amino acids such as lysine but also
Shewry et al. (1992) stated that the 1980s could in S containing cysteine and methionine (Table 1).
well be considered as the “decade of the HMW Moreover, as mentioned above, these non-gluten-
subunit”. The ratio of HMW:LMW-glutenin of proteins are concentrated in the periphery of the
wheat cultivars of widely differing baking quality grain and can make up to 37% of the total wheat
varied from 0.35-0.65 (according to data from Wie- protein of whole grain wheat (Hagel 2000 b, Figure
ser et al., 1994, Wieser and Kieffer, 2001). These 3).
variations make it plausible that breeders con-

Figure 3:
Relations between nitrogen content and proportions of albumin- and globulin-nitrogen of total nitrogen content from wheat
(cultivars: Rektor and Bussard, whole grain) from biodynamic (BD) and conventional (Conv.) agriculture, harvest 1996
(Hagel, 2000b).
26 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

As their content remains constant, their propor- ance between N and S, as S does not increase to the
tion of the total protein sharply declines with in- same degree as N (Hagel und Schnug, 1999; Hagel
creasing protein content of the grain. So increasing et al., 1998b). For instance, in Figure 4 the S con-
the N content of the grain by N-fertilization, of tents fall below the diagonal of the graph. So many
which bakers are very fond of for technological of the conventional wheat samples with high N
reasons, increases only S low gluten proteins, not S content have come very near or have already
rich albumins and globulins (Doekes and Wen- crossed the line of an N:S ratio of 17:1, indicating S
nekes, 1982; Wieser and Seilmeier, 1998). Conse- deficiency. Yet organically grown wheat with much
quently, for example, an increase of the protein lower N content is no guarantee for sufficient S
content from approximately 1.4 to 2.2% N of the supply (Hagel and Schnug, 1999). Figure 4 clearly
(biodynamic) wheat samples leads to a decline of demonstrates that the set of biodynamic samples
the proportions of the S rich albumins and globulins from harvest 1996 must be differentiated into two
from 37% to 24% of the total grain protein, respec- different sub samples featuring N:S ratios < and >
tively (Figure 3). 14.5. Biodynamic samples from harvest 1995 also
It becomes obvious that especially in conven- showed the same phenomenon of apparently differ-
tional agriculture the aim of high contents of grain- ent S supply including many samples with S defi-
N achieved by mineral fertilizers induces an imbal- ciency (Hagel and Schnug, 1997).

Figure 4:
Nitrogen and sulfur contents of wheat (cultivars Rektor and Bussard) from biodynamic (BD) und conventional (Conv.) agricul-
ture (harvest 1996). Regression lines R2 and R3 differentiate the biodynamic samples into two sub-samples N:S ratio <and >
14.5:1 (Hagel et al., 1998b)

Sulfur and baking quality doughs and higher baking volumes (Figure 8; Moss
et al., 1981).
With regard to gluten quality, S deficiency leads Interestingly, the features of S deficient wheat
to much firmer and less extensible doughs (Moss et described above (strong extensograms, stronger and
al., 1981; MacRitchie and Gupta 1993; Wrigley et tougher glutens and doughs) and shown in figure 5
al., 1984a). In Figure 5 the flour sufficiently sup- were just what breeders and bakers were aiming at
plied with S showed an extensogram with low en- for decades on their quest for cultivars with high
ergy (175 Brabender units at 50 mm extension). In technological quality. Also biochemically, S defi-
contrast, the dough of the flour featuring S defi- cient wheat shows characteristics of good baking
ciency was much firmer, with a resistance of 365 quality wheat: less polypeptides with low Mrs
Brabender units at 50 mm extension. Decreasing S (8,000-28,000, mainly albumins) and more poly-
contents lead to ever firmer doughs and low baking peptides with high Mrs of 51,000-80,000 (Wrigley
volumes, whereas S fertilization and increasing S et al., 1984 a), higher content of HMW-glutenin
content of the wheat grain induces less tough (Castle and Randall, 1987), increasing amounts of
Landbauforschung Völkenrode, Special Issue 283, 2005 27

HMW-glutenin (Seilmeier et al., 2001), and in- beginning of the 80s no severe and relatively few
creasing ratio of HMW:LMW glutenin (MacRitchie cases of S deficiency (24% of all samples) could be
and Gupta, 1993; Seilmeier et al., 2001). observed in rape. At the end of the 80s the situation
had changed dramatically: Only 1% of the rape
samples were sufficiently supplied with S (Schnug
and Haneklaus, 1994). In northern Germany an S
application of 50 kg/ha is recommended (Schnug,
1991) for rape to avoid yield deficits through S de-
ficiency.
Wheat is a crop which hungers after much less S
than rape. But also with wheat S deficiency has
become a problem leading to yield losses of up to
30% (Bloem et al., 1995). In contrast to rape, S
deficiency in wheat cannot be compensated by
foliar applications of SO4-fertilizers (Schnug et al.,
1993), because surplus S gets quickly translocated
into the vacuoles, from which a re-translocation for
Figure 5: the protoplasma of plant cells and their functions
Extensographs for flour (cultivar OLYMPIC) with nor- can only occur at a very moderate level (Bell et al.,
mal and low content of sulfur. Control (___): 0.146% S, 1990; Cham 1990; Clarkson et al., 1993). If wheat
1.82% N, N:S = 12.5:1. Flour with low sulfur content
insufficiently supplied with S shows a N:S ratio
(---): 0.089% S, 1.72% N, N:S = 19.3:1 (Wrigley et al.,
1984 a). BU = Brabender Units wider than 17:1, such flour leads to excessively
tough and firm doughs and thus lower baking vol-
umes (Wrigley et al., 1984b; Byers et al., 1987;
Haneklaus et al., 1992; Bloem et al., 1995).

Figure 6:
Development of atmospheric SO2- sulfur deposition, use
of sulfur containing fertilizer and content of sulfur in Figure 7:
leaves of rape (Brassica napus) in Northern Germany Loaf volume of flour derived from German wheat varie-
(Schnug and Haneklaus, 1994) ties depending on sulfur and protein concentration in the
grain (Haneklaus et al., 1992).
This development in wheat breading went “well”
and led to cultivars with higher baking volumes It is important to keep in mind that these reduc-
until the moment when real S deficiency appeared. tions of baking volume occur not because of exces-
Due to the successful installation of desulfurization sively soft glutens and doughs (as 30-50 years ago)
plants, a drastic reduction of the deposition of S in but because of excessively firm ones: The pressure
the ecosystems occurred. The application of S low of the fermentation gases cannot sufficiently over-
mineral fertilizers also increased. By 1980 the aver- come the loafs' tough structure and thus produces
age deposition of S in northern Germany was up to lower baking volumes. Obviously, the breeding
35 kg/ha x year. This amount then decreased and in process selecting wheat types featuring the charac-
1990 was 60% less (Schnug and Haneklaus, 1994; teristics of S deficiency mentioned above has
Figure 6). In the same period, the concentration of passed its optimum. When, in addition, a second S
S in rape leaves decreased from 8 to 3 mg/g. At the deficiency occurred as a changed ecologic-
historical situation and decreased S depositions,
28 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

unforeseen problems arose in baking technology. S the contrary, because of the softening effect of an
fertilization now induced higher baking volumes increasing content of grain S on the resistance of
(as known previously through N fertilization; Fig- the dough, thus leading to higher baking volume
ure 7; Haneklaus et al., 1992), not because of any (Moss et al., 1981; Figure 8).
strengthening impact to the dough structure, but, on

Figure 8:
Relations between content of sulfur and a) resistance of dough and b) baking volume. N0, 50 und 100 = nitrogen application in
kg ha-1 (including different sulfur applications of 0-50 kg ha-1 (Moss et al., 1981). BU = Brabender Units.

Similar phenomena were observed with S fertili- fertilizer, but in part (except the control) MgCl2 in
zation trials on organic farms located in the coastal order to identify any effects in grain yield resulting
area of Northern Germany with very low rates of S from the magnesia in the S fertilizer (MgSO4), but
deposition (Hagel, 2000c). The variability in the N there were none. The N:S ratio of the control was
content of the wheat samples shown in Figure 9 15.4 showing low S supply near to the limits. In-
was only due to the field’s variation, not to any N creasing N content of these samples induced higher
fertilization. One part of the samples received no S baking volumes only up to a certain optimum of
Landbauforschung Völkenrode, Special Issue 283, 2005 29

approximately 1.95% N. Higher N contents low- (elemental S) and 13.9 (MgSO4), which were sig-
ered the baking volume (Figure 9), probably be- nificantly lower than the control. Here with increas-
cause of too firm doughs, though no extensograms ing N content no depression in loaf volume oc-
were performed. The other part of the samples re- curred. Instead a linear relation between the pa-
ceived S applications of 20, 40 and 60 kg ha-1 (as rameters was to be observed (Figure 9).
elemental S and MgS04). N:S ratios were 14.1

Figure 9:
Relationships between nitrogen content and baking volume (Rapid-Mix-Test = RMT) of wheat (cv. RENAN) of a sulfur fer-
tilization trial on an organic farm (harvest 1998; location: Tröndel) (Hagel 2000 c). +S, sulfur fertilization: 20, 40 and 60 kg S
ha-1 as elemental sulfur and MgSO4-sulfur.

The effect of a S fertilization softening the pro- Warmth, baking quality and sulfur
tein matrix of wheat was not only demonstrated on
locations where S was lacking but even on sites We also have to deal with the impact of warmth
sufficiently supplied with this element. For this with regard to the rheologie of wheat, because S
purpose up to 400 kg S/ha were applied to wheat and warmth are closely linked. S is exceptional for
grown on an organic farm (Hagel et al., 1999). its many allotropic modifications induced simply
Though the S content of the straw was increased by by different temperatures as described in many
50% by these quantities, the S content of the grain textbooks (Mortimer, 1996; Cotton et al., 1999).
and the flour remained unaffected. Also the N con- E.g. S changes from rhombic crystals into mono-
tent and the N:S ratio of the flour were not altered cline crystals upon mild heating. Further heating
significantly (Table 2). But already 200 kg S ha-1 delivers a yellow readily flowing liquid, then a red
lowered the resistance of the gluten significantly highly viscous substance which is turned into a
(the impact of 100 kg S ha-1 only slightly differing rubber like plastic material upon sudden cooling in
from that) (Table 2; Figure 10). This effect was not water and so on. The spicy flavors of e.g. mustard,
influenced by a shift in the amount of protein frac- onion and garlic with their S containing glucosi-
tions, especially HMW-glutenin (Table 2). Also nolates are termed “hot” not by chance. Numerous
different amounts of glutathione of the flour are therapeutic measures make use of these substances
probably not the reason, if the experiments as in in nutrition and medicine (from spices to warmth
this case are performed with flour sufficiently stimulating baths). Looking at the phenomena,
stored (Kieffer et al., 1998). there are many relationships between S and
warmth. So let us have a closer look to what hap-
30 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

pens with the baking quality of wheat grown at dif- peratures, especially during the grain filling period
ferent temperatures. of the wheat. Fajersson (1975) demonstrated differ-
It is well known that climate influences baking ent baking volumes of wheat (at comparable protein
quality by altering yield and/or the protein content contents) from climatically different years (Figure
of the wheat (Svensson, 1974; McDonald et al., 11).
1983). I will not focus on that now, but rather on
different baking qualities induced by different tem-

Table 2:
Content of nitrogen and sulfur, N:S ratio of flour and resistance of gluten (measured in Newton) of wheat of a sulfur fertilisa-
tion-trial (0-400 kg S/ha). Multiple-Range-Test: D = 5 %. Gliadin and Glutenin = RP-HPLC-analyses, (proportions (%) of the
different subunits from total gliadin and glutenin (Hagel et al. 1999).

Gliadin Glutenin

kg S/ha % N %S N:S Resistance Z5 Z1,2 ¦Z D J Zb HMW LMW

0 1.80 0.103 17.5 0.544a 3.9 4.5 8.4 49.4 42.2 3.7 21.9 74.4
50 1.77 0.103 17.2 0.523ab 3.6 4.2 7.8 47.9 44.3 3.7 20.6 75.7
100 1.86 0.107 17.4 0.444ab 3.7 4.4 8.1 47.8 44.1 3.8 21.6 74.6
200 1.83 0.100 18.3 0.441bc 3.6 4.2 7.8 48.0 44.2 3.4 21.4 75.2
400 1.95 0.105 18.6 0.370c 3.6 4.3 7.9 49.0 43.1 3.6 22.7 73.7

Figure 10: Figure 11:

Extensograms of wheat gluten of a sulfur fertilization Crude protein and baking volume of wheat from climati-
experiment. Variants: 0 and 400 kg S ha-1 (Hagel et al., cally differing harvest years (1950, 1952, 1953). Mean of
1999). five cultivars each (Fajersson, 1975).

In Sweden warm and dry climatic conditions of the fruiting period led to loaf volumes much
(mean day temperatures of 20 °C) during grain fill- lower than expected with regard to the protein con-
ing periods of 1994 and 1995 led to high gluten tent (Figure 12). Although the authors did not inves-
strength with low bread volumes (Johansson and tigate rheological parameters in detail, their descrip-
Svensson, 1999). Investigating the effects of tions of these samples with loaf volumes considera-
weather parameters on some Swedish wheat culti- bly below normal (subnormal mixing requirements
vars Johansson and Svensson (1998) found that the and poor dough handling) characterizes excessively
temperature, specially during the grain filling pe- strong doughs exactly. Excluding these “irregular”
riod, was the most important weather parameter ex- samples increased the correlation coefficients be-
plaining only 34% of the variation in grain protein tween protein content and loaf volume from 0.76 to
concentration, but 49% of the variation in mixogram 0.97. The cultivar Chiefkan in particular was “highly
index in spring wheat. Finney and Fryer (1958) susceptible to the damaging effects of high tempera-
found with hard red winter wheat samples from dif- tures during fruiting”. Also Johansson and Svensson
ferent states of the US and thus different climatic (1999) observed that the susceptibility of wheat cul-
conditions, that increases in accumulated degrees of tivars with regard to warmth influences differed.
temperatures above 90°F (32°C) during last 15 days
Landbauforschung Völkenrode, Special Issue 283, 2005 31

Figure 12:
Relations between loaf volume deviations from those expected and temperature during the last 15 days of the fruiting period
for 391 hard red winter wheat samples. Letters indicate samples from different states of the US and 20 different experimental
stations, 90° F = 32° C (Finney and Freyer 1958).

Jahn-Deesbach (1981) carried out pot experi- and 23.9°C were applied from a very early growth
ments with wheat. With anthesis, they were trans- stage (tillering). The results provide valuable in-
ferred from outdoors into growth chambers. These formation as they indicate different susceptibility of
variants only modestly supplied with N showed grain quality parameters to warmth: At comparable
better farinograms (higher energy) under the influ- concentrations of grain protein sedimentation val-
ence of warm temperatures compared with cool ues were increased already at temperatures of
conditions. In these experiments it nevertheless 21.1°C (Figure 15a), while mixogram areas were
remained unclear, if rheological differences were not different from their pattern until a temperature
only due to temperature or partly also to secondary of 23.9°C was attained (Figure 15b).
effects on grain protein concentration. Later this These results once more demonstrate that warmth
handicap was tackled successfully in experiments is an important parameter influencing grain quality
by Schipper et al. (1986) and Schipper (1991). characteristics by strengthening protein structure
They grew wheat in field experiments (warmer or and dough. Further evidence was also provided
cooler sites during the grain filling period) and from wheat cultivars grown in glasshouses at dif-
growth chambers and managed to achieve variants ferent temperatures and under different N applica-
with comparable grain protein content. In both en- tions (Randall and Moss 1990). One half of the
vironments, warmer temperatures during grain fill- samples was moved at 30 (low N) and 34 days
ing period produced dough extensograms with (high N) after anthesis to a “hot” glasshouse (23-
lower extensibility, higher resistance and higher 26°C average daily temperature with a maximum
energy. Some examples of the many results are temperature up to 36°C). The other half remained in
shown in Figure 13 and 14. Though samples grown the “cold” environment (18°C). Though grain N
at higher temperatures had somewhat higher glu- concentration of the wheat samples grown at differ-
tenin:gliadin ratios, this could not explain the dif- ent temperatures did not differ significantly, the
ferences in extensograms (Schipper et al., 1986; maximum resistances of the doughs were signifi-
Schipper, 1991). So possibly conformational cantly higher from wheat samples grown under the
changes in the protein structure may be the reason “hot” temperature regime, while extensibility was
for these rheological differences. lowered (Table 3). Randall and Moss (1990) also
Sosulski et al. (1963) conducted growth chamber point to the fact that indeed sulfur deficiency and
experiments with wheat grown at different moisture higher temperatures have very much in common
and N levels. Different temperatures of 16.7, 21.1 with regard to baking quality: “Sulfur deficiency
32 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

increases dough resistance and decreases extensibil- mediated through effects on grain sulfur as sulfur
ity, and in the present work, raising the temperature concentration was largely unaffected by tempera-
caused similar changes. However, the effect of ture treatment”.
temperature on dough resistance is unlikely to be

Figure 13:
Influence of different temperatures during grain filling period on wheat (cultivars: MONOPOL, CARIBO, KANZLER) of a
clima-field-experiment (harvest: 1986) on the extensogram of doughs (Schipper 1991). Locations: GRI = Grimersum (cool
climate); GI = Gießen (warm climate), CP = crude Protein; EX = extensibility; RES = resistance; E = energy

Table 3:
Effects of temperature on grain nitrogen and dough resistance and extensibility in three wheat cultivars, in two experiments
with contrasting nitrogen levels (Randall and Moss 1990).

OLYMPIC HARTOG SKUA

Experiment Cool Hot Cool Hot Cool Hot
Grain N (%)
low N 1.51 1.72 1.78 1.88 1.63 1.72
high N 2.45 2.33 2.55 2.42 2.24 2.24
Differences: N: P < 0.001; temperature: n.s.; cultivar: P < 0.01
Maximum resistance (E.U.)
low N 190 225 238 252 148 178
high N 290 383 290 345 190 215
Differences: N: P < 0.001; temperature: P < 0.001; cultivar: P < 0.001
Extensibility (cm)
low N 16.9 16.3 20.7 18.0 16.8 15.9
high N 23.7 21.5 27.3 26.1 23.6 22.9
Differences: N: P < 0.001; temperature: P < 0.001; cultivar: P < 0.001
Landbauforschung Völkenrode, Special Issue 283, 2005 33

Figure 14:
Influence of different temperatures during grain filling period of wheat (cultivar: SCHIROKKO) from a pot experiment in a
growth chamber in 1984 on the extensogram of dough (Schipper 1991), BU = Brabender units

Figure 15:
a) Relationship between protein content and sedimentation value of wheat grown at different temperatures approx. 32 days
after anthesis (Sosulski et al. 1963).
b) Relationship between protein content and mixogram area of wheat grown at different temperatures approx. 32 days after
anthesis (Sosulski et al., 1963).
34 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

It becomes clear that gluten structure, rheological observing their allergic symptoms (rash). They tol-
performance and the baking quality of wheat are erate the spelt, which was not modified so inten-
not given, but are reactions of the plant as a living sively by breeders during the last decades. But
organism to certain impulses from the environment. wheat leads to skin reactions. After doubling the
Here S and warmth belong to the most prominent gluten content of baby food (< 2 years old) in Swe-
and important factors. If there is sufficient S as a den there was a 300% higher incidence of celiac
substance from “below” (soil, groundwater, fertil- disease. After reducing gluten content, a reduction
izer) and insufficient warmth from above (cool occurred to the normal occurrence of this illness
weather, which can be regarded as little S as a (Ivarsson et al., 2000). Gluten-sensitivity is not
process, not as a substance), the wheat plant will confined to the small intestine (celiac disease) but
tend to lower proportions of HMW-glutenin and also causes an inflammation of the nervous system
softer glutens and doughs. If on the other hand with chronic migraine. This could be cured in 9
there is S deficiency from “below” and hot weather from 10 cases by strictly eliminating wheat from
(much S from “above”, which means S as a proc- the diet (Hadjivassiliou et al., 2002).
ess, not as a substance) during grain filling period, Again several questions may arise from these
the wheat plant will produce increased amounts of phenomena: Was this alarming situation always the
HMW-glutenin and tougher glutens and doughs. It same or are we experiencing a sneaking develop-
is well known in biological science that all factors ment that is only the top of the iceberg? Is merely a
applied to living organisms (light, water, warmth, poor human immune system the reason for the in-
fertilizers etc.) show an optimum, when their input crease of allergies or does food quality play an im-
is increased. Healthy organisms and sustainable portant role? Is wheat and its protein no longer a
systems are, on the long run, only achieved when harmless staple food? Could a shift in wheat plant
care is taken not to destroy this delicate equilibrium constitution towards S deficiency symptoms be the
of factors producing an optimum. With regard to reason for all the problems?
the baking quality of wheat breeders and cereal More research should be done with regard to
scientists obviously failed to achieve this aim by wheat breeding with rigorous reference to the hu-
breeding their cultivars on the background of ample man being as a whole and his / her nutritional
S depositions in the ecosystems. They (involuntar- needs.
ily) selected plants showing definite characteristics
of S deficiency (higher proportions of HMW-
glutenin, stronger gluten and dough) even under Acknowledgements
conditions of ample S supply. I suppose they also
selected plants with a high warmth susceptibility as I would very much like to thank Anke Fleck for
this also delivers firm protein structure. When this editing and Kenneth Fraser for language revision of
environmental pollution was stopped and S supplies this paper.
returned to natural conditions, even with a non-S
craving plant like wheat, problems arose with the
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Landbauforschung Völkenrode, Special Issue 283, 2005 37

Relationship between sullfur deficiency in oilseed rape (Brassica napus L.) and its
attractiveness for honeybees
Silvia Haneklaus1, Anja Brauer1, Elke Bloem1 and Ewald Schnug1

Abstract1 flowering, characteristic changes of macroscopic S

deficiency are to be seen in color and shape of the
Oilseed rape showing macroscopic symptoms of petals. It was observed repeatedly that S deficient
sulfur deficiency influences the behavior of honey- oilseed rape is less attractive for honeybees. These
bees, something that has been observed repeatedly findings were, however, subjective, while bias-free
in production fields. The symptomatology of sulfur experimental studies have not been carried out so
deficiency in cruciferous crops is characteristic dur- far.
ing the whole vegetation period. The peculiarity of Oilseed rape is one of the most important Euro-
sulfur deficiency symptoms during flowering de- pean melliferous crop for beekeepers as it is an im-
pends on the moment when sulfur becomes a limit- portant foraging plant in early summer. In Germany,
ing factor. An early appearance of sulfur deficiency oilseed rape is grown on an area of about 1.27·106 ha
is regularly related to the change of the petal color (Anon 2004). The main pollinators in oilseed rape
from bright to pale yellow, or even white petals. At are insects of the family Apidea (e.g. honey bees,
the same time, the petals are modified in size and wild bees and bumble bees) (Corbet, 1992; Wil-
shape. By comparison, a late occurrence of sulfur liams, 1996) and the significance of honeybees as
deficiency usually results in the change of color pollen vectors for seed set and yield has been de-
mentioned earlier, while other morphological pa- scribed in the literature (Steffan-Dewenter, 2003).
rameters are not affected. It was the aim of this pa- Although oilseed rape is self-pollinating (Saure,
per firstly to provide a condensed description of 2002), the cross-pollination rate, predominately by
sulfur deficiency symptoms in oilseed rape during honeybees, was estimated to be about 20% (Downey
the vegetation period, secondly to determine the et al. 1980). According to Olsson (1960) the cross-
influence of the sulfur supply on morphological pollination rate may vary in relation to genotype and
characteristic of oilseed rape petals, and thirdly to climatic conditions between 5 % and 95 %. By
present for the first time data about the attractive- comparison, on fields where composite hybrid oil-
ness of flowering oilseed rape for honey bees in seed rape varieties are grown or male-sterile lines
relation to the S supply. for breeding of restored hybrid cultivars, these
plants have a high dependence on pollination by
Key words: flower color, honey plants, petal defor- vectors (Steffan-Dewenter, 2003). Thus, determin-
mation, pollen ing the influence of the S supply of oilseed rape on
its attractiveness for foraging honeybees is a funda-
mental contribution from both the agronomic and
Introduction ecological point of view. It was the aim of this paper
to provide a comprehensive description of macro-
Macroscopic sulfur (S) deficiency was first ob- scopic S deficiency symptoms in oilseed rape during
served on production fields in 1981 (Schnug and the vegetation period with special attention being
Haneklaus 1994a), and more then 20 years later it is paid to visual symptoms during flowering, in order
still the most widespread nutrient disorder in north- to quantify the influence of the S supply on morpho-
ern Europe (URL://www.pb.fal.de). The signifi- logical parameters of the flowers and last, but not
cance of the S supply for crop production, crop least to show first results about the attractiveness of
quality and plant health has been outlined for exam- flowering oilseed rape for bees in relation to the S
ple by Schnug and Haneklaus (1998), Schnug supply.
(1997) and Haneklaus et al. (2004). Visual symp-
toms of S deficiency in cruciferous crops are very
specific and can be addressed in the field throughout Materials and methods
the whole vegetation period. Oilseed rape provides
an important source of nectar and pollen for honey- Two field experiments with winter oilseed rape
bees, which are attracted by the bright yellow color were conducted at Braunschweig (E 10° 27`, N 52°
of the crop in bloom (Pierre et al. 1999). During 18`). In the first experiment S was applied at rates of
50 kg S ha-1 in fall and 100 kg S ha-1 in spring to the
1
Institute of Plant Nutrition and Soil Science, Federal cultivar Bristol. N was applied at a rate of 200 kg N
Agricultural Research Centre (FAL), Bundesallee 50, ha-1. The plot size was 40 m2 and each treatment had
38116 Braunschweig, Germany
38 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

four replicates. For a detailed description of the ex- more difficult to identify than other nutrient defi-
perimental design see Salac (2004). Growth stages ciency symptoms (Bergmann, 1993). Brassica spe-
of oilseed rape were recorded according to the code cies such as oilseed rape, however, reveal character-
number of the BBCH scale (Strauss et al. 1994). istic macroscopic symptoms of S deficiency that can
be found throughout the vegetation period. As a
Bee traps supplement to the description of S deficiency symp-
A beehive was placed in front of the experimental toms, illustrative digital colour images (WWW No.)
field on 19 April 2004. At the start of flowering can be retrieved from the World Wide Web
(BBCH 60), in each plot four white and four yellow (URL://www.fal.pb.de). Physiological changes in
dishes were positioned at a height corresponding plant metabolism as a result of S deficiency are de-
with that of the crop plant. The bees were collected scribed for instance by Schnug (1988) and Schnug
on two following days (20 April 2004 and 21 April and Haneklaus (1994a).
2004).In the second experiment, macroscopic symp-
toms of S deficiency on leaves and flowers were Macroscopic S deficiency symptoms of oilseed rape
visible in the cultivar Smart in relation to mineral N before winter (BBCH 1-19)
fertilization (100 and 200 kg N ha-1) and application Even before winter, during the early growth of oil-
of manure (0 and 4.8 t ha-1). The plot size was 65 m2 seed rape, leaves may start to develop symptoms of
and each treatment had four replicates. For experi- S deficiency (WWW 2). Though the plants are still
mental design see Rogasik et al. (2004). small, symptoms can cover the entire plant (WWW
3). Sulfur fertilization before or at sowing will en-
Plant sampling and analysis sure a sufficient S supply, particularly on light,
In total, 10 individual flowers from 10 different sandy soils and promote the natural resistance of
plants with different degrees of visual S deficiency plants against fungal diseases (Haneklaus et al.,
symptoms (extreme, severe, none) were collected on 2004)
4 May 2004 (BBCH 65) and 40 or 80 petals ana-
lyzed. The petals were carefully separated by using Macroscopic S deficiency symptoms of oilseed rape
tweezers and directly fixed on object slides. For the from the start of the main vegetation period until
determination of length and diameter of each petal, appearance of inflorescences above upper leaves
the object slides were scanned and the images inter- (BBCH 30 - 59)
preted afterwards automatically by employing the Plants suffering from severe S deficiency, show a
ArcView 3.2 software package (Esri, 1999). characteristic marbling of the leaves. The chlorosis
For the determination of the amount of pollen starts from the leaf's edge spreading over intercostal
produced the anthers of 10 flowers were placed in areas but the zones along the veins always remain
1.5 ml Eppendorf tubes. The pollen was dissolved green (Schnug, 1988) (WWW 4). Deficiency symp-
from the anthers by using dimethylether. Then the toms in younger, fully developed leaves of oilseed
anther peduncles were removed, the ether vaporised rape at the start of stem elongation begin to appear
and finally the amount of pollen weighed. when the total S concentration drops below 3.5 mg
The differences in color of the oilseed rape petals g-1 S in double low varieties (Schnug and Hanek-
were determined colorimetrically by employing the laus, 1994a, b).
method of Miyamjima et al. (2000). From each level Chlorosis very rarely turns into necrosis (Schnug,
of S supply (extreme S deficiency, severe S defi- 1988, Ulrich et al., 1993) as it does with nitrogen
ciency, sufficient S supply) 100 petals from at least and magnesium deficiency, which is an important
25 different plants were collected and shock frozen criterion for differential diagnosis. Even under con-
in liquid nitrogen and freeze-dried before analysis. ditions of extreme S deficiency where an oilseed
rape plant shows severe disorders it will not wilt
Statistical analysis (WWW 6).
The software package CoHort (Anon, 1990) was A characteristic secondary symptom of severe S
used for ANOVA (Tukey-Kramer test). deficiency is the reddish purple color due to the en-
richment of anthocyanins in the chlorotic parts of
Brassica leaves (WWW 8). Under field conditions,
Results and discussion the formation of anthocyanins starts 4 - 7 days after
chlorosis. In particular those leaves not fully ex-
panded produce spoon-like deformations when
Sulfur deficiency symptoms of oilseed rape during struck by S deficiency (WWW 9). The reason for
the vegetation period this is a reduced cell growth rate in the chlorotic
Severe S deficiency symptoms were often de- areas along the edge of the leaves, while normal cell
scribed in the literature as being less specific and growth continues in the green areas along the veins,
Landbauforschung Völkenrode, Special Issue 283, 2005 39

so that S deficient leaves appear to be more succu- during ripening (BBCH 71 - 99)
lent. The grade of the deformation is stronger the The strongest yield component affected by S defi-
less expanded the leaf is when the plant is struck by ciency in oilseed rape is the number of seeds per
S deficiency (WWW 10). Marbling, deformations pod, which decreases significantly (WWW 16)
and anthocyanin accumulation can be detected up to (Schnug, 1988). As described earlier for leaves, the
the most recently developed small leaves inserted in branches and pods of S deficient plants are often red
forks of branches (WWW 11). or purple colored due to the accumulation of antho-
cyanins. Extremely low numbers of seeds per pod,
Macroscopic S deficiency symptoms of oilseed rape in same cases seedless 'rubber pods' are characteris-
plants during flowering (BBCH 60 - 69) tic symptoms of extreme S deficiency.
During flowering S deficiency causes one of the
most impressive symptoms of nutrient deficiency: Influence of the S supply on morphological parame-
the 'white blooming' of oilseed rape (WWW 12). ters of oilseed rape flowers and the attractiveness
The white color presumably develops from an over- for honey bees
load of carbohydrates in the cells of the petals Honeybees are attracted by scent, colour and form
caused by disorders in the protein metabolism, of the honey-bearing plants, but it is the scent which
which finally ends up in the formation of leuco- has the fastest and strongest impact (Menzel et al.
anthocyanins (Schnug and Haneklaus, 1995). As 1993). Honey bees might assess the amount and
with anthocyanins in leaves, the symptoms develop concentration of nectar in each flower by employing
strongest during periods of high photosynthetic ac- different senses: directly by visual access to the nec-
tivity. Besides the remarkable modification in color, tar (Throp et al. 1975, Willmer et al. 1994), or by
size and shape of oilseed rape the petals change, too. olfactory sensation (Heinrich 1979; Galen and
This apparently influences the attractiveness of oil- Kevan, 1983), indirectly by an indicator of the re-
seed rape for honeybees as according to initial per- ward for foraging such as colour (Gori, 1983; Weis,
sonal observations this is seen as well as changes in 1991), flower size (Galen and Neport, 1987; Eckhart
the petal color, a weaker scent and a reduced num- 1991), or the particular floral structures (Bell et al.,
ber of bees. A verification of this appraisal would be 1984; Gonzalez et al., 1995).
of utmost significance for beekeepers and farmers
alike in order to warrant a high yielding oilseed rape Influence of the S supply on volatiles from oilseed
crop and honey harvest. In two field experiments the rape flowers
influence of the S supply on morphological parame-
ters of oilseed rape flowers and the behavior of bees Volatiles released during flowering of plants fa-
was investigated and the first results are presented cilitate flower recognition by the honeybee and thus
below. increase their foraging efficiency. The chemical
analysis of volatiles from various plant species re-
Macroscopic S deficiency symptoms of oilseed rape vealed a multiplex composition of floral odors with

Table 1:
Influence of the S nutritional status on the shape of petals in field grown oilseed rape plants at main flowering (BBCH 65).
S Status (n) Mean diameter Mean length Mean D:L ratio
(D) (L)
(mm) (mm)
Extreme S deficiency 40 5.2 12.5 0.41
Severe S deficiency 80 6.0 13.5 0.45
Sufficient S supply 80 10.0 16.4 0.61
LSD5% 0.29 0.40 0.015

Table 2:
Influence of the S nutritional status on the absorbance at 440 nm of rapeseed petals at main flowering (BBCH 65).
S status Sample (mg) Absorbance Absorbance
at 440 nm g-1 dry matter
Extreme S deficiency 21.8 0.654 30.0
Severe S deficiency 28.5 0.952 35.6
Sufficient S supply 21.2 1.575 74.3
40 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

more than 700 different compounds that were found 8 mm, the time for searching was drastically pro-
in 60 families of plants (Knudsen et al. 1993). The longed from 10.4 to 124.3 seconds (Spaethe et al.,
mechanisms by which honeybees process this com- 2001).
plex chemical information and adapt their behavior
accordingly are as yet unknown (Wadhams,1994).
A total of 34 different compounds were found in
volatiles of oilseed rape (Tollsten and Bergström,
1988; Robertson et al., 1993; McEwan and Smith,
1998). The main volatiles from oilseed rape flowers
were 3-hydroxy-2-butanone > 2,3-butanedione >
dimethyl disulfide >> formaldehyde > 3-methyl-2-
butanone > dimethyl trisulfide (Robertson et al.,
1993). Omura et al. (1999) determined nitriles and
isothiocyanates in large quantities in the floral vola-
tiles of Brassica rapa. Honeybees use volatiles for
discrimination whereby a conditioning threshold
was determined for individual components (Pham-
Delégue et al., 1993). Previous studies have shown
that the S supply increases the glucosinolate in Figure 1:
Influence of severe S deficiency on deformation of petals
vegetative plant tissue, seeds and petals of oilseed
by modification in diameter (D) and shape of petals ex-
rape (Schnug, 1988, 1993). Additionally, 2-phenyl- pressed by the diameter:length ratio (D/L) from field
ethyl isothiocyanate yielded limited conditioned growing oilseed rape plants at main flowering (BBCH
responses in honey bees, but was an active compo- 65).
nent after being learned in a complex mixture of
volatiles (Laloi et al., 2000). Thus a relationship
between the S-containing compound, intensity of the Influence of the S supply on the petal color of oil-
scent and finally the attractiveness to honey bees seed rape
seems possible.
On S deficient sites, yellow and white petals exist
side by side, thus excluding genetic influences and
Influence of the S supply on the size and shape of
indicating nutritional effects. Changes in the colour
petals of oilseed rape
of the oilseed rape petals are possibly related to in-
Severe S deficiency also causes deformations of creasing sugar concentrations in the plant tissue due
leaves and petals (Schnug and Haneklaus, 1994a). If to disorders in the protein metabolism. By pigment
S deficiency strikes the plant early in the vegetation formation, plants prevent excessive accumulation of
period, the size of the petals is reduced most se- free sugars. One major pigment causing the yellow
verely and instead of a bright yellow color, the char- colour of rapeseed flowers is the flavonol querceta-
acteristic white flowering can be observed (see gatin and its isorhamnetin 3-glycoside (Harborne,
above). In comparison, if S deficiency occurs later 1967). Glycosylation of flavonols has a hypsochro-
in the vegetation period the reduction in size and mic effect, which might lead to a shift of the absorp-
changes in color are distinctly less. In cases where S tion spectra to the UV range, which is invisible to
deficiency sets in shortly before flowering, the petal the human eye. Another hypothesis to explain the
size remains unaffected, while changes in color can change in color is that the synthesis of colorless an-
still be seen. thocyanins is increased (Schnug and Haneklaus,
Egg shaped petals are characteristic of extreme 1995). The influence of the S nutritional status on
and severe S deficiency, which are a result of the the absorbance at 440 nm is shown in Table 2.
reduction in diameter and length of the petals. The The differences in the absorbance were strongest
progression of deformations in relation to the S sup- between petals showing extreme S deficiency and
ply was assessed by establishing the relationship those plants with a sufficient supply, but also verifi-
between the diameter of the petals and the quotient able for extreme and severe S deficiency (Table 2).
of diameter and length (Figure 1). Similar results The results are in agreement with those found by
were found by Schnug and Haneklaus (1994a). A Schnug and Haneklaus (1995).
classification of plants into three groups of S supply
(extreme S deficiency, severe S deficiency and suf- Influence of the S supply on the pollen content of
ficient S supply) revealed that the petal diameter oilseed rape
may be reduced by 50 % and petal length by 24 %
Oilseed rape offers ample pollen, which is of high
as a result of enduring S deficiency (Table 1).
relevance for the development of the honeybee
The size of flowers was an important criterion for
population after winter (von der Ohe and von der
bumble bees as with decreasing diameter, from 25 to
Landbauforschung Völkenrode, Special Issue 283, 2005 41

Ohe, 2002). Besides this, the pollen supply contrib- flowering wild radish plants to white flowering
utes to a satisfying and healthy development of the cross-wild F-1 hybrids, while bumble bees showed
bee hive (von der Ohe and von der Ohe, 2002). Von no such preference (Lee and Snow, 1998).
der Ohe and von der Ohe (2002) showed that geno- The dishes were only installed for two days in
typical differences in the pollen content were not order to limit the losses of honeybees. Yellow dishes
significant, while abiotic factors such as climatic are attractants for honeybees which use yellow
conditions had a distinct impact. The determination flowering plants for foraging (Saure, 2002). The
of the pollen content revealed that S deficiency did results reveal that a significantly lower number of
not affect the supply (Table 3). honeybees was attracted and finally collected in the
white dishes than in the yellow ones. This result was
consistent on both days. During the second day a
Table 3. significantly lower number of bees was gathered,
Influence of the S nutritional status on the pollen content which suggests a rapid messaging within the bee-
of oilseed rape at main flowering (BBCH 65). hive.
S status Pollen content (g)

Extreme S deficiency 0.020

Severe S deficiency 0.022
Sufficient S supply 0.023

Ongoing studies investigating the influence of the

S supply on the nectar content and quality of oilseed
rape in relation to the S supply under greenhouse
conditions revealed that both parameters were not
influenced by the treatment. Thus it may be con-
cluded that S deficient oilseed rape offers a nutri-
ment, which is comparable to that of a sufficiently
supplied plant in both the amount and quality of Figure 2:
pollen and nectar, respectively. Differences in the Number of collected bees in relation to sampling date and
attractiveness of S deficient oilseed rape therefore dish colour (Y=Yellow; W=White) at main flowering
must be related exclusively to scent and morpho- (BBCH 65).
logical features.

Influence of the S supply on the attractiveness of Conclusions

flowering oilseed rape for honey bees
For studying the attractiveness of oilseed rape for S deficiency results in significant morphological
foraging honey bees in relation to the S supply un- changes such as shape and color. Additionally, the
der field conditions the experimental design of the scent might also be related to the S nutritional status
field experiments was not appropriate because of the of the plant. In contrast, pollen and nectar content
missing spatial distance of at least 200 m (von der and quantity are obviously not influenced by the S
Ohe, 2004) between S deficient and plants with a nutrition, so both factors can be excluded from be-
sufficient S supply. This is essential for assessing ing the causal reason for different attractiveness of S
behavioral differences related to this nutritional fac- deficient and sufficiently supplied plants for honey
tor. The collection of honeybees in white and yellow bees. Bees proved to be more attracted to yellow
dishes in plots with different S application rates than white dishes so that next to scent and shape this
must therefore only be treated as strictly indicative parameter seems to be relevant for foraging honey-
for the behaviour under natural conditions with bees. Further research with free flying bees will be
white and yellow flowers (Figure 2). carried out in field experimentation in order to an-
Hill et al. (2001) found out that the foraging be- swer these open questions.
havior of honeybees was related among other things
to the colour of the flowers and that a white and
yellow colour, together with blue yielded discrimi- Acknowledgements
native behavior in relation to reward volume and
quality. It is also interesting in this context that The authors gratefully acknowledge Dr. W. von
some insects such as syrphid flies preferred yellow der Ohe and K. von der Ohe, Niedersächsisches
42 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

Landesinstitut für Bienenkunde, Celle for introduc- Laloi D, Bailez O, Blight MM, Roger B, Pham-Delègue
ing us to the world of honey and bees. Special M-H, Wadhams LJ (2000) Recognition of complex
thanks needs to Herbert Daybell (Agrimedia, Bottes- odors by restrained and free-flying honeybees, Apis
ford) for the linguistic editing of this paper. mellifera. J. Chem. Ecol. 26:2307-2319
Lee T N, Snow A A (1998) Pollinator preferences and the
persistence of crop genes in wild radish populations
(Raphanus raphanistrum, Brassicae). Am. J. Bot.
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Landbauforschung Völkenrode, Special Issue 283, 2005 45

Influence of drought and flooding on sulfur nutrition of deciduous trees at the whole
plant level
Cornelia Herschbach

Abstract1 alba, Quercus robur, stress concept, sulfur, sulfide

detoxification
In deciduous trees of the temperate zone sulfur
nutrition is strongly influenced by environmental
conditions. However, the effects observed during Introduction
drought in oak (Quercus robur) and during flooding
in poplar (Populus tremula x P. alba) do not consist Plants are living in a changing environment. The
to the ‘demand-driven control’ model of sulfur environment changes in the course of the day, dur-
nutrition. Moreover, the observed changes could ing the year, from season to season and between
either be originate from general stress reactions in years as a consequence of climate variation and cli-
the case of drought stress or from adaptation mate change. Especially long-living organism like
mechanism in the case of flooding. During drought trees that live more than a century have to cope with
stress the sulfate loaded into the xylem was a high variability’s of environmental factors during
diminished in mycorrhizal-oak roots and so was their lifetime. For example, water supply, tempera-
sulfur transport in the phloem, probably by ture, and light intensity are subjected to global cli-
diminished loading of sulfur into the phloem. After mate change. This, especially trees have to adapt
the ‘demand-driven control’ model of sulfur physiological processes to the changing environ-
nutrition these findings lead to assume an increment ment. These reactions physiological allow the plant
in reduced sulfur contents, mostly of glutathione in to compensate stress caused by environmental
shoot and root tissues, which however was not changes and to modulate the rate of growth its se-
observed. Obviously, the reduced water availability nescence and the onset of reproductive growth.
seems the reason for the decreased loading of sulfate Deciduous tree species from the temperate zone,
into the xylem and the diminished sulfur transport in such as oak, beech or poplar, show differences in
the phloem. If oak seedlings were simultaneously they sensitivity to environmental factors like
subjected to elevated pCO2 these lead to an drought and flooding. Since most tree species,
increased resistance against drought probably due to which are not domesticated they possesses a high
the changed pre-disposition. genetic variability and have developed ecotypes,
Water logging, i.e. anoxic conditions in the which are acclimated to stand specific environ-
rhizosphere, caused increasing cysteine contents in mental factors. Therefore, it is difficult to define
lateral roots of poplar. Since activity of APS reduc- stress reactions of trees. Different models have been
tase the key enzyme of the sulfate assimilation published aimed to describe stress reactions (Beck
pathway disappeared below the detection limit and, and Lüttge, 1990; Tesche, 1995; Brunold, 1996;
the sink strength of the roots for sulfur from the Larcher, 2001). The simplified model of Tesche
shoot was decreased the enhanced cysteine must be (1995) shows an alarm reaction and adaptation
formed by a process uncoupled from sulfate reduc- within the normal variability of a plant (Figure 1)
tion under these conditions. H2S produced in the that ensures high vitality. However, plant may lose
rhizosphere by sulfate reducing bacteria could be part of their variability by adaptation to the envi-
taken up into root cells in analogy to hydrogen sul- ronment even within the range of the normal vari-
fide exposure of leaves. Increasing cysteine contents ability of growth. If the intensity and/or duration of
may than be the consequence of sulfide detoxifica- stress exceeds the normal variation, the plant first
tion indicated by an enhanced O-acetylserine shows an alarm reaction which depends on the stress
(thiol)lyase (OASTL) activity during flooding. Pop- factor. During mild stress conditions the plant can
lar is a flooding tolerant species, so the capability of cope with the stress and will probably adapt to the
sulfide detoxification may be a means of stress changed environment. However, the fitness of the
avoidance and/or stress tolerance during water log- plant may than be reduced. If the plant is attacked
ging. by additional stress or the duration of stress pro-
ceeds the extend to which a plant is able to cope
Key words: drought stress, flooding, glutathione with this situation depends on its pre-disposition and
(GSH), phloem transport, Populus tremula x P. on its capability to avoid or tolerate the conse-
quences of the specific stress factor. If the plant is
able to adapt to the stress situation it is called eus-
1
Albert-Ludwigs-University Freiburg, Institute of Forest tress and the plant may show an enhanced resis-
Botany and Tree Physiology, Chair of Tree Physiology, tance. When the plant is unable to manage the in-
Georges-Köhler-Allee 053/054, 79110 Freiburg, Germany
46 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

creased stress, reaches the boundaries to cope with it reduce sulfate and assimilate it into Cys and Met
and finally dies this is called distress. (Saito, 1999; Droux et al., 2000; Leustek et al.,
2000) in both, photosynthetically active tissues as
well as in heterotrophic tissues in roots or stems (c.f.
Herschbach and Rennenberg, 2001b; Herschbach
2003). The contribution of sulfate reduction in het-
erotrophic organs to the whole plants’ needs for
reduced sulfur, however, is still unknown. For re-
duction the relatively inert sulfate has first to be
activated by ATP sulfurylase which forms adeno-
sine 5’-phosphosulfate (APS) and pyrophosphate
(PPi, Brunold, 1990). In higher plants APS is di-
rectly reduced to free sulfite via APS reductase
(Gutierrez-Marcos et al., 1996; Setya et al., 1996;
Suter et al., 2000). From studies with Arabidopsis
Figure 1: thaliana root cultures it appears that this reaction
An altered model of stress reactions after Tesche (1995). controls the flux through the whole sulfate reduction
A plant with a high vitality is in the center of the model. If pathway (Vauclare et al., 2002). In the next step the
a factor of stress has affected the plant, an alarm reaction sulfite produced is reduced to sulfide without a re-
is induced followed by an adaptation mechanism. Addi- lease of intermediates by a sulfite reductase. O-
tional stress such as prolonged duration of a stress factor acetylserine(thiol)lyase (OASTL) catalyses the final
or an additional factor leads to eustress or distress. reaction of assimilatory sulfate reduction forming
Cys (Giovanelli, 1990). In this reaction sulfide is
transferred to O-acetylserine (OAS) which itself is
Stress reactions can be observed at different lev- synthesized by serine acetyltransferase (Giovanelli,
els. Morphological changes are most obvious, but 1990). The availability of OAS can limit the rate of
prior to morphological symptoms differences are Cys formation (Neuschwander et al., 1991; Saito et
measurable at the level of physiological processes al., 1994) and, therefore, provides a regulatory link
and/or gene expression (Brunold et al., 1996; between nitrogen, carbon and sulfur metabolism
Larcher, 2001). For example: before the leaves wilt (Brunold et al., 2003; Kopriva and Rennenberg,
as a consequence of drought stress, a decreasing pre- 2004). O-acetylserine(thiol)lyase and serine acetyl-
down water potential is detectable (Schwanz et al., transferase co-operates in a multienzyme complex in
1996). Also changes within other metabolic proc- which protein-protein interactions are based on the
esses, i.e. photosynthesis, chlorophyll fluorescence, OAS concentration (Hell et al., 2002; Hell, 2003).
antioxidant levels can be detected before visible Cys can further be used for Met synthesis (Gio-
symptoms appear (Brunold et al., 1996; Larcher, vanelli, 1990; Droux et al., 2000), protein formation,
2001). or glutathione production. Synthesis of glutathione
Global environmental conditions have changed (GSH) occurs in the cytosol as well as in the stroma
rapidly over the last century. As a consequence of of the plastids (Bergmann and Rennenberg, 1993).
human activities atmospheric pCO2 has increase In both compartments GSH is produced by the con-
from 290 to 350 ppm and is expected to double in secutive action of J-Glu-Cys synthetase (J-ECS),
this century (Hasselman, 1997; Houghton, 1997). synthesizing J-Glu-Cys (J-EC) from Glu and Cys,
Since atmospheric pCO2 contributes to the green- and glutathione synthetase (GSH-S), adding Gly to
house effect, it is also assumed that mean global the C-terminal end of J-EC (Bergmann and Rennen-
surface temperature will rise by about 1-3.5 berg, 1993). GSH functions as a storage and trans-
(www.ipcc.ch/present/graphics.htm). As conse- port form of reduced sulfur (Rennenberg 1984), is
quence, precipitation and evaporation patterns will involved in the regulation of sulfur nutrition
change and forests and other ecosystems will be (Hawkesford, 2000; Herschbach and Rennenberg,
exposed to drought and flooding events (Rennen- 2001a,b; Kopriva and Rennenberg, 2004), and is an
berg et al., 2004). essential component of the plants’ defense system
Sulfur is an essential macro-nutrient for growth for abiotic and biotic stress (Foyer and Rennenberg,
and development of plants. As essential part of the 2000; Tausz et al., 2004).
plants primary metabolism the use of sulfur in To all plants sulfur is available in the soil in its
growth and development is strongly affected by the oxidized form as sulfate. Sulfate is distributed
environmental changes indicated above. Within cells within the plant via a range of sulfate transporters
the amino acids cysteine (Cys) and methionine which are expressed in different tissues and com-
(Met) are essential constituents of proteins and, partments of the cell and are differently sensitive to
therefore, for growth and development. Plants can sulfur deficiency (Buchner et al., 2004). Since SO42-
Landbauforschung Völkenrode, Special Issue 283, 2005 47

reduction is thought to mainly occurred in leaves trees subjected to water stress showed down regula-
(Brunold, 1990), the surplus of reduced-sulfur must tion of enzymes involved in the anti-oxidative sys-
be transported out of leaves and, subsequently, tem. The activity of these enzymes increased if oak
loaded into the phloem for transport into the sink seedlings were simultaneously subjected to elevated
organs of the plant (Herschbach and Rennenberg, rather than ambient pCO2. The authors concluded
2001a,b). Organs assumed to be sinks for reduced that under elevated pCO2 leaf tissues of the oak
sulfur include young leaves, developing seeds and seedlings had a higher metabolic flexibility to cope
heterotrophic stem and root tissues. Still this view is with oxidative stress. After the stress concept of
based on carbon metabolism it is surprising, that Tesche (1995) elevated pCO2 enhanced stress resis-
mature leaves are no source-organs to supply young, tance against drought in oak seedling.
developing leaves of oak (Schulte et al., 1998) and This was also evident when the sulfur nutrition
poplar (Hartmann et al., 2000) with reduced-sulfur. was investigated (Table 2). After the drought period
Moreover, young poplar leaves (Hartmann et al., of 21-days transport of sulfur from mature leaves
2000) and poplar roots (Herschbach, 2003) are able into bark or root tissues was turned off if oak seed-
to reduced their own sulfate. Nevertheless, sinks lings were cultivated at ambient pCO2. In contrast,
must communicate with sources and vice versa to sulfur transport was still observed in seedlings
signal the demand for S in order to regulate sulfate grown at elevated pCO2 (Schulte et al., 1998). The
uptake by the roots but also the whole-plant supply extent of drought tolerance, however, was dependent
of reduced sulfur. According to the ‘demand-driven on mycorrhization of the oak seedlings. At elevated
control’ model of S nutrition this signal is GSH pCO2 drought diminished 35S-sulfur export out of
which regulates sulfate uptake as well as sulfate leaves of non-mycorrhizal oak seedlings whereas
reduction (Rennenberg, 1995; Lappartient and this was not observed in mycorrhizal seedlings. Al-
Touraine, 1996). though S transport into lateral roots was diminished
The presented review summarizes published lit- in both, mycorrhizal and in non-mycorrhizal roots,
erature on the influence of drought and flooding on the GSH content of the roots remained unchanged
the sulfur nutrition of deciduous trees. The observed (Schulte, 1998). After the ’demand-driven control’
effects are discussed with respect to the ‘demand- model sulfate uptake and sulfate transport into the
driven control’ model of sulfur nutrition and with xylem should remain unchanged under these condi-
respect to the stress concept of Tesche (1995). tions (Rennenberg, 1995; Lappartient and Touraine,
1996; Herschbach and Rennenberg, 2001a). Still
mycorrhizal oak seedlings showed decreasing rates
Influence of drought on the sulfur nutrition of of sulfate loaded into the xylem during drought
oak (Quercus robur) stress (Seegmüller, 1998). Obviously, the effects of
drought on sulfur nutrition are not consistent with
Effects of drought in combination with elevated the ‘demand-driven control’ model. In conclusion,
pCO2 were analyzed under controlled and natural this example supports the assumption that the pre-
growth conditions (see Wullschleger et al., 2002). disposition of the plant is very important for the
These investigations clearly showed that stress re- extent of drought stress. The diminished sulfur
sponses to drought dependent on the pre-disposition transport in the phloem and the reduced rate of sul-
of the plant, e.g., whether the tree was exposed to fate loaded into the xylem was the result of water
elevated pCO2 or not. For the consequences of deficiency and not a consequence of a changed sul-
drought for sulfur nutrition detailed data are only fur status.
available for the drought tolerant Quercus robur.
Pre-dawn water potential was diminished after 21-
days withholding water supply in mycorrhizal and Influence of flooding on the sulfur nutrition of
non-mycorrhizal oak seedlings independent both at poplar (Populus tremula x P. alba)
ambient and elevated pCO2 (Table 1, Schulte et al.,
1998, Schwanz and Polle, 2001). However, at ele- A long-term strategy of adaptation to flooding is
vated pCO2 the reduction was less pronounced. the formation of aerenchyma to prevent anoxia in
These findings corresponds to the observation that roots. Short-term effects of flooding result in a shift
water-use efficiency increased under elevated pCO2 from respiration to glucose fermentation, predomi-
(Saxe et al., 1998). After re-watering, pre-dawn wa- nantly ethanol fermentation by using reserved car-
ter potential recovered in Quercus robur within a bohydrates (reviewed in Armstrong et al., 1994;
few days (Schwanz and Polle, 2001). Whereas pho- Drew 1997). This is accompanied by diminished
tosynthesis was diminished due to drought stress, no synthesis of housekeeping proteins and an induction
changes were found in chlorophyll, carotenoids and of anaerobic stress proteins (Christopher and Good,
soluble proteins (Table 1, Schwanz et al., 1996). 1996). Toxic ethanol contents could be prevent by
Moreover, in this study it was demonstrated that ethanol transport into the xylem and transport to the
48 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

shoot with the transpiration stream (reviewed in hyde and acetic acid (Kreuzwieser et al., 1999). Al-
Armstrong et al., 1994; Drew, 1997). The most im- though pigment contents were slightly reduced and
portant consequence is the diminished ATP avail- carbon assimilation was diminished to 70% of con-
ability and, the decreased energy charge within the trol poplar trees after 14 days of flooding (Kreuz-
roots (Sieber and Brandle, 1991; De Simone et al., wieser et al., 2002), soluble carbohydrates increased
2002). This could influence transport processes in- in leaves and phloem exudates (Herschbach et al.,
cluding nutrient uptake, xylem loading, phloem 2004). Also in Fraxinus excelsior a floodplain tree,
unloading and consequently growth and develop- glucose increased in phloem exudates due to flood-
ment. Therefore, more glucose originating from the ing (Bartles, 2001). It appears that an increased
phloem-mediated carbon transport from the leaves transport of carbohydrates to the roots, probably
or from storage tissues is required to keep up from reserve mobilization, could meet the higher
growth, development and nutrient uptake. demand of carbohydrates for glucose fermentation
in the roots to maintain a high energy charge. How-
ever, this was not observed with oak (Bartels, 2001),
Table 1: which is a moderate flooding tolerant tree species.
Effects of drought on biometric and physiological parame- Rather, soluble carbohydrates in phloem exudates of
ters. Oak (Quercus robur) seedlings grown from acorns oak increased only during the 14-days period of
were cultivated under controlled growth conditions either recovery from flooding. To maintain metabolic
in a greenhouse or in environmental growth chambers.
Water supply was withdrawn for 3- to 4-weeks.
processes during flooding synthesis of anaerobic
proteins such as enzymes of the fermentation path-
way, glycolysis and enzymes to prevent post-anoxic
Atmospheric pCO2 Ambient Elevated stress are induced in tolerant species (Christopher
and Good, 1996). Although it may be assumed that
Predawn water potential1 = p protein contents changed due to this induction after
Photosynthesis1 p p flooding, non-uniform results were found for poplar
Chlorophyll1 = = (Kreuzwieser et al., 2002; Herschbach et al., 2004)
Carotinoids1 = = and, protein contents of flooded oak roots remained
Soluble protein1 = =
unaffected after long-term flooding (Kreuzwieser et
SOD activity in leaves1,2 p n
al., 2002). Soluble nitrogen compounds did not
Catalase activity in leaves2 p p
change in poplar roots, though several amino com-
Ascorbate peroxidase activity = n
in leaves1
pounds decreased in flooded oak roots (Kreuzwieser
Redox state (GSSG)2 et al., 2002). Both, the increased content of TSNN
n n
Redox state (ascorbate)2 and of soluble carbohydrates in phloem exudates of
p p
1
Schwanz et al., 1996, 2Schwanz and Polle, 2001 flooded oak trees may indicate an inhibition of
phloem unloading of amino compounds in the roots,
In the flooding tolerant poplar ethanol is produced since therein amino compounds decreased and solu-
from anaerobic glucose fermentation in flooded ble carbohydrates were unaffected (Bartels, 2001).
roots and the bulk is loaded into the xylem and Whereas the nitrogen metabolism remained unaf-
transported with the transpiration stream to the fected during anoxic conditions in poplar (Kreuz-
leaves where the ethanol introduced into the leaves wieser et al., 1999, 2002) flooding clearly affected
carbohydrate metabolism by oxidation to acetalde- the sulfur metabolism (Herschbach et al., 2004).
Even after 7 days of flooding the key enzyme of the

Table 2:
Effects of drought on oak (Quercus robur) seedlings with different pre-dispositions due to mycorrhization and atmospheric
pCO2. Oak seedlings were grown from acorns in environmental growth chambers under long-day conditions. To accomplish
drought stress, water supply was withdrawn for 21-days. n.d., not detectable.

Non-mycorrhizal Mycorrhizal
Atmospheric pCO2 ambient elevated ambient elevated

Pre-dawn leaf water potential1 p p p p

Total plant biomass1 = = = p
Root biomass1 = p = =
GSH content in leaves2 = = = =
35
S-sulfur export out of mature leaves1 n.d. p n.d. =
Proportion of 35S-sulfur remained in the shoot1 n.d. n n.d. =
Proportion of 35S-sulfur imported into lateral roots1 n.d. p n.d. p
GSH content in lateral roots2 = = = =
1
Schulte et al. 1998; 2Schulte 1998
Landbauforschung Völkenrode, Special Issue 283, 2005 49

Table 3:
Effects of flooding on sulfur nutrition of poplar (Populus tremula x P. alba). Results from Herschbach et al. (2004) are sum-
marized. n.d., not determined.

7 days of 14 days of After 7 days of recovery from

flooding flooding 15 days of flooding

APS reductase activity in leaves p p p

OASTL activity in leaves p p p
Cys content in leaves = = =
GSH content in leaves = = =
35
S-sulfur export out of mature leaves = n.d. n.d.

GSH content in phloem exudates n = =

Cys content in phloem exudates = = =

APS reductase activity in roots p p =

OASTL activity in roots = n n
Cys content in roots n n n
GSH content in roots = = n
Proportion of 35S-sulfur imported into lateral roots p n.d. n.d.

sulfate assimilation pathway, the APS reductase, conditions in the rhizosphere due to sulfate reducing
completely disappeared (Herschbach et al., 2004). bacteria (Dassonville and Renault, 2002). This sul-
This may be an indication that energy-consuming fide could be taken up into root cells in analogy to
enzymes of anabolic pathways are eliminated in hydrogene sulfide fumigation of leaves (Rennenberg
flooded roots to save energy. Indeed, the incorpora- and Polle, 1994). Since sulfide is phytotoxic because
tion rate of 35S-sulfate into insoluble cellular com- it inactivates metalloenzymes by forming disulfides,
pounds was diminished and, consequently, the bio- it must be detoxified. One strategy may be the me-
mass increment was reduced (Herschbach et al., tabolization to non-toxic compounds, such as thiols
2004). Based on the ‘demand-driven control model’ as described by Fürtig et al., (1996) for Phragmites
of sulfur nutrition enhanced amounts of GSH would australis. In this case, a greater activity of O-
be expected in flooded roots when the GSH depend- acetlyserine(thiol)lyase (OASTL), the enzyme
ent APS reductase activity is down-regulated (Lap- which forms Cys from O-acetylserine (OAS) is ex-
partient and Touraine, 1996; Vauclare et al., 2002). pected and was really detected after 14 days of
Nevertheless, the GSH content in the roots of flooding in poplar roots (Table 3, Herschbach et al.,
flooded poplars remained unaffected. Though 2004) and in roots of several herbaceous plants after
unlikely (Bick et al., 1998, 2001; Kopriva and Ko- feeding sulfide (Pearson and Havill, 1988). After 4
privova 2004), it cannot be excluded that Cys acts as days in hydroponic culture poplar roots fed with
a feedback signal to prevent APS reductase expres- sulfide showed also increased OASTL activity. This
sion during anoxia. Indeed, in poplar roots Cys in- clearly indicates that sulfide can be detoxified in
creased under this conditions (Table 3, Herschbach roots under anoxic conditions and can be used for
et al., 2004). However, where does the sulfide in- Cys synthesis uncoupled from sulfate assimilation.
corporated into Cys comes from, if APS reductase These results demonstrate that changes in the sulfur
activity is not detectable? Protein breakdown seems state of plants must not necessarily correlate to the
not the reason for the increased Cys content in lat- ‘demand-driven control’ model of sulfur nutrition.
eral poplar roots, because the content of soluble pro- Moreover, increasing Cys contents under anoxic
tein increased (Kreuzwieser et al., 2002) or re- conditions from flooding could be a strategy in
mained unchanged (Herschbach et al., 2004) during stress tolerance and stress adaptation (see Fig 1).
flooding. Export of sulfur out of mature leaves was
not effected by flooding, but the proportion of sulfur
transported into lateral roots decreased (Table 3, Conclusions
Herschbach et al., 2004). Therefore, the increased
Cys content does not originate from enhanced sulfur The influences observed within the sulfur metabo-
transport to the roots and additionally, Cys must be lism during drought and flooding do not support the
synthesized uncoupled from sulfate assimilation. ‘demand-driven control’ model of sulfur nutrition as
High amounts of H2S are produced under anoxic a sole possibility to explain regulation of sulfur nu-
50 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

trition. Moreover, the observed effects could be best Brunold C, Rüegsegger A, Brändle R (1996) Stress bei
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Landbauforschung Völkenrode, Special Issue 283, 2005 53

Chemical behavior of soil sulfur in the rhizosphere and its ecological significance
Zhengyi Hu1, Silvia Hanekalus2, Zhihong Cao1 and Ewald Schnug2

Abstract1 sponses to S fertilization of more than 20 different

agricultural crops ranged from 4% to 81% (Cao et
Sulfur naturally occurs in valences of –2 to +6. Vari- al., 1996).
ous organic sulfur compounds can be found in soils. The rhizosphere is a key zone with view to the
The rhizosphere is a key zone with view to the mechanisms of soil nutrient dynamics (Darrah et
mechanisms of soil nutrient dynamics. This contribu- al., 1993). Physico-chemical processes at the soil-
tion summarizes the current knowledge about the root interface differ considerably from those in the
chemical behavior of sulfur in the rhizosphere and its non-rhizosphere soil. The effect of plant growth
ecological impact and highlights future research on soil nutrients in the rhizosphere was studied
needs. intensively for P (Gahoonia et al., 1992; Zoyza et
al., 1997), N, K, Ca and Mg (Moritsuka et al.,
Key words: arylsulfatase, elemental sulfur, soils, sulfur 2000). Only limited data is, however, available for
fertilization, rhizosphere the effect of plant growth on the chemical
behavior of S in the rhizosphere, which is
nevertheless required in order to assess agronomic
Introduction and ecological impacts in relation to the local S
cycle. This paper summarizes the present
Human activity highly influences the sulfur (S) cy- knowledge about the chemical behavior of soil S in
cle through anthropogenic emission from fossil fuel the rhizosphere.
burning. Global SO2 emissions from anthropogenic
sources increased about 20-folds in 1985 compared to
1850 (Brimblecombe et al., 1989). This increase was Chemical behavior of soil S in the rhizosphere
strongest between 1940 and 1970 in Europe and North
America, but then with the introduction of clean air Oxidization of S0 in the rhizosphere and non-
acts coming into force the rend was reversed (Brim- rhizosphere
blecombe et al., 1989). However, SO2 emissions are Elemental S (S0) is used as a fertilizer to satisfy
still increasing in Asia. Here the S emissions increased the S demand of cop plants. This reduced S needs
from 33.7 Tg in 1990 to 39.2 Tg in 1997, and peak val- to be oxidized to SO4-2 before it becomes plant
ues of 40-50 Tg are expected for the year 2020. China available. Oxidation of S0 in soils is primarily a
contributes with 66% of the total S emissions (David, et microbial process (Wainwright, 1984). The
al., 2000). activity of thiobacilli is highly important for the
Atmospheric S loads are closely linked to soil qual- oxidation of elemental S (McCaskill and Blair,
ity and an imbalanced S nutrition of plants (Hu, 1987). Heterotrophic micro-organisms are other
2002a; McGrath et al., 1995; Schnug, et al., 1998). S0 oxidizers in soils (Wainwright, 1984).
Atmospheric S depositions vary regionally in China Elemental S is oxidized by thiobacilli to sulfuric
and follow industrial activities (Wang et al., 2000). So, acid. The application of S0 together with
the hat total S deposition was 95 kg S/ha at the Ex- inoculation decreased soil pH rapidly from about
perimental Station of Red Soil Ecology, Yingtan, Chi- 7.3 to 3.2 after 12 weeks of incubation. Adding
nese Academy of Sciences in 1998/1999 (Hu et al., thiobacilli together with S0 to the rhizosphere
2002b), and the soil pH value decreased by 0.6 units yields a significantly faster oxidation than
since 1992 (Xu et al., 2004). The excess of S may application of S0 on its own (Fan et al., 2002).
have a negative effect on the soil-plant system, for Grayston et al. (1991) isolated 273 bacterial
example on flooded paddy soils. Here, S will be re- phylas and 70 fungal species from the rhizosphere
duced to H2S, which obstructs plant growth (Hu et al., of canola (Brassica napus). From these 273
2002a). In contrast, atmospheric S depositions are not bacterial isolates, 245 (89.7%) oxidized S0 to
sufficiently high in order to satisfy the demand in re- thisosulfate or tetrathionate, and 133 (48.7%)
mote areas of China (Hu et al., 2002a). Yield re- oxidized S0 to SO4-2. All 70 fungal isolates
oxidized S0 to SO4-2. Bacterial isolates showed the
1
State Key Laboratory of Soil and Sustainable Agriculture, highest S0 oxidization rate (Table 1).
Institute of Soil Science, Chinese Academy of Sciences, The rhizosphere is a key zone with view to the
Nanjing, 210008, P. R. China. mechanism of soil nutrient dynamics. Physico-
2
Institute of Plant Nutrition and Soil Science, Federal Agri-
chemical processes in the soil-root interface differ
cultural Research Centre (FAL), Bundesallee 50, D-38116
Braunschweig, Germany considerably from those in the non-rhizosphere
54 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

soil. A rhizobag culture experiment demonstrated that rhizosphere (Figure 1). In non-vegetated soil
the oxidation of S0 in the rhizosphere and non- samples the S content of microbial bio-mass was
rhizosphere varied in dependence on soil moisture generally and significantly lower than in the
content and soil type (unpublished data). The vegetated treatments (Hu et al., 2003), because
oxidation rate of S0 was generally lower under cropping increases the biological activity
waterlogged (1 cm water depth) than aerobic (Castellano et al., 1990).
conditions (80% water holding capacity; Figure 2). On
a paddy soil originating from lime rock, the oxidation
rate of S0 was higher in the rhizosphere of rice than in 100
Rhizosphere
non-rhizosphere under waterlogged and aerobic 90
conditions (Figure 2). However, these differences Non-rhizosphere
80

Percent of ES oxidization (%)

were not observed on the paddy soil originating from 70
granite. The reason could possibly be different 60
contents of plant available S and micobiological
50
species.
40

30
14
20
RH NRH
Biomass-S content (mg kg-1)

12 10

10 0
waterlogged (1cm ) Aerobic (80% WHC)
8
100
6
90 Rhizosphere
a a A B a a A B
4 Non-rhizosphere
80
Percent of ES oxidation (%)

2 70
D c C c d d c c
0 60
Non-vegetated Oilseed rape Non-vegetated Rice 50
(aerobic) (aerobic) (waterlogged) (waterlogged)
40
30
Figure 1: 20
Concentration of microbial biomass-S (MB-S) in the
10
rhizosphere (RH) and non-rhizosphere (NRH). Different
letters (a,b) and (A, B) indicate significant differences 0
between RH and NRH at p<0.05 and p<0.01 level (student waterlogged (1cm ) Aerobic (80% WHC)

T-test).Different letters (c, d) and (C, D) indicate significant Figure 2:

differences of MB-S in RH and NRH relative to no- Oxidization of elemental S (ES) in the rhizosphere of
vegetated soils at p<0.05, p<0.01 level(student T-test), rice in dependence on water management and soil type
respectively; source: Hu et al. (2003). (upper: paddy soil originated from lime rock; lower:
paddy soil originated from granite; unpublished data).

Soil microbial biomass S in the rhizosphere and non-

rhizosphere Variations in the chemical behavior of S in the non-
Soil microbial biomass is defined as the living part rhizosphere and rhizosphere
of soil organic matter (Chapmam, et al., 1987). The In a rhizobag experiment it was demonstrated
microbial biomass S in agricultural soils varied that the distribution of S fractions in the
between 4.4% and 4.9% in non-vegetated soils and 5.2 rhizosphere and the non-rhizosphere soil varied in
and 8.8% in vegetated soils (Saggar et al., 1981; dependence on the crop type (Table 2). More total
Chapmam, et al., 1987; Wu, et al., 1994). Despite its and inorganic SO42--S was found in the
small size, the microbial bio-mass is a highly active rhizosphere of oilseed rape and rice (Table 2),
fraction that acts as the driving force behind which supposedly relies on mass flow to the roots
mineralization-immobilization and oxidation- (Barber, et al., 1995). More organic S was found
reduction processes. A rhizobag culture experiment in the rhizosphere of oilseed rape, while inverse
demonstrated that the S content of microbial mass was results were obtained for rice (Table 2). A possi-
6.3 mg S kg-1 in the non-rhizosphere soil and 11.8 mg ble explanation is that the turnover of organic
S kg-1 in the rhizosphere soil of rice (Hu et al., 2003). matter was hampered under anaerobic conditions
The S content of microbial bio-mass was up to 72% (Williams et al., 1967). Stanko-Golden (1991)
higher in the rhizosphere of rice than in the non-
Landbauforschung Völkenrode, Special Issue 283, 2005 55

Table 1:
Number of S0-oxidizing bacterial isolates from the rhizosphere and rhizoplane of canola grown in a growth chamber (source:
Grayston et al., 1991).
Soil Area of isola- Total isolates Number of isolates producing
tion S2O32-/S4O62- SO42- S2O32-/S4O62-
and SO42-
Haverhill Rhizosphere 56 49 (87.5%)* 25 (44.6%) 25 (44.6%)
Rhizoplane 43 42 (97.7%) 30 (69.8%) 30 (69.8%)
Carrot River Rhizosphere 31 26 (83.9%) 15 (48.4%) 14 (45.2%)
Rhizoplane 40 38 (95.0%) 20 (50.0%) 20 (50.0%)
Asquith Rhizosphere 19 18 (94.7%) 7 (36.8%) 7 (36.8%)
Rhizoplane 32 29 (90.6%) 13 (40.6%) 10 (31.2%)
Laird Rhizosphere 15 11 (73.3%) 6 (40.0%) 5 (33.3%)
Rhizoplane 37 32 (86.5%) 17 (45.9%) 13 (35.1%)
Total bacteria 273 245 (89.7%) 133 (48.7%) 124 (45.4%)
*Sulfur oxidizers as percentage of total isolates.

Table 2:
Contents of different S Fractions (mg S kg-1) in the rhizosphere (RH), non-rhizosphere (NRH), and the RH to NRH ratio (mean;
source: Hu et al., 2003).
Water Non- RH/NRH Total S fractions
man- vegetated S Organic S fractions Inorganic S fractions
agement /cropping Total Ester Carbon Resid- Total Soluble Ad-
organic bonded bonded ual inor- SO42- sorbed
ganic SO42-
Aerobic Non- RH 141.9a 99.3a 20.4a 11.7a 67.2a 42.6a 33.0a 12.0a
condition vegetated NRH 133.9a 91.4a 20.1a 13.8a 57.2a 42.5a 28.8a 13.7a
Oilseed RH 122.3a 99.6a 30.0b 14.6a 53.8A 44.0a 34.0a 10.0a
rape NRH 120.4a 87.6a 44.5a 17.3a 25.8B 32.8b 23.0b 9.8a
Ratio 1.02 1.13 0.67 0.84 2.08 1.34 1.48 1.02
Water- Non- RH 145.3a 96.0a 24.0a 15.7a 56.3a 49.3a 43.0 a 6.3 a
logged vegetated NRH 133.0a 87.8a 27.0a 14.4a 46.4b 45.2a 40.4 a 4.8 b
condition Rice RH 155.2a 29.6B 6.0B 11.0a 12.6B 125.6A 110.3A 15.3A
NRH 131.2a 91.2A 33.6A 10.7a 46.9A 40.0B 34.7B 5.3B
Ratio 1.18 0.33 0.18 1.03 0.27 3.14 3.18 2.89
*Values followed by different letters (a, b), and (A, B) indicate significant differences between RH and NRH at p < 0.05,
and p < 0.01 level (student T-test), respectively.

Table 3:
Concentrations (mean value r SD, n=4) of different S fractions (mg S kg-1) in the rhizosphere (RH) and non-rhizosphere (NRH)
in dependence on soil and crop type (source: Hu et al., 2002c).
Soils Treatment RH/ Total S Sulfur fractions
NRH Total S in Adsorbed Ester Carbon Residual Total S in SO42- in HI-
0.01 M SO42- bonded bonded 0.01 M 0.01 M reducible
CaCl2 Ca(H2PO4)2 Ca(H2PO4)2 S
Haplic Fallow RH 202r2 13.9 r 1.3 13.8 r 1.9 76.0 r 5.1 19.7 r 1.4 79.0 r 8.6 39 r 2 28 r 2 104 r 8
Acrisol NRH 182r14 14.8 r 0.4 13.3 r 0.9 75.3 r 2.5 18.1 r 2.1 69.4 r 9.7 38 r 1 28 r 1 103 r12
Wheat RH 193 r 17 15.2 r 1.8 10.8 r 2.0 48.0 r 3.1 19.2 r 3.0 99.0 r 7.8 36 r 5 26 r 3 74 r 4
NRH 175 r 7 9.8 r 0.7 14.0 r 1.1 56.0 r 4.1 22.3 r 3.3 72.3 r 9.3 33 r 2 24 r 1 80 r 6
Oilseed rape RH 179 r 5 8.8 r 1.3 5.5 r 1.4 58.6 r 5.8 18.7 r 2.0 87.4 r 6.9 23 r 2 14 r 0 73 r 6
NRH 170 r 9 5.5 r 0.5 9.8 r 1.3 60.8 r 5.7 20.7 r 2.4 72.9 r 7.2 22 r 1 15 r 1 76 r 6
Radish RH 194 r 9 8.7 r 1.4 5.4 r 1.0 75.3 r 1.5 19.5 r 1.4 85.5 r 9.9 24 r 2 14 r 1 89 r 9
NRH 174 r 10 5.7 r 0.9 9.0 r 1.7 86.9 r 1.7 21.2 r 1.4 51.4 r 6.3 22 r 1 15 r 2 102 r 1
Hortic Fallow RH 141 r 6 19.2 r 2.7 4.9 r 0.7 40.1 r 3.1 1.3 r 0.1 75.4 r 4.1 32 r 4 24 r 3 64 r 2
Anthrosol NRH 130 r 9 20.3 r 3.1 3.9 r 1.5 32.4 r 2.8 0.1 r 0.1 73.2 r 8.3 38 r 3 24 r 3 57 r 2
Wheat RH 131 r 10 19.8 r 2.0 5.0 r 1.8 34.2 r 2.9 1.6 r 0.2 70.1 r 7.6 33 r 1 25 r 2 59 r 3
NRH 131r 2 22.1 r 4.0 1.8 r 2.7 43.4 r 2.5 <LLD 63.3 r 3.7 38 r 2 24 r 3 67 r 2
Oilseed rape RH 122 r 5 13.2 r 1.6 -0.4 r 1.0 36.4 r 1.2 1.8 r 1.2 71.3 r 4.5 20 r 2 13 r 1 49 r 4
NRH 130 r 3 16.4 r 4.0 1.3 r 2.2 40.2 r 1.9 0.1 r 0.1 71.7 r 2.7 30 r 3 18 r 3 58 r 2
Radish RH 137 r 5 13.8 r 0.7 0.11 r 0.6 40.7 r 1.3 1.4 r 0.2 80.7 r 5.9 26 r 4 14 r 1 55 r 1
NRH 115 r 6 10.8 r 4.6 0.60 r 3.3 51.1 r 5.2 0.2 r 0.1 52.5 r 6.9 18 r 2 11 r 1 63 r 4
note: <LLD < Lower Limit of Detection; RH rhizosphere; NRH non-rhizosphere (bare soil)
56 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

reported that soil moisture was positively related with rape while opposite results were found for rice
organic S. With view to rice the soil moisture is of (Table 2). Other crops such as wheat and radish
minor relevance, because there are oxidizing condi- also showed higher levels of residual S in the
tions in the rhizosphere due to aeration tissues from rhizosphere (Table 3). Rice had a higher ability to
the top to the roots which promote the activity of mi- utilize residual S from the soils which could be
crobes and sulfatase (Han et al., 1982, Freney et al., related to its aeration tissues.
1966). In all treatments with plants, the content of
More ester-bonded S was found in the non- soluble SO42--S and adsorbed SO42--S was higher
rhizosphere of oilseed rape and rice (Table 2). Hu et in the rhizosphere than in the non-rhizosphere
al. (2002c) observed similar results for oilseed rape, (Table 2). This can not be attributed generally to a
wheat and radish (Table 3). The reason could be a higher mineralization in the rhizosphere, because
higher arylsulfatase activity in the rhizosphere as it is the organic S content was higher in the
this enzyme, which catalyzes the decomposition of rhizosphere of oilseed rape (Table 2). Enhanced
sulfate esters (Fitzgerald, 1978). Han et al. (1982) mass flow of SO42--S to the rhizosphere after min-
found, however, that the arylsulfatase activity was eralization of organic S in the non-rhizosphere is
higher in the rhizosphere than in the non-rhizosphere supposedly the reason for this effect. Wind (1995)
of rice (Table 4). Additionally, the activity of micro- found that the concentrations of SO42-, S2O32- at
organisms is higher in the rhizosphere as they use root the rhizosphere of rice were related to rice plant-
exudates as an energy source (Yan et al., 1993). Thus, ing. The same author found more SO42- in the
the rhizosphere soils had a higher organic C content rhizosphere (300 Pmol kg-1) of rice than in the
than the non-rhizosphere soils (Hu et al., 2003). non-vegetated (110 Pmol kg-1) treatment.
Carbon-bonded S is not related to plant S uptake
(Lee et al., 1979), though S may be mineralized from
all organic S fractions (Li et al., 2001). Amino acids, Ecological effects of soil S transformations in
such as cysteine and methionine are the major compo- the rhizosphere
nents of carbon-bonded S (Tabatabai et al., 1982; Fre-
ney et al., 1986). S-containing amino acids do not ac- Grayston et al. (1991) selected eighteen isolated
cumulate in free forms, because they are rapidly de- bacteria, which showed an increased efficacy of in
graded in aerobic soils (Fitzgerald et al, 1978). Paul vitro S oxidization for inoculating seeds, together
and Schmidt (1961) reported that the cysteine and me- with applications of elemental S. Results indicated
thionine content was slightly higher in the rhizosphere that inoculation with 14 phyla increased canola
than in the non-rhizosphere soil. Other experiments leaf size, and root and pod dry weight at maturity
revealed no significant differences existed between the was promoted by seven phyla. The shoot material
two compartments (Hu et al., 2002c; Table 2, 3). had higher iron, sulfur, and magnesium contents
These results indicate that carbon-bonded S is of mi- after inocultion by two of the eighteen bacterial
nor importance for the S nutrition of crops than for isolates (Table 5). In case of three isolates the
instance ester sulfate. treatment had a detrimental effect on the growth
of the fungal pathogens, Rhizoctonia solani AG2-
350 1, R. solani AG4, and Leptosphaeria maculans
300
Vegetated soil
“Leroy”. Besides a direct fungicidal effect of
300
elemental S, the initiation of S induced resistance
mechanisms through an enhanced oxidation of S0
concents of SO4 /S2O3 content

250 Non-vegetated soil

may explain the latter effect (Haneklaus et al.,
200
2004).
(umol)

150
150
Sulfur in nature occurs in valences from -2 to +6
110 (Hu et al., 2002a). Many types of organic S com-
100 pounds were found (Morra et al., 1997, Hu et al.,
50
2002a). Internal cycling reactions are responsible
0
for maintaining a biologically available S supply
0 through mineralization of organic substrates and
SO4 S2O3 redox transformation of inorganic species (Hu et
Sulfur fractions
al., 2002a). Speciation of S in natural organic mat-
Figure 3: ter could provide a clear understanding not only of
SO42- and S2O32- content in the non-rhizosphere and bio-geochemical transformations of S, but also of
rhizosphere of rice (Wind , 1995) the role of organic S in the complexation of toxic
trace metals (Xia et al., 1998). Here, S-containing
The amount of residual-S was significantly higher in functional groups in humic substances may play
the rhizosphere than in the non-rhizosphere of oilseed an important role in complex formation with trace
Landbauforschung Völkenrode, Special Issue 283, 2005 57

Table 4:
Comparison of arylsulfatase activity in non-rhizosphere and rhizosphere soil of the different rice varieties grown on Pila clay
loam and Maahas clay (source: Han et al., 1982).
Treatment Weeks after transplanting
0 2 4 6 8
Pila clay loam soil*
Non-rhizosphere soil 36 9.3 12.9 16.0 11.3
Rhizosphere soil of different rice varieties
IR-8 36 25.5 31.3 45.1 54.6
IR-667 36 13.0 18.9 21.5 22.6
C-4 36 18.2 37.2 26.5 42.2

Maahas clay soil*

Non-rhizosphere soil 7 5.8 5.4 4.4 5.8
Rhizosphere soil of different rice varieties
IR-8 7 9.5 10.8 9.1 12.1
IR-667 7 8.2 8.7 9.1 11.2
C-4 7 10.4 10.4 8.1 10.4
* Cite from original text

Table 5:
Sulfur, iron, and magnesium content of canola shoots and pods after seed inoculation with sulfur-oxidizing rhizosphere
(source: Grayston et al., 1991).
Treatment Plant tissue Mg (mg) S (mg) Fe (Pg)
Control Shoots 9.3 ± 1.6 21.6 ± 2.8 439 ± 64
Isolate No 13 Shoots 11.1 ± 1.1 23.2 ± 2.4 657 ± 155*
Isolate No. 14 Shoots 11.9 ± 1.2* 28.1 ± 1.2* 727 ± 118*
Note: Plants grown in 2 kg of soil amended with prilled S0 fertilizer (50Pg g-1) in growth chamber. The control
was inoculated with an autoclaved culture of isolate 10. Means of five replicates ± SD. *Significant increase
above control (p<0.05).

metals such as Cd, Co, Ni, Pb, Zn, As, and Hg (Xia et soil redox processes. Some reports have shown
al., 1998). that iron plaque may be a barrier to the uptake of
Conclusions heavy metals, such as Cu, Ni, Mn, As, Cd (Taylor
and Crowder, 1983; Greipsson, 1994; Liu et al.,
Only few studies about the chemical behavior of soil 2004a, b). Effect of chemical behaviors of soil S
S in the rhizosphere were carried out (Hu, et al., in the rhizosphere and iron plaque induced by S
2002c, 2003, Wind , 1995; Grayston et al., 1991; Han, transformation is therefore of particular interest.
et al., 1982) so that information about factors influenc-
ing S transformation processes in the rhizosphere is
still limited. In this context, the soil water regime, Acknowledgments
plant species, soil type, soil characteristics are parame-
ters, which need to be paid more attention to. This work was jointly supported by the Knowl-
A number of wetland plants, such as rice, have been edge Innovation Program of CAS (ISSASIP0205),
shown to oxidize the rhizosphere, a process which the Natural Science Foundation of China (Project
may serve to protect against the entry of reduced phy- No. 49801011), and the Bilateral Chinese/German
totoxins, such as Mn2+, Fe2+, and S2- (Armstrong et al., Co-operation of the Ministries of Agriculture.
1978). Iron plaque is commonly formed on the roots
of aquatic plant species, such as Oryza sativa, and is
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60 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants
Landbauforschung Völkenrode, Special Issue 283, 2005 61

Measuring fluxes of reduced sulfur gases

Beate Huber1 and Werner Haunold2

Abstract12 global sulfur budget is the exchange between at-

mosphere, soils and vegetation (Rennenberg, 1991;
This paper gives an overview about techniques for Kesselmeier, 1991). Especially the lack of knowl-
measuring fluxes of reduced sulfur gases used in edge in diurnal and seasonal flux variations is criti-
ecological sciences. Measuring fluxes reduced of cal for estimations on regional and global scale. In
sulfur gases (H2S, COS, CH3SH, DMS, CS2) in at- the last decade budgeting global sulfur cycles
mospheric concentrations needs extensive measure- showed progress (Chin and Davis, 1993), but is not
ment equipment. Because the concentrations of re- yet completed (Watts, 2000).
duced sulfur gases in the atmosphere are very low -
in the range of parts per trillion (pptv) - it is neces-
sary to concentrate the gases with a cryogenic sam- Gas chromatographic analysis of reduced sulfur
pling system. For analyzing reduced gases a gas gases
chromatographic system with a flame photometric
detector is used. Fluxes of reduced sulfur gases be- Measuring reduced sulfur gases is carried out in
tween soil, plants and atmosphere are usually de- two main steps: (1) sulfur gases are cryogenically
termined with dynamic chamber systems. Flux esti- trapped from atmospheric samples and (2) they are
mations on ecosystem scale require micrometeo- analyzed by a gas chromatograph (GC) with a flame
rological methods. photometric detector (FPD) (Haunold et al., 1992;
Hofmann et al., 1992a).
Keywords: reduced sulfur gases; analysis of atmos-
pheric trace gases; cryogenic trapping; flux meas- Cryogenic collecting
urements; dynamic chambers; micro-meteorological The air samples are concentrated by pumping at-
methods mospheric air through cryogenic collectors, which
are cooled in liquid argon (- 186°C). The reduced
sulfur gases with melting points between - 86°C and
Introduction - 138°C freeze in the collectors, while N2 and O2
pass the traps. Haunold et al. (1992) use 20-cm U-
Reduced sulfur is present in the atmosphere in shaped borosilicate glass tubes with 10 mm outer
several gaseous species, COS (carbonyl sulfide), diameter and 6 mm inner diameter. A 5 cm plug of
DMS (dimethylsulfide), H2S (hydrogen sulfide), silanized quartz wool is inserted at the collector out-
CS2 (carbon disulfide) and CH3SH (methyl mercap- let to increase sampling efficiency. The air samples
tan, methanethiol). Reduced volatile sulfur com- are collected with sampling rates between 100-200
pounds, which are released to the oxygen-rich at- ml per min. Under atmospheric conditions usually a
mosphere, are chemically oxidized during their life- volume of 5 l air is sampled in 30 min. The use of
time and end up finally as sulfur dioxide (SO2), sul- liquid argon (- 186°C) instead of cheaper liquid ni-
furic acid, particulate sulfate and methane sulfonate trogen (- 196°C) has the advantage that O2 is just
(Andreae and Jaeschke, 1992). These compounds not trapped. Before use the glass collectors have to
are again removed from the atmosphere and re-enter be conditioned. Each trap is kept under vacuum
the biosphere by dry and wet deposition (Andreae conditions for a few minutes and flushed with puri-
and Jaeschke, 1992). fied nitrogen to remove water vapor and residual air.
In the atmosphere sulfate aerosols play an impor- During the sampling procedure humidity from am-
tant role, because they act as cloud condensation bient air is also trapped, which causes dramatic H2S
nuclei, increase albedo of clouds and influence in losses, when humidity is liberated together with
this way the global radiation budget (Crutzen, 1976; H2S. Haunold et al. (1992) developed a two-step
Charlson et al., 1987; Andreae, 1992). Atmospheric desorption procedure (cold desorption and warm
sulfur originates from anthropogenic and numerous desorption) to retain co-trapped water in the traps
natural sources. One of the major uncertainties in when H2S is liberated (as described below). Hof-
mann et al. (1992a) use similar cryogenic sampling
1
equipment. But before trapping the gases with liquid
GSF Research Center for Environment and Health, argon Hofmann et al. (1992a) remove humidity
Institute for Soil Ecology, Ingolstädter Landstrasse 1, D-
86764 Neuherberg, Germany
from air samples in a Nafion dryer. Additionally
2
Zentrum für Umweltforschung, Johann-Wolfgang- Hofmann et al. (1992a) let pass the air through a
Goethe-Universität Frankfurt am Main, Georg-Voigt- cotton-wadding filter as an oxidant scavenger to
Strasse 14, D-60325 Frankfurt am Main, Germany avoid especially DMS losses. Atmospheric concen-
62 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

trations of oxidants, like O3, show daily patterns. compounds are commercially available (Vici Met-
Hofmann et al. (1992a) could show that during an ronics, Santa Clara, California, USA). Haunold et al.
afternoon with high ozone concentrations by sam- (1992) constructed a permeation oven, which kept
pling without a cotton wadding no DMS was found, the standards at a constant temperature of 30°C in
whereas in samples collected with a cotton wadding special glass bottles that are flushed with nitrogen.
DMS was present. Between 0.025 and 10 ml of the standard gas sam-
ples are injected to the gas chromatograph using gas
Gas chromatographic system tight syringes.
Haunold et al. (1992) developed a light-weight Detection limits depend on the sensitivity of the
(5 kg) portable gas chromatograph, suitable for field detector and on the collected air volume. The re-
operation. It is equipped with a packed column ported detection limit is 10 pg sulfur per sample
(Carbopack BHT 100, Supelco, Bellefonte, Penn- (Haunold et al., 1992). Usually air volumes of 2 l to
sylvania, USA) and a commercially available flame 5 l are cryogenic collected. Haunold et al. (1992)
photometric detector (FPD 84XO/8500, Perkin- and Hofmann et al. (1992a) describe for their similar
Elmer, Norwalk, Connecticut, USA). The specialty systems detection limits under 10 pptv depending on
of this gas chromatograph is the very small oven in the different sulfur compounds.
comparison to commercially available GC systems. The collection efficiency of the cryogenic sam-
Temperature control of the analytical column is pling process has been tested by sampling and ana-
achieved by Peltier elements, which heat and cool a lyzing gas from dilute calibration gas mixtures (pptv
circular metal block (only 12 cm in diameter and range) with two sampling loops in series. At sam-
1 cm in height) containing the chromatographic col- pling rates between 100 ml and 200 ml 94 % to
umn. The operating conditions of the column oven 96 % of the reduced sulfur gases were found in the
range between - 20°C and 120°C, with heating fist trap (Haunold et al., 1992).
/cooling rates of 30°C min-1. Nitrogen is used as
carrier gas.
Determining fluxes of reduced sulfur gases
Analysis of atmospheric samples
Methods to study the trace gas exchange between
After trapping the sulfur gases the cooled sam- biosphere and atmosphere developed from diverse
pling tubes are integrated into the carrier gas stream scientific disciplines, like atmospheric chemistry,
of the GC. As mentioned above Haunold et al. micrometeorology, ecology, botany and more. The
(1992) developed a two-step desorption procedure different disciplines developed multiple approaches
to retain co-trapped water in the traps. In the first depending on different research topics and consid-
desorption step the sample loop is brought from - ered scales. For determining the fluxes of reduced
186°C to - 79°C in a bath of dry ice and ethanol sulfur gases on small scales between soil, plants and
(Figure 1). At this temperature, CO2 and the low the atmosphere dynamic chambers are used, for
boiling sulfur gases H2S and COS are volatilized studying fluxes on ecological scale micrometeo-
completely and transported into a capillary cold trap rological methods like the gradient method are ap-
by the carrier gas (liquid argon, - 186°C) were they plied.
are focused again. This so called “cold desorption”
step needs 5 min time. After the sampling trap is Dynamic chambers
closed, the focus trap is transferred to warm water
(+ 30°C) and the first analytical run starts. This The most frequently used technique is the dy-
“cold desorption” step is important, because it has to namic chamber technique. This technique is rela-
be avoided that H2S is coming into contact with tively low in cost, simple to operate, and can be
traces of liquid water. This would cause dramatic used in laboratory (Livingston and Hutchinson,
H2S losses. For analyzing DMS and CS2 a second 1995). Dynamic chambers are enclosures for soil,
desorption step in warm water (+ 30°C, “warm de- plants or soil and plants, they are flushed with an air
sorption”) and a second analytical run is necessary stream of a certain flow rates (chamber air is ex-
to set free these higher boiling sulfur compounds. changed about once in 10 to 15 min). Often fans are
Hofmann et al. (1992a), who eliminated water be- used to support the air mixture inside the chamber.
fore cryogenic collecting with the Nafion drier, are For flux estimations an air sample at chamber inlet
desorbing gases together in one “warm desorption” and an air sample at chamber outlet is collected si-
step. multaneously. Flux is calculated from the concentra-
tion difference between inlet and outlet, taking into
Calibration, detection limits and sampling efficiency account flow rate through the chamber and soil or
plant surface area.
For calibration Haunold et al. (1992) is using Not only the construction but also materials used
gaseous standards. Permeation sources of the sulfur for chambers are very important, because reduced
Landbauforschung Völkenrode, Special Issue 283, 2005 63

Figure 1:
Gas chromatographic system with connected traps for cold and warm desorption (Haunold et al., 1992; Huber, 1994).

sulfur gases, especially H2S, are reactive. As a Furthermore the quality of air, which is used to
thumb all “smelling” materials should be avoided, flush the dynamic chambers is very important (Ta-
as we as all materials that react on surface or are ble 1). An experiment with spruce trees in the lab
porous. Only inert materials should be used, like where the dynamic chamber was flushed with air,
Teflon, stainless steel and glass. A further important which contained no H2S showed clearly emission of
feature especially for plant chambers is a good light H2S, depending to light/dark phases (Rennenberg et
transmittance of the used materials. al., 1990; Huber, 1994). An experiment with spruce
in the Bavarian forest, where the chamber was
flushed with ambient air, which contains H2S in
Table 1: varying concentrations, showed in most cases H2S
Comparison of laboratory and field experiments with deposition (Huber, 1994). When sulfur free air is
spruce trees. In the lab the dynamic chamber was flushed used to flush dynamic chambers the gradient be-
with H2S-free air from a bottle. In the field experiment the tween plant and atmosphere is artificially high and
chamber was flushed with ambient air with various H2S
concentrations. <N means concentration under detection
emissions are to observe, which are not to found
limit; positive H2S flux means emission; negative H2S when ambient air with varying ambient sulfur gas
flux means deposition and n is number of measurements concentrations is used. More recent budget papers
(Huber, 1994). even ignore results of chambers flushed with “sulfur
free” air (Watts, 2000).
Dynamic cham- H2S H2S flux n
ber flushed with: concentration (nmol m-2 h- Micrometeorological methods
1
chamber inlet )
(pptv) Trace gases are both emitted and absorbed by
“H2S free” air soils and plants. The atmosphere near earth’s surface
+0.26 to is almost always turbulent, and the trace gases are
(laboratory <N 53
+2.1 rapidly diffused to or from the surface. Diffusion by
conditions)
Ambient air +4.39 to turbulence is many orders of magnitude larger than
<N to 228 31
(field conditions) -23.5 molecular diffusion (Lenschow, 1995). This turbu-
lent exchange processes can be measured in several
64 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

ways. Direct measurement of trace gas fluxes re- soils, plants and atmosphere on small scale. They
quires fast-response concurrent measurement of are relatively easy to handle and relatively low in
vertical air velocity and trace gas species. More so- cost. Very important are the use of inert materials
phisticated micrometeorological methods such as for chamber construction and the use of air with
eddy correlation await the development of sufficient sulfur gases in ambient concentrations to flush the
sensitive and fast sulfur detectors. The most com- chambers. For flux estimations on ecosystem scale
mon derived technique is the so-called gradient micrometeorological methods are used. The micro-
method (Lenschow, 1995), measuring sulfur gas meteorological methods are more costly and need
concentrations parallel in different heights. Addi- much more experience for selecting measuring site,
tionally a set of micrometeorological data (such as measuring heights and interpretation.
wind direction, wind speed, temperature, barometric
pressure) for calculations of vertical fluxes is
needed. The measurement equipment is fixed at Acknowledgements
micrometeorological towers. The lower part of the
atmosphere, the so-called atmospheric boundary We would like to thank Dr. Peter Schröder, GSF
layer is divided in several sub-layers: a surface Research Center for Environment and Health, Neu-
layer, a mixed layer and an entrainment zone. The herberg, for correcting the manuscript.
height of atmospheric boundary layer is varying
from a few of tens of meters, as it is typically over
land at night, to several kilometers when surface is References
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schow, 1995). So the choice of measurement heights Andreae MO (1992) The global biogeochemical sulfur
is of high importance for later gradient interpreta- cycle: a review. In: Moore B, Schimel D (eds) Trace
gases and the biosphere. UCAR/Office for Interdisci-
tion. Also the position of the measuring tower in a plinary Earth Studies, Boulder, Colorado, pp 87-128
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gases with micrometeorological methods. Hofmann dreae MO, Kesselmeier J (1993) COS and H2S fluxes
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3:73-76
micrometeorological methods were compared: eddy Haunold W, Georgii HW, Ockelmann G (1992). Gas
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66 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants
Landbauforschung Völkenrode, Special Issue 283, 2005 67

The global sulfur cycle and China's contribution to atmospheric sulfur loads
Jürgen Kesselmeier

Abstract1 nutrient availability. Sulfur compounds play a

crucial role in the atmosphere (Andreae and
Sulfur is playing a crucial role in biological Crutzen, 1997, Charlson et al., 1992; Chin and
processes and is exchanged with the environment. Davis, 1995; Kesselmeier et al., 1997) and have
Several biogenic volatile and reactive sulfur substantial biogenic sources in addition to the
compounds are released into the atmosphere where anthropogenic ones. An overview about sources and
they are oxidized and join the fate of the estimated emission ranges according to Andreae and
anthropogenically produced sulfur gases. Some Jaeschke (1992) is given in Figure 1. By oxidation
compounds may reach the stratosphere. Sulfur to sulfate sulfur compounds are involved in aerosol
emissions from biogenic and anthropogenic sources particle and cloud production. This way they
together account for roughly 100 to 180 TG a-1. contribute to the regulation of the radiative budget
However, S-gases, such as carbonyl sulfide (COS), of the earth. According to the latest IPCC report
are mainly deposited and consumed by the (2001), the direct radiative forcing of sulfate
biosphere. The exchange of sulfur between the particles contributes substantially to a cooling of the
biosphere and the atmosphere and the fate within the earth. Estimates of the indirect effect, i.e. cloud
troposphere/stratosphere are summarized for oceans production and its role in absorbing and reflecting
and terrestrial surfaces. Regarding the role of sulfur radiation, are highly uncertain but may even be of
within the atmosphere, Chinese emissions are higher importance.
shortly discussed in view of the current declining
anthropogenic release of SO2 in China.
Sulfur exchange over oceans and continents
Keywords: sulfur, biosphere, atmosphere, ocean,
land surface, hydrogen sulfide, methyl mercaptan, For a sufficient understanding of the sulfur cycle,
carbonyl sulfide, carbon disulfide, dimethyl sulfide, a more detailed picture and a closer look into sulfur
dimethyl disulfide, sulfur dioxide, aerosol, clouds speciation is needed. We may discern several sulfur
compounds being emitted from different sources.
Anthropogenic sources mainly emit sulfur dioxide
Introduction which is oxidized to sulfate. Biogenic sources emit
substantial amounts of other S species, such as
Sulfur as an essential nutrient for living organisms hydrogen sulfide (H2S), methyl mercaptan (CH3SH),
can be found everywhere in our environment. carbonyl sulfide (OCS, often called COS), carbon
Sources and role of anthropogenic sulfur gases disulfide (CS2), dimethyl sulfide (CH3SCH3, DMS)
contributing to atmospheric pollution are well and dimethyl disulfide (CH3SSCH3, DMDS). These
described in the literature (Lefohn et al., 1999). The compounds are summarized as reduced volatile
negative effects on lakes and forest ecosystems as sulfur compounds. Regarding the distribution of
well as on humans have caused immense efforts to anthropogenic and biogenic sources an interesting
cut down the release of sulfur form anthropogenic gradient is found between the two hemispheres
sources, mainly combustion processes. Air pollution (Bates et al., 1992) as shown in Figure 2.
prevention within the last decades resulted in a Anthropogenic sources are significantly higher in
significant decrease of SO2 emission and thus S Northern latitude whereas the southern hemisphere
deposition in industrialized countries from 100 to 10 is better described by biogenic sources, a feature
kg ha-1 a-1). This decrease led to a significant which can be attributed to the larger marine areas in
recover of natural ecosystems, but caused a the southern hemisphere.
substantial loss of sulfur for agriculture. Especially Table 1 summarizes the atmospheric lifetimes of
cruciferous plants with a high sulfur demand reacted several sulfur species. As shown, the S species may
with substantial profit cuts. Hence, the sulfur be sorted into two groups, the first containing the
deficiency in cultivated plants had to be reactive compounds with lifetimes in the range of
compensated by increased sulfur fertilization. hours and days, and the second group containing
Furthermore, we have to keep in mind that sulfur is only COS with a lifetime of years, though 25 years
not only contributing to air pollution (acid rain) and is at the upper edge of all estimates. Of special
interest are DMS and COS. Besides sulfate
1
Max Planck Institute for Chemistry, Biogeochemistry containing sea spray, marine DMS is the main
Department, Joh.-J.-Becher-Weg 27, 55128 Mainz, component of global sulfur emission, whereas COS
Germany is the most stable compound in the atmosphere and
68 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

Figure 1:
Estimated ranges of global emissions of volatile sulfur compounds (Tg a-1) according to Andreae and Jaeschke (1992).

is taken up by vegetation and soils, the two radiation budget, temperature algal growth and
compartments representing the dominant sinks for DMS release. Over 700 papers have been published
this sulfur species. dealing with this subject, which seems to be neither
Based on the atmospheric lifetimes we may proved nor weakened.
discuss the cycling and the role of these compounds
over the marine and terrestrial environments as Table 1:
shown in the Figures 3 and 4. The oceans are the Tropospheric lifetimes of tropospheric sulfur gases
dominant source of biogenic volatile sulfur according to Warneck (2000)
compounds. DMS is the most important sulfur 0.1 days
DMS
species released by abiotic cleavage of dimethyl CH3SH 0.4 days
sulfoproprionate (DMSP), which is produced by DMDS 2.2 days
several algae and released into the seawater upon H2S 3 days
cell destruction (Malin and Kirst, 1997). COS, the CS2 7.2 days
second important marine sulfur species is produced SO2 1-40 days
by photochemical degradation processes of organo- COS 25 years
sulfur compounds (Ferek and Andreae, 1984). The
other sulfur species are of minor importance in The sulfur cycle above terrestrial surfaces exhibits
terms of marine emissions. COS with its long the same principal processes and mechanisms as
tropospheric lifetime may be transported into the described for the marine site. Several reduced sulfur
stratosphere where it underlies photochemical species are produced within the soil and released
photolysis and oxidation delivering sulfate particles into the atmosphere, where they underlie the same
as nutrients for the stratospheric sulfate layer fate as found over the oceans. However, there are
(Junge-Layer) around our globe. DMS and other some special terrestrial features. Soils and terrestrial
reactive sulfur trace gases enter oxidation processes vegetation are dominant sinks for COS (Chin and
in the troposphere producing sulfate particles, which Davis, 1993; Kesselmeier and Merk, 1993;
contribute to particle production, cloud Kesselmeier et al., 1999; Kuhn and Kesselmeier,
condensation nuclei (CCN) and cloud production. 2000; Kettle et al., 2002). This uptake is quite well
Both, particles as well as clouds influence the understood and is mainly based on the activity of an
radiation budget as indicated above. In case of the enzyme, the carbonic anhydrase, which is found in
marine DMS source, the so-called CLAW all biological organisms (Protoschill-Krebs et al.,
hypothesis (Charlson Lovelock, Andreae and 1992 & 1995 & 1996). The enzymatic process could
Warren, 1987) caused intensive discussions during recently be modeled by Schenk et al. (2004). In
the last decade. According to this hypothesis, DMS addition to its COS sink quality, terrestrial
emission from algae controls a feedback mechanism vegetation also emits sulfur compounds into the
with a coupling between DMS release, cloud albedo, atmosphere. Reports on the emissions of all reduced
species can be found in the literature. Of special
Landbauforschung Völkenrode, Special Issue 283, 2005 69

Figure 2:
Distribution of global sulfur emission sources between the hemispheres according to Bates et al. (1992). Note the decrease
of anthropogenic sources towards the southern hemisphere.

Figure 3:
Sulfur cycle within and above the ocean.

interest is the release of DMS by higher plants, contrast to the DMS production in the oceans this
among them tropical rain forest trees (Andreae and DMS release is based on biological degradation and
Jaeschke, 1993; Kesselmeier et al., 1993). In can also be found in case of decomposing leaf litter
70 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

Figure 4:
Sulfur cycle within and above terrestrial surfaces.

(Kesselmeier and Hubert, 2002). This DMS release on the meteorological tower of the Institute of
from terrestrial sources with its potential impact on Atmospheric Physics, Chinese Academy of Sciences
atmospheric chemistry and physics needs further in Beijing during 23–24 November 2001. The
investigation. authors found roughly 600 to 1700 ppt at the 8 m
All above indicated processes enclosing sources level, 400 to 1500 ppt at 160 m and 400-1300 ppt at
and sinks are summarized in budget estimates as 300 m. Within these data sets they observed clear
shown in Table 2. Though these numbers seem to concentration gradients with highest concentrations
show a reasonable balance of sources and sinks, it at the lowest level, clearly indicating COS sources at
has to be noted that great uncertainties exist for H2S the ground. Furthermore, in early November they
and CS2. Furthermore, COS deposition needs further observed fluctuations between 1000 and 7000 ppt
investigations, especially in case of the consumption for COS, 100-1200 for CS2 and 100-500 for H2S.
by different soil types. DMS emission by trees and Such high concentrations at the surface point to
forest urgently needs more investigations for a anthropogenic sources, mainly traffic. It is
global extrapolation. Other poorly understood remarkable that these values for reduced sulfur
ecotypes are fresh water wetlands where data are compounds were comparable to concentrations of
sparse. SO2 in polluted areas. Figure 5 gives an overview of
SO2 atmospheric concentrations in several cities in
Table 2: China for 1990-1995 compared with some other
Balance of sources and sinks, biological as well as polluted areas in the world. For orientation, the
chemical, for reduced sulfur compounds according to World Health Organization (WHO) annual mean
Watts (2000)
guidelines for air quality standards are 50
SOURCE SINKS micrograms per cubic meter for sulfur dioxide.
COS 1.31 ± 0.25 1.66 ± 0.79 Though theses atmospheric data can be highly
*H2S 7.72 ± 1.25 8.50 ± 2.80 sensitive to local conditions they may be considered
*CS2 0.66 ± 0.19 1.01 ± 0.45 a general indication of air quality. As a result of
DMS 24.45 ± 5.30 no estimate several emission reductions since 1987 and the
*Note great uncertainties for H2S and CS2 almost complete shut down of old industrial
installations in the eastern part of Germany after the
reunion in 1989, Germany was able to reduce the
Atmospheric concentrations of sulfur compounds emission of SO2 during the last two decades by 90
in China % down to values of a few µg m-3 (see also
Wallasch 2003).
Reduced sulfur compounds are also of The above reported data show that the
anthropogenic origin. Yujing et al. (2002) measured anthropogenic sulfur load in China is high. The
vertical distribution profiles of COS at three levels Special Report on Emission Scenarios (SRES, IPCC
Landbauforschung Völkenrode, Special Issue 283, 2005 71

Figure 5:
Cities with reported levels of atmospheric pollutants in relation to WHO guidelines (bold line, 50 µg m-3) in 1990-1995.

2001) estimated an increase of annual SO2 nearly exclusively caused by coal burning power
emissions in Asia from 50-70 Tg a-1 (1990 data) to plants, as very recently observed during the "2003
80-110 Tg a-1 by 2020. However, recently published North American electrical blackout" (Marufu et al.,
data show that this trend to increasing values 2004).
obviously has been stopped (Carmichael et al.,
2002). In contrast to the predictions of the IPCC
report (2001) the emission load was constantly Conclusions
decreasing from the year 1995 to 2000 (Streets et
al., 2000a, b) and the authors estimate a decrease to Current anthropogenic release of SO2 in China is
lower values of 40-45 Tg a-1 by 2020. The change of declining. If this process continues, there will be
the trend is clearly caused by a decline of SO2 huge health benefits for the society. However, it has
emissions from 1995 to 2000 in China (2/3 of Asian to be accepted that the sulfur demand for
SO2!) due to a reduction in industrial coal use, slow- agricultural purposes will grow and, consequently,
down of the Chinese economy and a closure of the role of natural sources and cycles need to be
small and inefficient power plants. This relationship better understood. Furthermore, as a consequence of
is highly significant, as atmospheric SO2 pollution is the decrease of direct and indirect cooling effects
72 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

due to the decrease of sulfate aerosol particles, we Kettle A J, Kuhn U, von Hobe M, Kesselmeier J,
may observe an increase of the global warming. Andreae M.O. (2002) The global budget of atmospheric
This effect underlines the general necessity to carbonyl sulfide: Temporal and spatial modulation of
recognize other air pollution processes and to fight a the dominant sources and sinks. J. Geophys Res 107:
NO. D22, 4658, doi:10.1029/2002JD002187
further increase of radiatively active gases. Kuhn U, Kesselmeier J (2000) Environmental parameters
controlling the uptake of carbonyl sulfide by lichens. J.
Geophys. Res. 105:26783-26792
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historical anthropogenic global sulfur emission patterns
Andreae MO, Crutzen PJ (1997) Atmospheric aerosols - for the period 1850-1990. Atmos Environ 33:3435-3444
Biogeochemical sources and role in atmospheric Malin G, Kirst GO (1997) Algal production of dimethyl
chemistry. Science 276:1052-1058 sulfide and its atmospheric role. J Phycol 33:889-896
Andreae MO, Jaeschke WA (1992) In: Howarth RW, Marufu LT, Taubman BF, Bloomer B, Piety CA,
Stewart JWB, Ivanov MV(eds) Sulphur Cycling on the Doddridge BG, Stehr JW, Dickerson RR (2004) The
Continents. SCOPE 2003 North American electrical blackout: An accidental
Bates TS, Lamb BK, Guenther A, Dignon J, Steuber, RE experiment in atmospheric chemistry. Geophys. Res.
(1992) Sulfur emissions to the atmosphere from natural Lett. 31:L13106, doi:10.1029/2004GL019771
Carmichael, GR, Streets, DG, Calori, G, Amann, M, Protoschill-Krebs G, Kesselmeier J. (1992) Enzymatic
Jacobson, MZ, Hansen, J, Ueda, H (2002) Changing pathways for the consumption of carbonyl sulphide
trends in sulfur emissions in Asia: Implications for acid (COS) by higher plants. Bot Acta 105:206-212
Deposition, Air Pollution, and Climate. Environ Sci Protoschill-Krebs G, Wilhelm C, Kesselmeier J (1995)
Techn 36:4707-4713 The consumption of carbonyl sulphide by carbonic
Charlson RJ, Lovelock JE, Andreae MO, Warren SG anhydrase (CA) of Chlamydomonas reinhardtii grown
(1987) Oceanic phytoplankton, atmospheric sulphur, under different CO2 regimes. Bot Acta 108:445 - 448
cloud albedo and climate. Nature 326:655-661 Protoschill-Krebs G, Wilhelm C, Kesselmeier J (1996)
Charlson RJ, Schwarz SE, Hales JM, Cess RD, Coakley Jr Consumption of carbonyl sulphide by carbonic
JA, Hansen JE, Hofman DJ (19929 Climate forcing by anhydrase (CA) isolated from Pisum sativum. Atmos
anthropogenic aerosols. Science 255:423-430 Environ 30:3151-3156.
Chin M, Davis DD (1993) Global sources and sinks of Schenk S, Kesselmeier J, Anders E (2004) How does the
OCS and CS2 and their distributions. Global exchange of one oxygen atom by sulfur affect the
Biogeochem Cycles 7:321-337 catalytic cycle of carbonic anhydrase? Chemistry - A
Chin M, Davis DD (1995) A reanalysis of carbonyl Eur J 10:3091-3105. doi: 10.1002/chem.200305754.
sulfide as a source of stratospheric background sulfur Streets DG, Tsai NY, Akimoto H, Oka K (2000a). Sulfur
aerosol. J. Geophys. Res. 100:8993 -9005 dioxide emissions in Asia in the period 1985-1997.
Ferek RJ, Andreae M.O. (1984) Photochemical Atmos Environ 34:4413-4424
production of carbonyl sulfide in marine surface waters. Streets DG, Guttikunda SK, Carmichael G. (2000b). The
Nature 307:148-150 growing contribution of sulfur emissions from ships in
IPCC WGI Third Assessment Report (2001) Asian waters, 1988-1995. Atmos Environ 34:4425-4439
Kesselmeier J, Hubert A. (2002) Exchange of volatile Wallasch M (2003) EMEP Assessment Report.
reduced sulphur compounds between leaf litter and the Warneck P (2000) Sulfur compounds in the atmosphere.
atmosphere. Atmos Environ 36:4679-4686. In: Chemistry of the Natural Atmosphere (2nd Edition).
Kesselmeier J, Merk L (1993) Exchange of carbonyl Academic Press, San Diego, p 598
sulfide (COS) between agricultural plants and the Watts SF (2000) The mass budgets of carbonyl sulfide,
atmosphere: Studies on the deposition of COS to peas, dimethyl sulfide, carbon disulfide and hydrogen sulfide.
corn and rapeseed. Biogeochemistry 23:47-59 Atmos Environ 34:761-779
Kesselmeier J, Meixner FX, Hofmann U, Ajavon A, World Bank (1998) World Development Indicators, The
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tropical tree species in southern Cameroon. Yujing M, Hai W, Zhang X, Jiang G (2002) Impact of
Biogeochemistry 23:23-45 anthropogenic sources on carbonyl sulfide in Beijing
Kesselmeier J, Schröder P, Erisman J.W. (1997) City. J. Geophys. Res. 107(D24); 4769, doi:10.1029/
Exchange of sulfur gases between biosphere and the 2002JD002245
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Seiler W (eds) Transport and Chemical Transformation
of Pollutants in the Troposhere Vol 4, Biosphere-
Atmosphere Exchange of Pollutants and Trace
Substances (Slanina J ed.). Springer Verlag, Heidelberg,
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variables for the uptake of atmospheric carbonyl sulfide
(COS) by soil. J Geophys Res-Atmos 104 (D9):11577-
11584
Landbauforschung Völkenrode, Special Issue 283, 2005 73

Sulfur-rich proteins and their agrobiotechnological potential for resistance to plant

pathogens

Cordula Kruse1, Ricarda Jost2, Helke Hillebrand3 and Rüdiger Hell1*

Abstract1 gent taste deterres feeding insects and other animals

upon destruction of plant tissues, thereby releasing
Thionins, defensins and a number of other related the stored compounds and the corresponding de-
polypeptides form the group of small, sulfur-rich grading enzymes, myrosinase and alliinase. In the
defense proteins. They are processed from larger end the breakdown products isothiocyanate and al-
preproteins and mostly localized in walls of epider- licin exhibit toxicity to the enemy. Most of these
mal cells of seeds and leaves. In vitro they display compounds are preformed and stored until the plant
antimicrobial activity especially against fungi. Their is attacked. Only the indole glucosinolates appear to
genes can be constitutively expressed or induced by be inducible by defense pathways like the jasmonate
fungal pathogens, thereby supporting the host's de- signal transduction pathway (Bodnaryk, 1994).
fense against biotic stress. The effectiveness of Another inducible defense compound containing
thionins and defensins against phytopathogenic reduced sulfur is the phytoalexin camalexin that is
fungi has been demonstrated by overexpression in only produced upon fungal and bacterial infection in
transgenic plants. The observed enhanced resistance Brassicaceaen plants. It is derived from indole-3-
against a number of agriculturally important patho- acetaldoxime and carries a thiazole ring. Its synthe-
gens such as Alternaria ssp. and Fusarium ssp. has sis is triggered by the jasmonate and salicylate
prompted research on the biology of sulfur rich de- pathways. Camalexin shows toxicity towards both
fense proteins and attempts to improve the resis- kinds of pathogens (Tsuji et al., 1992). A surprising
tance of crop plants. discovery was the presence of elemental sulfur in
plants (Cooper et al., 1996). The redox biochemistry
Key words: glucosinolates, phytoalexins, thionins, and synthesis of S0 in living plant tissue is still un-
pathogens, defensins, sulfur-rich proteins clear, however, recent investigations provided evi-
dence for the widespread occurrence of elemental
sulfur as well as its function in defense against fun-
Sulfur-containing defense compounds gal and bacterial pathogens (Williams and Cooper,
2003). S0 may exist preformed but can also be in-
Sulfur-containing compounds and their metabo- duced upon infection and then accumulates in vas-
lism are well connected to plant stress resistance. cular tissue, presumably to prevent the spread of
Hardly any other element serves in so many differ- infections along the plant transport routes. It has
ent stress-related functions such as resistance against thus been suggested that plants since long possess
heat, cold, drought, flooding, heavy metals, organic 'man's oldest fungicide' (Williams and Cooper,
xenobiotics and reactive oxygen species 2004).
(Rennenberg and Brunold, 1994). The role of sulfur One of the best investigated sulfur-containing
in biotic stress resistance is less investigated, but defense compounds in plants to date are sulfur-rich
there is strong evidence that innate defense mecha- proteins. They can be grouped into several classes,
nisms against plant pathogens are based on sulfur including thionins, defensins, lipid-transfer proteins,
compounds in several important cases. Whether snakins and others, according to their primary amino
sulfur nutrition and the sulfur status of a plant affect acid sequences and distribution (Garcia-Olmedo et
its ability to form protective sulfur compounds is al., 1998). They all share a relatively small size of 4
currently under investigation. Secondary sulfur to 11 kDa, mostly polar amino acid composition,
compounds that often are limited to special plant several disulfide bridges (2 to 6) and, as a conse-
families are mostly involved in herbivore resistance. quence, a rather compact tertiary structure. They
Prominent examples are the glucosinolates of the also share the notion that relatively little is known
Brassicacea and alliins of the Liliaceae. Their pun- about their precise physiological functions and
mechanisms of action. It can not be excluded that
1
Heidelberg Institute of Plant Sciences (HIP), University sulfur-rich proteins carry out a number of different
of Heidelberg, 69120 Heidelberg, Germany functions in vivo in addition to defense (Florack and
2
Research School of Biological Sciences, The Australian Stiekema, 1994). Among these protein families the
National University, Canberra ACT 0200, Australia thionins and defensins appear to be most important
3
BASF Plant Science GmbH, Technology Management, for plant defense against pathogens. They have been
67117, Limburgerhof, Germany
74 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

intensively investigated with respect to signal trans- mammalian and insect defensins and was thus re-
duction pathways and agrobiotechnology as judged named plant defensins. Their primary as well as
from numerous patent applications (see patent three-dimensional structure is more conserved
homepages: http://www.uspto.gov/patft/index.html; within this group as compared to other thionin
http://ep.espacenet.com/espacenet/ep/en/e_net.htm). classes. Remarkably, these proteins are not only
Many thionins, thionin-like proteins and defensins ubiquitously throughout the plant kingdom but also
have been isolated from seed and leaf material of a widespread in other organisms, including mammals,
huge variety of different plants, including but not insects and molluscs (Thomma et al., 2002). Plant
limited to members of the Brassicacea, Compositae defensins are 45 to 54 amino acids in length, carry a
and Leguminosae families. Within these groups positive net charge at physiological pH and have 8
Raphanus, Brassica, Sinapis, Arabidopsis, Dahlia, cysteine residues that form four disulfide bridges.
Cnicus, Lathyrus and Clitoria are prominent exam- The three-dimensional structure of several plant
ples (Patent numbers: US 5.689.043; US 5.689.048; defensins has been determined. They all consist of a
US 5.824.869; US 6.187.904; US6.605.698). Fur- triple-stranded ȕ-sheet and an Į-helix in parallel
ther proteins have been isolated and characterized orientation. This organization is largely conserved in
from Amaranthus, Capsicum, Briza and related defensins from other organisms and belongs to the
monocot and dicot species (US 5.691.199; US superfamily of cysteine-stabilized Į-helix / ȕ-sheet
6.521.590; US 20030096985) as well as from proteins (Thomma et al., 2002). The overall struc-
Heuchera and Aesculus (US 5.750.504), Allium (US ture is amphipathic, quite compact and stable
5.773.694) and Impatiens (US 6.150.588). The pro- (Almeida et al., 2002). Plant defensins (PDFs) are
teins described showed a wide range antifungal ac- encoded by gene families of different sizes. Arabi-
tivity and some were also active against Gram- dopsis thaliana as the best characterized plant at the
positive bacteria, yeasts, insects or nematodes. Anti- genetic level contains 13 defensin genes and 2 de-
fungal activity was mostly measured by using Fusa- fensin-like genes. Earlier studies (Penninckx et al.,
rium culmorum strain IMI 180420 as a test organism 1996; Epple et al., 1997a) divided the defensins into
for in vitro bioassays (Broekaert et al., 1990). A two subgroups, PDF1 and PDF2. The first group
great variety of suitable test strains used to assess contains seven defensins, of which five are very
the biocidal properties of such proteins are listed in similar at the nucleotide level and identical at the
patents US 5.942.663, US 5.919.018 and US amino acid level (PDF1.1, 1.2a, 1.2b, 1.2c, 1.3;
5.986.176. Efficient thionin or defensin genes can Thomma et al., 2002), suggesting very recent ge-
potentially form valuable traits in crop plants, either nomic duplication events. The situation in crop
by using transgenic overexpression or by marker- plants is much less investigated, but EST databases
assisted introgression into elite lines. This article for rape, rice and barley indicate the presence of
will therefore focus on properties of thionins and gene families. Expression analysis of the defensin
defensins that are relevant for plant protection and gene family in Arabidopsis revealed differential
summarize the approaches to improve plant resis- expression patterns. Most genes are expressed con-
tance making use of these sulfur-rich proteins. More stitutively in one or more organs. Specifically,
detailed overviews about biological aspects are PDF1.1 is expressed in seeds and siliques, PDF2.1
available for thionins (Bohlmann and Apel, 1991; in seeds, siliques and roots, PDF2.2 in all organs
Garcia-Olmedo et al., 1998) and more recently for except seeds and stems, and PDF2.3 is present in all
plant defensins (Thomma et al., 2002). organs except roots. In addition, pathogen infection
induces PDF1.2 in several developmental stages via
the jasmonate and ethylene signaling pathways
Genomic organization of gene families, expres- (Thomma and Broekaert, 1998; da Silva Conceicao
sion and structure of the thionin and defensin and Broekaert, 1999). Mutants with defects in these
proteins pathways are susceptible to Botrytis cinerea due to
the lack of expression of inducible defensins
By definition thionins and defensins belong to a (Thomma et al., 1998). This finding strongly under-
group of polypeptides with 10% to 20% cysteine lines the efficiency of these sulfur-rich proteins for
residues that exhibit toxic activity towards cells of pathogen defense. Furthermore, 11 of the Arabidop-
bacteria, fungi and mammals. Thionins were dis- sis defensin genes carry a predicted signal peptide
covered first as abundant component of wheat flour for secretion into the apoplast, hence are localized to
(cited in Apel et al., 1990). Their molecular organi- the primary infection sites. In contrast, PDF1.4 and
zation was finally elucidated in context with the PDF2.4 appear to contain no signal sequence and
detection of leaf-specific thionins (Bohlmann and may stay in the cytoplasm with so far unknown
Apel, 1987). In earlier studies thionins were grouped functions.
into several classes, of which the gamma thionin Thionins occur exclusively in the plant kingdom
class later turned out to be structurally related to but are still much less conserved among each other
Landbauforschung Völkenrode, Special Issue 283, 2005 75

than the defensins. The size of the mature polypep- of radish (Florack and Stiekema, 1994; Thomma et
tide chains is also 45 to 55 amino acids, but primary al., 2002). It appears that especially the germinating
sequences show less homology. Signatures of the seedling requires antimicrobial activities as protec-
cysteine residues are highly conserved, although the tion against pathogens during this critical develop-
number of disulfide bridges varies between 3 and 4 mental stage. Later on both sulfur-rich protein types
in thionins from evolutionary distant species. Three- were found in mature leaves as well. In all cases
dimensional structures have been determined for these proteins were excreted into the cell wall, in
several thionins and revealed a conserved L-shaped many cases preferentially within the surface cell
structure formed by two parallel Į-helices (long arm layers of the plant organ. This localization makes
of L) and two ȕ-sheets (short arm of the L; sense since the apoplast is the primary site of con-
Bohlmann and Apel, 1991; Garcia-Olmedo et al., tact by a pathogen and would allow immediate in-
1998). The overall structure is again amphipathic, teraction. Indeed, accumulation of apparently induc-
but somewhat less compact and heat stable com- ible leaf cell-wall thionins has been observed around
pared to the defensins. All of the Arabidopsis thion- the infection sites in case of barley and powdery
ins and so far most of the thionins from other plant mildew interaction (Ebrahim-Nesbat et al., 1989;
species possess amino-terminal domains with signa- Apel et al., 1990). As already mentioned the intra-
tures for transport via the endoplasmatic reticulum cellular targeting is carried out by signal sequences.
to the apoplast. In addition, thionin presequences These may also be responsible for the occasionally
reveal a carboxy-terminal domain that is highly observed vacuolar localization of some barley thion-
acidic. Interestingly, this domain harbors six cys- ins (Reimann-Philipp et al., 1989) and missing as
teine residues and is also strongly conserved be- already mentioned from two of the Arabidopsis de-
tween thionins of different species, suggesting a fensins with putatively cytosolic localization
conserved and essential function. It was assumed (Thomma et al., 2002).
that the acidic residues could neutralize the basic The mechanism of toxicity of sulfur-rich proteins
amino acid residues of the central thionin domain in has long been debated, involving speculation about
the pre-proprotein, but the precise function is un- the role of the highly conserved amphipathic and
known. N- and C-terminal domains are post- compact structure provided by the disulfide bridges
translationally processed, leaving mature thionins (Florack and Stiekema, 1994; Garcia-Olmedo et al.,
with a size of approximately 5 kDa (Apel et al., 1998). However, in several cases structurally closely
1990). According to the Arabidopsis Sequence Ini- related sulfur-rich proteins generated contrasting
tiative Arabidopsis thaliana contains 4 thionin- results in antimicrobial activity tests in vitro and in
coding genes grouped into two subfamilies. Of these vivo, leaving the actual toxicity determinants in the
only two genes have been characterized (Epple et respective proteins unclear (Thomma et al., 2002).
al., 1995), whereas genomic analyses suggested 50- Recently electrophysiological measurements using a
100 copies in the barley genome (Bohlmann et al., ȕ-purothionin from wheat flour revealed a possible
1988). Expression analysis showed that THI2.1 is general mechanism of toxicity based on in vitro as-
inducible by pathogens, wounding and chemicals says with artificial lipid bilayer membranes and
via the jasmonate pathway, while THI2.2 is constitu- mammalian cell lines (Hughes et al., 2000). The
tively expressed (Epple et al., 1995; Bohlmann et authors observed the formation of cation-selective
al., 1998). Knock-out mutants of thionins have not ion channels upon interaction of purothionin with
been reported, but constitutive overexpression of plasmalemma components and concluded that this
THI2.1 leads to enhanced resistance of Arabidopsis effect causes the dissipation of ion concentration
to Fusarium oxysporum infection (Epple et al., gradients that are essential for cellular function.
1997b), pointing to the importance of thionins for However, these assays were not carried out with
pathogen defense. The inducibility of thionins and authentic pathogenic fungi.
defensins helps to save valuable resources in the Membranes of the model fungi Neurospora crassa
absence of pathogens. It is interesting to speculate and Saccharomyces cerevisiae were shown to be
whether reduced sulfur is available in sufficient permeabilized by defensins at low concentrations.
amounts under less than optimal sulfur supply, Defensins from radish and Dahlia merckii were ap-
thereby reducing the defense potential of an attacked plied and their effect monitored using uptake of a
plant. fluorescent dye into fungal cells as reference
(Thevissen et al., 1999). The authors suggest direct
peptide-phospholipid interactions that can be sup-
Localization and mechanism of toxicity pressed by cations in the medium. It is concluded
that cations alter the conformation of the binding
Thionins and defensins were originally discovered site and that successful permeabilization is linked to
as protein components of seeds: thionins were found the fungal growth inhibition. The mechanism of
in barley endosperm and defensins in the seed coat toxicity of defensins thus seems to be different from
76 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

that of thionins. The drawback of this and other and displayed 7- to 8-fold less lesions compared to
studies (Thevissen et al., 1996; da Silva Conceicao control wild type and azygous plants upon infection
and Broekaert, 1999) again consists in the lack of with Alternaria longipes. The degree of resistance in
information on the reaction of membranes of phyto- the transgenic lines correlated closely with the pro-
pathogenic fungi. tein level of AFP2, unequivocally demonstrating the
function and suitability of plant defensins for fungal
resistance.
Biotechnology approaches to enhance resistance A most promising demonstration of the suitability
in crop plants of defensin expression is the transformation of rice
by Agrobacterium tumefaciens with a construct con-
Breeding and plant transformation both aim at the sisting of the 35S promoter and the Wasabi defensin
transfer of genes or effective alleles that confer im- from Japanese Radish (Wasabia japonica; Kanzaki
proved resistance to economically relevant crop et al., 2002). The Wasabi defensin was especially
genotypes. One approach to this end is the identifi- selected for its toxicity against rice blast disease, a
cation and transfer of key components of resistance worldwide fungal pathogen which causes severe
responses. Examples are the R-genes as specific damage and reduced yield. The Wasabi protein was
receptors for the recognition of pathogens. Broad- present in transgenic rice lines, with the best lines
spectrum disease resistance may be expected from reaching resistance levels comparable to a rice culti-
overexpression of the NPR1 and PAD4 genes that var carrying the true blast resistance gene in leaf
seem to mediate responses for the salicylate signal- lesion tests. The resistance was stable over several
ing pathway (Rommens and Kishore, 2000). A sec- generations, suggesting a durable and wide-
ond approach employs enhanced expression of spectrum resistance against various rice blast races
downstream responses such as thionins and de- in the field.
fensins. Some of these proteins show a direct and Despite several unsuccessful (and often unpub-
broad spectrum of antifungal activities in vitro. Ide- lished) attempts these positive results have spurred
ally this property would copy those of insecticidal the transformation of barley and wheat with anti-
proteins from Bacillus thuringiensis showing toxic- microbial proteins (Dahleen et al., 2001). Fusarium
ity against pathogenic fungi but being harmless head blight (Fusarium graminearum) is one of the
against animal and human cells. A number of ex- most devastating diseases for wheat, durum and
periments have attempted to enhance pathogen resis- barley. Only a limited number of genotypes of
tance by overexpression of sulfur-rich proteins in wheat and barley with only partial resistance have
plant models or crops. A list of successful ap- been found. The resistance trait that has been iso-
proaches is given in Tab. 1. However, it should not lated apparently is under the control of multiple
be overlooked that, despite strong antimicrobial ac- genes and functions independently of the gene-for-
tivities of the respective proteins in in vitro bioas- gene interactions that provide resistance against
says, similar experiments have also failed to confer barley and wheat pathogens like powdery mildew
resistance for mostly unknown reasons (De Bolle et (Blumeria graminis) and stem rust (Puccinia
al., 1996; citations in Florack and Stiekema, 1994; graminis). Fusarium head blight resistance is there-
Broekaert et al., 1995; Epple et al., 1997). fore a challenge for breeders, making insertion of
The earliest published example of transgenic expres- individual genes into cereals an attractive alterna-
sion of a sulfur-rich protein refers to an Į-thionin tive, although transformation of these recalcitrant
from barley (Carmona et al., 1993). Expression in species is still ineffective and cost intensive. Several
tobacco was driven by the constitutive Cauliflower approaches using barley and wheat thionins are un-
Mosaic Virus 35S promoter and could be demon- der way, supported by the US Department of Agri-
strated by the presence of the Į-thionin in tobacco culture (Dahleen et al., 2001, and references
protein extracts. Increased resistance against two therein). These approaches are further complicated
pathovars of Pseudomonas syringae was observed, by the requirement of strong spike-specific promot-
that clearly correlated with the amount of Į-thionin ers for the expression of thionins at the preferred
present in the different transgenic tobacco lines. infection site of Fusarium culmorum and F.
The first overexpression of a plant defensin was graminearum that still need to be isolated.
carried out using a similar construct of 35S pro- An enhanced approach to use antifungal proteins
moter and the antifungal protein 2 (AFP2) from rad- against fungal pathogens is represented by fusions
ish (Raphanus sativus) and tobacco as heterologous that consist of a defensin and a single chain antibody
host (Terras et al., 1995). The AFP2 protein was (Peschen et al., 2004). The single chain antibody
shown to have antifungal activity against Alternaria was isolated by phage display and selected for sur-
brassicicola, Botrytis cinerea and Fusarium cul- face determinants of Fusarium ssp.. A translational
morum in vitro. Transgenic T2 lines of tobacco were fusion of radish AFP2 and antibody CWP2 was ex-
tested for disease resistance using a leaf lesion test pressed in Arabidopsis and yielded strongly en-
Landbauforschung Völkenrode, Special Issue 283, 2005 77

Table 1:
Reported successful approaches to express sulfur-rich proteins in transgenic host plants to enhance resistance against phyto-
pathogenic fungi and bacteria.

Protein Source Plant transformed Resistance tested Reference

Į-Thionin Barley Tobacco Pseudomonas syringae Carmona et al., 1993

RsAFP2 Radish Tobacco Alternaria longipes Terras et al., 1995
defensin
Thi2.1 Arabidopsis Arabidopsis Fusarium oxysporum Epple et al., 1997
thionin
Viscotoxin A3 Mistletoe Arabidopsis Plasmodiophora brassicae Holtorf et al., 1998
Leaf thionin Oat Rice Xanthomonas campestris Ohashi et al., 2001
Pseudomonas plantari
Tobacco Phytophtora infestans
Wasabi defensin Japanese Rice Magnaporthe grisea Kanzagi et al., 2002
radish (blast fungus)
Į-Thionin, Barley, Wheat and Fusarium graminearum Dahleen et al., 2001
seed hordothionin wheat barley
RsAFP2 + Radish Arabidopsis Fusarium oxysporum Peschen et al., 2004
antibody

hanced resistance against Fusarium oxysporum. proteins. Genomic and bioinformatic approaches are
Interestingly, expression of the CWP2 antibody under way to identify expression patterns of interest
alone already increased resistance, pointing to a to use the underlying promoters to drive defense
potentially new avenue of antifungal strategies. gene expression in transgenic plants. Finally, most
AFP2 expression alone also was effective, but the research is still carried out with model species for
assumed targeting of the AFP2-CWP2 fusion pro- good reasons. Lack of genomic and expression in-
tein to the invader and presumed concentration of formation together with elaborate and inefficient
the sulfur-rich protein at the infection site had an transformation protocols still hamper progress with
additive effect on resistance. The specificity of this crop plants, but at the end of the day this is where
recognition was demonstrated by the lack of resis- the sulfur-rich defense proteins are required. Classi-
tance against the fungal pathogen Sclerotinia scle- cal selection of resistant genotypes using sulfur-rich
rotinum, which is not recognized by the CWP2 anti- proteins as a target supported by marker-assisted
body. breeding could be an alternative approach. However,
Such experiments provide proof-of-function of the the above listed requirements of biotechnology and
suitability and effectiveness of sulfur-rich proteins consumer safety make this approach difficult. It will
as targets of plant defense. Of course a number of be very interesting to see how the wealth of know-
constraints have to be overcome for successful ap- ledge on sulfur-rich defense proteins will be used in
plication in biotechnology. One is the lack of the future to improve crop resistance against impor-
knowledge about the molecular determinants of tox- tant fungal pathogens
icity on both the sulfur-rich protein side as well as
the fungal membrane side. If this problem was
solved protein engineering would allow to screen for Acknowledgements
active proteins with broad specificity against fungi The authors wish to thank the German Science
and possibly bacteria but reduced toxicity against Foundation (DFG) for financial support within For-
mammalian cells. At this point thionins and de- schergruppe 383.
fensins from natural sources can be expressed as
recombinant proteins or isolated and selected for
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80 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants
Landbauforschung Völkenrode, Special Issue 283, 2005 81

Crop response to sulfur fertilizers and soil sulfur status in some provinces of China

Shutian Li1, Bao Lin1 and Wei Zhou1

Abstract12 measures. At present, it is necessary to supply S for

balanced fertilization. From 1996 to 2002 we
Field trials and demonstrations were conducted to conducted field trials/demonstrations in some crops
investigate sulfur fertilizer effects on crops in some such as corn, wheat, rice, soybean and oilseed rape
provinces of China, and soil sulfur status in to study crop response to S fertilizers, and selected
Heilongjiang, Henan, Shaanxi and Jiangxi provinces some provinces to investigated soil S status.
was also evaluated. Results showed that sulfur
application could increase crop yield by 6.9%, 6.8%
9.4%, 11.8% and 8.1% on average, respectively, for Materials and methods
corn, wheat, rice, soybean, and oilseed rape. The
effect of ammonium sulfate or potassium sulfate on From 1996 to 2002 field trials/demonstrations of
crop yield was better than gypsum or elemental sulfur fertilizers on main crops such as corn, wheat,
sulfur. The rational application rate for elemental rice, soybean and oilseed rape were conducted in
sulfur and sulfate sulfur sources was 60 kg ha-1 and Heilongjiang, Jilin, Henna, Shaanxi, Hubei and
30 kg ha-1, respectively. Sulfur application increased Jiangxi provinces in China. Many sulfur sources
S uptake by both grain and straw. For cereal crops such as ammonium sulfate, potassium sulfate,
sulfur content and total uptake of straw was more gypsum, single superphosphate and elemental sulfur
than that of grain, but opposite result was obtained were tested. Application rate ranged from 30 to 120
for soybean. According to the critical level of soil kg S ha-1. According to the results from field
available sulfur in upland soil determined by experiments critical value for soil available S were
calibration study, which was 20.0 mg S kg-1, about determined.
41.4%, 35.6%, 42.7% and 38.5% of tested soil From 1997 to 2001 soil samples from upland soils
samples was S deficient in Heilongjiang, Henan, were collected in Heilongjiang, Henan, Shanxi and
Shaanxi and Jiangxi province, respectively. Jiangxi provinces. Soil total S, available S and
organic C were tested and evaluated.
Keywords: crop response, sulfur fertilizer, soil Organic C were determined by Walkley-Black
sulfur, critical value (Nelson and Sommers, 1996). Total soil S was
determined by acid oxidation with HNO3, HClO4,
H3PO4 and HCl (Page et al., 1982), followed by
Introduction ICP-AES to determine sulfate in the digest. Soil
available sulfur was determined turbidimetrically
There has been three phases in balanced (Hesse, 1971) after extraction with 0.01 mol l-1 Ca
fertilization which was on the basis of organic (H2PO4)2 by shaking for 1 hour under soil to
fertilizer application in China, i.e. only nitrogen solution ratio of 1 : 5. Total S in the plant materials
application in 1950’s, combined use of nitrogen and was determined by the procedure of Lisle et al.
phosphorus fertilizer in 1960’s and integrated (1994) in which 0.5 g of plant materials was
application of nitrogen, phosphorus, potassium and digested using a wet oxidation technique involving
micronutrient fertilizer since the mid of 1970’s. an acid mixture of HNO3, HClO4 and HCl and
However, the secondary nutrients such as sulfur, sulfate in the digests was determined by ICP-AES.
calcium, magnesium has not been paid more
attention. Sulfur is an essential nutrient for plant
production and the amount of sulfur uptake by plant Results and discussion
is similar to that of phosphorus. The potential
occurrence of sulfur deficiency in Chinese Crop responses to sulfur fertilizers
agricultural soils has increased due to high amount From 1996 to 2002 total of 99 field trials and
of N, P and K applied, intensive and increased crop demonstrations were conducted on corn, wheat, rice,
production, increased use of high analysis S-free soybean and oilseed rape in Helongjiang, Jilin,
fertilizers, and more recently anti-pollution Henan, Shaanxi, Hubei and Jiangxi provinces.
Results showed that in cereal crops sulfur
application increased grain yield of corn, wheat and
1
Soil and Fertilizer Institute, Chinese Academy of rice by 6.9%, 6.8% and 9.4% on average,
Agricultural Sciences, Beijing 100081, China respectively. In economic crops sulfur could
82 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

increased yield of soybean and oilseed rape by (Figure 1). Zhang et al. (1997) also indicated that
11.8% and 8.1%, respectively. The average yield the critical value of soil available S extracted by
increase and S efficiency for these crops are listed in 0.01 mol l-1 Ca(H2PO4)2 was 20 mg kg-1 for upland
Table 1. crops such as oilseed rape, soybean and wheat.
However, the critical value of soil available S
Table 1: obtained by many scientists in other countries was
Effects of sulfur application on different crop yield. lower than 20 mg kg-1 (Donahue et al., 1983; Blair
Crops No. of Average yield S et al., 1993; Zhao et al., 1994). The reason is that in
trials increase efficiency China planting intensities and crop yield are higher
kg ha-1 % kg grain than that in other countries, and large amount of S
kg S-1 was removed from agricultural field. Furthermore,
large amount of N, P, and K applied in crop
Corn 31 456 6.9 10.1 production need more S for nutrient balance.
Wheat 6 388 6.8 7.5
Rice 39 603 9.4 15.1
Soybean 13 260 11.8 6.7 Table 2:
Oilseed rape 10 140 8.1 2.9 Effect of sulfur sources and application rate on crop yield.
Sulfur source Application No. of Average
rate trails yield
There were some differences in crop responses to kg ha-1 increase
various sulfur sources. At the same application rate %
ammonium sulfate or potassium sulfate increased Elemental 30 51 6.8
crop yield more than gypsum or elemental sulfur. sulfur
For elemental sulfur application rate of 60 kg S ha-1 45 68 8.4
was better than lower rate, further increase S rate 60 55 9.6
could not increase crop yield. For sulfate-S sources
such as gypsum, potassium and ammonium sulfate 90 11 9.6
the increase effect on crop yield with 30 kg S ha-1 120 7 9.1
application was similar to that of 45 kg S ha-1
application rate (Table 2). So, for elemental sulfur Gypsum 30 15 8.1
and sulfate sulfur sources the rational application
45 15 8.3
rate was 60 kg ha-1 and 30 kg ha-1, respectively.
Ammonium 30 14 9.6
Sulfur uptake by crops sulfate or
potassium 45 25 9.5
Total S in straw and grain was determined after sulfate
harvest. Results showed that sulfur application did
not significantly increase S content in grain but
increased S content in crop straw to some extend.
However, sulfur application increased total S uptake Soil sulfur status in some provinces
by both grain and straw due to the increase of the From 1997 to 2000 total of 191, 222, 307 and 104
yield. For cereal crops sulfur content and total soil samples were collected from upland soil in
uptake of straw was more than that of grain. But Heilongjiang, Henan, Shaanxi and Jiangxi province,
opposite result was obtained for soybean, i.e. sulfur respectively. Soil available S and total S (Table 4
content and total uptake of grain was much more and Table 5) were determined. According to the
than that of straw. Wheat needed more S than other above critical level of soil available sulfur in upland
crops (Table 3). This indicated the nutritional soil 41.4%, 35.6%, 42.7% and 38.5% of collected
difference of S in various crops. soil samples was S deficient in Heilongjiang, Henan,
Shaanxi and Jiangxi province, respectively (Table
Determination of critical values for soil available S 4). S deficiency existed in each soil type and the
According to field experiments the relationship content of available S was variable among soil
between soil available S extracted by 0.01 mol l-1 samples. Statistic analysis showed that there was
Ca(H2PO4)2 and the relative grain yield (yield significant relationship between total soil S and
without S/yield with S × 100%) showed that the organic C in four provinces (Table 6). But the
critical level of soil available sulfur for upland and correlation coefficient was higher in Heilongjiang
paddy soil was 20.0 mg kg-1and 25.0 mg kg-1, and Jiangxi provinces than in Henan and Shaanxi
respectively, estimated by Cart-Nelson method provinces where soils are calcareous with higher pH
Landbauforschung Völkenrode, Special Issue 283, 2005 83

Table 3:
Average sulfur concentration in plant tissues and total S uptake by crops.
Crop Sulfur rate S concentration S uptake Total uptake
kg S ha-1 mg kg-1 kg S ha-1 kg S ha-1
Grain Straw Grain Straw Grain + Straw
Corn 0 1031 1241 5.6 6.3 11.9
30 1036 1493 5.9 8.1 14.0
60 1022 1406 6.1 8.1 14.2
Wheat 0 1322 2904 7.0 15.1 22.1
30 1416 3075 7.8 16.7 24.5
60 1301 3015 7.5 18.4 25.9
Soybean 0 3968 1178 6.5 2.3 8.7
30 3568 1136 6.9 2.4 9.2
60 3679 1333 7.9 3.2 11.1
Rice 0 653 1014 4.8 5.3 10.1
45 734 1161 6.0 6.7 12.7

Table 4:
Soil available sulfur in four provinces of China.
Province Sample Range Mean C.V. Distribution frequency
No. mg kg-1 mg kg-1 % %
”20 20.1~40 40.1~60 >60
mg kg-1 mg kg-1 mg kg-1 mg kg-1
Heilongjiang 191 7.1 - 106 29.1 62.5 41.4 38.1 14.7 5.8
Henan 222 6.1 - 278 32.6 91.4 35.6 42.8 13.5 8.1
Shaanxi 307 4.6 - 255 30.4 85.2 42.7 33.8 12.4 11.1
Jiangxi 104 6.6 - 165 31.2 90.7 38.5 45.1 7.7 8.7

Table 5:
Soil total sulfur in four provinces of China.
Province Sample Range Mean C.V. Distribution frequency
No. mg kg-1 mg kg-1 % %
”200 201~400 401~600 >600
mg kg-1 mg kg-1 mg kg-1 mg kg-1
Heilongjiang 191 102 -1334 514 46.7 2.1 38.2 24.1 34.6
Henan 222 41 - 808 347 49.0 18.9 46.9 25.2 9.0
Shaanxi 307 33 - 1541 364 50.3 22.1 41.7 26.4 9.8
Jiangxi 104 117 - 895 511 35.8 4.8 25.0 33.7 36.5

Table 6:
Relationships between soil available S, total sulfur and organic C (r).
Province Samples Organic C vs total S Organic C vs available S Total S vs available S
No.
Heilongjiang 191 0.452*** 0.341*** 0.497***
Henan 222 0.219*** NS NS
Shaanxi 307 0.173** 0.244*** 0.313***
Jiangxi 104 0.603*** NS NS
** P<0.01, *** P<0.001, NS, not significant

and sulfur may co-precipitated or co-crystallized Total soil sulfur was different in four provinces.
with calcium carbonate (Tisdale et al., 1985; On average, total S was higher in Heilongjiang and
Roberts and Bettany, 1985). However, in Jiangxi provinces than in Henan and Shaanxi
Heilongjiang and Jiangxi provinces soil is neutral or provinces. In Heilongjiang and Jiangxi Provinces
acidic, so no free or co-precipitated gypsum can total S in more than 90% of soil samples was above
exist and organic sulfur is the main source of total S. 200 mg kg-1 and more than 30% above 600 mg kg-1.
84 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

100 100

Relative yield (%)

90 90
Relative yield (%)

80 80

70 Upland 70 Paddy soil

60 60

50 50
0 10 20 30 40 50 60 70 0 10 20 30 40 50 60 70 80 90 100
-1
Soil available S (mg kg ) Soil available S (mg kg-1 )

Figure 1:
Critical value determination for soil available sulfur.

But in Henan and Shaanxi provinces total S in most Murray, London

of soil samples was less than 400 mg kg-1 (Table 5). Lisle L, Lefroy RDB, Anderson GC, Blair GJ (1994)
Methods for the measurement of sulphur in plant and
soil. Plant Soil 164:243-250
Nelson DW, Sommers LE (1996) Total carbon, organic
Conclusions carbon and organic matter. In: Sparks DL, Page AL,
Helmke PA, Loeppert RH, Soltanpour PN, Tabatabai
Sulfur fertilizers could increase crop yield by MA, Johnston CT, Sumner ME (eds) Method of Soil
6.8% to 11.8%.Crop responses to ammonium sulfate Analysis, Part 3: Chemical Methods. SSSA, Madison,
and potassium sulfate were better than gypsum and WI, pp 995-996
elemental sulfur. The rational application rate of Page AL, Miller RH, Keeney DR (1982) Methods of Soil
sulfur was 30 kg ha-1 and 60 kg ha-1 for sulfate-S Analysis, Part 2: Chemical and Microbiological
fertilizers and elemental sulfur, respectively. The Properties, 2nd edn SSSA, Madison, WI, pp 506-509
Roberts TL, Bettany JR (1985) The influence of
critical value for soil available sulfur was 20 mg kg-1
topography on the nature and distribution of soil
and 25 mg kg-1 for upland and paddy soils, sulphur across a narrow environmental gradient. Can J
respectively. About 41.4%, 35.6%, 42.7% and Soil Sci 65:419-434
38.5% of tested soil samples was S deficient in Tisdale SL, Nelson WL, Beaton JD (1985) Soil Fertility
Heilongjiang, Henan, Shaanxi and Jiangxi province, and Fertilizers, 4th ed. Macmillan Publishing Company,
respectively. Sulfur application in balanced New York, pp 292-302; pp 548-553
fertilization strategies need to be considered in crop Zhang JZ, Zhu WM, Hu ZY, Ma YH, Zhang LG, Wang J
production. (1997) Soil S status and crop responses to S application
in Anhui province. China Sulphur Agric 20:80-84
Zhao FJ, McGrath SP (1994) Extractable sulphate and
organic sulphur in soils and their availability to plants
Acknowledgements Plant Soil 164:243-250

Part of this work was done in the Key Laboratory

of Plant Nutrition Research of the Ministry of
Agriculture, China. The financial support of The
Sulphur Institute (TSI) and the former SulFer Works
Inc. of Canada are greatly acknowledged.

References

Blair GJ, Lefroy RDB et al (1993) Sulfur soil testing.

Plant Soil 155/56:383-386
Donahue RL, Miller RW, Shickluna JC (1983) Soils - An
Introduction to Soils and Plant Growth Fifth edition,
USA, pp 305-330
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Landbauforschung Völkenrode, Special Issue 283, 2005 85

The sulfur cycle in the agro-ecosystems in southern China

Chongqun Liu1 and Xiaohui Fan1

Abstract1 ing broken down by microorganisms, once again sul-

fate will be released; (3) With a dry and wet atmos-
The total sulfur content in soils of China ranges pheric S deposition significant amounts of S are ap-
from 100 - 500 mg kg-1. The organic sulfur in soils of plied to the soil in southern China; (4) S incorporated
southern China accounts for 86 - 94% of the total S. into the soil after applying organic manure and min-
However, solely the inorganic sulfur (sulfate) can be eral S fertilizers; and (5) S losses by off-take with
directly taken up and utilized by plants. The mean harvest products and leaching through percolating soil
total S content, organic S and available S in the culti- water (Figure 1).
vated soils of southern China is 299 mg S kg-1, 267
mg S kg-1 and 34 mg S kg-1, respectively. The S min-
eralized in the paddy soils of southern China is about Sulfur fractions and transformation processes in
3.8 - 15.6% of the organic sulfur, with an average of soils in southern China
9.6%. The amount of the organic S mineralized is 15.0
- 33.1 mg S kg-1 soil. Inorganic sulfide in the soil and The total S content in different soil types in China
the elemental S in fertilizers are oxidized to sulfate by ranges approximately from 100 - 500 mg kg-1 (Liu,
the S-oxidizing bacteria. The oxidation of S in the soil 1995). In the southern humid areas, S in soils mainly
is associated with many factors such as temperature, consists of the organic S. The organic S content
moisture, the number of the S-oxidizing bacteria, and amounts to 86 - 94% of the total S, whereas only 6 –
the particle size of elemental S. In most of the paddy 14% of the total S belongs to the inorganic S fraction.
soils in China, after flooding them, the concentration Inorganic S comprises of readily soluble S and ad-
of soil H2S was below 0.03 mg l-1, and thus below the sorbed S (sulfate). According to statistics of 2,800 soil
toxicity threshold. In southern China, the S input in samples taken from 10 provinces in southern China
the S balance comes from S fertilizers (25.8 kg ha-1), (Liu, 1995), the mean content of total S, organic S and
wet deposition (13.4 kg ha-1), and irrigation water (9.2 available S was 299 mg kg-1, 267 mg kg-1 and 34 mg
kg ha-1), with a total input of 50.8 kg S; the main S kg-1, respectively (Table 1).
output parameters are S-removal by harvest products
(32.1 kg ha-1), leaching (19.9 kg ha-1), and runoff (7.2
kg ha-1), with a total removal of 59.2 kg ha-1. If one Table 1:
does not take into accounts the sulfur input from dry The mean sulfur content of different fractions in soils of
deposition, the input and the output of sulfur are southern China (Liu, 1995).
nearly balanced. Nevertheless, the contribution of dry Total S Plant Organic Organic S
S deposition is presumably in the range of the wet available S S
deposition, however, these estimates as well as those (mg kg-1) (%)
for the gaseous S losses need verification by corre- Mean 299 34 267 89
sponding measurements. Range 207-480 23-67 178-419 86-94

Keywords: Agro-ecosytems, sulfur balance, sulfur

cycle
Each year about 1 - 3% of the soil organic is mineral-
ized to sulfate; at the same time, about the same quan-
Introduction tity of sulfate is fixed in the soil organic matter
(Nriagu, 1978). After ten types of paddy soils from
The S cycling in farmland can be described as trans- southern China were incubated for 10 weeks at 30q C
fer processes in the “soil-plant-atmosphere” system and at 60% of the water holding capacity (WHC), 3.8
and the following major S pools and transformation - 15.6% of the organic S was mineralized, with a
processes can be identified: (1) Soil S can be divided mean value of 9.6%, (Zhu et al., 1982). Hu and Zu
into two main fractions, the organic and the inorganic, (2002) found a similar value with 10.6% (6.7 -
with organic S being the predominant part, which un- 19.8%). These values correspond with about 15 to 33
dergoes microbial decomposition and final formation mg S kg-1 soil (Zhou, 2004).
of sulfate; (2) Sulfate, after being taken up by crop The oxidation-reduction reaction of soil S exerts
plants, is incorporated into organic S compounds. strongly the S nutrition and soil pH. The oxidation of
With animal and plant residues, or of animal excre- elemental S is an acidifying process. Elemental S, H2S
ments, organic S is supplied to the soil, and after be- and FeS2, are oxidized to SO42- by S-oxidizing bacte-
ria. The acid sulfate paddy soils in the coastal area of
1 China contain larger amounts of sulfide. Under oxi-
Institute of Soil Science, Chinese Academy of Sciences,
Nanjing 210008, China
dizing conditions sulfuric acid is produced, and the
86 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

Figure1:1:
Figure
Sulfurcycling
Sulfur cycling inha
(kg plough
-1 land inland
) in arable Southern ChinaChina (Liu, 1995, 2000)
in southern

soil pH is reduced to a pH of 2 - 3. Elemental S is a and bog land. In rice fields under a long continued
commonly used fertilizer. Only after the elemental S submergence, sulfates are reduced and H2S is formed;
oxidizes to sulfate by S-oxidizing bacteria in the soil, often insoluble FeS and ZnS is precipitated, and
can the plant absorb it. According to the study of Li et which may sometimes result in Zn-deficiency and Fe-
al. (1998), the oxidation of S in the soil was markedly deficiency. In addition, the formed H2S is toxic to rice
influenced by the temperature and moisture; phospho- plants at higher doses. Yu and Liu (1964), however,
rus and organic substances may enforce the oxidation stated that in most of the paddy soils in southern
of elemental S, and with the reduction in particle size China, the soil pH was about 6.5 - 7.0 after flooding
the rate of oxidation will increase. The S-oxidizing and the concentration of hydrogen sulfide was below
power of a soil is associated with the number of cer- 0.03 mg l-1, which would be below the threshold level
tain sulfur-oxidizing microbes in the soil. of direct toxic effects on plants.

Table 2: Sulfur input by fertilization

Production of single superphosphate (SP) in China.
Year Total P SP % SP in Sulfur in In China, single superphosphate (SP) is used in
fertilizer total P SP large quantities as a mineral fertilizer, and during the
(P2O5 t104) fertilizer (S t104) period of the 1960s - 1990s, single SP always ac-
(%) counted for 70% of the total production of phosphate
1980 231 165 71.3 141 fertilizers. Although from 1990 to 2000 the relative
1990 412 289 70.3 248 production of single superphosphate was reduced to
2000 663 364 54.9 312 55% of the total phosphate fertilizer output, its abso-
t104 = ten thousand tons** lute output was still increasing year by year, from 2.90
million tons in 1990 to 3.60 million tons in 2000. If
calculated according to the country’s total cultivated
The reduction of S is caused by the sulfate-reducing area of land of 130 million hectares, on an average
bacteria, which are present in sewage water, sludge 25.8 kg S ha-1 per year are applied, which can satisfy
Landbauforschung Völkenrode, Special Issue 283, 2005 87

the needs of most of the farm crops in Southern China Fowler (1978) estimated that in Britain the amount of
(Table 2). SO2 settled by dry deposition was 1.0 × 106 t yr-1,
In China, the commonly used organic manure in- whereas that settled by wet deposition was 0.6×106 t
cludes farmyard manure, human feces and urine, yr-1. Estimating the dry deposition by using the Gar-
green manure and crop straw. In recent years, straw land model, differences between calculated and meas-
has been used mostly as fuel, fodder and as industrial ured values may be very high and thus often inade-
raw material, but very little is directly returned to the quate. However, in China there are no reliable data
farmland. Meanwhile, the area for planting green ma- and thus 50% SO2 input as dry deposition delivers
nure crops is becoming increasingly small. Hence, only an approximate value.
human feces and urine as well as animal excrements 10
have become the main source of organic manure.
China Agriculture Yearbook 2000 shows that in China
1.2 billion tons of human and animal excrements were Table 4:
produced a year, which contain 356,000 t of S. On an Average wet sulfur deposition in southern China (kg ha-1).
average, about 9.5 t of human and animal excrements Province Wet S deposi- Range
was applied to each hectare of cultivated land each tion
year, corresponding to 2.4 kg S added to each hectare Yunnan 14.4 5.0 - 23.2
of land each year (Table 2). Anhui 17.3 1.0 - 54.0
Jiangsu 23.5 8.0 - 40.0
Zhejiang 24.2 13.5 - 32.0
Table 3: Jiangxi 26.7 14.0 - 40.0
Sulfur content of animal and human excreta in China. Fujian 32.3 19.2 - 44.9
Guangdong 33.5 17.0 - 56.0
Num- Amount of S content Guangxi 34.4 20.9 - 48.0
ber* Excreta (t·104) Hunan 39.0 37.5 - 41.9
(107) t·107
Draft animal** 15 76 15.2 Average 27.3 14.4 - 39.0
Sheep 29 4 2.6 Sources: Liu (1984, 2000), Zhang and Gong (1987)
Pig 45 22 6.7
Poultry 270 13 8.1
Table 5:
Human 120 60 3.0
Mean sulfur content of irrigation water in southern China
Total - 122 35.6 (mg l-1).
Average - 9.4 t ha-1 2.4 kg ha-1 Province No. of Even S Range
*Number of animals/humans samples concentra-
**Cattle, horse tion
Jiangxi 76 1.94 0.71 - 7.64
Zhejiang 36 1.86 1.10 - 3.28
Hunan 36 1.69 0.90 - 2.83
Sulfur input by atmospheric depositions Guangxi 38 2.32 1.96 - 3.93
Guangdong 74 2.94 0.81 - 6.85
S deposition in the southern provinces of China
Average 260 2.23 0.71 - 7.64
ranges between 14.4 and 39 kg ha-1 yr-1, with an aver-
age of 27.3 kg ha-1 yr-1. In the mountain and hilly dis-
tricts of Southern China, the runoff volume accounts
for 1/2 of the annual precipitation (Table 4). Sulfur in irrigation water
The atmospheric dry S deposition may be directly
absorbed by the vegetation, soil and water surface. In general, irrigation water originates from rivers,
Experiments have shown that even plants supplied reservoirs, wells, ponds, etc. According to statistics of
with adequate soil sulfate are able to absorb 25 - 30% 260 water samples taken from 5 southern provinces,
of their S from the atmosphere (Brady, 1984). Terman the mean S content of irrigation water was 2.2 mg l-1,
(1978) calculated that half of the plants' S demand ranging from 0.7 - 7.6 mg l-1 (Table 5). A comparison
could be supplied by absorbing SO2 from the air. Ac- of the S content of irrigation water in 5 provinces in
cording to Wu’s study by using 35S (Wu et al., 1991), southern China, the mean S content of the reservoir
the atmospheric S taken up by soybean and corn ac- water, the well water and the river water was 1.7, 1.8
counted for 11.0 % and 23.6 %, respectively, of the and 1.91 mg l-1 respectively, and thus very similar.
total amount of S taken up by the plant. The SO2 dis- Water of ponds had a higher S concentration of 2.9
charged by the atmosphere to the soil undergoes rap- mg l-1 (Table 6).
idly transformation processes. As has been shown by the study of International
According to Garland approximately 50% of the Rice Institute (Wang et al., 1976), rice plants may take
SO2 is applied by dry deposition (Garland, 1978). up 54 % of the S supplied by irrigation water. A
concentration of at least 6 mg S l-1 in the irrigation
88 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

centration of at least 6 mg S l-1 in the irrigation water between 0.1-1.0 %. Cereals have a rather low S con-
will satisfy the S demand of the plant (Wang et al., tent (0.1 - 0.3 %), while oil crops have a distinctly
1976). For rice crops in southern China irrigation wa- higher S content (0.2 - 0.9 %). Most of the straw is
ter will supply about 9 kg ha-1 S if 7,500 m3 of water used as a fuel or industrial raw material and only
with a concentration of 2.2 mg l-1 is applied and 54 % rarely returned to the field so that the S off take with
of the S utilized by the plant harvest products increased (Ye, 1995). As straw of
cereal crops has about the same or even higher S con-
centrations than grain, significant S amounts are re-
Table 6: moved by the harvest products (Table 7).
Mean sulfur concentration in irrigation water of different The S removal is the product of S concentration and
origin (mg l-1)
yield. The grain of the rice plant has for instance a low
Province River Reser- Well Pond S content, but yield is regularly high, so that the S
voir removal may be as high as 12.7 kg ha-1. In southern
Jiangxi 2.60 1.74 1.87 1.01 China, the S removal is on an average 24.0 kg ha-1 for
Guangdong 2.17 0.72 1.76 5.96
oilseed rape, 18.3 kg ha-1 for wheat and 17.3 kg ha-1
Zhejiang - 1.83 - -
Hunan 1.36 - - 2.05
for sugarcane (Table 8).
Guangxi 1.13 - - 2.94 The favorable growth conditions in southern China
such as the ample heat and abundant rainfall, a long
Average 1.91 1.74 1.84 2.92
season for crop growth, and a high cropping index,
make it feasible to plant 2 - 3 crops per year. The
Table 7: commonly practiced rotation systems in southern
Sulfur concentration of grain and straw of various crops China are: early rice-late rice, wheat-rice, rapeseed-
(%). rice, peanuts-rice, and rapeseed-peanuts-rice. Among
these systems, the rapeseed-peanut-rice rotation re-
Crop Grain Straw Grain/straw
ratio*
moves most S with 45.9 kg ha-1, followed by the rota-
Rice 0.093 0.12 1:0.9 tion of rapeseed - rice with 36.7 kg ha-1, and the rota-
Wheat 0.154 0.31 1:1.1 tion of wheat-rice with 31.0 kg ha-1 (Table 9).
Corn 0.113 0.099 1:1.2
Oilseed 0.995 0.404 1:1.5
rape 0.259 0.078 1:1.6 Sulfur losses by leaching
Soybean 0.179 0.159 1:0.8
Peanut 0.204 0.077 1:2.2 Sulfur leaching losses are closely related to soil prop-
Sesame erties, climatic conditions, farming practices and fer-
*dry weight tilizer application rates, which may be as high as 310
kg S ha-1 yr-1 (Freney et al., 1983). In southern China,
the annual precipitation ranges from 1,200-2,000 mm,
Table 8:
Sulfur removal by different crop plants.
with a distinct division between the wet season and
the dry season. In the wet season, there is a high rain-
Crop Yield S removal fall, and a great deal of water is drained out of the
(t ha-1) (kg ha-1)* field by leaching. In the dry season, however, the per-
Sugarcane 57.6 17.3
colation water is dramatically reduced. In Yingtan,
Oilseed rape 1.5 24.0
Wheat 3.7 18.3
Jiangxi Province, during April to June 2003, the rain-
Rice 6.3 12.7 fall was 919 mm, which accounted for 68.7 % of the
Corn 4.6 10.7 annual precipitation. At the same time 80% of the wa-
Peanut 3.0 9.2 ter was leached (Liu, 2003). In contrast, in the second
Banana 19.8 7.5 half of the year, leaching losses are only minor.
Tobacco 1.8 7.1
Orange 6.9 6.9
Soybean 1.7 6.5 Table 9:
Sesame 1.0 3.7 Sulfur uptake by some crop rotations in southern China.
*Removal (grain + straw)
Rotation system S uptake (kg ha-1)
Rapeseed-peanut-rice 45.9
Rapeseed-rice 36.7
Sulfur uptake by crops Wheat-rice 31.0
Rice-rice 25.4
Soil S is removed mainly by crop uptake and off Peanut-rice 21.9
take with harvest products, leaching and surface run- Mean 32.1
off. In southern China, farm crops have a S content
Landbauforschung Völkenrode, Special Issue 283, 2005 89

Table 10:
S leaching losses during the growing season of some crops
Crop Treatment** S added S leaching loss % of S added Location
(kg S ha-1) (kg S ha-1)
Wheat Control 0 13.0 21.0 Jiangsu (2002)
(Nov-Mar)* SSP 70 27.7

Rice Control 0 22.7 29.4 Jiangsu (2002)

(Jun-Oct)* SSP 48 36.8

Rapeseed-Peanut rotation Control 0 25.9 14.9 Jiangxi (2003)

(Nov-Jun)* ES 75 37.0
Peanut
Control 0 12.3 20.6 Jiangxi (2003)
(Apr-Jun)*
GYP 71.5 27.0
Average 32.1 21.8
*Growing season
**SSP, single superphosphate; ES, elemental S, GYP, gypsum

In southern China, during the growing season of rice, and irrigation water (9.2 kg ha-1), with a total input of
wheat, oilseed rape and peanuts, the leaching losses of 50.8 kg S; the main S output parameters are S-
S ranged from 13 - 37 kg ha-1. If no S was applied, the removal by harvest products (32.1 kg ha-1), leaching
average leaching loss was 18.5 kg ha-1. When S was (19.9 kg ha-1), and runoff (7.2 kg ha-1), with a total
added, the average loss was 32.1 kg ha-1, accounting removal of 59.2 kg ha-1 (Table 11). If one does not
for 21.8% of the applied S (Table 10). Apparently the take into accounts the sulfur input from dry deposi-
type of fertilizer influences leaching losses, too. In the tion, the input and the output of sulfur are nearly bal-
tea garden fertilizer trials in Zhejiang in 2002, potas- anced. Nevertheless, the contribution of dry S deposi-
sium sulfate yielded the highest S leaching losses with tion is presumably in the range of the wet deposition,
35.2 kg ha-1 yr-1, which was 3 times higher than in the however, these estimates as well as those for the gase-
control plots with 10.6 kg ha-1 yr, and about 2 times ous S losses need verification by corresponding
higher than in the gypsum treatment with 15.7 kg ha-1 measurements.
yr-1. Elemental S applications resulted in the lowest
sulfate leaching losses with 12.4 kg ha-1 yr-1 as it
needs to be oxidized by microorganisms. Table 11:
S balance in soils of Southern China (kg ha-1 yr-1).
Input Output
Sulfur losses by runoff and soil erosion Mineral S fertilizer 25.8 Crop removal 32.1
Organic manure 2.4 Leaching 19.9
Wet deposition 13.4 Runoff 7.2
According to the determination made by the Red Soil Irrigation 9.2
Station at Yingtan, Jiangxi Province, the average an- Total 50.8 59.2
nual runoff volume for the Orthic Acrisols (Ao) culti-
vated land < 5º was 115 mm (Zhang and Zhang, 1995).
The average S content in the runoff was 0.30 mg l-1, References
and S lost by runoff was 3.5 kg ha-1 yr-1. For the culti-
vated land < 5º, the mean quantity of the eroded soil Brady NC (1984) The Nature and Properties of Soils, 9th ed,
was 33 t ha-1 yr-1. The eroded soil had an average total Macmillan Publishing Company, USA, pp 315-318
S content of 111mg kg-1, and the eroded soil through- Fowler D (1978) Dry deposition of SO2 on agricultural
out the year contained 3.7 kg ha-1 S. Consequently, on crops. Atmos Environ 12:369-373.
the red soil sloping land < 5º the annual quantity of S Freney et al. (1983) The sulphur cycle in soil, in the global
biogeochemical sulphur cycle. SCOP 19:129-201.
lost by runoff and by the soil erosion was 7.2 kg ha-1 S.
Garland JA (1978) A dry and wet removal of sulphur from
the atmosphere. Atmos Environ.12:349-362.
Hao J, He K (1996) China Environmental Science 16:208-
Sulfur balance on agricultural soils in southern 212.
China Hu Z, Cao Z, (1998) Organic S mineralization rates and
potentials of soils selected in Southern China. Proceeding
In southern China, the S input in the S balance comes of the International Workshop on Sulphur Fertilizer Sse
from S fertilizers (25.8 kg ha-1), rainfall (13.4 kg ha-1), for Chinese Agriculture, Hefei, China, pp 138-143
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pheric sulfur under the rapeseed-rice rotation system in
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fur in soil, Symposium on Sulfur Research and Its Use in
China, Hefei, China
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of Fujian and Yunnan Provinces. Acta Pedolegica 21:438-
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quirements in Southern China. Proceedings of the Interna-
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Sulphur Requirements, Availability, and Commercial. TSI,
Beijing, China
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water and their effect on soil S status in Anhui, Guang-
dong, Jiangxi, and Sichuan Provinces. Journal of Anhui
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Aspects. Tech. Bull. Sulphur Institute, Washington, DC
Wang CH, Liem TH, Mikkelsen DS (1976) IRI Research
Institute Bulletin No.47
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Ye D (1995) A preliminary study on the sulfur in straw. Soil
Agrochemistry Bulletin 10:35-41
Yu T, Liu Z (1964) Oxidation-reduction processes in paddy
soils and their relations to growth of rice, Acta Pedologica
12:380-389
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the rainwater, surface water and groundwater in South
China. Soil Bulletin 41:170-187
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Landbauforschung Völkenrode, Special Issue 283, 2005 91

An Agricultural Sulfur Information System for China

Youhua Ma1, Hongxiang Hu1, Qiang Wang1, Xiaoli Liu1, Yanping Zhao1, Hongxia Liang1 and Zhaoming Zhu1

Abstract1 Materials and methods

An Agricultural Sulfur Information System was Data sources, design outline, hardware and software
developed for China by using Visual Basic, API The basic data from different regions, soil types
function of MapGis software and Access database and crops were obtained from the results of the Chi-
software in Chinese Windows 98. According to the nese agricultural sulfur research for past twenty
data and the demand of production, five application years. Based on GIS as the core technology, the spa-
modules were developed, including modules of soil tial data and related attribute were combined and
sulfur states, sulfur nutrition in crop, sulfur fertilizer analyzed and were linked and treated with GIS.
effect, balance of soil sulfur, update and setting. The MapGis, popular GIS software in China, was se-
developed system is an effective information man- lected as development platform and Visual Basic as
agement tool for managers of fertilizer producers development language
and sale departments and agricultural scientific re- Hardware: CPU (central processing unit) basic fre-
search departments. quency 733M, memory 128M, HD 20G, scanner
(Uniscan A600). Software: Windows 2000 Chinese
Key words: geographic information system, soil, Operating System, Visual Basic 6.0, Photoshop 6.0,
sulfur fertilizer Chinese Office 2000.

System construction, economy and society benefit

Introduction analysis
The incidence of soil S deficiency is increasing In the current Geographic Information System,
rapidly throughout China and the agronomic bene- spatial objects can be described from three aspects,
fits of plant nutrient S are now widely known. Nu- namely positional information, non-positional in-
merous field experiments conducted in China have formation (attribute information) and time informa-
clearly shown that crop yields increased by adding S tion. Spatial data in computer are characterized with
fertilizers and the sulfur fertilization improved crop encoding technique in mode of point, line and area.
quality and increased their market value. According And data sets are built among objects. Positional
to statistics of S field experiments from many Chi- information is recorded with positioning data (also
nese provinces, Sulfur fertilization averagely in- called geometry data), which reflects geographic
creased crop yields by over 10% for most major distribution of the phenomena of nature. Non-
agricultural crops such as rice, rapeseed, wheat, positional information is recorded in attribute data,
soybean, peanuts (TST, 2001; Zhang J, 2001; Huang which describe the nature phenomena, the character-
et al., 2002). istics of object quality and quantity. A piece of farm-
An Agricultural Sulfur Information System for land, for example, the concrete position can be
China was built in order to supply information man- known by its geometry data, longitude and latitude,
agement tool about Chinese soil sulfur status, plant while the content of sulfur in corresponding farm-
sulfur nutrition and effective application of S fertil- land is called attribute data.
izers for the departments of agricultural technologi- There are several popular and wonderful GIS
cal extension, fertilizer production and distribution, software in China such as MapGIS from China Ge-
agricultural research and education so that they can ology University, GeoStar from Wuhan University
distribute S fertilizers suitable to local soil, crop etc. These GIS software supply a great deal of API
kinds and climate conditions. Meanwhile the farm- functions and controls. It is easy and convenient to
ers could learn related agricultural S knowledge transfer these functions and controls with advanced
such as diagnoses of S deficiency and could decide programming language such as Visual Basic to de-
whether, how and when to apply S fertilizers. velop the system (Gong Jianya, 2002). This system
was developed with MapGIS as developing platform
and implemented by transferring the API functions
and controls with Visual Basic.
As mentioned above, the incidence of soil S defi-
ciency is increasing rapidly throughout China and
1
Department of Soil Science and Agrochemistry, Anhui serious S deficiency is emerging in Chinese agricul-
Agricultural University, Hefei, 230036, China ture, which would result in the decrease of crop
92 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

yields and productivity. It is estimated by TSI, that Since Access is a relative database, its develop-
the S demand deficit is projected to increase to 2.7 ment environment and language are characterized
million tons by 2010 with the continuous increase of with relational database. But some data are not rela-
agricultural production and S-free high-analysis tional and must be classified, sorted and transformed
fertilizer use. The loss of grains would reach 30 mil- first. If they were input without treatment, there
lion tons for the S deficiency, which should not be would be many problems. Firstly, characters are
neglected (total Chinese grain: 430.7 million tons in double byte occupying much space of dish and
2003). memory, that results in unnecessary resource waste
Agricultural Sulfur Information System for China and it is difficult to carry out maintenance and to
could make people understand the importance of update. Secondly, fields are described by Chinese
sulfur in Chinese agriculture and find out the Chi- characters with much repetitiveness, which breaches
nese soil sulfur status and the response of crops to S the principle of the smallest redundancy, the rela-
fertilizer so that the research results of S fertilizer tionship among fields are also not clear with ineffec-
could be extended quickly throughout China. tive utilization by system.. Therefore these fields in
system should be transformed, e.g. long fields are
System design split or given corresponding coding.
Founding on GIS, the system design would solve
the problem how to build on the base of demand and Database construction
feasibility analysis. The objective of general func- The independent soil sulfur database was con-
tion design is to solve how to carry out the system, structed in this system for the querying, updating
the main task of which is to divide function modules and modifying. In the database, with sampling place
in subsystems and to determine the links among as key word the fields such as soil code, soil type,
modules and their descriptions On the selection of soil parent material, the sampling regions (province,
coordinate system, national coordinate of the system city county), available S content, pH, organic mat-
in 1980 was chosen as the system horizontal coordi- ter, sampling depth, remark were set up. The sample
nate and the height datum of national geodetic coor- place was given four fields in order to query with
dinate system in 1980 was selected as the system different rank administrative districts
height datum. In China due to incomplete foundational digital
Basing on the system analysis, four function mod- materials compared with developed countries, the
ules were determined in the system according to the most spatial data were obtained by scanning of maps
purpose and demand of the system building. with scanner and digitizing with input edit module
(1) Data Management module: Management on of MAPGIS . In the system it, the maps of province
input of soil sulfur data and related spatial data, and boundary of 1:1 million were selected. The map
operation for modifying, updating, appending, delet- base management subsystem supplies the flexible
ing and view build. and intuitionistic way to input data and some ap-
(2) Specialty Management Module: Management proaches to query data with effective management
on diagnosing of the corps S deficient, symptom for various maps.
identification of crop S deficiency, analyses of rea- Attribute data, the important parts of spatial data,
son for S deficiency and the build of specialty are edited, modified and stored with the sub-system
knowledge base of attribute management of MAPGIS. In this way, it
(3) Application Function Module: According to ensures data integration, compatibility and unifica-
the aim of the system, select similar information tion to reduce development difficulty and conven-
system as reference to build the corresponding func- ient to use.
tion module based on.
(4) Assistant Function: Establishment of the help Database management
system with detailed content and convenient usage Management of database includes definition of
data, query of data, renewal of data, construction of
Classification and transformation of data data and usage of view as well as construction and
The data sources from many channels lead to in- application of index. Definition of data means defi-
consistency in using nomenclature and criterion of nition of the built database structure and determina-
partial data. Nomenclature and measure criterion are tion relative mode. Query of data is the content
unified and standardized on the condition of same search of built database. Because soil S contents are
meaning and content. For example, the “acreage” main objectives to be queried, the kinds of data are
and “ppm” were transformed into “hm2 ” and “mg built separately. The update includes inserting,
kg-1 ” in measure unit; and “slope” in definition of modifying and deleting. These functions are in-
topography was changed into “the middle and bot- cluded in data input module
tom part of hills” according to current standard.
Landbauforschung Völkenrode, Special Issue 283, 2005 93

Results and Discussion for S deficiency was more reliable than soil test.
Plants diagnoses of S deficiency have made great
Based on database, application system manages progress in recent years. Plant sample position is
and utilizes the data resource in system. According important to S deficiency diagnose for plants weak
to existent data and production requirements, this S recycle and mature leaves accumulate more S than
system develops five application modules including younger organs .It is thought that the total S content
soil S status, crop S nutrition, fertilizer effects, soil S in full unfold younger leaves or leaves developed
balance, update and setting. well on 1/3 upper could reflect plant S nutrition
Soil S status subsystem is mainly used to query status. In system volumes of pictures for crop S de-
soil S status from different regions and parent mate- ficiency were chosen to build special picture data-
rials. This system provides two approaches to in- base. With abundant pictures and text, the system
quire the soil S status. One is by the maps of admin- provided the symptoms of S deficiency of crops and
istrative area, and another is by the maps of soil par- analyzed the reason of S deficiency for farmers.
ent materials. Based on MAPGIS platform, the op- Farmers are more concerned about effect of S
erating platform of the sub-system was built by call- application. The S fertilizer effect subsystem pro-
ing control and API (Application Programming In- vides effects of S application on crop yields, quality
terface) function supplied by MAPGIS with Visual and market value in different regions of China, and
basic. Soil S contents and other related information gives S fertilizer recommendation (e.g. S fertilizer
could be searched by selecting language in SQL type, application rates and methods) special for dif-
(Structured Query Language) through the location of ferent regions and crops in China. In the soil S bal-
mouse in administrative map. ance subsystem the data for soil S balance such as
Because of complexity of soils, diagnose of plants atmosphere sulfur, soil sulfur, irrigation water sulfur

Figure1:
Primary interface of the system.

Figure 2:
Example of interface for querying soil S in Anhui province, China.
94 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

Figure3:
Example of interface for the detailed soil S status.

Figure 4:
Example of crop S nutrition interface.

and ground water sulfur etc were analyzed to obtain Web Geography Information System) is paid atten-
local soil S balance in Chinese farmlands. The data- tion and welcome by more and more people, for it
base in the system could be updated to ensure the not only solves the problem of expensive price for
practicability of this system, but only administrator GIS software, but also reduces the cost of collecting
could update database, and different users are given geography spatial data and improves the sharing
different power limits degree and extension of the geography information.
An example of the primary interface is presented As the developing direction of GIS it is necessary to
in Figure 1. Examples of querying for soil S status integrate this system with internet in the future.
are presented in Figures 2 and 3, and of crop S nutri-
tion interface in Figure 4. As the outcome of com-
bining information technology and soil-fertilizer and Acknowledgments
plant-nutrition technology, this system is explored
for its developing outline and implemented methods. Project (No.2002-350) was supported by the Ex-
By this system, soil S deficiency status, effects of S cellent Young Teachers Program of the Minster of
fertilizer application and soil S balance of input and Education, PR China (EYTP)
output in Chinese different regions could be directly
queried, and for S deficiency regions the fertilization
recommendation of NPK should be transferred to References
that of NPKS to supply balance nutrients to improve
soil fertility, to increase yields and to meet the in- Gong J (2002), The Basic of Geography Information Sys-
tem (in Chinese). Science Press, Beijing
creasing requirement of grain by China.
Huang J, Ma Y, Zhang D (2002): The effect of sulfur fer-
With increasingly maturation and popularization tilizer on crops and application methods (in Chinese),
of the internet technology, WebGis (World-Wide- Anhui Agricultural Bulletin 8:50-51
Landbauforschung Völkenrode, Special Issue 283, 2005 95

The Sulphur Institute (TST) 2001: A Comprehensive Re-

port on Plant Nutrient Sulphur and Sulphur Fertilizer
Use and Research in China
Zhang J, Ma Y, Zheng L, Liu L, Zang L, Si Y, Liu L,
Schnug E ( 2001) Crop responses to sulphur fertiliza-
tion in Anhui province, China. In: Proceedings of 12th
World Fertilizer Congress, August 3-9, Beijing, China,
pp 1312-1332.
96 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants
Landbauforschung Völkenrode, Special Issue 283, 2005 97

Global sulfur requirement and sulfur fertilizers

D.L. Messick1, M.X. Fan1 and C. de Brey1

Abstract1 nutrients with balanced ratios for plant nutrition.

The increasing demand for sulfur fertilizers and
The world sulfur fertilizer deficit is projected at their use in agriculture will provide significant bene-
close to 11 million tons per year by 2012, with Asia fits to both fertilizer manufacturers and farmers
and the Americas as the most sulfur deficient re- through the next decade.
gions in the world. Pollution controls, intensified
cropping, and the absence of sulfur from high-assay Key words: sulfur, sulfur deficiency, sulfur fertiliz-
fertilizers are combining to produce a growing ers, sulfate-containing compound fertilizers,
worldwide deficiency in soil sulfur, needed for high elemental sulfur enriched fertilizers, micronized
crop yields and crop quality, that only the use of sulfur products
plant nutrient sulfur products will solve. Sulfur defi-
ciency is increasingly becoming one of the major
limiting factors to further sustainable increases in Introduction
agricultural production and fertilizer use efficiency,
and also is stimulating growth in farmers’ demand Sulfur (S) is one of the major essential plant nutri-
for sulfur-containing fertilizers, which is becoming a ents, and it contributes to an increase in crop yields
greater potential market for the fertilizer industry to by providing direct nutritional value and improving
develop innovative technologies and products for the use efficiency of other essential plant nutrients,
this market potential. Most sulfur-containing fertil- particularly nitrogen (N) and phosphorus (P). As
izer materials can be divided into three groups: 1) agricultural productivity has increased, the demand
Sulfate-containing; 2) Sulfur-containing, and 3) for all nutrients has increased. While N fertilization,
Liquid. Sulfate-containing fertilizers provide most in particular, and to lesser degrees, P and potassium
of the fertilizer sulfur applied to soils. The most (K) fertilization needs have been addressed, S has
significant and popular sources are ammonium sul- emerged as the fourth major nutrient for the fertil-
fate, single superphosphate (SSP), potassium sul- izer industry. This trend will only continue and will
fate, potassium-magnesium sulfate and gypsum. be exacerbated with the reduction of sulfur dioxide
These materials have the advantages of supplying emissions, which have served as a significant source
sulfur primarily as a component of multi-nutrient of S for crop production for a number of years. Fur-
fertilizers in a sulfate form that is immediately thermore, the increased trend to use high-analysis
available for plant uptake. Elemental sulfur- fertilizers devoid of sulfur, combined with declining
containing fertilizers are the most concentrated sul- levels of soil organic matter, a significant potential
fur carriers. Elemental sulfur has to be oxidized into source of S, have reduced soil S content to levels
the sulfate form before plant uptake, which limits its where S is increasingly becoming a limiting factor
availability immediately after application to soil. to higher yields and production.
Micronized sulfur products have improved the effec- Ammonium sulfate and single superphosphate
tiveness of elemental sulfur by providing elemental (SSP) dominate the current available worldwide
sulfur in a physical form so that it can be used for supply in so far as volume of fertilizers used con-
direct application and bulk blending with little dust taining S, representing 83% of the approximately 10
and be more readily converted to the sulfate form in million tons of S applied in fertilizers annually.
soil. Fertilizer manufacturers are introducing new While these traditional sources will be in use for a
products to meet the increasing demand of the sulfur number of years to come, production is limited and
fertilizer market, including specially formulated future availability may diminish due to competing
sulfate-containing compound fertilizers or elemental production processes. These materials, including
sulfur enriched compound fertilizers based on spe- potassium sulfate as well, belong to a broader group
cific crop and soil needs. These sulfur modified or of what are termed “S fertilizers with sulfate carri-
enriched compound fertilizers using either sulfate or ers” as opposed to “elemental S-based S fertilizers.”
elemental sulfur or a combination of the two have The elemental S-based S fertilizers are newer on the
several advantages, including improved chemical scene and refined production technologies for a se-
and physical properties; and providing multi- ries of these types of products have gained attention
in recent years. These products are gaining market
share, and a growing array of S fertilizers are avail-
1
The Sulphur Institute, 1140 Connecticut Avenue, N.W., able to accommodate different soil, crop and appli-
Suite 612, Washington, DC 20036, U.S.A. cation conditions and situations.
98 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

The rising demand in sulfur fertilizer mental, agricultural research and educational insti-
requirements tutes, the fertilizer industry and local farmers by
different research, extension and education pro-
In 2001, almost 10 million tons of S was applied grams. These programs have made great progress.
to soils worldwide through fertilizers. The current For example, since 1993, TSI, collaborating with 15
potential S fertilizer market is estimated to accom- institutions throughout China as a cooperative net-
modate an additional 9.4 million tons annually. With work has achieved significant advances in evalua-
increased food production raising S requirements, tion of S fertilizer requirements and promotion of S
and assuming slower expansion rates for S applica- fertilizer use in Chinese agriculture, identified more
tion in accordance with recent history, the unful- than 30% of arable soils in China, equivalent to
filled requirement for S fertilizers is projected to about 40 million hectares, are S deficient. Sulfur
grow to 11.0 million tons by 2012. fertilizer significantly increased crop yields in 468
A regional breakdown of world S deficits is field trials, 87% of the total trials completed, with
shown in Figure 1. Asia is the region manifesting average yield increases from 7% to 30%. With the
the greatest S shortfalls. Intensified agricultural increased awareness of the importance of S in agri-
production, pressured by the backdrop of food self- culture, S fertilizer production and use in China is
sufficiency goals and limited land resources in the growing. In 1999, the Chinese government recog-
globe’s two most populous nations, China and India, nized S as a plant nutrient, encouraging production
has created the S nutrient imbalance. Asia’s annual of S-containing NPK compound fertilizers. In 2002,
S fertilizer deficit, currently estimated at over 5 mil- the total S-based NPK compound fertilizer output
lion tons, will increase to 6 million tons by 2012, reached 4.6 million tons, providing 500,000 tons S.
with over 70% represented by China and India. It is estimated that S containing compound fertilizer
China currently applies about 3 million tons S to production capacity will increase to over 7.0 million
agricultural soils every year, mostly from SSP (12% tons, supplying about 700,000 tons S by 2005.
S) and ammonium sulfate (24% S), at an average In India, following the recognition of the benefits
rate of 15 kg S/ha sown area. However, the total of S fertilizer for Indian agriculture from the TSI-
annual crop requirement for plant nutrient S is about Fertilizer Association of India (FAI)-International
4.5 million tons, resulting in a total 1.5 million tons Fertilizer Industry Association (IFA) cooperative
S deficit, which will increase to 2.4 million tons by project, the Indian government amended the Fertil-
2012 indicating the need for corrective measures. In iser Control Order (FCO) by including the S content
India, the total S containing fertilizer production in of fertilizers as a part of product specifications in the
2001 was close to 5 million tons, providing 700,000 FCO. According to the new amendments of FCO,
tons S, and the total crop requirement was about 2.2 all manufacturers must specify the minimum guar-
million tons, which resulted in a 1.5 million tons anteed S content for listed fertilizers and print the S
deficit. This deficit is projected to increase to 1.9 content on the fertilizer bag. This change in the FCO
million tons in 2012, which will provide a large has helped bring S into the mainstream of balanced
market for the fertilizer industry. nutrient application. It is expected that S fertilizer
use in India will increase significantly over the com-
ing decade and make a greater contribution to in-
creasing agricultural production through balanced
fertilization, including S.
The Western European S market is one of the
most advanced in the world. The significant drop in
sulfur dioxide (SO2) emissions since the 1970s, cou-
pled with intensive agronomic practices including
the use of high-analysis, S-free fertilizers spurred
the region to action to correct the deteriorating S
nutritional status. Sulfur deficiency was qualified as
a major nutritional problem in arable crops. Com-
Figure 1: prehensive agricultural research and extension sys-
Regional plant nutrient sulfur deficit in 2012. tems facilitate farmers’ response to the deficit. It is
projected that the market will have a deficit level of
500,000 tons in 2012 within Western Europe, as the
To develop these two biggest Asian S markets, increased need for S, becomes more prominent par-
The Sulphur Institute (TSI) has continuously ticularly in the North. Additional commercial op-
worked on promotion of S fertilizer use, increasing portunities are expected to arise in Eastern Europe,
public awareness and knowledge about the role of S as several countries project SO2 reductions in part
in agriculture at various levels, including govern- resulting from their entry into the European Union.
Landbauforschung Völkenrode, Special Issue 283, 2005 99

The current Eastern European S deficit of over The trend to increase the N, P, and K analyses of
300,000 tons is expected to rise to 400,000 tons by fertilizers over the last four decades gradually
the end of the decade. squeezed out most of the S in the major N, P and K
In North America, the reduction in atmospheric fertilizers, urea, diammonium phosphate (DAP) and
deposition of SO2 combined with crop intensifica- potassium chloride (MOP), respectively. What was
tion continues to determine S deficiencies. The U.S. once removed because it was considered incidental,
Environmental Protection Agency recently esti- is now required.
mated that SO2 emissions decreased 33% between
1983 and 2002, and by 31% between 1993 and Multi-nutrient sulfur fertilizers
2002, indicating an acceleration of emission reduc- Ammonium sulfate is mostly produced as a co-
tion. Continued reductions in SO2 emissions and product of other industries. An estimated 70% of
increased yields are expected to expand areas of S global output originates from the production of
deficiency. The North American deficit for S fertil- caprolactam, an intermediate for the manufacture of
izers is expected to increase from the current 1.2 synthetic fibers. A small amount is recovered from
million tons to 1.4 million tons by 2012. Some re- coke oven gas, with most of the remainder produced
search institutions are evaluating the need to in- synthetically from sulfuric acid and ammonia. In
crease current S fertilizer recommendations in line 2000, approximately 18 million tons of ammonium
with existing trends. Currently about 1.6 million sulfate fertilizers were produced, equivalent to over
tons S was applied annually in North America 4 million tons of S. Over 3 million tons of S equiva-
through fertilizers, mostly as ammonium sulfate. lent are used directly, with the remainder used for
The level of S consumption is expected to increase, blending with other fertilizers. The main advantages
as numerous fertilizer concerns are developing mar- of ammonium sulfate are low hygroscopicity and
keting efforts to increase new sulfate and elemental chemical stability. It is a good source of both N and
S fertilizer production. S. The acid-forming reaction of ammonium sulfate
Latin America is developing as a market for S can be advantageous in high pH soils and for acid-
fertilizer. Agricultural production increased signifi- requiring crops. When ammonium sulfate is used for
cantly over the last decade, which in conjunction direct application as a N source, much more S is
with the rising use of high-analysis fertilizers leads applied incidentally than is typically required. In
to increasing instances of S deficits, particularly in addition to this N/S imbalance, excessive soil acid-
Argentina. The largest fertilizer consumer, Brazil, is ity can develop when frequent high rates are applied
an important and growing user of ammonium sulfate to poorly buffered soils.
and SSP. The current increased market opportunity Improvements in the ammonium sulfate formula-
in Latin America is estimated at 700,000 tons, and is tion processes allow for increasing shares of larger-
projected to rise to at least 900,000 tons by the end sized granular material, which is easy to handle and
of the decade. desirable for bulk blending. This has greatly in-
creased application options and spreading perform-
ance. Ammonium sulfate is also popular in Europe
Sulfur fertilizer sources in the manufacture of compound fertilizers, such as
ammonium nitrate plus ammonium sulfate. One
There are two types of S fertilizers: those that are grade of 26-0-0-14S is very popular in the European
in the sulfate form and those that need to go through market. Other specialty grades with differentiated
a chemical reaction to get into the sulfate form for N/S ratios also exist. The 26-0-0-14S grade is made
plant uptake. The bulk of S fertilization comes from by granulating ammonium sulfate in the presence of
multi-nutrient fertilizers that are already in the sul- ammonium nitrate solution or neutralizing sulfuric
fate form. Ammonium sulfate, SSP, and potassium acid with ammonia in an ammonium nitrate solution
sulfate (K2SO4) are the leading products by volume. and then granulating.
Although these products were originally applied for Mixtures of ammonium nitrate and ammonium
their N, P, and K content, respectively, they are in- sulfate are affected by United Nations transportation
creasingly recognized for their S content in its own classification limits (Annon, 2001). In the current
right. Sulfur is not called the fourth nutrient in vain. regulations, if the ammonium nitrate content is less
All major multi-nutrient S fertilizers provide S in than 45% the product is deemed non-hazardous for
the form of the sulfate anion, readily available for land transport. If the ammonium nitrate content is
uptake by plants. Adding to the array and sophisti- greater than 45% but less than 70%, and the total
cation of available S products, elemental S in vari- combustible/organic material content is less than
ous formulations and liquid fertilizers are capturing 0.4%, then the product is UN Class 5.1 (an oxidizer)
increasing shares of S fertilization, mainly in the under UN2067, SP 307. Materials with ammonium
developed world, at present. nitrate contents above 70% and containing ammo-
nium sulfate are prohibited as fertilizers under these
100 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

regulations. Other local regulations may also apply. relatively stable with a tendency to decline; the ma-
All are subject to change and current regulations jority of P capacity expansion plans include tradable
should be reviewed regularly by those intending to compound fertilizers and ammoniated phosphates;
formulate products containing ammonium nitrate. this contributes further to S deficiencies and the
In production of these materials, limiting ammo- need to replace the foregoing S source.
nium nitrate content can frequently result in a grade Potassium sulfate is the main S-containing potash
that has S content too high for the crop requirement. fertilizer. It contains 42 to 44% K (50 to 53% K2O)
This adds to increasing use of these materials in and 17 to 18% S. For purposes of this discussion
bulk blends. Approximately 2.7 million tons of potassium-magnesium sulfate is also included. The
ammonium sulfate is produced annually in Western current global market for these materials is ap-
Europe from all manufacturing processes. Histori- proximately 1.6 million tons of products, equivalent
cally, this material was shipped to developing coun- to close to 300,000 tons of S per year. About half of
tries for use as a fertilizer, but today, increasing global production is mined directly from potash and
amounts have been used within Western Europe for sulfate salts or brines requiring no additional S.
the development of sulfur-containing fertilizers. Potassium sulfate can also be produced based on the
Recently, some new urea based sulfate-containing reaction between potassium chloride and sulfuric
fertilizers, (40-0-0-9S) and granulated urea sulfur acid, known as the Mannheim Process. Potassium
(38-0-0-13S) were launched in the European market. sulfate is normally used for situations and crops
These sulfate containing multi-nutrient compound susceptible to high chloride and salt concentrations;
fertilizers have several advantages, including lower it is facing increased competition from potassium
hygroscopicity than either constituent individually, nitrate as a chloride-free potash fertilizer, thus sig-
and have a satisfactory N/S ratio for direct applica- naling another potential source of S deficit. Potas-
tion purposes. sium-magnesium-sulfate is a double salt and con-
Ammonium sulfate can also be used in clear liq- tains 22% K (27% K2O), 11% Mg and 22% S. It
uids to make solutions of fertilizer containing N and has the advantage of supplying multi-nutrients, K,
S. Sulfur concentrations in solutions based on am- Mg and S and is frequently included in mixed fertil-
monium sulfate solution can vary from 1 to 9%. In izers on soils deficient in these three nutrients. They
liquid formulations made with ammonium sulfate are particularly useful when low levels of chloride
and containing P, the typical S concentrations range are desired, as is often the case for crops such as
from 1 to 3%, although S concentrations can be tobacco, potatoes, peaches, some legumes and turf
reached from 5 to 7% with lower P. grass.
In other developments relating to by-product am- Kieserite (MgSO4.H2O), usually listed as a sulfate
monium sulfate production, a new nickel production based Mg fertilizer, is produced from a natural salt
process is expected to co-produce ammonium sul- deposit and is a highly concentrated two-nutrient
fate: high-pressure acid leach of nickel lateritic ores fertilizer containing 15 to 17.5% Mg and 20 to 23%
came on stream in Oceania. Moreover, in North S. Kieserite has a neutral reaction regarding soil
America and Europe, ammonia-based flue-gas acidity, and thus it is suitable for all soil types. Ow-
desulfurization technology will produce ammonium ing to its high solubility, both the Mg and the S are
sulfate at a coal power plant and an oil sands pro- immediately available to the plant. Kieserite is a
ject. The increasing availability of the inexpensive suitable fertilizer for either direct or blended appli-
by-product sulfuric acid may encourage increased cation, and can also be used in clear liquids and
production of ammonium sulfate - particularly if foliar sprays. Commercial kieserite products are
credit can be obtained for its S values. available in both fine and granular forms in the
Single superphosphate was once the most impor- European market.
tant phosphate source in the world and still is a ma- Gypsum (calcium sulfate) is not as widely used as
jor fertilizer in China, India, Brazil, Australia and a fertilizer compared to ammonium sulfate. Most
New Zealand due to its P and S contents. Single calcium sulfate is commercially available in forms
superphosphate contains 12 to 22% phosphate and that are not as easy to handle, blend, and spread. A
10 to 14% S and is an excellent source of P, S and more important reason for its limited use as a fertil-
calcium. The occurrence of S deficiencies has been izer, however, is its relatively low analysis. One
delayed in many areas of the world because of the notable exception is the use of gypsum in peanut
involuntary addition of S when large amounts of (groundnut) production. The calcium is required for
SSP were used to supply P. Its calcium content, proper plant pegging.
ranging from 18 to 21%, can be important in soils Within Europe, there is another group of fertiliz-
low in this nutrient. ers that can contain S. These are compound fertiliz-
Total S content in SSP used in 2000 was 4.0 mil- ers that are produced by the nitrophosphate process
lion tons, mostly produced in Brazil, China, India, and/or the mixed acid route. Nitrophosphate fertil-
Australia and New Zealand. Production of SSP is izers are, as the name implies, fertilizers produced
Landbauforschung Völkenrode, Special Issue 283, 2005 101

by a process involving treatment of phosphate rock temperature and moisture, play an important role in
with nitric acid. determining rates of S oxidation. A third critical
After separation of the major part of the calcium physical factor influencing oxidation is particle size
nitrate, phosphoric acid is neutralized with ammonia of the applied elemental S. Finer particle size in-
to produce a fertilizer. The remaining calcium ni- creases the oxidation rate, as the greater specific S
trate, not typically recognized for its nutritive value, surface area provides for greater access and action
and known for its effect on phosphorus availability, by microbes. The application of coarse elemental S
can be converted into calcium sulfate nitrate by sul- historically produced low yield response in S-
fate addition. deficient annual crops, attributable to low oxidation
While not a necessarily common method, the rates associated with large particle size. The ele-
solution obtained by reaction of nitric acid with mental S fertilizer industry has come a long way
phosphate rock can also be treated by the addition of since those early days.
a soluble sulfate to precipitate part or nearly all of Elemental S can be readily incorporated into N/P
the calcium as calcium sulfate. In commercial proc- fertilizer materials to provide 5 to 20% sulfur with
esses, ammonium sulfate, potassium sulfate, and various technologies. However, the use of elemen-
sulfuric acid have been used. The calcium sulfate tal S in combination with ammonium nitrate should
may be separated by filtration and removed to form be avoided, and is prohibited in some jurisdictions,
a higher grade product, or allowed to remain in the for safety reasons. Monoammonium and diammo-
product. Compound fertilizers produced by the ni- nium phosphates (MAP or DAP) containing from
trophosphate process can have S concentrations about 5 to 20% S can be made by applying a hy-
varying from 2 to 21% according to a recent survey draulic spray of elemental S at 1.4 kg/cm2 during
conducted by TSI. drum or pan granulation. Recently, a new sulfate
Ammonium sulfate, SSP, and potassium sulfate and elemental sulfur-enriched MAP fertilizer was
materials remain important S sources; however, developed in North America, containing 15% sulfur,
their stable to declining production base, against the ammonium-nitrogen and phosphate. This granular
backdrop of growing S deficiencies, and the increas- fertilizer containing 50% elemental S and 50% sul-
ing sophistication and understanding of fertilizer fate-S provides readily available S for early plant
actions have attracted new S sources that are in- uptake and residual S for later in the growing sea-
creasing market share. Sulfur fertilizer producers son. It is suitable for bulk blending with other
are introducing new products to meet diversified and granular fertilizers or direct application.
specific application requirements. These can be New Zealand and Australia, along with the United
categorized broadly into elemental S-based fertiliz- States and Canada, were at the forefront in elemen-
ers and liquid S formulations. tal S fertilizer research and technology, with S defi-
ciencies recognized and addressed since the 1950s.
Elemental sulfur fertilizers Most research was oriented to areas of deficiency,
The use of elemental S as a fertilizer is increasing suitable diagnostic tests, plant S requirements, S
mostly in the developed world and is projected to cycle modeling, oxidation modeling of elemental S,
continue. Limited, if any, expansion of sulfate- and development of effective S fertilizers. This re-
containing carriers has resulted in industry giving search led to the development of suitable elemental
attention to elemental S as a means to correct S defi- S fertilizers including the methodologies to incorpo-
ciencies. Two features of elemental S highlight its rate elemental S with fertilizers, either during proc-
use as a controlled-release fertilizer for permanent essing or into the finished product. Sulfur enriched
pastures and crops. First, it is the most concentrated SSP is one of the examples, which is popular in
S form, which lowers transport and application Australia and New Zealand. Single superphosphate
costs. Secondly, it offers reserve availability. Ele- is enriched with elemental S to make mixtures con-
mental S is converted to sulfate over time. Thus, taining 18 to 35% sulfur. The added S is superior in
availability is a function of this process, which de- its residual effect to the sulfate in the SSP. This S-
pends on the elemental S particle size, soil microor- enriched SSP has received attention in the area with
ganism activities, and environmental factors. Ele- high leaching losses of plant nutrients because of its
mental S fertilizers are now manufactured in Oce- potential for reducing sulfate leaching loss and also
ania, North America, Western Europe and West providing available sulfate to meet crop needs dur-
Asia. ing the whole growing season. More recent S fertil-
The effectiveness of elemental S as a fertilizer is izer research in New Zealand was directed towards
governed by its oxidation rate, which is a biological the development of technology to produce fine-
process carried out principally by bacteria of the particle elemental S suitable for incorporation into
genus Thiobacillus. The bacteria feed on elemental high-analysis P fertilizers or as a degradable granu-
S and oxidize it to the sulfate form, making S avail- lated product appropriate for dry blending. An
able to plant roots. Physical factors, including soil emulsifying process was developed to overcome the
102 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

spontaneous ignition problem when grinding ele- In conclusion, the demand for micronized elemen-
mental S. tal S and elemental S-modified compound fertilizers
Sulfur bentonite products are manufactured by a is increasing worldwide, especially in Oceania,
number of processes, with molten S blended with North America and Western Europe. In North
swelling bentonite clays and solidified into useable America, elemental S consumption for fertilizer use
forms, usually granules or pastilles. This material was estimated at close to 300,000 tons in 2000, and
has gained popularity in North America and to a is projected to climb to 500,000 tons by the end of
limited degree in Western Europe. Generally, re- the decade, assuming a modest annual growth rate
search results indicate that particle sizes of 0.15 mm of 6%. Western European efforts to reduce atmos-
to 0.20 mm or smaller are required if elemental S is pheric S also have created a huge market for the S
to be fully effective during the growing season in based fertilizer industry in the coming decade, with
which it is applied. The modern concept behind S elemental S expected to take a portion of this mar-
bentonite fertilizers is that after application the ben- ket.
tonite or other binding agent absorbs moisture from
the soil, causing it to expand and subsequently dis- Liquid sulfur fertilizers
persing the material into minuscule elemental S par- Low water solubility hampers the use of main-
ticles that oxidize rapidly. A product with a range stream sulfate fertilizers such as ammonium sulfate
of particle sizes is preferable in many circumstances, and potassium sulfate, in liquid or suspension fertil-
allowing for short-term and long-term release. A izer formulations, which have gained importance.
water-degradable product containing 90% S granu- Ammonium thiosulfate solution (ATS) is a popular
lated with bentonite clay is most widely produced. source of S for use in liquid fertilizers because of its
Produced in pastille and granular forms, these prod- solubility and compatibility with various ions. Fer-
ucts can be used in bulk blends, direct soil applica- tilizer-grade ATS in its commercial form is in a 60%
tions, and suspensions as a plant nutrient S source. aqueous solution with a (12-0-0-26S) analysis. It is
Recent innovations in production technology and compatible in any proportion with neutral to slightly
anti-dusting agents resulted in the marketing of acidic phosphate-containing solutions or suspen-
more effective products, such as a combination of S sions, as well as with aqueous ammonia (NH3) and
and sulfate product that offers both immediate avail- N solutions. It is not compatible with anhydrous
able sulfate and slow release S together to maximize NH3 or strong acids; thus, a wide variety of N-S, N-
S supply for plant nutrition. P-S, and N-P-K-S formulations are possible utilizing
Alternative formulations of elemental S, particu- this material. Ammonium thiosulfate can be applied
larly tried in Oceania, included mixtures with phos- directly by drip, sprinkler or flood irrigation. It does
phate rock, SSP, either molten or in dry form. Ad- not corrode metal piping nor clog spray nozzles.
hesion of elemental S to finished products, such as Thiosulfate S is unique in that it exists in two oxida-
triple superphosphate (TSP), DAP, and urea, offered tion states, making it more suited to the S uptake
new opportunities. This approach is an alternative patterns of most plants; it decomposes in the soil to
to the methodology to form elemental S into gran- form approximately equal amounts of sulfate and
ules or prills using bentonite or other binders. A elemental S. The sulfate is available immediately
new process was developed, which solved some whereas the elemental S is gradually converted to
problems regarding S fertilizer application in sulfate by bacterial oxidation. Ammonium thiosul-
flooded and non-flooded crops and pastures, includ- fate may be synthesized by reacting SO2 and NH3 in
ing improved S dispersion from the granule and aqueous solution forming at first ammonium sulfite,
better spatial distribution characteristics. A product, which reacts further with elemental S to form ATS
with micronized S bonded with special binders onto solution. Alternatively, NH3 may be absorbed in an
granules of high-analysis TSP is also available. The ATS solution, reacted with SO2, then further reacted
process establishes an elemental S coating on the with hydrogen sulfide to form ATS solution and S.
surface of the TSP's granules. The S is non- Ammonium thiosulfate has gained prominence in
leachable, but in a form that is readily oxidized by North America and is growing in use and impor-
soil microorganisms. The special coating process tance in Europe, because of its versatility and high S
involves the creation of an adhesive film on the sur- concentration in fluid formulations. It is estimated
face of the granules by spraying minute quantities of that the total production capacity in North America
water into a tumbling bed. The S-based dry coating reached about 1.4 million tons in 2000 and 700,000
material is applied after the adhesive film is estab- tons of ATS (180,000 tons S) were consumed. Fu-
lished. This product offers a valid combination for ture North American demand for ATS is expected to
situations requiring high-analysis fertilizers and the continue to grow due to overall increasing recogni-
need to apply S. An expanded product line is avail- tion of the sulfur benefits and higher recommenda-
able using other granular fertilizers, including DAP, tion rates.
MAP, and urea.
Landbauforschung Völkenrode, Special Issue 283, 2005 103

Table 1:
Product nutrient analysis.
Sulfur Fertilizers Content (%)
S N P2O5 K2O
Ammonium nitrate with ammonium sulfate or 7 to 16 up to 30 0 0
ammonium nitrate sulfate
Ammonium nitrate with gypsum 3 to 6 24 to 27 0 0
Ammonium phosphate sulfate 6 to 17 variable variable 0
Ammonium polysulfide 40 to 45 20 to 21 0 0
Ammonium sulfate 24 21 0 0
Ammonium sulfate liquid 9 8 0 0
Ammonium thiosulfate solid 43 19.5 0 0
Ammonium thiosulfate solution 26 12 0 0
Calcium nitrate with sulfur 1 to 5 15 0 0
Calcium sulfate (dihydrate gypsum) 17 to 18 0 0 0
Calcium sulfate (hemihydrate gypsum) 19 to 22 0 0 0
Calcium sulfate (anhydrite gypsum) 22 to 24 0 0 0
Fortified SSP 28 to 50 0 5 to 16 0
Iron pyrites 54 0 0 0
Magnesium sulfate (Epsom salt) 13 0 0 0
Magnesium sulfate (Kieserite) 10 to 23 0 0 0
Micronized sulfur* 50 to 99 0 0 0
Mixed-grade NKs with sulfur 5.2 to 10 variable 0 variable
Mixed-grade NPs with sulfur 2 to 21 variable variable 0
Mixed-grade NPKs with sulfur 2 to 17 variable variable variable
Mixed-grade PKs with sulfur 2 to 15 0 variable variable
Nitrogen-sulfur solutions 2 to 6 7 to 35 0 0
Potassium magnesium sulfate 22 0 0 22
Potassium sulfate 17 to 18 0 0 48 to 52
Potassium thiosulfate 17 0 0 25
Single superphosphate - SSP 11 to 14 0 16 to 20 0
Sulfur (elemental) 50 to100 0 0 0
Sulfur bentonite 90 0 0 0
Sulfur-coated DAP 12 12 to15 40 0
Sulfur-coated MAP 12 8 to 10 44 0
Sulfur-coated TSP 10 to 20 0 38 to 43 0
Sulfur-coated urea 10 to14 38 to 40 0 0
Sulfur with micronutrients 2 to 80 0 0 0
Urea with sulfur 5 to 6 40 0 0
Urea sulfuric acid 9 to 18 10 to 28 0 0
Zinc sulfate 11 0 0 0
*Includes wettable/dusting powders (dry powder) and flowable sulfur (liquid suspension)

The largest producer of ATS has developed other season use and suitable for all crops, particularly
liquid S fertilizers: ammonium polysulfide solution cereals, oilseed rape, and grass. For foliar applica-
(20-0-0-40S), potassium thiosulfate (0-0-25-17S, tions, (35-0-0-1.7S) and (20-0-0-1.7S) are marketed,
particularly suited as a starter fertilizer) and calcium as are other fertilizers with S, based on ATS tailored
thiosulfate solution, for crops and situations requir- to individual requirements.
ing these other nutrients besides S. Thiosulfates Potassium sulfate tends to react with ammoniacal
(S2O32-) are non-corrosive and non-hazardous to N, phosphates, and metal ion impurities to form
handle; they also are well adapted to the methods insoluble deposits. The largest producer of potas-
used to apply fertilizer solutions. They are clear, sium sulfate in North America developed a grade
liquid fertilizers that are suitable for direct applica- twice as soluble as ordinary potassium sulfate, pro-
tions or blending, offering versatility to farmers and duced as a dry, fine crystalline material with a (0-0-
fertilizer retailers. Manufacturers produce thiosul- 49-17S-1Mg) analysis. This breakthrough increased
fates in North America and Western Europe. New the use of potassium sulfate in liquid formulations
liquid formulations include (26-0-0-3.1S), for early and fertigation. The product also has a low salt in-
104 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

dex, reducing the impact on salt-sensitive soils and Ceccotti SP (1994) Sulphur fertilizers: An overview of
crops. It is more stable in solution at low tempera- commercial developments and technological advances.
ture than potassium nitrate, thus reducing problems Sulphur in Agric 18:58-64
of salting out during storage, transport, and applica- Ceccotti, SP, Morris R, Messick DL (1998) A global
overview of the sulphur situation: Industry’s back-
tion. ground, market trends, and commercial aspects of sul-
phur fertilizers. In: Schnug E (ed) Sulphur in Agroeco-
systems. Kluwer Academic Publishers, The Nether-
Conclusions lands, pp 175-202
Hagstrom GR (1986) Fertilizer sources of sulphur and
The S fertilizer industry has developed materials their use. In: Tabatabai MA (ed) Sulphur in Agriculture.
adapted and suited to particular crop and soil man- American Society of Agronomy, Inc Publisher, Madi-
agement situations. (Table 1) Traditional sources, son, Wisconsin, USA
ammonium sulfate and SSP will continue to lead in Messick DL, de Brey C, Fan MX (2002) Sources of sul-
phur, their processing and use in fertiliser manufacture.
consumption for S fertilizers in the near-term. How- Proceeding 502: International Fertiliser Society, York,
ever, elemental S-based materials will become more UK
readily available for dry fertilizer applications and Rasmussen LK (2002) Production of ammonium nitrate
thiosulfates will continue to gain in popularity for fertilizers with sulphur. Presentation to the Ammonium
fluid fertilizer applications. Sulfur, unlike N, P, and Nitrate Producers Study Group. Tucson, Arizona, USA
K fertilizers, offers a much wider range of products, The Sulphur Update, (2003) The Sulphur Institute. Wash-
which provide versatility for a variety of appli- ington DC, USA
cations. However, farmers, fertilizer dealers, exten-
sion agronomists, and others in the agricultural
community need to better understand how these
products work for optimal performance. The fertil-
izer industry needs to invest more on education and
promotion programs to accelerate commercialization
of S products as both a fertilizer and soil amend-
ment, which will provide significant benefits to both
fertilizer manufacturers and farmers.

References

Anon (2001) Recommendations on the Transport of Dan-

gerous Goods: Model Regulations. (The Orange Book)
United Nations
Bixby DW, Beaton JD (1976) Sulphur Containing Fertil-
izers: Properties and Applications. Technical Bulletin
17, The Sulphur Institute Washington DC, USA
Blair GJ (2002) Sulphur Fertilisers: A Global Perspective.
Proceedings 498: International Fertiliser Society Con-
ference, York, UK.
Blair, GJ (1993) Sulphur sources for agriculture in South
and Southeast Asia and China. Proc Int Symp on Pre-
sent and Future Raw Material and Fertilizer Sulphur
Requirements for China, Beijing, China, 15-17 June
1993, TSI, Washington, DC, United States; Chinese
Sulphuric Acid Industry Association, Beijing, China
and Chinese Soil and Fertilizer Institute, Beijing, China,
pp 87-105
Blair GJ, Lefroy RDB, Dana M, Chaitep W (1995) De-
velopment and evaluation of sulphur containing fertiliz-
ers in Australia and New Zealand. Proc Int Work on
Current and Future Plant Nutrient Sulphur Require-
ments, Availability, and Commercial Issues for China,
Beijing, China 9 Mar 1995, TSI, Washington DC,
United States, pp 57-74
Braithwaite AC, Brown MW (1994) Sulphur in New
Zealand: A review of processing technique. Sulphur in
Agric 18:9-22
Landbauforschung Völkenrode, Special Issue 283, 2005 105

Sulfur in organic farming

Hans Marten Paulsen1

Abstract1 ferring thereto on agricultural products and food-

stuffs (EU, 1991).
Beyond the natural role of sulfur as plant nutrient,
in organic farming it is an important fungicide and
acaricide. S as plant nutrient has to be kept at a suf- Sulfur as fungicide and acaricide
ficient level because it can help in saving nitrogen
and in reducing nitrogen leaching. S influences the Limiting legislation on pest-, disease- and weed-
nitrogen fixation of legumes, which is the essential control in organic farming is given as guideline of
microbiological process for plant production in or- worldwide validity by the IFOAM Basic Standards
ganic farms. S is determining quality aspects of of Organic Production and in European law by the
feedstuffs and other products. An adequate S nutri- Council Regulation (EEC) No 2092/91 of 24 June
tion of plants is therefore essential. But in organic 1991 (EU, 1991). Additional restrictions are given
farming practice negative S balances are found. To by different organic grower associations in the
decide about fertilization needs, organic farmers whole world, which are listed in Willer and Youseffi
need to know about S flows in soils, S supply to (2004). According to the EEC 2092/91 pests,
plants, necessary S contents in plants and also about diseases and weeds shall be controlled by a
S availability in soils, in organic materials and in combination of the following measures: Choice of
different fertilizers. Various S-containing fertilizers appropriate species and varieties, appropriate
are approved in organic farming and could be used rotation program, mechanical cultivation
to correct S imbalances. Due to its low S content procedures, protection of natural enemies of pests
and low S availability manure application is of low through provisions favorable to them (e.g. hedges,
importance for the S nutrition of plants. nesting sites, release of predators) and flame
weeding. Only in cases of immediate threat to the
Keywords: Acaricide, elemental sulfur, fertilizers, crop may recourse be had to direct measures with
fungicide, organic farming, sulfur fertilization, sul- products referred to in Annex II of the regulation. In
fur fertilizers organic viniculture, organic fruit and vegetable
growing elemental S (S0) is a main and essential
agent of plant protection to keep the internal and
Introduction external quality (Palm and Klopp, 2004; Kienzle,
2004; Hofmann, 2004; Table 1).
In organic farming the input of chemo-synthetic
fertilizers is forbidden. Sulfur (S) in organic farms
can be supplied together with S containing approved Table 1:
fertilizers or raw S from natural sources. Even if S Target organisms for elemental S (S0) application and
deficiencies in plant nutrition are reported in common doses used in organic vine- and pomefruit pro-
conventional agriculture, S fertilization in organic duction according to Palm and Klopp, 2004; Kienzle,
farms is not of practical importance up to now. 2004; Hofmann, 2004.
In organic farming the use of pesticides is strictly
limited to natural sources and has to be certified by S0 as fungicide:
the control bodies in advance (IFOAM 2002; EU, Powdery mildew in vine (Uncinula necator, Oidium
1991). S used as fungicide and acaricide is of special tuckeri)
importance in organic vine- and pomefruit- Powdery mildew in tomatoes (Oidium lycopersicum)
Apple scab, pear scab (Venturia spp.)
production. In the following article the importance
Cherry leaf spot (Blumeriella jaapii)
of S, S balances and S use in organic agriculture are Leaf rust on plum (Tranzschelia pruni spinosae)
reviewed and described. The legal base used for the
discussion and description is the Council Regulation S0 as acaricide:
(EEC) No 2092/91 of 24 June 1991 on organic pro- Pear bud, grape bud (Eriophyes piri, E. viti)
duction of agricultural products and indications re- Rust mite in vine (Phyllocoptes vitis)

S0-dosage per year:

1
Institute of Organic Farming, Federal Agricultural Re- Pome fruits: 21-27 kg S0 per meter crown height divided
search Station (FAL),Trenthorst 32, 23847 Westerau, in up to 30 applications
Germany Vine: up to 9 applications between 3.6 an 4.8 kg ha-1
106 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

Winkler and Stein (2004) summarized risk as- (Berkelmann-Löhnertz and Kauer, 2003; Hofmann,
sessments and findings for S0 in the environment 2003). S0 used as acaricide in organic farming can
when used as plant protection agent as follows. S0 not be substituted up to now (Pfeiffer, 2003).
has low toxicity for mammals, birds and fish and
high no-observed-effect-concentration (NOEC) val-
ues for plants. Soil application of 10 and 100 kg ha-1 Sulfur as plant nutrient
S0 lowered N- and C-mineralization. The legislative
limit of a level of 75 % of the N- and C- S is an essential plant nutrient influencing internal
mineralization in S0-treated soil in comparison to and external quality, plant growth, health and nutri-
untreated soil after 100 days was reached after 14 ent efficiency of agricultural crops. In plants S is
and 66 days respectively. S0 is relatively immobile involved in the composition of amino acids, in the
in soils and is leached as sulfate (SO4) after incorpo- determination of the protein content, in aspects of
ration and oxidation in the soil sulfur cycle. S0 is baking quality, in the formation of secondary plant
hydrophobic and nearly not watersoluble. When components and pharmaceutical components, in the
reaching surface waters it is incorporated in the soil nitrogen metabolism of plants and in the resistance
after sedimentation. Additional SO4-loads to waters of plants against pests and diseases.
from oxidation under aerobic conditions are irrele- According to the Council Regulation (EEC) No
vant under consideration of natural water contents. 2092/91 the fertility and the biological activity of
S0 is toxic for green algae (e.g. Scenedesmus subspi- the soil must be maintained or increased, in the first
catus) and water fleas (e.g. Daphina magna). There- instance, by the cultivation of legumes, green ma-
fore safe distances to waters are necessary when S0 nures or deep-rooting plants in an appropriate multi-
is applied. S0 is toxic for different non-target terres- annual rotation program, incorporation of livestock
tial arthropodes (e.g. Trichogramma cacoecie) but manure from organic livestock production and by
further studies on the toxicity of S0 for arthropodes incorporation of other organic material, composted
are necessary. Due to this restricted knowledge on or not, from holdings producing according to the
the effects of S0-application on non-tagret-terrestial rules of this regulation. Other organic or mineral
arthropods, Winkler and Stein deduced, that a final fertilizers, mentioned in Annex II, may, exception-
risk assessment for S0 in the environment according ally, be applied, as a complement to the extent that
to the rules of the German plant protection law adequate nutrition of the crop being rotated or soil
(PflSchG, 1998) is not possible at the moment. Sev- conditioning are not possible by the methods men-
eral S0-products have a new admission for the use as tioned before. In organic farming S can be applied
plant protection agent. Even if in organic farming as a component of approved fertilizers (Table 2) to
legislation no limits in dosage is given, German or- compensate expected or acute S deficiencies. S from
ganic farmers have to keep to the application restric- sulfate (SO4) sources is readily plant available
tions of the German plant protection act. But a natu- whereas S0 has to be oxidized in soil before plant
ral limit on S0 application used as acaricide e. g. in uptake. The oxidation speed of S0 is limited by high
organic apple production is set by biological bal- particle sizes (Fox et al., 1964, Gupta et al., 1998,
ances because high S0 doses are killing beneficial Paulsen, 1999) and small populations of thiobacteria
mites (e.g. Amblyseius spp.) as well. Those mites are in soil (Schnug and Eckhardt, 1981).
natural predators of spider mites that are non con-
trollable in organic farming (Palm and Klopp, 2003)
and are urgently needed to keep a natural balance.
But still S0 as fungicide is of high importance in Table 2:
organic pest management and is an essential tool in Approved S containing fertilizers in organic farming ac-
organic vine and fruit production. The legal restric- cording to the Council Regulation (EEC) No 2092/91.
tions are under discussion but the lacks in knowl- Fertilizer S content
edge on environmental effects have to be filled to
ensure a reasonable future use of S0 in organic agri- Potassium sulfate 18 % SO4-S
cultural systems (Kühne and Friedrich, 2003). Re- Kieserite* 22 % SO4-S
search on alternatives to S0 as fungicide is focusing Epsom salt 13 % SO4-S
Gypsum (from natural sources) 14 % SO4-S
on direct measures like different plant strengtheners
Calcium carbonate with S (gypsum 2-4 % SO4-S
based on SiO2, different plant extracts, milk prod- from natural sources)
ucts, NaHCO3, lactic acid bacteria and other micro- Elemental S (from natural sources)* 80 % S0-S
organisms and on resistant plants. As indirect con- *
Use has to be authorized by the inspection body
trol measures supporting of soil antagonist popula-
tions and removal of plant residues are reported
Landbauforschung Völkenrode, Special Issue 283, 2005 107

Table 3:
Dry matter- (DM), N- and S-contents of cattle slurry (n=14) and cattle farmyard manure (n=43) from organic farms in
England (Shepherd et al., 2002).
Slurry Farmyard manure
Mean Range SD Mean Range SD
DM (%) 7.9 1.0-12.0 3.57 DM (%) 21.0 13.0-38.0 5.83
Total N (kg m-3) 2.5 0.3-4.1 1.19 Total N (kg t-1) 5.2 2.9-7.8 1.16
S (kg m-3) 0,29 0.03-0.53 0.139 S (kg t-1) 0.8 0.3-1.8 0.30
Values expressed on a fresh volume or weight basis

Organic materials used in fertilization have low S ciency expert knowledge is needed to avoid misin-
contents and low S availability (Eriksen et al., terpretations.
1995). Ranges of S and N contents of manure and
slurry from organic farms in England were surveyed
by Shepherd et al., 2002 (Table 3). The N/S ratios of
slurry (1/0.12) and farmyard manure (1/0.15) are
wide.
Furthermore the mineralization of organic S from
organic materials added to soils is mainly dependent
of the C/S ratio of the materials (Figure 1). From
manures with C/S ratios between 430 and 735 be-
tween 47 % and 127 % from the organic S were
mineralized to SO4-S respectively. Mean values
ranged between 5 % (horse manure) and 31 %
(chicken manure). Digested materials had a rela-
tively constant S mineralization of up to 97 %, de-
creasing with increasing C/S ratio (Tabatabai and
Shae, 1991). According to the values given in Table
3 and figure 1 from 16 kg S applied together with 20
t farmyard manure per hectare only 2.6 kg S would
be plant available. Farmyard manure and slurry
therefore are only poor S sources in organic plant
nutrition. Figure 1:
Due to the lower yield level in organic farms Mineralization of organic S from waste materials with
compared to conventional farming, S uptake and S different C/S ratios added to soils. Mean values of five
demand of the crops are lower as well. Therefore S soils as difference between treated and untreated soil
fertilization is not common in organic farms up to (after Tabatabai and Chae, 1991).
know. But S balances determined in a survey in
Denmark (Table 4) are showing that normal organic
crop rotations already have negative S balances Additionally due to the lower yield levels in or-
(Erikson et al., 2002). ganic production critical nutrient thresholds for S
So it must be expected that in high S demanding and other plant nutrients extracted from field sur-
crops or in years with favorable growth conditions veys and fertilization trials (Schnug et al., 1997,
and with high yield levels an insufficient S nutrition, Haneklaus and Schnug, 1998; Bergmann 1993) have
at least in parts of the vegetation time, will likely to to be revised and must be adopted to yield expecta-
be occur in organic plant production as well. Be- tions of organic production. Only an exact knowl-
cause soil structure and water movement are deter- edge on S demands of crops grown in systems with
mining the S supply to a large extent (Bloem et al., lower yield expectations can result in an adequate S
1998) it is necessary to have a close look on site fertilization strategy in organic farms.
specific conditions influencing the S supply to S and N nutrition of plants are metabolically
plants. linked (Hawkesford et al., 1994; Amâncio et al.,
Because organic farms rely on mineralized soil- 1998). In grassland and crops the application of S
nitrogen, temporary N-deficiency in early spring is has been shown to increase the efficiency of N use
widespread and can be mixed up with S deficiency by plants. Adequate S supply is increasing the N-
symptoms (Schnug and Haneklaus, 1997). Therefore recovery and reduces N losses from the system
in organic farms for the identification of S defi- (Brown et al., 1999; Schnug and Haneklaus, 1994).
So also in organic farming the control of the S nutri-
108 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

Table 4:
Sulfur balance (kg ha-1) in an organic crop rotation as average of year, location and cropa (Eriksen et al., 2002).
Inputb Output Balancec
Deposition Manure Irrigation Plants Leaching
Year
1997-1998 10 4 9 3 34 -13ab
1998-1999 10 3 6 3 34 -18ab
1999-2000 10 3 0 2 19 -7a

Location
Jyndevand 10 4 15 2 32 -6a
Foulum 7 2 0 3 34 -28b
Flakkebjerg 13 5 0 2 20 -4a

Crop
Barley 10 7 5 3 31 -12a
Grass-Clover 10 0 4 0 22 -8a
Winter Wheat 10 8 6 4 30 -11a
Parley/pea 10 0 5 4 33 -22b
a
Main effects did not interact
b
Assuming no variation between replicates
c
Values with the same letter are not significantly different within the group (P<0.005)

tion of plants could help in saving nitrogen and in References

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Landbauforschung Völkenrode, Special Issue 283, 2005 111

Sulfur nutrition and its significance for crop resistance – a case study from Scotland
Ioana Salac1, Silvia H. Haneklaus1, Elke Bloem1, Elaine J. Booth2, Karene G. Sutherland2, Kerr C. Walker2 and
Ewald Schnug1

Abstract1 in the defense system of plants (Schnug and Cey-

nowa, 1990; Schnug et al., 1995a). Soil-applied S
Severe sulfur deficiency causes a decrease in yield increased the resistance against various fungal dis-
and has a negative impact on crop quality. Besides eases in different crops under greenhouse (Wang et
this, a higher susceptibility of crops to certain dis- al., 2003) and field conditions (Schnug et al., 1995a;
eases was observed. Sulfur fertilization proved to Bourbos et al., 2000; Klikocka et al., 2004; Bloem et
lower disease incidence and severity of fungal infec- al., 2004; Salac et al., 2004). Based on these find-
tions in different crops. The sulfur metabolism pro- ings the concept of SIR (Sulfur Induced Resistance)
vides several potential mechanisms by which plants was developed (Schnug, 1997).
are able to tackle biotic stress. The identification of
these processes and adaptive control of sulfur in-
duced resistance (SIR) against fungal diseases offers The concept of Sulfur Induced Resistance (SIR)
the opportunity to develop natural plant protection
measures by means of targeted fertilization strate- The S metabolism of plants offers different possi-
gies. In the present paper, the results from a field bilities to tackle with biotic stress. It includes an
experiment in Scotland are summarized, which re- increased synthesis of natural compounds (e.g. H2S,
flect the influence of the sulfur nutritional status on cysteine, methionine, glutathione), the degradation
sulfur-containing metabolites and infection with of glycosides (e.g. glucosinolates) and the synthesis
fungal diseases. of new compounds (e.g. phytoalexins; Figure 1)
(Haneklaus et al., 2004). Supposedly, these S-
Key words: cysteine, glutathione, glucosinolate, containing defense compounds are released in a
Pyrenopeziza brassicae, sulfur induced resistance chain reaction triggered by the pathogen and con-
(SIR) trolled by the S status of the plant (Haneklaus et al.,
2004, Figure 1).
Cysteine is the precursor of all relevant S-
Introduction containing metabolites putatively involved in SIR
(Figure 1) and therefore it might be assumed that
Since the beginning of the 1980s severe sulfur (S) cysteine is one of the cornerstones of plant resis-
deficiency can be observed regularly under field tance against pathogens. Previous studies have
conditions in the northern parts of Europe because shown that the cysteine concentration in plant tis-
of continuously decreasing S inputs to agro- sues is strongly related to the S nutritional status of
ecosystems (Schnug and Pissarek, 1982; Schnug and plants (De Kok, 1990; Schnug, 1997) and that cys-
Haneklaus, 1994). High S demanding cruciferous teine is enriched in resistant plant tissues
crops reacted first to a reduced S supply (Schnug (Vidhyasekaran, 2000). Cysteine can be rapidly de-
and Pissarek, 1982) and about 10 - 15 years later, graded to H2S or metabolized to other compounds
low demanding crops such as cereals and sugar beat that are putatively involved in pathogenesis (Figure
also showed S deficiency (Schnug et al., 1993; 1).
Schnug et al., 2000). In Scotland, the infection of H2S is fungitoxic and plants have the ability to
oilseed rape plants by fungal pathogens such as release H2S and other gaseous S compounds into the
Pyrenopeziza brassicae (anamorph: Cylindrospo- atmosphere by different enzymatic reactions
rium concentricum) (P. brassicae) and Leptosphae- (Schroeder, 1993; Burandt et al., 2001; Bloem et al.,
ria maculans (anamorph: Phoma lingam) increased 2004). Glutathione (Ȗ-glutamyl-cysteinyl-glycine)
during the 1980s (Brokenshire et al., 1984). This (GSH) was found to accumulate rapidly in response
phenomenon was attributed to the drastically re- to fungal attack (Vanacker et al., 2000; Bloem et al.,
duced atmospheric S depositions in this region 2004; Salac et al., 2004) and this was proven to be
(Dore et al., 2003) as S was found to play a key role related to pathogenesis (Gullner and Kömives,
2001). Glucosinolates (GSLs) undergo hydrolysis,
1 catalyzed by the enzyme myrosinase, to produce an
Institute of Plant Nutrition and Soil Science, Federal
array of products of which isothiocyanates are a
Agricultural Research Centre (FAL), Bundesallee 50, D-
38116 Braunschweig, Germany major component (Luethy and Matile, 1984). These
2
Scottish Agricultural College, Ferguson Building, Craib- compounds, and other products of GSL hydrolysis,
stone Estate, Bucksburn, Aberdeen, AB21 9YA, Scotland have been shown to be toxic or inhibitory to many
112 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

Figure 1:
Sulfur metabolites and pathways putatively involved in chain reactions of SIR in Brassica species (Haneklaus et al., 2004).

species of fungi and bacteria (Greenhalgh and on disease incidence and severity of fungal diseases
Mitchell, 1976; Mithen et al., 1987; Doughty et al., was tested and set in relation to extent and variation
1991). Phytoalexin synthesis is induced after infec- of S-containing metabolites in order to perceive
tion, involving de novo synthesis in the infected triggers and magnitude of SIR.
plant tissue (Hammerschmidt and Nicholson, 2000).
The involvement of phytoalexins in SIR is obscure
and can only be speculated from the dependency of Material and methods
their precursors on S. High levels of pathogenesis-
related proteins were found to be related with en- Design of the field experiment
hanced disease resistance in plants (Bohlmann, A quadri-factorial field experiment was carried
1999; van Loon, 1999). However, their possible role out in 2001/2002 in Aberdeen, Scotland (W 2o 13`,
in SIR still requires empirical proof. The signifi- N 57o 12`; 60 m a.s.l) on a loamy sand (Humic Pod-
cance of the formation of elemental S in plants for zol according to the FAO classification system). The
defense has been discovered only recently (Williams plot size was 40 m2. Plots were arranged in a split-
et al., 2002), but the exact mode of action is still plot design in four blocks. Two oilseed rape culti-
unclear. vars with different susceptibilities against P. brassi-
Most investigations on the putative role of S- cae were grown: Bristol (B; susceptible) and Lipton
containing compounds in SIR were carried out in (L; resistant) (HGCA Recommended List WOSR
vitro and in pot experiments. Factors governing ini- 2003). For defining the growth stages (GS) of oil-
tialization and strength of SIR need to be tested, seed rape the BBCH scale was used (Strauss et al.,
however, under field conditions in order to identify 1994).
and regulate resistance mechanisms by means of S was applied as K2SO4 to the soil at rates of 0
targeted S applications. In a field experiment in (S0) and 100 kg S ha-1 (S100). The K supply was bal-
Scotland, the influence of soil-applied S fertilization anced by fertilizing adequate amounts of KCl. The S
Landbauforschung Völkenrode, Special Issue 283, 2005 113

dose was split in two equal parts in autumn (GS 04) GSH and GSL content were determined by HPLC
and in spring (GS 14 - 15). N was supplied as analysis according to Hell and Bergmann (1990) and
NH4NO3 at rates of 100 and 200 kg N ha-1. 100 kg N Rosa (1992), respectively.
ha-1 was applied to all plots at the start of the vegeta-
tion period (GS 14 - 15) and an additional 100 kg N Statistical calculations
ha-1 was fertilized at the beginning of stem elonga- For statistical analysis the SPSS software package
tion (GS 30) to those plots receiving a higher N version 10 was employed (SPSS, 1999). The GLM
dose. multivariate procedure was applied to assess the
Specific fungicides were used against P. brassicae influence of the treatments on individual parameters.
infections. Either no fungicides were applied or the Cultivar, S, N and fungicide were tested as fixed
plots received 0.4 L ha-1 flusilazole (250 g L-1) plus factors. N and fungicide treatment delivered no sta-
carbendazim (125 g L-1) in autumn (GS 12) and in tistical differences with respect to the investigated
spring (GS 30), respectively. parameters and therefore their effect is not shown in
the present paper. In order to test the influence of
Disease assessment infections by P. brassicae on the cysteine and GSH
The development of P. brassicae was followed up content a one factorial ANOVA was carried out.
during the whole growth period. Since visible symp- The Student-Newman-Keuls test was used to deter-
toms of P. brassicae do not usually occur before mine which means were significantly different from
February/March, during autumn-winter samples each other at the 5 % significance level (LSD5%).
were taken every 1 to 2 weeks by randomly choos-
ing 10 plants from non-treated fungicide plots. After
incubating them in a damp chamber over night, the Results and discussion
parameters disease incidence (%-age of plants in-
fected) and disease severity (%-age of leaf area in- Infections by P. brassicae were the most impor-
fected) were visually assessed. When macroscopic tant fungal disease in winter oilseed rape in
symptoms of infections by P. brassicae became 2001/2002. Infections by L. maculans and P. para-
visible in the field, the level of fungal infection was sitica were also found, but only at low levels. Dis-
assessed visually and directly in all plots at monthly ease progression throughout the vegetation period is
intervals. Besides assessing infections caused by P. illustrated for P. brassicae in Figure 2. Usually, P.
brassicae, plants were also rated for other major brassicae infects winter oilseed rape plants soon
fungal diseases (e.g. Leptosphaeria maculans, Per- after emergence of the seedlings (Gilles et al.,
onospora parasitica, Alternaria brassicae, Scle- 2000). During experimentation, first infections were
rotinia sclerotiorum, Botrytis cinerea). found in mid-late October and maximum values for
disease incidence and severity were determined in
Sampling procedure late March/April. At this time, the disease incidence
Younger, fully developed leaves of winter oilseed was 91 % if no fungicides were applied (Figure 2).
rape were randomly taken from each plot at the be- Values of > 25 % plants infected by P. brassicae at
ginning of stem elongation (GS 50 - 53). Whole-leaf stem extension indicate a severe infection (Steed
samples were split and either shock frozen in liquid and Fitt, 2000). The corresponding value for disease
nitrogen and finally freeze-dried, or dried in a venti- severity was 13 % (Figure 2). In plots where fungi-
lated oven at 60° C until constancy of weight. Addi- cides were applied the disease incidence and sever-
tionally, leaf disc samples (16 mm) from leaf areas ity of P. brassicae were lower compared to non-
with visible symptoms of P. brassicae infections (+ treated fungicide plots, but differences were not
infection) and without visible symptoms (- infec- consistently significant. P. brassicae is a hemi-
tion) were taken from the upper third of the crop. biotrophic fungus, which means that it becomes
Leaf disc samples were shock frozen in liquid nitro- necrotrophic in the late developmental stage (Ashby,
gen before being freeze-dried. 1997), a characteristic that might be significant with
view to processes involved in SIR (see below). At
Plant analysis the time of leaf sampling (GS 50 - 53), additional
infections by L. maculans (3 % plants infected; 0.01
Oven-dried leaf samples were fine-ground to a % leaf area infected) and P. parasitica (13 % plants
particle size < 0.12 mm using a Retsch ultra- infected; 0.2 % leaf area infected) were found (data
centrifugal mill and the total S content was deter- not shown).
mined by X-ray fluorescence spectroscopy accord- Disease incidence and severity of P. brassicae
ing to Schnug and Haneklaus (1999). Freeze-dried were independent of the cultivar (Figure 2), though
leaf material and leaf disc samples were fine-ground differences had been expected because of their di-
in a coffee mill or a mortar, respectively prior to the vergent rating (HGCA Recommended List WOSR
analysis of organic S compounds. The free cysteine, 2003). There is circumstantial evidence that resis-
114 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

% %
100 S Fertilization S 15 S Fertilization S

Infected leaf area

12
Infected plants

75
9
50
6
25 3
0 0

Ja er
O er
Ja er

ec r

M y

ne
Fe ary
O ber

ov r

ch
ec r

il
M y

ne

ay
ov r

Fe ry

ch

il
ay

D be
N obe
D be
N obe

r
r

pr
b
b

pr

ua
ua

Ju
a

ar
Ju

M
ar

em
M

em
em

em
em

nu
em

nu

A
A

br
ct
br
ct

pt
pt

Se
Se

B S0 B S100 L S0 L S100
Figure 2:
Disease progression of Pyrenopeziza brassicae expressed by the percentage of infected plants (left) and the percentage of
the infected leaf area (right) in winter oilseed rape in plots without fungicide applications in relation to cultivar and S rate.

tance against P. brassicae in new cultivars is over- Free cysteine and GSH are S-containing com-
come after a few years by changes in the metabo- pounds of the primary plant metabolism. These me-
lism of pathogen (Karolewski et al., 2004). tabolites were found to be involved in plant resis-
Since the S nutritional status of the plant was re- tance against fungal pathogens (Vidhyasekaran,
ported to have a strong impact on its natural resis- 2000; Gullner and Kömives, 2001). The effect of S
tance against pathogens (Schnug et al., 1995a), S fertilization and cultivar on the cysteine and GSH
was applied in autumn and spring in order to suffi- content in leaf discs infected and non-infected by P.
ciently supply the crop and to promote resistance brassicae is shown in Table 1. S fertilization in-
mechanisms. However, in the present study the S creased the cysteine and GSH content in leaf discs,
applications did not influence disease progression of whereby differences were not consistently signifi-
P. brassicae traceably (Figure 2), which indicates cant (Table 1). In greenhouse and field experiments,
that S supply, S uptake, S resistance mechanisms De Kok et al. (1981), Schnug et al. (1995b) and
and virulence of the pathogen did not fully coincide. Bloem et al. (2004) found a significant relationship
Nevertheless, the data reflect changes in the plant S between S status and the cysteine and GSH content.
metabolism caused by S fertilization in combination Relevant in this context is that effects in Aberdeen
with fungal infections, which contribute to uncover might have been masked due to the smaller range of
mechanisms underlying SIR. In this experiment spe- variation of the plant S status.
cial attention was paid to the metabolites cysteine,
GSH and GSLs because of their direct dependence 8 S0 S100
on the S supply (De Kok et al., 1981; Schnug, 1988; b
b
Total S content (mg g )
-1

Schnug et al., 1995b; Schnug 1997) and their appar- 6

ent link to SIR (Haneklaus et al., 2004).
The efficacy of S fertilization can be best verified 4 a a
by determining the total S content (Figure 3). S fer-
tilization significantly increased the total S content 2
from 4.2 mg S g-1 to 7.9 mg S g-1 in Bristol and from
4.2 mg S g-1 to 7.3 mg S g-1 in Lipton (Figure 3). In
0
the control plots, the total S content in the leaf tissue Bristol Lipton
was in the range of latent S deficiency (3.5 - 6.5 mg
S g-1), i.e. that though no macroscopic symptoms Figure 3:
were visible, the S status was not sufficient for a Influence of S fertilization on the total S content in
younger, fully developed leaves (d.w.) of two winter oil-
high yielding crop (Schnug and Haneklaus, 1998). seed rape varieties at the start of stem elongation.
The S supply had no influence on disease incidence
and severity of P. brassicae (Figure 2). This might The increase in the content of cysteine and GSH
indicate a temporal discrepancy between S fertiliza- was higher in infected leaf discs compared to non-
tion and S uptake. Another explanation could be that infected leaf discs (Table 1). Differences in the cys-
the S doses were not sufficiently high to initiate teine and GSH content between the two cultivars
SIR. Here, a regular S fertilization throughout the were not significant (Table 1).
growing season might yield the desired effect.
Landbauforschung Völkenrode, Special Issue 283, 2005 115

Table 1:
Influence of S fertilization on the cysteine and glutathione content in leaf discs (d.w.) of two winter oilseed rape varieties at
the start of stem elongation.

Cysteine Glutathione
Treatment
(µmol g-1 ) (µmol g-1)

min max mean min max mean

+ Infection

S0 0.10 0.44 0.27 4.2 10.3 7.2

Bristol
S100 0.30 0.64 0.47 7.6 13.7 10.7

S0 0.01 0.35 0.18 2.6 8.7 5.6

Lipton
S100 0.22 0.56 0.39 7.1 13.1 10.1

LSD5% 0.24 4.26

- Infection

S0 0.73 0.83 0.78 11.3 13.3 12.3

Bristol
S100 0.84 0.94 0.89 13.1 15.1 14.1

S0 0.70 0.80 0.75 12.5 14.5 13.5

Lipton
S100 0.83 0.93 0.88 13.8 15.8 14.8

LSD5% 0.74 1.41

In Figure 4, the influence of infections by P. bras- continuous and consistently high infection severity
sicae on the cysteine and GSH content at two ex- for P. brassicae existed, particularly from the start
perimental sites, in Aberdeen (Scotland) and Braun- of the vegetation period onwards, and the S status
schweig (Germany) is shown. When plant material being sub-optimum, more S is bound in cysteine and
was visually infected by P. brassicae, a significant GSH in non-infected tissues. In the infected plant
2.5-fold and 1.6-fold decrease of the cysteine and tissues these metabolites were eventually consumed
GSH content, respectively was found in Aberdeen during metabolic protection processes thus yielding
(Figure 4; Table 1). In contrast, in experiments with significantly lower values.
the same cultivars in Braunschweig in 2002, infec- Secondly, the possibility exists that the plant tis-
tions by P. brassicae resulted in an increase of the sue was severely and lastingly damaged by the
cysteine and GSH content at the site of infection pathogen resulting in a shift of anabolic in the fa-
(Figure 4; Bloem et al., 2004). Additionally, the vour of catabolic processes. Previous investigations
activity of the enzyme L-cysteine desulfhydrase revealed no differences between dry weights of
increased (Bloem et al., 2004). Other researchers leaves in inoculated and non-inoculated pea leaves
also showed that fungal infections generally yield an by Mycosphaerella pinodes (Garry et al., 1996).
increase in the GSH content (Vanacker et al., 2000; Necrotic leaf areas are composed of dead cells and
Gullner and Kömives, 2001; Williams et al., 2002). assuming a complete degradation and/or transloca-
Two scenarios are possible which could explain tion of cysteine and GSH in/from necrotic plant tis-
these different findings. Firstly, on sites with a sue, this would imply that if ” 50/60 % (Bris-
higher S supply, reflected in higher total S concen- tol/Lipton) and ” 17/33 % (Bristol/Lipton) of the
trations (4.8 mg S g-1 in Braunschweig vs. 4.2 mg S leaf disc area is impaired by P. brassicae at the time
g-1 in Aberdeen), a correspondingly higher cysteine of sampling (see Figure 2), a significant decrease in
(0.7 µmol g-1 in Braunschweig vs. 0.5 µmol g-1 in the cysteine and GSH content might be expected in
Aberdeen) and GSH content (12.1 µmol g-1 in visually infected leaf discs whereby causal reasons
Braunschweig vs. 9.7 µmol g-1 in Aberdeen) can be remain speculative (see above). In other words, only
found in the leaf tissue. Besides this, an increased if > 60 % of the leaf disc area in case of cysteine and
synthesis of GSH on the Braunschweig site was > 32 % in case of GSH is severely impaired by P.
obviously related to a certain disease severity (Salac brassicae, reflected in corresponding necroses, the
et al., 2004). In comparison in Aberdeen, where a decreases may be attributed to metabolic changes in
116 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

% Braunschweig Aberdeen
150

Relative change of the cysteine

100

and GSH content

50
cysteine GSH
0
cysteine GSH
-50
-100
-150
Bristol Lipton
-200
cysteine GSH cysteine GSH
(µmol g -1) (µmol g-1)
- Infection 0.59 a 10.8 a 0.84 a 13.2 a
Bristol + Infection 1.39 b 13.7 b 0.36 b 8.95 b
- Infection 0.57 a 11.6 a 0.82 a 14.2 a
Lipton
+ Infection 1.31 b 15.3 b 0.28 b 7.86 b

Figure 4:
Influence of infections by P. brassicae on the cysteine and GSH content in leaf discs (d.w.) of two winter oilseed rape varie-
ties at the start of stem elongation in Braunschweig (2002) and Aberdeen (2002) (source for Braunschweig: Bloem et al.,
2004).

the decaying leaf tissue. These simple calculations low compared to values of up to 7.8 µmol g-1 found
reveal that the latter scenario may apply for leaf for the variety Cobra by Booth et al. (1991).
tissues severely impaired by the pathogen. Glucobrassicanapin, which was found to have
Glucosinolates are S-containing secondary com- biocidal properties (Peterka and Schlosser, 1989),
pounds, which are protective against fungal patho- was the predominant alkenyl GSL in the leaf tissue
gens (Mithen et al., 1987; Schnug and Ceynowa, of winter oilseed rape (Table 2). As its concentration
1990; Doughty et al., 1991; Zukalová and Vašák, was not influenced by the S supply, its significance
2002). Alkenyl GSLs are supposed to take part in in preformed resistance appears negligible. As a
the general resistance of plants against fungal response to infection an increased indole and aro-
pathogens, whereas the synthesis of indole and aro- matic GSL content was determined in the plant tis-
matic GSLs may be involved in the induced resis- sue (Doughty et al., 1991; Giamoustaris and Mithen,
tance (Zukalová and Vašák, 2002). So far, however, 1995). Besides the degradation of GSLs, a selective
no relationship between GSL content or GSL profile accumulation of indole and aromatic GSLs could be
in vegetative tissues and crop resistance has been mediated physiologically and might contribute to
verified (Chen and Andreasson, 2001). Three pre- the resistance of plants (Haneklaus et al., 2004).
dominant alkenyl GSLs were detected in leaves of The cultivars Bristol and Lipton differed signifi-
winter oilseed rape in the present study: glucobras- cantly in the progoitrin content (Table 2), but this
sicanapin (4-pentenyl glucosinolate), gluconapin (3- GSL has no antifungal properties (Mithen et al.,
butenyl glucosinolate) and progoitrin (2-hydroxy-3- 1987; Peterka and Schlosser, 1989). The mean
butenyl glucosinolate) (Table 2). Glucobrassicin (3- progoitrin content in the leaf tissue was 0.7 µmol g-1
indole methyl glucosinolate) and gluconasturtiin (2- for Lipton and 0.4 µmol g-1 for Bristol (Table 2).
phenyl ethyl glucosinolate) were the main indole
and aromatic GSLs, respectively found in the vege-
tative tissue (Table 2). S applications increased the Conclusions
individual and total GSL content in younger leaves
of winter oilseed rape at the start of stem elongation Alternative plant protection measures are gaining
in both varieties, but differences proved to be statis- increasing interest for conventional and organic
tically not significant (Table 2). Schnug (1997) farming systems. Up till now nutrient induced resis-
found a significant close correlation between S tance mechanisms are well known (Datnoff et al.,
status (from severe to excess S supply) and GSL 2003), but still of minor importance in agricultural
content (from 3 µmol g-1 to 52 µmol g-1) in younger, production. Sulfur induced resistance (SIR) was first
fully developed leaves of B. oleracea. The total observed for oilseed rape by Schnug et al. (1995a)
GSL content ranged from 2.8 µmol g-1 to 5.4 µmol and will be of high relevance in S-deficient produc-
g-1 in Lipton and Bristol (Table 2), which is fairly tion areas. This, however, requires targeted S fertili-
zation strategies, which prompt SIR on production
Landbauforschung Völkenrode, Special Issue 283, 2005 117

Table 2:
Influence of S fertilization on the individual and total glucosinolate (GSL) content in younger, fully developed leaves (d.w.)
of two winter oilseed rape varieties at the start of stem elongation.

Treatment Glucobrassicanapin Gluconapin Progoitrin

(µmol g-1) (µmol g-1) (µmol g-1)

min max mean min max mean min max mean

Bristol S0 1.9 3.1 2.5 0.38 0.63 0.51 0.12 0.46 0.29
S100 2.1 3.3 2.7 0.40 0.65 0.53 0.25 0.59 0.42

Lipton S0 1.5 2.7 2.1 0.32 0.56 0.44 0.50 0.83 0.67
S100 1.9 3.2 2.6 0.31 0.57 0.44 0.58 0.98 0.76

LSD5% 0.83 0.17 0.23

Treatment Glucobrassicin Gluconasturtiin Total GSL

(µmol g-1) (µmol g-1) (µmol g-1)

min max mean min max mean min max mean

Bristol S0 0.11 0.19 0.15 0.19 0.33 0.26 2.8 4.8 3.8
S100 0.15 0.24 0.19 0.26 0.40 0.33 3.3 5.3 4.3

Lipton S0 0.10 0.18 0.14 0.22 0.36 0.29 2.9 4.8 3.9
S100 0.11 0.20 0.15 0.25 0.39 0.32 3.3 5.4 4.4

LSD5% 0.06 0.09 1.34

fields. In this context, the presented research work influence L-cysteine desulfhydrase activity in Brassica
revealed that: napus L. J Exp Bot 55(406):2305-2312
- S fertilization increased the cysteine, GSH and Bohlmann H (1999) The role of thionins in the resistance
GSL content; of plants. In: Datta SK and Muthukrishnan S (eds)
Pathogenesis-related proteins in plants. CER Press, Inc.,
- disease incidence and severity during the vegeta- pp 207-234
tive period obviously play a major role in SIR as Booth EJ, Walker KC, Schnug E (1991) Effect of site,
changes in the GSH and cysteine content showed foliar sulphur and nitrogen application on glucosinolate
corresponding variations; content and yield of oilseed rape (Brassica napus L.).
- for initializing SIR, the S supply needs to follow Proc. 8th Int. Rapeseed Congress, Saskatoon, Canada,
the actual metabolic demand, which means that: (a) pp 567-572
doses higher than the physiological demand might Bourbos VA, Skoudridakis MT, Barbopoulou E, Venetis
be required; (b) split doses need to be applied in K (2000) Ecological control of grape powdery mildew
order to match the S demand for S induced proc- (Uncinula necator)
http://www.landwirtschaftmrl.badenwuerttem-
esses against fungal infections. berg.de/la/lvwo/kongress/SULFUR.htlm
Brokenshire T, Channon AG, Wale S (1984) Recognizing
oilseed rape disease. Publication 135, The Scottish Ag-
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Landbauforschung Völkenrode, Special Issue 283, 2005 121

Metabolic background of H2S release from plants

Ahlert Schmidt1

Abstract1 assimilation and the whole reaction sequence from

sulfate to cysteine is localized in the chloroplast.
Sulfate nutrition has been shown to be beneficial for The needed energy in form of ATP and ferredoxin is
plant health. Emission of H2S has been analyzed as generated by the electron transport chain. As sulfate
one possible target for a defense mechanism. In this activation is discussed already in the general
review the possible reactions leaving to sulfide are introduction section, I will give some information to
summarized and the recent developments for sulfide the sulfite reductase. This enzyme catalyzes the
generation from either the sulfite reductase or reduction of sulfite to sulfide using reduced
different cysteine-specific desulfhydrases are ferredoxin as electron donor (Figure 1). The sulfite
analyzed. Mechanisms for the formation of COS is bound to siroheme and is reduced without free
(carbonyl sulfide) and its degradation to CO2 and intermediates to siroheme-bound sulfide (Murphy et
sulfide in plants are discussed. It is shown that al., 1974), which than is liberated to free sulfide.
sulfide is toxic for plants itself inhibiting H2S will be assimilated by the cysteine synthase (O-
mitochondrial respiration. The present paper acetyl-L-serine thiol(lyase) [OASTL]) or it could be
summarizes the possible reactions concerning emitted from the plant to the environment. Some
sulfide formation and emission. aspects to be mentioned: 1) Some plants have only
one gene for the sulfite reductase and this might be a
Key words: H2S emission, cysteine, O-acetyl-L- limiting step for assimilatory sulfate reduction. 2)
serine (thiol)lyase, cysteine catabolism, cysteine Sulfide formed is effectively bound to cytochromes
desulfhydrase, COS metabolism, sulfide toxicity thus affecting respiration and possibly other iron-
containing complexes as well, which will be
discussed later. 3) These KM-data for sulfide binding
Introduction are in the same range as cyanide (µM), which
suggests that the plant should control the free H2S-
Plant health is influenced by sulfur starvation; pool in order to avoid toxic side effects of H2S.
sulfur nutrition therefore is mandatory for good Therefore the incorporation of sulfide to L-cysteine
plant growth. It has been shown, that the reduction using the cysteine synthase should be the most
of SO2 emission has led to sulfur shortage especially efficient way to keep its concentration low to avoid
in Cruciferae leading to higher susceptibility inhibitory effects. However, the reported KM-data
towards infection, which has been shown especially for the cysteine synthase have been too high so far
for rape (Schnug et al., 1993, 1995). This for this explanation (Schmidt and Jäger, 1992). Only
observation has been coined SIR (sulfur-induced recently our understanding of low sulfide
resistance). Whereas the mechanisms involved in concentrations and efficient cysteine formation
the SIR are not understood so far, is seems clear that seems to be resolved due to finding exceptionally
more than just one specific metabolic process seems low KM-data for the cysteine synthase in the
to be involved in this SIR syndrome. It has been micromolar range (Wirtz et al., 2004)
shown, that plants can emit sulfide to the If sulfide assimilation will not consume all sulfide
environment (Schmidt et al., 1980; Sekiya et al., generated by the sulfite reductase it could be emitted
1982a; Rennenberg, 1984, 1989). Therefore it was to the environment. Some aspects of H2S toxicity
speculated that release of H2S by plants could affect will be discussed in the last section. It might be
bacterial and fungal growth and contribute to SIR in speculated here that the sulfide generated by the
rape fertilized with a surplus of sulfate. Possible sulfite reductase due to the reduction of sulfate is
reactions leading to H2S have been analyzed and primarily used for cysteine formation and that
will be discussed here in some detail. sulfide needed for biosynthesis of iron-sulfur centers
and coenzymes is handled as sulfide generated from
cysteine by metabolic steps discussed later. The
Sulfide formation catalyzed by the sulfite regulation of the sulfite reductase and thus
reductase regulation of sulfide formation by this enzyme is not
understood so far, but possibly the generation of
Sulfide is generated in the process of sulfate sulfite by the APS reductase might be the limiting
step for H2S-generation by this pathway (Schmidt
and Jäger, 1992).
1
Institut für Botanik, Universität Hannover, Herrenhäuser Sulfide formed in this way would be localized
Str. 2, 30419 Hanover, Germany
122 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

within the chloroplast, since the sulfite reductase is a about 10-fold lower as its original substrate for
chloroplastic enzyme (Schmidt, 1969, Schmutz and cysteine formation with O-acetyl-L-serine (see
Brunold, 1985; Brunold and Suter, 1989). however the new resultz by Wirzt et al., 2004).
Furthermore it was found, that sulfide was light Since the cysteine synthase in plants is present in
dependent (Sekiya et al., 1982b), which would be high amounts (at least using the assay with O-
expected if the energy needed for assimilatory acetyl-L-serine and H2S; Schmidt and Jäger, 1992)
sulfate reduction is regenerated by the electron this side reaction of L-cysteine degradation is
clearly a possibility for H2S-formation in plants.
However, there are differences of the cysteine
synthases to cysteine desulfhydrases to be discussed
later. The intermediary enzyme-bound amino-
acrylate is not hydrolyzed by water to decompose to
ammonia and pyruvate (Burandt, 2002) but it is
stable and can only be released by addition of either
sulfide, cyanate or other thiol groups (Figure 2).
Especially L-cysteine itself can be used instead of
H2S forming a thiazolidine derivative (Figure 2) and
the dithiotreithol (DTE) can be used as well leading
to the corresponding DTE-cysteine compound with
the release of H2S as shown for bacteria (Mino and
Ishikawa, 2003) and seems to be valid for plants as
well; glutathione is not active in this reaction,
possibly favoring GSH as a mass thiol in plants
(unpublished data).

Sulfide formation catalyzed by L-cysteine

desulfhydrase
transport chain.
Figure 1: Cysteine degradation by an L-cysteine
A general scheme for sulfide formation by the sulfite desulfhydrase catalyzes the formation of sulfide,
reductase. ammonia and pyruvate in a stochiometric relation of
1:1:1 as shown in Figure 3. This reaction is well
characterized from the bacterium Treponema where
Sulfide formation catalyzed by cysteine synthase it has been crystallized (Chu et al., 1999; Bertoldi et
al., 2003). It shows, that L-cysteine reacts with a
The cysteine synthase catalyzes the formation of pyridoxal phosphate, forming a bound
L-cysteine from O-acetyl-L-serine and H2S as aminoacrylate similar to the situation discussed
shown in Figure 2. Plants contain isoenzymes of the above for the back reaction of the cysteine synthase.
cysteine synthases in the cytosol (OASTL a), the However, this aminoacrylate intermediate is not
chloroplast (OASTL b) and the mitochondrion stable but hydrolyzed directly with water to
(OASTL c). The isoenzymes have different catalytic pyruvate, ammonia and sulfide in a stochiometric
properties; especially the KM-data for the substrates way (Figure 3). Whereas such enzymes are found in
sulfide and O-acetyl-serine vary and the pH-optima bacteria and are normally used for cysteine
are different as well (Table 1). For L-cysteine degradation under energy shortage (cysteine
synthesis an aminoacrylate bound to the pyridoxal catabolism). Such activities have been found in
phosphate is generated at the active site of the higher plants as well, however, the differentiation
cysteine synthase. This amino acrylate contains an between back reactions of a cysteine synthase and
activated C-C double bond, which can accept free correct L-cysteine desulfhydrase activity has been
sulfide (HS-) to generate L-cysteine (Figure 2). It difficult. Therefore the corresponding genes have to
has been found by isotopic exchange reactions be isolated and the pure protein has to be at hand for
(Schmidt, 1977) that L-cysteine can be used as a critical examination of the reactions involved and
donor for the aminoacrylate intermediate as well (a the corresponding products formed. Genetic
partial back reaction; Figure 2) which leads to H2S evidence from Brassica rapa genotypes however,
formation using cysteine as a substrate. Therefore clearly shows, that cysteine synthase and L-cysteine
the cysteine synthase has an inherent capability to desulfhydrase activity are different in analyzed lines
H2S-formation from L-cysteine. The KM for the showing that these reactions can be dissected by
back-reaction using L-cysteine as a substrate is careful analysis (Burandt et al., 2002). The
Landbauforschung Völkenrode, Special Issue 283, 2005 123

General scheme with OAS Isotopic exchange reaction

L-Cysteine desulfhydrase reaction Direct thiohemiketamine formation

:
2-Methyl-2,4-thiazolidine-dicarboxylate formation
Figure 2:
Reactions around the cysteine synthase protein.

characterization of a plant L-cysteine desulfhydrase Sulfide formation catalyzed by L-cysteine

by recombinant proteins is still missing, however an desulfhydrase (NifS) forming alanine
enzyme from Synechocystis has been characterized
recently (Kesser, 2004). Another reaction of a possible L-cysteine
desulfhydrase has been found during
124 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

OAS-TL = L-Cysteine synthase reaction; DES-Reaktion = L-Cysteine desulfhydrase-reaction;

CAS-Reaktion = ß-Cyanoalanine-reaction
Table 1:
KM-data for cysteine synthases from Arabidopsis (Burandt, 2002).

characterization of the nitrogenase biosynthesis in

bacteria where reduced sulfur is needed for iron-
sulfur centers. The donor for the labile sulfide in
these centers has been shown to be L-cysteine and
this activity is termed as "NifS-type reaction“. This
enzyme was needed for the iron-sulfur cluster
formation in nitrogenase formation. It catalyzes the
formation of elemental sulfur and alanine, according
to Figure 4. This NifS protein is a L-cysteine
desulfhydrase with a pyridoxal phosphate as
cofactor. Again an aminoacrylate should be formed
with the release of sulfide. Obviously the Figure 3:
aminoacrylate is not hydrolyzed to ammonia and The L-cysteine lyase reaction: L-cysteine reacts with
water and the products formed are free sulfide, pyruvate
pyruvate but instead the double bond seems to be
and ammonia.
reduced thus forming alanine. Therefore an electron
donor is needed. These electrons obviously could
come from sulfide being oxidized to elemental
sulfur. However, recent evidence shows the
formation of free sulfide in the presence of DTT
(Mühlenhoff et al., 2004). This could indicate that
dithiothreitol functions as an electron donor for
alanine formation. It is suggest that the formation of
elemental sulfur is a side reaction when no other
electron donor is available; so this reaction should
be analyzed in more detail. However, the formation
of alanine is a good indication for NifS related
activity. A gene for NifS-type L-cysteine Figure 4:
desulfhydrases of Arabidopsis has been found with a Cysteine catabolism by a stereospecific L-cysteine
signature for chloroplasts. The recombinant protein desulfhydrase (NifS). Such genes have been found for
was shown to specifically form alanine as discussed mitochondria and chloroplasts of Arabidopsis and are
correlated to the NifS type proteins. The catalyze the
above (Leon et al., 2002). Therefore this enzyme formation of L-alanine and elemental sulfur.
could, after reduction of elemental sulfur to sulfide,
attribute to the formation of free sulfide.
Landbauforschung Völkenrode, Special Issue 283, 2005 125

Figure 5:
The cystine lyase reaction forming L-cysteine-persulfide.

cysteine desulfhydrase has been identified in our

Sulfide formation catalyzed by D-cysteine laboratory recently (At1g48420; Riemenschneider et
desulfhydrase al., 2004). We have so far no function assigned for
D-cysteine nor do we know how it is synthesized.
Besides the L-cysteine desulfhydrase plant do One might speculate that it could be formed with a
contain a cysteine desulfhydrase which specifically transaminase from ß-mercaptopyruvic acid (see later
uses D-cysteine as substrate which is abbreviated discussion) or by a racemase transforming L-
here as D-cysteine desulfhydrase (lyase) as shown in cysteine to D-cysteine. Even a synthesis via O-
Figure 7 (Schmidt, 1982, 1987; Schmidt and Erdle, acetyl-D-serine and sulfide according to the cysteine
1983). This enzyme activity is present in each plant synthase cannot be ruled out so far, but we hope to

Figure 6:
Cystine metabolism involving cystine lyase and a sulfurtransferase.

analyzed so far with prominent activities within clarify these possibilities having the recombinant
plant species used for agriculture such as Zea mays, enzyme available.
Triticum aestivum, Avena sativum, Secale cereale,
Oryza sativa, Solanum tuberosum, Beta vulgaris,
Brassica napus, Arabidopsis and in suspension Sulfide formation catalyzed by
cultures of Nicotiana tabacum (Schmidt, 1982; ß-mercaptopyruvate metabolism
Schmidt and Erdle, 1983; Rennenberg, 1983;
Rennenberg et al., 1987) The activity of the D- An important metabolic intermediate for sulfur
cysteine enzyme is different in Brassica napus metabolism is ß-mercaptopyruvic acid (ß-MEP); it
strains showing clearly that it genetically coded is an excellent donor for sulfurtransferases
(Burandt et al., 2001). This enzyme catalyzes the (Papenbrock and Schmidt, 2000). Although the
formatin of H2S, ammonia and pyruvate as shown formation of ß-mercaptopyruvic acid has not been
for Escherichia coli (Nagasawa et al, 1985, 1988). shown in plants so far, we can speculate its
The gene for the D-cysteine desulfhydrolase has formation either by a cysteine transaminase, a
been identified in E. coli as yedO (Soutourina et al., cysteine aminooxidase or a cysteine dehydrogenase
2001). The corresponding gene for a plant D- according to Figure 8. Once formed, ß-MEP can be
126 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

used as sulfur donor for ß-MEP sulfurtransferases. yielding H2CO3 and sulfide as discussed in the
In the genome of Arabidopsis a gene family for beginning of this chapter. This might be a salvage
sulfurtransferases has been characterized with 18 pathway to capture H2S losses caused by COS
members (Bauer and Papenbrock, 2002) These formation.
enzymes contain a cysteine in its active site wich
accepts the sulfide from the donor forming a
persulfide. This persulfide than can be used for
different biosynthetic pathways including free
sulfide formation according to Figure 9 (Papenbrock
and Schmidt, 2000) The function of only one
sulfurtransferase has been identified so far for the
molybdate cofactor biosynthesis (Matthies et al.,
2004). So we can speculate, that other functions of
sulfurtransferases (rhodaneses) for sulfur
metabolism should be discovered in the future.
Mercaptopyruvate formation by a transaminase

Figure 7:
The D-cysteine desulfhydrase (lyase) reaction. Mercaptopyruvate formation by an L-amino acid
oxidase

Sulfide formation from COS catalyzed by Figure 8:

carbonic anhydrase Possibilities of cysteine catabolism by mercaptopyruvic
acid.
COS is a substance, which is emitted from plants
in low concentrations. COS will react with a
carbonic anhydrase yielding H2CO3 and sulfide Some remarks on sulfide toxicity
(Protoshill-Krebs and Kesselmeier, 1992). This
reaction favors sulfide formation, the backward Sulfide is toxic to microorganisms and it was
reaction has not been demonstrated so far. One shown that H2S retards growth of E. coli if
might speculate about this pathway in the following concentrations exceed µM concentrations (Sohn
context: H2S has been shown to react with ribulose 2000). H2S has a binding affinity to chelated iron in
bisphosphate carboxylase forming thioglyceric acid the same range as cyanide or oxygen. It will bind to
3-phosphate besides the normal PGA (Brändle and hemes of the mitochondria, thus blocking respiration
Martin, 1971; Lorimer, 1989). Thus thioglyceric and ATP-formation. The observed growth inhibition
acid is a normal intermediate within the chloroplast in E. coli is obviously due to H2S binding to the
if H2S is formed. So it might be speculated, that the cytochrome a3 for oxygen uptake partly inhibiting
corresponding thiopyruvic acid is formed as well. It ATP-formation. Due to shortage of ATP there is less
has been shown further, that the Rubisco enzyme sulfate reduction and H2S is removed by
forms directly pyruvate without a PGS intermediate assimilation and the growth inhibition is thus
in the range of 1 % of the CO2 fixation rate releaved leading to a growth cycling in E. coli. The
(Andrews and Kane, 1991). By decarboxylation of KM data for H2S inhibition are in the in the µM
PEP acetyl-CoA is formed and if the thiopyruvic range and this similar to cyanide inhibition.
acid is used, than COS should be formed. This Therefore inhibition of oxygen uptake can be
activity has been shown to be localized within the expected for plant mitochondria. We have analyzed
chloroplast as well (Kubis et al., 2004). COS formed sulfide inhibition of oxygen uptake with isolated
in that way would leave the chloroplast; than it will mitochondria from potatoes and pea leaves. These
be picked up by the CO2 hydratase in the cytoplasm
Landbauforschung Völkenrode, Special Issue 283, 2005 127

Figure 9:
Possibilities of cysteine catabolism by sulfurtransferases.

Figure 10:
A generalized scheme for cysteine-dependent formation of sulfide.

data are summarized in Table 2 (Huchzermeyer and uptake by mitochondria and thus ATP-formation in
Schmidt, unpublished results). As can be seen the Ki plants as well. It should be expected that H2S will
data for oxygen uptake inhibition are in the range of bind to other heme-type iron as well including the
10 µM, showing that H2S is inhibiting oxygen siroheme of the sulfite reductase and the nitrate
128 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

reductase, since these can be inhibited by cyanide as Burandt P (2002) Isolierung und Charakterisierung von
well. This would suggest that H2S takes an indirect Cystein-abbauenden und H2S-freisetzenden Enzymen
control over nitrate reduction as well, if the aus höheren Pflanzen. Dissertation, Universität
siroheme of the nitrite reductase is blocked by H2S. Hannover 2002
Burandt P, Papenbrock J, Schmidt A, Bloem E, Haneklaus
S, Schnug E (2001):Genotypical differences in total
sulfur contents and cysteine desulfhydrase activities in
Table 2: Brassica napus L. Phyton 41:75-86
Toxic effects of sulfide on respiration. Chu L, Ebersole J, Kurzban GP, Holt SC (1999)
Potato mitochondria: Ki for H2S Cystalysin a 46-kDa L-cysteine desulfhydrase from
Treponema denticola: biochemical and biophysical
without addition 40 µM characterization. Clin Infect Dis 28:442-450
1 mM GSH 11 µM Clausen T, Kaiser JT, Steegborn C, Huber R, Kessler D
100 µM SHAM 14 µM (2000) Crystal structure of the cystine C-S lyase from
Pea leaf mitochondria: Ki for H2S Synechocystis: Stabilization of cysteine persulfide for
(+30 µM DCMU) FeS cluster biosynthesis. Proc Natl Acad Sci USA
without addition 35 µM 97:3856-3861
1 mM GSH 9 µM Jones PR, Manabe T, Awazuhara M, Saito K (2003) A
100 µM SHAM 19 µM new member of plant CS-lyases. A cystine lyase from
Arabidopsis thaliana. J Biol Chem 278:10291-10296
Kessler D (2004) Slr0077 of Synechocystis has cysteine
desulfurase as well as cystine lyase activity. Biochem
Biophys Res Commun 320:571-577
An overview of reactions involved Krämer E, Schmidt A (1984a) Oxidation of cysteine to
cystine by membrane fractions of Chlorella fusca
The possible reactions leading to free sulfide are Planta 160:235-242
summarize in Figure 10, showing the close Krämer E, Schmidt A (1984b) Membrane-bound cysteine
correlation of cysteine metabolism and sulfide oxidases in spinach Chlorella Synechococcus and
formation in plants. Although we can not give a Rhodopseudomonas In: Sybesma RT (ed) Advances in
Photosynthesis Research III. W Junk Publishers, The
precise mechanism of enhanced plant tolerance to
Hague, pp 6525-6528
microbial damage by efficient sulfur nutrition, the Kubis SE, Pike MJ, Everett CJ, Hill LM, Rawsthorne S
data accumulated so far clearly support the concept (2004) The import of phosphoenolpyruvate by plastids
of sulfate induced resistance (SIR) in plants (Bloem from developing embryos of oilseed rape Brassica
et al., 2004). Therefore the possible reactions of napus (L) and its potential as a substrate for fatty acid
cysteine metabolism and H2S formation have to be synthesis. J Exp Bot 55:1455-1462
analyzed in more detail for a better understanding of Lancaster JE, Shaw ML, Joyce MD, McCallum JA,
SIR induced plant health. McManus MT (2000) A novel alliinase from onion
roots Biochemical characterization and cDNA cloning.
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130 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants
Landbauforschung Völkenrode, Special Issue 283, 2005 131

The role of sulfur in sustainable agriculture

Ewald Schnug1 and Silvia Haneklaus1

Abstract 1 2 ments, and distractions, but these offer us little satis-

faction. Instead we suffer ever-increasing alienation
The term 'sustainability' has been used so many from our families, our communities, and the natural
times on facets of agriculture that it is meanwhile world.
difficult to understand its true origin. “Sustainable In a way agriculture may be a special segment
development” has been defined in 1987 by The within human societies as its sustainability is intrin-
Brundtland Commission as: “development that sic under any circumstances, simply because no
meets the needs of the present without compromis- food, no man! Fertilizers provide food for plants but
ing the ability of future generations to meet their still fertilizers are often named together with pesti-
own needs”. For agriculture this implies primarily cides as 'agrochemicals' which is to a great extent
the sustainable use of natural resources such as wa- misleading: fertilizers provide essential minerals
ter, soil and atmosphere. This contribution high- without no plants can grow. In contrast, pesticides
lights the role of a single plant nutrient in achieving are as essential for plants as aspirin to man. Several
sustainability in agriculture. A sufficient sulfur sup- authors have identified pesticides as key issues
ply secures level and quality of yields, improves counteracting sustainability, for instance Friedrich
plant health through stimulation of natural resistance Engels, who wrote already in 1876: "Schmeicheln
processes and alleviates the ecologically hazardous wir uns nicht so sehr mit unseren menschlichen
side effects of nitrogen fertilization on surface and Siegen über die Natur. Für jeden solchen Sieg rächt
groundwater bodies as well as on the quality of the sie sich an uns“, followed years later by the famous
atmosphere. Beside this the sulfur supply of agricul- Rachel Carson who wrote in her famous book “Si-
tural crops affects also neighboring compartments of lent Spring“ (1954): “The chemical war can not be
agro-ecosystems by providing indirectly food for won, and a life is caught in its violent crossfire.“
insects. But also fertilization has its black spots in view
for sustainability like for instance the loss of nitro-
Key words: atmosphere, fertilization, food safety, gen and phosphorous from agro-ecosystems, the
food security, nitrogen losses, ozone, sulfur, sustain- pollution of atmosphere and water-bodies with ni-
ability trogen compounds, the waste of non-renewable P-
resources through inefficient fertilization strategies,
the charging of soils with heavy metals and radioac-
Introduction tivity through fertilization of waste materials and P-
fertilizers) and the charging of soils with hazardous
Few words have been so often used and few organic compounds, pharmaceuticals and infectious
words have been so often abused as the word 'sus- materials.
tainability'. In many cases claiming for 'sustainabil- This contribution highlights the role of a single
ity' is simply claiming for 'profitability'. In a world plant nutrient in achieving sustainability in agricul-
where making profit is the key indicator for being ture: sulfur. A sufficient sulfur supply secures level
successful, the true meaning of sustainable devel- and quality of yields, improves plant health through
opment is often forgotten. 'Sustainable development' stimulation of natural resistance processes and alle-
has been defined in 1987 by The Brundtland Com- viates the ecologically hazardous side effects of ni-
mission as: “development that meets the needs of trogen fertilization on surface and ground water
the present without compromising the ability of fu- bodies as well as on the quality of the atmosphere.
ture generations to meet their own needs”. Fact is Beside this the sulfur supply of agricultural crops
that our society is far away from being on the track affects also neighboring compartments of agro-
towards sustainable development like Wendel Berry ecosystems indirectly by providing food for insects.
stated in 2002: “We currently live in the economy
and culture of the “one-night stand“. Industrialism
has provided us innumerable commodities, amuse- Sulfur fertilization and agricultural economy

One often used criterion for justifying fertilization

1 as a component of sustainable development in agri-
Institute of Plant Nutrition and Soil Science, Federal
Agricultural Research Center (FAL), Bundesallee 50, culture is the allegation that fertilization alleviates
38116 Braunschweig, Germany world hunger. Kimbrell (2002) reveals this as a
132 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

great mistake, because “world hunger is not created losses from agriculture and the function of oilseed
by lack of food but by poverty and landlessness, rape as a forage crop for honey bees.
which deny people access to food. Industrial agricul-
ture actually increases hunger by raising the cost of Surface ozone concentrations
farming, by forcing tens of millions of farmers off Over the last decade surface ozone concentrations in
the land, and by growing primarily high-profit ex- rural areas increased on average by 1.8 µg m-3 yr-1
port and luxury crops". (Schnug, 1997). At the same time S concentrations
The general contribution of fertilization to sus- declined at a constant rate of 0.45 mg yr-1 (Schnug,
tainability is addressed directly to the success of the 1997). Assuming that: a) H2S emissions from plants
farm enterprises and simply aims at improving the decline together with the sulfur supply (Collins,
profit of production. 1997; Rennenberg, 1984) linearly on a rate of 0.57
In this context sulfur plays an extraordinary role nmol m-2 h-1 (calculated from data given by Schroe-
in the history of fertilization: free and in surplus, der (1993)); b) crops have an average leaf area index
amounts delivered by atmospheric pollution until of 1; c) crops assimilate and reduce sulfur on aver-
the beginning of the 1980s sulfur deficiency is today age of 100 days a year and 10 h a day; and d) H2S
the most common nutrient disorder in Northern degrades O3 in a 1:1 ratio; then up to 75% of the
European crop plants. The reason are the stringent observed increase in surface ozone could be attrib-
clean air acts introduced at the end of the last cen- uted to the decrease in the total amount of S turn-
tury, which caused atmospheric sulfur depositions to over in the 'green part' of the ecosystem. The figures
drop from over 100 kg ha-1 S down to 10 kg·ha-1 S given here are only an estimate and may change
within only 20 years. The positive effect of sulfur depending on the factors considered, but they still
fertilization to a sulfur-starving crop can easily be outline the important function of sulfur assimilation
demonstrated in field experiments. Difficulties arise and reduction in the ecosystem. Despite the impor-
when trying to upscale results from field experi- tance of this for air quality, the higher sulfur inputs
ments to assess the impact of sulfur deficiency on in the past century enabled plants to adapt to in-
crop production in an entire country. Table 1 shows creasing environmental stress caused by increasing
an assessment of potential yield losses and their surface ozone concentrations and, vice versa, the
monetary value for two federal counties of Ger- decline of the sulfur supply within only one decade
many, where extended soil survey and hydro- (Schnug, 1997; Schnug and Haneklaus, 1994) may
geological information allows the classification of have serious consequences for the stability of recent
the cropping area according to the potential risk for ecosystems. For example, sulfur deficiency is
S deficiency. Applying the same calculation model thought to be one of the reasons why 50% of all
to the 7.600 km2 of grassland in this area (assuming forests are damaged, although sulfur emissions have
a loss of 10% under moderate and 20% under severe been cut down drastically over the past 10 years
S deficiency and an average N content of 2% in the (Umweltbundesamt, 1993). The effect is thought to
dry matter the potential N losses for this type of be due to the combination of reduced resistance (due
farming amounts to an additional 19.8 million kg N. to sulfur deficiency) and, at the same time, increased
Those two counties comprise roughly 17% of Ger- environmental stress (Will et al., 1997; Zhang and
manys cereal, and 27% and 12% of the entire oil- Rennenberg 1997).
seed rape and grassland area. Extrapolating the re-
sults from table 1 according to these figures, Ger- Nitrogen losses to the environment
man agriculture faces a potential monetary loss (po-
tential means a scenario without any sulfur fertiliza- Via the metabolism of amino acids, the utilization of
tion) of about 1.200.000.000 € per annum alone nitrogen and sulfur depend on each other, which
from yield losses in oilseed rape and cereal crop- means that for the efficient use of high nitrogen lev-
ping. els in agriculture, a sufficient sulfur supply is re-
quired. Therefore, increased ecological problems
from agricultural crop production are expected be-
Contribution of sulfur to sustainability in agri- cause the utilization of fertilizer nitrogen is dimin-
culture ished in sulfur deficient crops (Schnug et al., 1993).
This may result in increased nitrogen losses to the
Crops not only provide food and profit for man, environment, particularly by nitrate leaching into the
but also have also ecological functionalities. In the hydrosphere, or gaseous losses to the atmosphere.
context of this paper ecological functionality is de- On average, each kg of sulfur unavailable to satisfy
fined as the beneficial contribution of crops to eco- the plant's demand causes 15 kg of nitrogen with the
systems. As far as S is concerned, three examples potential to be lost to the environment. From the
shall be presented here: the contribution of crops to basic data presented in table 1 it was calculated that
the degradation of surface ozone, non-point nitrogen the potential annual loss of nitrogen due to insuffi-
Landbauforschung Völkenrode, Special Issue 283, 2005 133

Table 1:
Assessing the impact of sulfur deficiency on cop production in Brandenburg and Mecklenburg-Western-Pomerania (Germany).
Brandenburg Mecklenburg- Ȉ Yield loss Monetary Potential
Western (103 t) 1 loss N loss
Pomerania (106 €)2 (106 kg)3
Cereals
Total area (km2) 5650 5890 11540
Potential yield (t ha-1) 7
Modelled yield (103 t on 30% of area)
no S deficiency 1316 1568 2884 0
moderate S deficiency 1184 1411 2595 -289 -67 -11.5
severe S deficiency 1052 1254 2307 -577 -34 -5.8
Oilseed rape
Total area (km2) 1110 2330 3440
Potential yield (t ha-1) 3 4
Modelled yield (103 t on 30% of area)
no S deficiency 111 312 423 0 0
moderate S deficiency 89 250 339 -84 -20 -3
severe S deficiency 67 187 254 -169 -40 -6
1
calculated yield losses for cereals/oilseed rape: moderate S deficiency 10/20 and severe S deficiency 20/40 % of potential
yield; 2prices (€ t-1): 116 for cereals and 235 for oilseed rape; 3calculated for yield losses with 2% N in seeds

cient sulfur supply amounts to at least 300 million the nectar (Throp et al., 1975; Willmer et al., 1994),
kg of nitrogen, which is equal 10% of the total ni- or by olfactory sensation (Heinrich 1979, Galen and
trogen consumption of German agriculture. Kevan, 1983); indirectly by an indicator of the re-
ward for foraging such as color (Gori, 1983; Weis
Forage crops for honeybees ,1991), flower size (Galen and Neport, 1987; Eck-
Although oilseed rape is self-pollinating (Saure hart, 1991), or the particular floral structures (Bell et
2002), the cross-pollination rate, predominately by al., 1984; Gonzalez et al., 1995).
honeybees, was estimated to be about 20% (Dan et Volatiles released during flowering of plants fa-
al., 1980). According to Olsson (1960) the cross- cilitate flower recognition by the honeybee and thus
pollination rate may vary in relation to genotype and increase their foraging efficiency. The chemical
climatic conditions between 5 % and 95 %. By analysis of volatiles from various plant species re-
comparison, on fields where composite hybrid oil- vealed a multiplex composition of floral scents with
seed rape varieties are grown or male-sterile lines more than 700 different compounds that were found
for breeding of restored hybrid cultivars, these in 60 families of plants (Knudsen et al., 1993). The
plants depend on pollination by vectors (Steffan- mechanisms by which honeybees process this com-
Dewenter, 2003). First observations in field-grown plex chemical information and adapt their behavior
composite hybrids show increased problems with accordingly are as yet unknown (Wadhams, 1994).
pollination of hybrids in low sulfur environments. A total of 34 different compounds were found in
This problem can be attributed to the processes dis- volatiles of oilseed rape (Tollsten and Bergström,
cussed next. Oilseed rape provides an important 1988, Robertsonet al., 1993; McEwan and Smith,
source of nectar and pollen for honeybees, which are 1998). The main volatiles from oilseed rape flowers
attracted by the bright yellow color of the crop in were 3-hydroxy-2-butanone > 2,3-butanedione >
bloom (Pierre et al., 1999). Oilseed rape is one of dimethyl disulfide >> formaldehyde > 3-methyl-2-
the most important European melliferous crops for butanone > dimethyl trisulfide (Robertson et al.,
beekeepers as it is an important foraging plant in 1993). Omura et al. (1999) determined nitriles and
early summer. The main pollinators in oilseed rape isothiocyanates in large quantities in the floral vola-
are insects of the family Apidea (e.g. honey bees, tiles of Brassica rapa. Honeybees use volatiles for
wild bees and bumble bees) (Corbet, 1992; Wil- discrimination whereby a conditioning threshold
liams, 1996) and the significance of honeybees as was determined for individual components (Pham-
pollen vectors for seed set and yield has been de- Delégue et al., 1993). Previous studies have shown
scribed in the literature (Steffan-Dewenter, 2003). that the S supply increases the glucosinolate in
Honeybees are attracted by scent, color and form vegetative plant tissue, seeds and petals of oilseed
of the honey-bearing plants, but it is the scent, rape (Schnug, 1988, 1993). Additionally, 2-phenyl-
which has the fastest and strongest impact (Menzel ethyl isothiocyanate yielded limited conditioned
et al., 1993). Honey bees might assess the amount responses in honeybees, but was an active compo-
and concentration of nectar in each flower by em- nent after being learned in a complex mixture of
ploying different senses: directly by visual access to volatiles (Laloi et al., 2000). Thus a relationship
134 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

between the S-containing compound, intensity of the tion. Proc. EC workshop, Brussels, 2-3 March 1992, pp
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seems possible. Dan K, Downey RK, Klassen AJ, Stringam GR (1980)
Crops visited by bees show earlier petal fall, Rapeseed and Mustard. In: Fehr WR, Hadley HH (eds)
Hybridization of Crop Plants. American Society of
probably because they set flowers earlier, resulting Agronomy-Crop Science Scociety of America, Madi-
in a more uniform pod ripening and ease of harvest. son/ Wisconsin, pp 495-509
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and their hovering is the one of the most energy Federal Research Station, CH-8820 Waedenswil
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and Baker, 1983). During senescence of rapeseed Galen C, Kevan PG (1983) Bumblebee foraging and floral
flowers, which begins immediately after pollination, scent dimorphism: Bomus kirbyellus Curtis
(Hymenoptera: Apidae) and Poleminium viscosum
the yellow petal color vanishes and the petals shrink Nutt. (Polemoniaceae). Canadian Journal of Zoology,
quickly before falling to the ground. A pollinated 61: 1207 – 1213
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unpollinated S deficient one and thus less attractive selection on flower size in the sky pilot, Polemonium
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observed than in S sufficient crops, which are bright mellifera): sex phase of flowers and preferences among
yellow. nectar and pollen foragers. Oecologia 101:258-264
Gori DF (1983) Post-pollination phenomenea and
Smaller, whiter flowers may be less attractive to adaptive floral changes. In: Jones DE and Little RJ
bees only after previous experience and not because (eds) Handbook of Pollination Biology New York: Van
of a specific signaling. Even if sufficiently with S Nostrand Reinhold, pp 31-49
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effects when the bees can not distinguish pollinated scents - a checklist of volatile compounds isolated by
from non-pollinated flowers as reliable as they can headspace techniques. Bot. J. Linnean Soc 119:45-57
in rapeseed that is sufficiently supplied with S. Laloi D, Bailez O, Blight MM, Roger B, Pham-Delègue
Who could have imagined at the beginning of the M-H, Wadhams LJ (2000) Recognition of complex
1980s that the reduction of SO2 emissions from odors by restrained and free-flying honeybees, Apis
burning fossil fuels (Sendner, 1985) would have an mellifera. J. Chem. Ecol. 26:2307-2319
McEwan M, Smith WHM (1998) Identification of volatile
impact on honey production twenty years later?
organic compounds emitted in the field by oilseed rape
(Brassica napus ssp. oleifera) over the growing season.
Clinical Exp. Allergy 28:332-338
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Landbauforschung Völkenrode, Special Issue 283, 2005 137

Metabolism and catabolism of glucosinolates

Dirk Selmar1

Abstract12 (1999). This present paper, which is based on my

previous review (Selmar, 1999) is designed to pro-
Glucosinolates are sulfur containing natural prod- vide a brief overview of the entire biology and bio-
ucts with numerous metabolic specialties. In this chemistry of these natural products.
chapter, a brief overview on various aspects on its
metabolism and catabolism is presented. The bio-
synthesis of glucosinolates is similar to that of N O SO3
cyanogenic glucosides. It involves the conversion of R C
amino acids via aldoximes to corresponding thiohy- S glucose
droximates and the attachment of glucose. Glucosi-
nolates are accumulated in the central vacuole and Figure1:
are stored without any decay. When the cells are General structure of glucosinolates
desintegrated, the glucosinolates are hydrolyzed by
myrosinases. The resulting decomposition products Glucosinolates resemble cyanogenic compounds in
comprise a complex mixture of thiocyanates, many aspects, however, this group of compounds
isothiocyanates and nitriles, referred to as mustard contains sulfur atoms in the molecule. They are
oils. Due to their toxicity, these compounds exhibit characterized by the liberation of thiocyanates (mus-
an ecological significance as protective agents tard oils) or related nitrile compounds after being
against herbivores and microorganisms. decomposed (for review see Bones and Rossiter,
1996). Decomposition takes place when tissues of
Keywords: glucosinolates, mustard oil, myrosinase, glucosinolate-containing plants are damaged and
secondary sulfur compounds cells are destroyed. Similarly to cyanogenesis, this
post mortem process is initiated by the loss of cell
integrity, leading to contact of glucosinolates with
Introduction their hydrolytic enzymes. In contrast to widespread
cyanogenic glucosides, the occurrence of glucosi-
Glucosinolates are sulfur containing natural prod- nolates is restricted. Most of these compounds are
ucts which have achieved their scientific popularity found in the Capparales, however sporadic occur-
because their biology and metabolism represent in- rences also have been recorded for members of other
teresting systems to study various aspects of bio- families, e.g. Caricaceae, Euphorbiaceae, Sterculi-
chemistry and general biology of secondary plant aceae (Rodman et al., 1996). Glucosinolates and
products (Figure 1). The knowledge of liberation of their degradation products are important factors in
toxic reaction products from nontoxic precursors - plant defence against herbivores, as well as against
known as the mustard oil bomb - has contributed pathogens (for review see Louda and Mole, 1991).
significantly to an understanding of major principles In addition, they have significant allelopathic poten-
in compartmentation as well as so important aspects tial and are thought to be effective in defense against
of ecological biochemistry. Several special reviews ephemeral, unapparent plants or plant parts (Feeny,
focus on different aspects of glucosinolate research, 1976).
such as taxonomy (Rodman, et al., 1996), chemistry The presence of glucosinolates in the agricultur-
and ecology (Louda and Mole, 1991), biosynthesis ally important crop plant, rape (Brassica napus), is
(Halkier, 1999), genetics (Mithen, 2001), degrada- of great economic importance, because glucosi-
tion (Bones and Rossiter, 1996), methodology nolates reduce the feeding quality of rapeseed meal
(Poulton and M‡ller, 1993), and anti-carcinogenic drastically. However, with regard to our health, glu-
potential (Jongen, 1996; Verhoeven et al., 1997). cosinolates also reveal positive effects based on
Some more general reviews covering the entire field their anticarcinogenic potential. As a consequence
of glucosinolate research, are presented by Bennet et of the wide range of interest, glucosinolates are
al. (1998), Selmar (1999) and Wallsgrove et al. presently being studied in many different fields of
biology, biochemistry, agriculture, and medicine.

1
Technical University Braunschweig, Institute for Plant
Biology, Section for Applied Plant Biology, Mendels-
sohnstrasse 4, D-38106 Braunschweig, Germany
138 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

Chemical structures

Glucosinolates consist of a ß-thioglucose moiety,

a sulfonated oxime moiety, and a variable side
chain. The parent compound "glucosinolate" accord-
ing to the semisystematic nomenclature introduced
by Ettlinger and Dateo (1961), is presented in For-
mula 1, where R = H. The various glucosinolates are
derived by naming the side chain R as a prefix.
Some examples are given in Figure 2.
Up to now, about 100 different structures of glu-
cosinolates are known. Presumably, all are derived
biosynthetically from amino acids (Kutachek et al.,
1962; Underhill and Chisholm 1964). In analogy to
cyanogenic glucoside biosynthesis - the carboxyl
group is lost and the D-carbon is transformed into
the central carbon of the glucosinolates (see chapter
biosynthesis). The side chain R, therefore is identi-
cal to the substituent of the D-carbon of the amino
acid. Only seven glucosinolates correspond directly
to protein amino acids. In addition to the five amino
acids that also are utilized for cyanogen biosynthesis
(valine, leucine, isoleucine, phenylalanine and tyro-
sine), alanine and tryptophan also serve as precur-
sors for glucosinolates. The large variety of addi-
tional glucosinolates is either a consequence of
modification of the side chains, apparently taking
place at the glucosinolate level, or has its origin in
non-protein amino acids that are produced from pro-
tein amino acids by chain-lengthening processes. As
Figure 2:
an example 2-phenylethylglucosinolate is synthe- Glucosinolates and related isothiocyanates. Structures of
sized from homophenylalanine, which, in turn, is some common glucosinolates corresponding isothiocy-
derived from phenylalanine by chain elongation anates.
(Underhill et al., 1962). Glucosinolates synthesized
from methionine by side chain elongation, may have
up to 11 methylene-groups introduced (Kjær and In contrast to cyanogenic glucosides, variations of
Schuster, 1972a, b). In addition, oxidation of the the sugar moiety are not common in glucosinolates.
methionine sulfur to a sulfinyl or a sulfonyl group All known glucosinolates contain glucose bound as
(Dalgaard et al., 1977), or the loss of the methylthio a thioglucose derivative. The only variations known
group accompanied by the introduction of a terminal to occur within the sugar moiety are esterifications
double bond can lead to further modifications. with several organic acids, e.g., sinapinic acid (Lin-
These modifications at the amino acid level alone scheid et al., 1980; SØrensen, 1990), and in very few
result in four series of methionine-derived glucosi- cases, additional glycosylation is observed. In Hes-
nolates (Figure 2). Additionally, glucosinolate side peris matronalis, various apiosyl derivates of hy-
chains may be altered by hydroxylation, desatura- droxybenzyl- and dihydroxybenzylglucosinolates
tion, or methoxylation. Further diversifications are have been detected. Interestingly, these compounds
achieved by esterification or acylation of the hy- with a substituted thioglucose moiety are not hydro-
droxyl groups of the side chain. This can be demon- lyzed by myrosinases, suggesting a possible signifi-
strated by the pattern of glucosinolates present in cance of these compounds in being protected against
Arabidopsis thaliana: 23 of the identified glucosi- hydrolysis (S‡rensen, 1990). Thus, in analogy to the
nolates correspond to various benzoyl esters of the diglucosidic cyanogens, these compounds might
hydroxyl groups of the side chain (Hogge et al., represent metabolites that can occur within the
1988). In the most comprehensive list of structures, apoplastic space without being hydrolyzed, e.g. in
Ettlinger and Kjær (1968) presented 74 different the course of translocation processes.
glucosinolates.
Landbauforschung Völkenrode, Special Issue 283, 2005 139

Biosynthesis an amino acid that, in comparison to the original

compound, is elongated by a methylene group. The
The biosynthesis of glucosinolates includes three biochemical evidences for this scheme are based on
independent stages. First, the chain elongation of the analysis of 14C-labelled glucosinolates isolated
amino acids, secondly, conversion of the precursor from plants to which either 14C-labelled protein
amino acid into glucosinolates, and, finally, further amino acids, or >2-14C@ acetate, had been adminis-
modifications of the resulting glucosinolates. De- tered (Matsuo and Yamazaki, 1964; Chisholm and
tailed information on glucosinolate biosynthesis is Wetter, 1964) A corresponding mechanism for the
given in the excellent review of Halkier (1999). chain elongation for methione as precursors for the
methionine derived glucosinolates in Arabidopsis
Side chain elongation of precursor amino acids thaliana, was recently elucidated by Textor et al.,
Elongation of amino acid side chains prior to glu- 2004).
cosinolate biosynthesis has been studied in several
plants. The mechanisms involved are believed to be Biosynthesis of basic glucosinolates
similar to the formation of leucine from valine and In contrast to the biosynthesis of cyanogenic glu-
acetate (Figure 3). First, through transamination, the cosides, the intermediates involved in the conver-
amino acid is converted to the corresponding D-keto sion of the amino acids to glucosinolates are not yet
acid, followed by an incorporation of an acetyl resi- unequivocally identified. However, in vivo studies
due from acetyl-CoA. After isomerization, the com- with seedlings from various plants indicated that
pounds are oxidized. In the course of this NAD me- N-hydroxyamino acids, nitro compounds, oximes,
diated oxidation, the intermediate is decarboxylated. thiohydroximates, and desulfoglucosinolates are
The D-keto acid produced is transaminated to yield putative precursors of glucosinolates (for review see

Figure 3:
Side chain elongation of amino acids. In analogy to the conversion of valine to leucine, the methene group is introduced to
various other amino acids, which subsequently serve as precursors of glucosinolates.
140 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

Figure 4:
Biosynthesis of glucosinolates. Postulated scheme for the glucosinolate biosynthesis. Detailed information on is given by Halk-
ier (1999).

Underhill et al., 1973; Larsen, 1981; Halkier, 1999). Conversion of amino acids to oximes
Based on various experimental data, it is evident Independent studies of various glucosinolate-
that aldoximes are the final products of the first set containing plants indicate that, depending on the
of reactions leading to glucosinolates (Bennett et al., species, different enzyme systems are involved in
1993; Du et al., 1995). Nevertheless, the subsequent conversion of the amino acids into aldoximes.
steps in the biosynthetic pathway have not been elu- Analysis of microsomes isolated from young
cidated: neither the intermediates between aldoxi- leaves of Brassica napus established that chain
mes and thiohydroximates have been identified nor elongated amino acids are converted into the related
is any biochemical evidence available for potential aldoximes (Dawson et al., 1993; Bennett et al.,
enzymes involved in this transformation (Halkier, 1993). As this reaction is not inhibited either by
1999). Moreover, the sulfur donor for the thiol sul- carbon monoxide, or by other cytochrome inhibi-
fur is not known, although thioglucose can be ex- tors, nor by antisera toward NADPH-cytochrome
cluded (Wetter and Chisholm, 1968). In vivo studies P450-reductase, involvement of a cytochrome P450
reveal that several inorganic and organic sulfur could be excluded. However, inhibitors of flavin
compounds are incorporated into thiohydroximates. dependent enzymes (e.g., copper salts, diphenyl
Since cysteine was incorporated most efficiently in iodonium sulfate) were effective in inhibiting al-
these experiments, this amino acid is thought to be doxime synthesis (Bennett et al., 1993; Bennett et
the sulfur donor (Wetter and Chisholm, 1968). Fol- al., 1995a). Based on these results, it is concluded
lowing the introduction of sulfur, the thiohydroxi- that, at least in the biosynthesis of chain elongated
mates produced are glucosylated by a soluble UDPG glucosinolates in Brassica napus, flavin-containing
dependent transferase. In the final step of glucosi- mono-oxygenases are involved. Further characteri-
nolate biosynthesis, the resulting thioglucoside is zation by the means of various substrates indicated
sulfurylated by PAPS. The putative biosynthetic that chain elongated methionine homologues inhibit
pathway of glucosinolates is outlined in Figure 4. competetively oxidation of homophenylalanine. In
contrast, the oxidation of chain elongated methion-
Landbauforschung Völkenrode, Special Issue 283, 2005 141

ine homologues was not influenced by the corre- origin of glucosinolate biosynthesis and the manner
sponding aromatic and aliphatic amino acids. Thus, by which it was optimized (Bak et al., 1998).
in Brassica napus, at least two flavin containing
mono-oxygenases are involved in the biosynthesis Glucosylation and sulfurylation of thiohydroximates
of glucosinolates: one is responsible for the oxida- The final steps in glucosinolate biosynthesis are
tion of elongated aromatic and aliphatic amino ac- represented by the glucosylation ot the sulfhydryl
ids, and the other is specific for oxidation of chain group of the thiohydroximates and subsequent at-
elongated methionine derivatives. tachment of sulfate to the aldoxime function. Gluco-
In contrast, the corresponding enzyme systems sylation is performed by a soluble UDP-glucose:
isolated from young seedlings of Sinapis alba and thiohydroximate glucosyltransferase. Corresponding
Tropaeolum majus turned out to be cytochrome enzymes from Brassica juncea (Jain et al., 1990a),
P450 monooxygenases (Du et al., 1995; Du and Brassica napus (Reed et al., 1993), and Arabidopsis
Halkier, 1996). These enzymes have now been puri- thaliana (Guo and Poulton, 1994) have been puri-
fied and cloned. Also in Arabidopsis thaliana the fied and characterized. While these enzymes seem to
phenylacetaldoxime, which represents a precursor of be specific for thiohydroximates, they do not reveal
the benzylglucosinolate, is produced by the action of a marked substrate specificity with regard to differ-
a cytochrome P450 (Wittstock and Halkier, 2000). ences in the side chain.
A detailed presentation of these data and corre- Little is known about sulfation of desulfoglucosi-
sponding conclusions on the evolutionary relations nolates. The sulfate is introduced by PAPS
are given by Bak et al. (1998). Based on great ho- (3´-phosphoadenosine-5´-phosphosulfate). Only two
mology to cytochrome P450tyr, involved in the bio- corresponding sulfotransferases have been detected
synthesis of cyanogenic glucosides, it can be as- and purified: first from cress seedlings, Lepidium
sumed that the reaction mechanisms of these two sativum (Glendening and Poulton, 1988), and, sec-
enzymes are very similar. As the aldoxime synthesis ondly, from Brassica juncea cell cultures (Jain et al.
involved in cyanogenic glucoside biosynthesis is 1990b). Both enzymes investigated have very simi-
perfomed via N,N-dihydroxyamino acids, aldoxime lar properties. They catalyzed the sulfation of sev-
synthesis leading to glucosinolates, which is cata- eral different desulfoglucosinolates. Despite their
lyzed by similar cytochrome monooxygenases from low substrate specificity for desulfoglucosinolates,
S. alba and T. majus, should also include N,N- they do not catalyze the transfer of sulfate to other
dihydroxyamino acids as intermediates (Halkier, potential substrates, e.g. flavonoids, and phenylacet-
1999). aldoximes.
In seedlings of Chinese cabbage (Brassica
campestris), conversion of tryptophan into indole Side chain modification of basic glucosinolates
acetaldoxime, representing the first step in the bio-
synthesis of indole glucosinolates is catalyzed by a In addition to the side chain modification of the
membrane bound peroxidase (Ludwig-Müller and precursor amino acid, also the side chain of the syn-
Hilgenberg, 1988). Because the corresponding en- thesized glucosinolates can be modified. These
zymatic activity was also detected in several species modifications consist of hydroxylations and trans-
that do not contain glucosinolates, it was concluded formations of methylthio groups into methylsulfinyl
that the enzyme involved in the biosynthesis of in- groups, into methylsulfonyl groups, and, by elimina-
dole acetic acid in Chinese cabbage, is also involved tion, into terminal double bonds. The enzymes in-
in indole acetaldoxime production (Ludwig-Müller volved in these modifications have not been identi-
et al., 1990). Various comparative studies demon- fied, however, based on comprehensive genetic
strated a good correlation between the content of studies it can be deduced that chain modifications of
indolyl glucosinolates and peroxidase activity on aliphatic glucosinolates depend on three loci (Parkin
one hand, and the concentration of chain elongated et al., 1994; Mithen et al., 1995; Giamoustaris and
glucosinolates and the activity of flavin-containing Mithen, 1996). In spite of the great variation in ali-
mono-oxygenase on the other. These correlations phatic side chain structures, the genetic results indi-
suggest that aldoxime production in biosynthesis of cate that the diversity is the result of genetic varia-
the two different groups of glucosinolates present in tions of these three major loci.
Brassica is catalyzed by distinct enzyme systems Biochemical studies indicate that the enzyme that
(Ludwig-Müller et al., 1990; Bennett et al., 1995b). is responsible for the hydroxylation of 3-butenyl-
It appears that enzymes catalyzing conversion of glucosinolate to yield 2-hydroxy-3-butenyl-
amino acids into aldoximes within the glucosinolate glucosinolate in Brassica napus corresponds to a
pathway have evolved at least three times in a non- cytochrome P450 mono-oxygenase (Rossiter et al.,
homologous manner. This opens many doors for 1990).
speculation and discussion about the evolutionary The introduction of a Brassica-dioxygenase gene,
whose protein seems to be responsible for side chain
142 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

Figure 5:
Mustard oil formation. After hydrolysis of glucosinolates, the unstable intermediates rearrange. In general, the main reaction
products are isothiocyanates, but also nitriles and thiocyanates are produced.

modification of glucosinolates, into Arabidopsis rearrangement to yield thiocyanates has neither been
thaliana resulted in significant changes of the glu- isolated nor properly characterized. The presence of
cosinolate profile in the transformed plants (Li and ß-hydroxylated side chains results in spontaneous
Quiros, 2003). cyclization of isothiocyanates to produce oxa-
zolidine-2-thiones. A terminal double bond in the
side chain may result in the formation of epithioni-
Mustard oil formation triles, although for this reaction an epithiospecifier
protein is necessary (Figure 5). The complex mix-
All plants containing glucosinolates also contain ture of isothiocyanates, thiocyanates, nitriles and
enzymes that are capable of decomposing these possibly some other reaction products is termed as
compounds. These ß-glucosidases are generally mustard oil.
called myrosinases. The enzymatically catalyzed When tissues of glucosinolate-containing plants
loss of glucose yield in thiohydroxamate- are injured and cells are disrupted, myrosinases and
O-sulfonates which isomerize to thiohydroxamate- glucosinolates come into contact and mustard oil
O-sulfonates. These compounds rearrange by formation is initiated. This process has been de-
Loessen-type reaction with a concerted loss of sul- scribed graphically as a mustard oil bomb (Matile,
fate to yield isothiocyanates. However, not only 1980). Consequently, under in vivo conditions, hy-
isothiocyanates, but also the corresponding nitriles drolytic enzymes and glucosinolates are efficiently
are formed in greater or lesser amounts along with partitioned. Glucosinolates are localized in vacuoles
the concomitant liberation of elemental sulfur (Fig- (Grob and Matile, 1979; Helmlinger et al., 1983). In
ure 5). Nitrile formation is favored by low pH val- contrast, the localization of the myrosinase remained
ues and is also promoted by ferrous ions (for review unclear. It has long been known that myrosinases
see Larsen, 1981). Under post mortem conditions are localized in special cells, so-called myrosin cells
after tissue disruption, isothiocyanates normally are (Guignard, 1980). Myrosin cells are scattered
the predominant products, accompanied by smaller throughout most tissues of glucosinolate-containing
amounts of nitriles. In contrast, the aglycones of plants. As myrosin cells contain special granular
some glucosinolates (e.g., allyl, benzyl, and structures, called myrosin grains, and the presence
4-(methylthio)-butyl glucosinolates) undergo enzy- of myrosinase activity was detected in vacuolar frac-
matic degradation to thiocyanates. The mechanism tions (Matile, 1980), it was concluded that myrosi-
for thiocyanate formation is still unknown. The en- nase is localized inside the myrosin grains. Pres-
zyme presumably responsible for the corresponding ently, the localization of myrosinase in myrosin
Landbauforschung Völkenrode, Special Issue 283, 2005 143

cells has been confirmed by immunocytochemical from Sinapis alba (Xue et al, 1992) Brassica napus
studies. Myrosinase is localized in the cytosol, al- (Thangstad et al., 1993), and Arabidopsis thaliana
though it is associated with the membrane surface of (Chadchawan et al., 1993). Myrosinases are encoded
myrosin grains (Thangstad et al., 1990; Thangstad et by multigene families: 14 genes have been estimated
al., 1991). Apart from the presence of myrosinase in to be present in Brassica napus (Thangstad et al.,
the cytosol, enzyme activity also can be detected in 1993). Recently, a myrosinase from Sinapis alba
cell walls, corresponding to an apoplastic localiza- was crystallized (Burmeister et al., 1997). This en-
tion (Matile, 1980). zyme folds into a structure very similar to that of
Certainly, degradation of glucosinolates is initi- cyanogenic ß-glucosidases from white clover (Bar-
ated by the mixing of enzymes and substrates; how- rett et al., 1995), which supports the assumption that
ever, mustard oil formation is accelerated by con- myrosinases have been evolved from ancestral
comitant activation of the myrosinase by ascorbic O-glucosidases (Burmeister et al., 1997).
acid, which is localized in the vacuoles of intact
cells (Grob and Matile, 1980). The stimulation by
ascorbic acid appears to be due to conformational Ecological significance of glucosinolates
changes of the enzyme, probably as a consequence
of the reduction of disulfide bridging in the protein In a manner similar to cyanogenic glucosides,
(Bones and Rossiter, 1996). glucosinolates can be considered as preformed de-
The estimation of myrosinase activity in the pres- fense chemicals that are activated in case of emer-
ence of ascorbic acid causes various difficulties. Up gency. Many experimental data demonstrate the
to now, a wide array of methods for the determina- protective role of glucosinolates and their degrada-
tion of myrosinase activity has been described. tion products, respectively (For review see Louda
These vary from the simple photometric estimation and Mole, 1991; Oleszek, 1995). The pungent smell
to highly sophisticated assays using radioactively and taste of glucosinalates reduce the palatability of
labeled substrates. However, ascorbic acid - the ef- plants that conatin them to generalist herbivores,
fective activator of myrosinases - interferes with e.g., birds, slugs and insects (Chew, 1988; Glen et
most of these enzyme tests. Unfortunately, in the al., 1990). Because isothiocyanates can easily pene-
past such interferences were disregarded in many trate biomembranes, they can interact with epider-
scientific examinations of myrosinases. Whereas mal and mucosal skin, leading to painful irritations.
such failings have less effects when the activation of In addition, isothiocyanates can lead to various
myrosinases is not very distinctive, they are quite complaints (e.g., bronchitis, pneumonia, gastroen-
relevant in all cases where myrosinases are com- teritis, kidney disorders). Consequently, high con-
pletely inactive in the absence of ascorbic acid centrations of glucosinolates and isothiocyanates are
(Kleinwächter and Selmar, 2004). The authors pre- toxic to animals; although in general, adapted spe-
sented an interference-free HPLC-based quantifica- cialists such as the white cabbage butterfly (Pieris
tion method of the enzymatically produced glucose, brassicae) can handle these toxins (Siemens
by which the activation by ascorbic acid could be Mitchell-Olds, 1996). For the imagines of these spe-
estimated exactly (Kleinwächter and Selmar, 2004). cialized butterflies, glucosinolates are even attrac-
Interestingly, various other proteins have been tants that stimulate oviposition. Interestingly, the
identified in relation to myrosinases, namely my- oviposition stimulus has its origin in the glucosi-
rosinase binding proteins, myrosinase binding pro- nolates rather than in the isothiocyanates. This was
tein-related proteins and myrosinase-associated pro- clearly demonstrated by application of allyl glucosi-
teins (Falk et al., 1995; Taipalensuu et al., 1996). nolate and allyl isothiocyanate, respectively, to non-
The localization and putative function of these pro- host plants of the butterfly (Stadler, 1978).
teins has not yet been clarified, but it has been In addition to their protective function against
speculated that they are important for the activation herbivores, glucosinolates and their degradation
process of myrosinase as cell integrity is destroyed products also are important factors for the interac-
(Geshi and Brandt, 1998). tions of plants with microorganisms. In most cases
Myrosinases are the only known S-glucosidases; reported, the presence of glucosinolates enhances
they exhibit a pronounced substrate specificity to- the resistance of the plant against numerous pests
wards glucosinolates. The hydrolysis of other S- or (Giamoustaris and Mithen, 1996; Mayton et al.,
O-glucosides is only poorly catalyzed by these en- 1996). In Brassica napus, the content of glucosi-
zymes (Lein, 1972; Durham and Poulton, 1990). nolates increased significantly after being infected
Ascorbic acid activates most myrosinases at concen- with various pathogens (Doughty et al., 1991).
trations at about 1 mmol/l, whereas higher concen- However, the resistance is not caused by the glu-
trations inhibit myrosinase activity (Ohtsuru and cosinolates themself, but by their degradation prod-
Hata, 1973). In the meantime, cDNAs of several ucts, i.e., the isothiocyanates (Mayton et al., 1996;
myrosinases have been cloned and sequenced, e.g., Manici et al., 1997; Smolinska et al., 2003). In addi-
144 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

tion to numerous data on the protective function of factor in glucosinolate biosynthesis or accumulation,
glucosinolates against pathogens, there are also respectively.
quite opposite findings: high glucosinolate contents
in Chinese cabbage enhanced its susceptibility to
Plasmodiophora brassicae, the causal organism of Glucosinolates and nutrition
the clubroot disease. The reason for these contradic-
tions is not understood and may be attributed to dif- Many glucosinolate containing plants (e.g. cab-
ferences in the specificity of the pathogens involved. bage, kale, broccoli, Brussels sprouts, cauliflower,
Glucosinolates have been reported to have a sig- and horse radish) are used by man as foods or
nificant allelopathic potential and are thought to be spices. Thus, human metabolism often is affected by
involved in the defense of ephemeral, unapparent glucosinolates and their degradation products. These
plants or plant parts (Feeny, 1976). Several studies natural products are precursors of compounds with
indicate that, in analogy to other ecological effects, goitrogenic action in animals and humans. The ac-
this allelopathic impact is caused by isothiocyanates tive antithyroid compounds include isothiocyanates
rather than by the intact glucosinolates (Brown and as direct products of glucosinolate hydrolysis, and
Morra, 1995; Bialy et al., 1990; Oleszek, 1995). In thiocyanate ions as final decomposition products. As
contrast, some studies suggest that neither glucosi- mentioned above, rhodanide affects thyroid func-
nolates nor isothiocyanates have significant allelo- tions (van Etten, 1969). Moreover, in some plants,
pathic potential (Choesin and Boerner, 1991). These the goitrogenic effects of glucosinolates are strongly
differences may be explained by the use of different enhanced by specific degradation products, such as
plants species for the evaluation of the allelopathic oxazolidine-2-thiones (e.g., progoitrin, glucocon-
potential. ringin). These compounds inhibit the oxidation of
iodate to iodine, which strongly affects thyroid func-
tion.
Variations in the glucosinolate content Based on their toxic properties and their pungent
taste, glucosinolates are often classified as antinutri-
Like other secondary metabolites, also the concen- tive compounds. However, the special taste of glu-
tration of glucosinolates accumulated varies in a cosinolates and their degradation products, respec-
wide range. These variations depends upon both tively, is often desired by the consumer. Thus, nu-
genetic and environment. Individual variations are merous glucosinolate-containing plants are exten-
reported for a great number of species, e.g. Brassica sively consumed and represent important vegeta-
oleracea (Kushad et al., 1999), Brassica napus (Li bles. Generally, glucosinolate levels in fresh plant
et al., 1999 ; Kraeling et al., 1990), Arabidopsis parts (stems, leaves), based on fresh weight, are 0.1
thaliana (Kliebenstein et al., 2001) Tropaeolum % or less (van Etten et al., 1976). These moderate
majus (Kleinwächter, 2002). Even within one single concentrations do no not create health problems
plant, the glucosinolate contents might vary drasti- when glucosinolate containing vegetables or cole
cally, depending on the developmental stage (Rang- crops are consumed.
kadilok et al.; 2002, Brown et al., 2003) or on diur- In addition to the negative properties of glucosi-
nal rhythms (Rosa et al., 1994; Rosa 1997). nolates and their degradation products on human
Environmental influences on the accumulation of nutrition, these compounds also seem to have posi-
glucosinolates are described for nearly all factors tive effects. The consumption of glucosinolate-
known to influence plant metabolism, e.g. light and containing vegetables apparently reduces the risk of
temperature (Rosa and Rodriguesl, 1998), climatic developing cancer. Most evidence concerning the
conditions (Ciska et al., 2000; Vallejo, 2003), water anticarcinogenic effects of glucosinolate hydrolysis
stress (Bouchereau et al., 1996) or the presence of products comes from studies in animals (For review
high concentrations of heavy metals in the soil see Verhoeven et al., 1997; Jongen, 1996). How-
(Coolong et al, 2004). The most important factor to ever, epidemiological data concerning the cancer-
influence plant growth used by agronomists is the preventive effects of Brassica vegetables, including
application of fertilizer. As well the application of cabbage, kale, broccoli, Brussels sprouts, and cauli-
nitrogen (e.g. Fismes et al., 2000; Bloem et al., flower, also support this assumption (Verhoeven et
2001) as the application of sulfur significantly influ- al., 1997). The exact mechanism by which glucosi-
ences the amount of glucosinolates accumulated in nolates and their degradation products, respectively,
the plants. As sulfur fertilization in nearly all cases are involved in cancer prevention is not completely
so far analyzed results in a massive enhancement of understood. The anti-carcinogenic effects of isothio-
the glucosinolate content (e.g. Kim et al., 2002, cyanates appear to be mediated by tandem and co-
Bloem et al. 2001) it can be deduced that the sulfur operating mechanisms. First, carcinogen activation
available for the plants corresponds to a limiting by cytochromes P450 is suppressed, probably by a
combination of down-regulation of enzyme levels
Landbauforschung Völkenrode, Special Issue 283, 2005 145

and direct inhibition of their catalytic activities. ing glucosinolate plants with desired properties,
These effects lower the levels of carcinogens ulti- much basic research is still required. It seems feasi-
mately formed. In addition, these compounds pro- ble to increase the level of 4-methylsulfinylbutyl
mote the induction of phase 2 enzymes, such as glu- glucosinolate in order to increase the anti-
tathione transferases and NAD(P)H: quinone reduc- carcinogenic potential, and also to create seeds that
tase, enzymes that detoxify any residual electro- only contain traces of glucosinolates. Unfortunately,
philic metabolites generated by phase I enzymes. In and in contrast to the metabolism of cyanogenic
this manner, phase 2 enzymes destroy the ability of glucosides, there is nearly no information on the in
these residual compounds to damage DNA. (Zhang vivo metabolism of glucosinolates. Related knowl-
and Talalay, 1994; Zhang et al., 1994). edge about the accumulation, translocation, and
4-Methylsulfinylbutyl isothiocyanate (sulforap- turnover processes of glucosinolates is an important
hane), isolated from broccoli, turned out to be a po- precondition for understanding those metabolic
tent anticarcinogen. The isolated compound effec- processes that will be modified in the corresponding
tively induces phase II enzyme (Zhang et al., 1992). transgenic plants. More knowledge about glucosi-
In contrast to a protective action, a few isothiocy- nolates and their metabolism is required for success-
anates apparently have mutagenetic potential in ful biotechnological approaches.
mammal cells and in bacteria (Verhoven et al.,
1997). Nevertheless, as isothiocyanates block car-
cinogenesis by dual mechanisms and are present in References
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conversion of amino acids to aldoximes in the biosyn-
nolate hydrolysis products are considered to be good thesis of cyanogenic glucosides and glucosinolates.
candidates for creating "functional foods", designed Plant Mol Biol 38:725-734
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Levels up to 10% dry weight have been reported Wallsgrove RM (1993) Aldoximeforming microsomal
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Landbauforschung Völkenrode, Special Issue 283, 2005 149

Regulation of glutathione (GSH) synthesis in plants: Novel insight from Arabidopsis

Andreas Wachter1 and Thomas Rausch1

Abstract1 transcriptional/post transcriptional regulation,

GSH1 overexpression, stomata
During the past decade, cDNAs for the enzymes
catalyzing GSH biosynthesis, GSH1 (J-glutamyl-
cysteine synthetase) and GSH2 (glutathione Introduction
synthetase), have been cloned for several plant
species. Mutant complementation and Glutathione (GSH) is the predominant non-protein
characterization of the recombinant GSH1 and thiol compound in eukaryotic and prokaryotic cells.
GSH2 proteins have confirmed the predicted By its reversible oxidation to GSSG it represents a
enzymatic functions. Gene expression analysis has major cellular redox buffer. In higher plants, this
indicated that higher plants respond to biotic and buffer role is crucial for the cellular response to
abiotic stress factors with an upgraded glutathione increased formation of reactive oxygen species
(GSH) synthesis, for which the induction of GSH1 (ROS) caused by abiotic or biotic stress (May et al.,
appears to play a pivotal role. However, the 1998; Noctor et al., 1998; Ruiz and Blumwald,
expression of active GSH1 enzyme is regulated at 2002). Additional roles of GSH include its function
multiple levels, including transcriptional, i) as storage and long distance transport form for
translational and post-translational controls. Here assimilated sulfur (Brunold and Rennenberg, 1997),
we summarize recent research on the subcellular ii) as electron donor for the APS reductase reaction
compartmentation and regulated expression of the (Bick et al., 1998), iii) as binding partner for GST-
GSH1 enzyme in A. thaliana. Transgenic mediated conjugation of secondary plant metabolites
A. thaliana plants expressing GUS::EGFP fusions and xenobiotics (Marrs, 1996; Alfenito et al., 1998;
under the control of the AtGSH1-promoter revealed Wagner et al., 2002), and iv) as precursor for the
tissue- and cell type-specific differences in GSH1 heavy metal-binding phytochelatins (PCn) (Grill et
expression, and a pronounced developmental al., 1985; Howden et al., 1995a, b; Cobbett et al.,
modulation of the response to the stress hormone 1998; Cobbett, 1999; Ha et al., 1999; Cobbett,
jasmonic acid. When the AtGSH1 homolog from 2000). Furthermore, GSH also appears to act as
Brassica juncea, BjGSH1-1, was expressed in important developmental signal as revealed by its
A. thaliana under the control of the 35S promoter, influence on root meristem activity (Sanchez-
several lines showed a strong increase of GSH1 Fernandez et al., 1997; Vernoux et al., 2000) and
protein without a significant change of GSH flowering (Ogawa et al., 2004).
content. Conversely, co-suppression lines were GSH is synthesized in two ATP-dependent
obtained which revealed strong decreases of reactions, catalyzed by J-glutamylcysteine
AtGSH1 and BjGSH1-1 transcripts, GSH1 protein, synthetase (GSH1; EC 6.3.2.2.) and glutathione
and GSH content. In an attempt to selectively synthetase (GSH2; EC 6.3.2.3.; Figure 1). Higher
overexpress GSH1 protein in stomata, we plant GSH1 and GSH2 cDNAs have been cloned
transformed A. thaliana with a fusion between a and functionally expressed (May and Leaver, 1994;
strong, stomata-specific promoter (PRP4) and the Ullmann et al., 1996; Wang and Oliver, 1996). In
BjGSH1-1 coding sequence. While stomata-specific A. thaliana, GSH1 and GSH2 are present as single
expression could be verified, in situ labeling of GSH genes (May and Leaver, 1994; Ullmann et al., 1996;
with MCB did not reveal a significant increase in The Arabidopsis Genome Initiative, 2000). The in
guard cell GSH content. We conclude that to silico analysis predicted plastidic transit peptides for
engineer GSH1 activity in plants, the presence of both enzymes, but recent studies have indicated that
multiple expression controls has to be taken into only GSH1 is confined to the plastidic compartment,
account. whereas the larger part of GSH2 transcripts encode a
cytosolic protein (Wachter and Rausch, 2004;
Key words: Arabidopsis thaliana, glutathione Wachter et al, 2004).
synthesis, GSH1, GSH2, compartmentation, Previous investigations support the notion that in
response to several stress factors GSH1 (and to a
lesser extent GSH2) expression is strongly up-
regulated (Schäfer et al., 1998; Xiang and Oliver,
1
Heidelberg Institute of Plant Sciences (HIP), Im 1998). As an upgraded synthesis of GSH has been
Neuenheimer Feld 360, D-69120-Heidelberg, Germany
150 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

considered crucial for the cellular adaptation to and Willmitzer, 1992). The AtGSH1 promoter
oxidative stress (see above), several attempts have region was also amplified with 5’gatecs
been made to increase the stress tolerance of higher (5’GGGGACAAGTTTGTACAAAAAAGCAGGC
plants by ectopic overexpression of GSH1. Initially, TATCGATAT-GTAACACAATAAT-3’) and
the E.coli GSH1 enzyme, with or without a plastidic 3’gatecs (5’GGGGACCACTTTGTACAAGAAAG-
transit peptide (Noctor et al., 1996, 1998), was CTGGTGGTATATATAGCTCCTGCA-3’) primers
expressed under the regulation of the 35S promoter. and cloned, by use of the GatewayTM (Invitrogen,
Different plant species differed in their response to Karlsruhe, Germany) recombination system, into the
ectopic GSH1 expression, ranging from increased entry vector pDONR and subsequently into
stress tolerance (Zhu et al., 1999) to symptoms of destination vector pKGWFS7 in front of a fusion of
oxidative stress due to a GSH/GSSG imbalance the reportergenes EGFP and uidA.
(Creissen et al., 1999). For overexpression of BjGSH1-1, a 1639 bp
In A. thaliana, ectopic overexpression of its own fragment, containing the long 5’UTR sequence and
GSH1 gene caused only a minor increase of GSH the full length coding sequence of BjGSH1-1, was
content, whereas in antisense plants GSH content amplified by PCR using 5’BamUTRECS1 (5’-
was clearly reduced (Xiang et al., 2001). Previous ACTGGATCCAGCTCTCCACTGATAGGATTAT
studies on a redox-regulated 5'UTR binding factor -3’) and 3’SalECS1 (5’-TGACGTCGACTCAGT-
indicated that in addition to transcriptional AAAGCAGTTCCTGGAACACAGG-3’) primers.
induction, the expression of GSH1 protein also This fragment was digested with BamHI and SalI
appears to be under translational control (Xiang and and cloned into appropriate sites of vector pBinAR
Bertrand, 2000). Recently, Jez et al. (2004) (Höfgen and Willmitzer, 1992). To analyze the
described a post-translational redox control of tissue specificity of the promoter of the AtPRP4
GSH1 activity, adding an additional facet to the gene (at4g38770), 1552 bp upstream of the
regulation of GSH1 activity. In this report, we predicted start codon were amplified by PCR using
present new data i) on the regulation of the AtGSH1 primers 5’gatprp4 (5’-GGGGACAAGTTTGTAC-
promoter, ii) on the analysis of transgenic A. AAAAAAGCAGGCTAACACCTAGAACGCAGT
thaliana plants transformed with the AtGSH1 CAGG-3’) and 3’gatprp4 (5’-GGGGACCACTT-
homolog of Brassica juncea, BjGSH1-1, including TGTACGAAAGCTGGGTTGGGATTCTCACCCT
sense transformants and co-suppression lines, and CTGAGA-3’). By use of the GatewayTM
iii) on the targeted overexpression of BjGSH1-1 in recombination system, the promoter sequence was
guard cells. The results strongly support a multiple cloned into the entry vector pDONR, and,
control of GSH1 expression in plants. subsequently, into destination vector pKGWFS7 in
front of a fusion of the reportergenes uidA and
EGFP for plant transformation. For guard cell
Materials and Methods specific overexpression of BjGSH1-1, the coding
sequence was first amplified with primers
Plant material 5’Bamecs1 (5’-ACTGGGATCCATGGCGTTATT-
Arabidopsis thaliana, ecotype Columbia, was GTCTCAGGCAGGAGG-3’) and 3’Salecs1 (5’-
grown under greenhouse conditions (approx. 8 h TGACGTCGACTCAGTAAAGCAGTTCCTGGA
light period). Plant tissues for protein and RNA ACACAGG-3’) and, after digestion with BamHI
extraction were immediately frozen in liquid and SalI, cloned into appropriate sites of pBinAR
nitrogen and stored at -80°C. (resulting in pBinAR-BjGSH1-1). The AtPRP4
promoter was amplified using 5’Ncoprp4 (5’-
Gene constructs for plant transformation ACTGCCATGGAACACCTAGAACGCAGTCAG
G-3’) and 3’Kpnprp4 (5’-ACTGGGTACCTGGGA-
A 1605 bp fragment containing sequences TTCTCACCCTCTGAGA-3’) primers and
upstream of the predicted ATG start codon of subcloned into the pGEM-T (Promega) vector. The
AtGSH1 was amplified by PCR using 5’Bamecs (5’- promoter sequence was released from pGEM-T by
ATGCGGATCCATCGTATGTAACAATAATGG restriction with HincII and KpnI and ligated into
ATCTTGTAG-3’) and 3’Bamecs (5’-ATGCG- pBinAR-BjGSH1-1, which was digested with EcoRI
GATCCGGTATATTAGCTCCTGCAATTATAAC and KpnI and treated with Klenow fragment for
AATTC-3’) primers. The amplified promoter filling of 3’recessed ends before.
sequence was digested with BamHI and cloned into
appropriate site of the vector pBSK-LUC, Stable A. tumefaciens-mediated transformation of
containing the reportergene luciferase. The cassette A. thaliana by floral dip
of AtGSH1 promoter and LUC was cut out with
PvuII and XhoI and ligated into EcoRI/SalI sites of A. thaliana plants were transformed by the floral dip
the vector pBinAR for plant transformation (Höfgen method according to Clough and Bent (1998). After
transformation, seeds were screened on solid MS
Landbauforschung Völkenrode, Special Issue 283, 2005 151

medium containing 0.8 % agar and 50 µg ml-1 Histochemical analysis of E-glucuronidase (GUS)
kanamycin under sterile conditions and activity
transformants were transferred to soil after two
For analysis of GUS activity, tissue samples were
weeks.
treated with GUS staining buffer (100 mM
Na2HPO4/NaH2PO4, pH 7.0, 10 mM Na2EDTA, 0.5
Quantitative determination of transcripts by Real-
mM K3[Fe(CN)6], 0.5 mM K4[Fe(CN)6], and 0.08%
Time PCR
X-GlucA (Duchefa, Haarlem, The Netherlands) for
Total RNA was extracted from leaf tissue of 16 h at 37qC. Green tissues were bleached with
A. thaliana and transcribed in cDNA as described ethanol before examination.
before (Wolf et al., 2003). Real-Time PCR was
performed using the Platinum Taq-DNA Polymerase In vivo labeling of glutathione and confocal laser
(Invitrogen, Karlsruhe, Germany) and SYBR-Green scanning microscopy (CLSM) analysis
as fluorescent reporter in the Biorad iCycler.
Monochlorobimane (MCB) in vivo labeling of
Primers for the coding region of AtGSH1 were
glutathione was performed as described by
5’AtGSH1rt (5’-CAAGCTTGACGAATTTCAGG-
Hartmann et al. (2003). For confocal analysis of
AGC-3’) and 3’AtGSH1rt (5’-ACGCCACCCGA-
MCB fluorescence, LSM410 (Zeiss, Jena) was used
AACAACAG-3’). The BjGSH1-1 transcripts were
with the following settings: excitation 405 nm and
amplified with primers 5’BjGSH1rt (5’-AGTCGC-
emission longpass 420 nm, chlorophyll
CGATCCGAACTTG-3’) and 3’BjGSH1rt (5’-TTC-
autofluorescence was detected in parallel using 560
CGGTCCTGGAGCTTACG-3’). Primer sequences
nm longpass.
for actin (Act2/8) were reported previously (Ha et
al., 1999). A serial dilution of cDNA was used as
standard curve to calculate amplification efficiency
Results and discussion
for AtGSH1 and actin primers. Each reaction was
performed in triplicates, and specificity of
AtGSH1 and AtGSH2 are differentially
amplification products was confirmed by melting
compartmentalized
curve and gel electrophoresis analysis. Relative
abundance of AtGSH1 and BjGSH1-1 transcripts The formation of reactive oxygen species (ROS)
was calculated and normalized with respect to during abiotic or biotic stress exposure is not
Act2/8 mRNA according to the method of Muller et confined to a single compartment. Corroborating
al. (2002). this notion, the ascorbic acid-GSH cycle, which
eliminates ROS, is operative in different cellular
Immunoblot analysis compartments, including plastids, mitochondria,
peroxisomes and the cytosol (Jiménez et al., 1997,
Total protein extraction and immunoblot analysis
1998). Conversely, GSH1, the rate-limiting enzyme
were performed as described in Bogs et al. (2003).
of GSH synthesis, was recently shown to be
The primary antiserum was used in a 1:10,000
confined to the plastidic compartment, whereas the
dilution in 5% BSA.
second enzyme, GSH2, appears to be largely
cytosolic (Wachter and Rausch, 2004, Wachter et al,
Thiol analysis
2004) and only to a minor extent plastidic (Figure
For extraction of total thiols, 30 mg of deep- 1). These observations indicate that GSH and its
frozen grinded material was vortexed with 1 ml dipeptide precursor JEC have to be transported
extraction buffer (0.1 N HCl, 1 mM EDTA, 4 % non between different cellular compartments. Only
soluble Polyvinylpyrrolidon) and centrifuged for 30 recently, the first plant GSH transporters have been
min at 15,000 g and 4 °C. 50 µl of the supernatant identified (Bogs et al., 2003; Zhang et al., 2004),
was mixed with 50 µl 500 mM CHES (2-(N- however, their intracellular localization has not yet
Cyclohexylamino)ethane sulfonic acid) pH 9.4, 10 been determined. Future research will have to
µl 30 mM monobromobimane (MBB) and 10 µl 10 address how these transport processes are regulated
mM DTT and incubated for 15 min at room in an appropriate manner to meet the demands of the
temperature in the dark for MBB labeling of thiols. different cellular compartments for GSH, in
The reaction was stopped by adding 400 µl 10 % particular after stress exposure.
acetic acid and thiols were analyzed by HPLC.

Quantitative analysis of luciferase (LUC) activity

LUC activities of leaf samples were determined as
described by Lehr et al. (1999).
152 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

in transgenic A. thaliana plants transformed with a

AtGSH1 promoter-LUC (luciferase) construct.
peroxisome cytosol Conversely, in leaves of flowering plants this
GSH GSH GSH promoter was strongly activated. This conspicuous
? discrepancy indicates a differential sensitivity to JA
Gly + JEC and/or a change in endogenous JA content during
mitochondrion
JEC + Gly plant development.

JEC + Gly ? GSH

plastid
Table 1:
Glu Quantitative analysis of promoter activity in AtGSH1
+ JEC + Gly GSH
promoter-LUC transformants of different age. Leaves of
Cys 10-week-old (rosette stage) or 14-week-old (flowering
stage) plants (several independent primary transformants)
GSH GSH
were fed with 50 µM jasmonic acid (or water) via the leaf
base and incubated for 24 or 48 hrs. LUC activities before
(arbitrarily set to 100%) and after jasmonic acid treatment
Figure 1: were determined in total leaf extracts.
Compartmentation of GSH synthesis in plant cells.The Plant
GSH1 enzyme is confined to the plastids, whereas the individual LUC activity LUC activity
GSH2 enzyme is primarily localized in the cytosol, and, to 24 hrs after 48 hrs after
a minor extent, in plastids (Wachter and Rausch, 2004). JA-treatment JA-treatment
Indirect evidence suggests that, at least in some species, 10-week-old plants
GSH2 may also be found in mitochondria and
peroxisomes. Since GSH export from plastids appears to at16-1 6% 3%
be slow or absent (Meyer and Fricker, 2002), it has been at16-2 59% 97%
speculated that the product of the GSH1 reaction, JEC, at16-3 93% 42%
may directly exit from the plastid and be the precursor for at12-1 25% 23%
cytosolic GSH synthesis (Wachter, 2004; Wachter et al., at12-2 67% 24%
2004).
14-week-old plants

The AtGSH1 promoter shows a broad activity at6-9 520% 960%

spectrum during plant development and an age- at6-19 1820% 5410%
dependent response to the stress hormone jasmonic at6-20 360% 12360%
at6-21 690% 4530%
acid
Previous studies have shown that up-regulation of
GSH synthesis is, at least under certain conditions,
achieved by an increased transcription of the GSH1 In BjGSH1-1 sense transformants of A. thaliana, the
gene. We have generated transformed A. thaliana total cellular GSH content remains largely
lines expressing a EGFP::GUS fusion under the unaffected, whereas co-suppression lines show
control of the AtGSH1 promoter. Histochemical reduced contents of GSH, GSH1 protein, and
analysis of several independent transformants has AtGSH1 transcripts
shown that despite a broad activity range in different
organs and cell types, the AtGSH1 promoter appears In an attempt to manipulate the expression of
to be particularly active in vascular tissue, GSH1 protein by ectopic expression of a transgene,
trichomes, stipules, flowers, embryos and root tips we have transformed A. thaliana with a full length
(Wachter, 2004). Our results confirm the notion that GSH1 cDNA from Brassica juncea (BjGSH1-1;
despite its wide activity window, the AtGSH1 AJ563921), expressed under the control of the 35S
promoter shows a pronounced developmental promoter; note that for this transformation we
component. As the stress hormone jasmonic acid included the full 5'UTR sequence. A larger number
has previously been shown to induce the expression of independent transformants were isolated and
of GSH1 (Xiang and Oliver, 1998), we have analyzed for GSH1 protein content (Figure 2),
analyzed the response of the AtGSH1 promoter to endogenous AtGSH1 transcripts and BjGSH1-1
JA in plants of different age. Surprisingly, we transcripts (Figure 3), and for their GSH and
observed an induction or repression of promoter cysteine contents (Figure 4). The immunoblot
activity, depending on plant age (Table1). In leaves analysis (Figure 2) revealed six GSH1-
of rosette stage plants, JA caused a significant overexpressing lines, whereas seven lines showed a
down-regulation of promoter activity as determined clear decrease of GSH1 protein as compared with
wildtype plants. Note that in the overexpressing
Landbauforschung Völkenrode, Special Issue 283, 2005 153

lines the size of the ectopically expressed BjGSH1-1 increase (less than 20%) of GSH, whereas their
protein was identical with the predicted size of the cysteine contents resembled that of wildtype plants.
mature protein after removal of the transit peptide, Thus, despite a strong increase of correctly
indicating import into plastids and correct processed GSH1 protein the GSH content was
processing. Selected overexpressing and putative co- barely affected. A cysteine limitation cannot a priori
suppression lines were analyzed for their AtGSH1 be excluded, however, another possible explanation
and BjGSH1-1 transcript amounts by Real-Time could be the formation of enzymatically inactive
PCR (Figure 3). Co-suppression lines showed a GSH1 protein.
drastic decrease of the endogenous AtGSH1 Recently, Jez et al. (2004) have demonstrated a
transcript and only 3 % of the BjGSH1-1 transgene redox-mediated post-translational regulation of
expression level of the overexpression lines. The GSH1 activity, operating via an intramolecular
amount of endogenous AtGSH1 transcript was disulfide formation. It is noteworthy that the E. coli
significantly lowered in overexpression lines as GSH1 enzyme previously used to boost GSH
compared to wildtype plants. synthesis in plants does not show this type of
regulation.

50 700
cysteine
glutathione 600
40

glutathione [nmol/gFW]
cysteine [nmol/gFW]

500

30
400

Figure 2:
300
Immunological analysis of BjGSH1-1 transformants with 20

an GSH1 antiserum reveals overexpression and co- 200

suppression lines. A, immunoblot analysis of GSH1 10
expression in mature leaves of BjGSH1-1 transformants 100

and wildtype plants (wt). B, amidoblack staining of the

0 0
membrane shows equal loading of total protein. 20 µg of

wt
c
3
5
11

17

20
21

24

8
9
10
13

19
26

d
m te
wt
wt

wt

wt

w
n
total protein per sample were separated by SDS-PAGE

ea
line
(10% gel), followed by immunoblot analysis. Figure 4:
Cysteine and glutathione contents in mature leaves of
A. thaliana transformants expressing BjGSH1-1
(including long 5’UTR) under control of the CaMV-35S
promoter. Thiol contents were determined for several
independent transformant lines (including overexpression
and co-suppression lines; see Figs.4&5) and five different
wildtype (wt a to wt f) samples.

Guard cell-specific expression of BjGSH1-1 protein

does not affect the cytosolic GSH content
In previous attempts to increase the stress
tolerance of plants by ectopic overexpression of
Figure 3: GSH1, the transgene was expressed under the
Real-Time PCR analysis of expression of AtGSH1 (and regulation of the 35S promoter, which conveys a
BjGSH1-1) in leaves of wildtype plants and four more or less constitutive expression. Recently it was
independent BjGSH1-1 transformant lines.Data are shown that stress-induced stomatal closure is
normalized with respect to actin expression. For AtGSH1, mediated by ROS, and a particular role could be
data are standardized relative to wildtype values (=100%), assigned to dehydroascorbic acid dehydrogenase
for BjGSH1-1 relative to expression of line 9 (=100%). (DHAR), a key enzyme of the ascorbic acid-GSH
cycle (Chen and Gallie, 2004). This enzyme uses
GSH as electron donor for ascorbic acid reduction.
With respect to their GSH and cysteine contents, the Based on the hypothesis that a change in stomatal
co-suppression lines showed a strongly reduced GSH synthesis capacity could equally affect
GSH content, with a concomitant minor increase in stomatal regulation, we have developed a strategy to
cysteine content (Fig. 4). Conversely, transgenic selectively overexpress genes of GSH synthesis (or
lines exhibiting a strong increase of GSH1 protein the ascorbic acid-GSH cycle) in guard cells. For this
(Figure 2, lines 9, 10 & 13) showed only a minor
154 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

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tolerance highlight its central role as an important S- yeast Schizosaccharomyces pombe. Plant Cell 11:1153-
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and/or redox state. These attempts have as yet met glutathione in poplar leaves. Plant Cell Environ 26:965-
975
only moderate success, one of the reasons certainly
Höfgen R, Willmitzer L (1992) Transgenic potato plants
being the multiple ways by which GSH synthesis is depleted for the major tuber protein patatin via
regulated in vivo, including transcriptional and post- expression of antisense RNA. Plant Sci 87:45-54
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mutant of Arabidopsis thaliana. Plant Physiol
107:1067-1073
Acknowledgements Howden R, Goldsbrough PB, Andersen CR, Cobbett CS
(1995b) Cadmium-sensitive, cad1 mutants of
Arabidopsis thaliana are phytochelatin deficient. Plant
We gratefully acknowledge support of the DFG
Physiol 107:1059-1066
(FOR383), the Südzucker AG, and the KWS SAAT
AG to TR.
Landbauforschung Völkenrode, Special Issue 283, 2005 155

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Landbauforschung Völkenrode, Special Issue 283, 2005 157

Ecological significance of H2S emissions by plants - a literature review

Pia Wickenhäuser1, Elke Bloem1, Silvia Haneklaus1 and Ewald Schnug1

Abstract1 of foliar-applied elemental S (Jolivet, 1993). In

comparison, little is known about soil-applied S in
The emission of several volatile reduced sulfur sulfate form, which may have a strong influence on
gases (H2S, COS, DMS, CS2 and methylmercaptan) plant resistance by directly stimulating biochemical
from various plant species was determined in vari- processes in the primary and secondary metabolism
ous experiments. From these volatile substances H2S (Schnug, 1997). In fertilizer experiments under field
is one of the most important sulfur gases emitted by conditions it could be shown that soil-applied S fer-
higher plants in response to an excess of sulfur. So tilization significantly reduced fungal infections of
far, a correlation between soil applied sulfur fertili- oilseed rape with light leaf spot (Pyrenopeziza bras-
zation and H2S emission of agricultural crops was sicae), grapes with powdery mildew (Uncinula ne-
not proven, but it was shown in field experiments cator) and potato tubers with stem cancer (Rhizoc-
that sulfur fertilization and the sulfur nutritional tonia solani) (Schnug et al., 1995a; Bourbos et al.,
status, respectively had a significant effect on fungal 2000; Klikocka et al., 2004). The results of these
infections in oilseed rape. These findings underline experiments indicate that different S metabolites are
the concept of sulfur-induced resistance (SIR) of involved in disease resistance, which were induced
plants. H2S is highly fungi toxic and therefore a rela- by S fertilization and thus underpinning the concept
tionship between increasing hydrogen sulfide emis- of sulfur induced resistance (SIR) (Schnug et al.,
sions of plants and a higher resistance of crops 1995a; Haneklaus et al., 2004). An improved under-
against pests and diseases can be assumed. A better standing of how S is involved in the stress resistance
understanding of the natural defense system of do- of plants together with efficient fertilizer strategies
mesticated plants based on the release of H2S may are a challenge for future agricultural production
contribute to a significant reduction of the input of techniques. The aim of S fertilizer strategies will be
fungicides in agriculture and thus to more sustain- to maximize the inherent potential stress resistance,
ability in crop production. In organic farming, sulfur which otherwise would not be expressed due to an
induced resistance may play a major role for main- insufficient S supply, whilst maintaining an envi-
taining plant health. From environmental point of ronmentally and economically sustainable farming
view the degradation of toxic surface ozone concen- (Schnug, 1997).
trations by plant-released H2S is another process of The mechanisms of SIR are not yet fully under-
ecological relevance. stood. Mechanisms to tackle with biotic stress,
which are provided by the S metabolism involve
Key words: hydrogen sulfide, sulfur induced resis- among others glutathione, phytoalexins and glucosi-
tance, SIR, surface ozone nolates (Haneklaus et al., 2004). The release of vola-
tile S compounds is putatively an important mecha-
nism in SIR, too. The emission of several volatile
Sulfur induced resistance – release of H2S reduced S gases (H2S, COS, DMS, CS2 and me-
thylmercaptan) from various plant species was de-
The significance of sulfur (S) for the resistance of termined (Schröder, 1993). Under growth conditions
crops against pests and diseases became evident at with an excessive S supply significant amounts of
the end of the 1980’s. At this time macroscopic S gaseous S compounds are released into the atmos-
deficiency became a widespread nutrient disorder phere from which H2S is the most abundant gas
because of the desulfurization of industrial emis- emitted (Rennenberg, 1991). The release of H2S is
sions in Western Europe (Booth et al., 1991). At the thought to be actively regulated by the plant me-
same time infections of oilseed rape with Pyrenope- tabolism rather than being a metabolic side-product.
ziza brassicae spread out in regions which where An indication for the first hypothesis is that H2S
never infected before (Schnug and Ceynowa 1990; emissions could be observed also under field condi-
Schnug et al., 1995a). tions with a moderate sulfur supply (Rennenberg,
It has been known since long time that S has pro- 1991). Anyway, an excess S supply by atmosphere
tective effects against pests and diseases. Most of and pedosphere induces the emission of volatile S
this knowledge is, however, restricted to the effects compounds by plants. The release of H2S occurs
when the influx of S compounds via leaf or root in
1
Institute of Plant Nutrition and Soil Science, Federal the form of cysteine, sulfate, SO2 or COS exceeds
Agricultural Research Centre Braunschweig-Völkenrode, the conversion of these S sources into protein, glu-
Bundesallee 50, D-38116 Braunschweig, Germany
158 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

tathione, methionine and other S containing com- ing crops and cut plant parts reacts completely dif-
pounds (Rennenberg, 1991). The emission of H2S is ferent, and consequently higher H2S emissions were
comparable with a pressure valve for the plant to measured from detached leaves and leaf discs than
dispose of excess S (Filner et al., 1984). It has been from whole plants. Extrapolation of H2S emissions,
suggested that the release of H2S regulates, homeo- which were measured from detached leaves or plant
statically the size of the cysteine pool and thus parts will therefore lead to an overestimation of the
maintains it at a low level because of its cytotoxic- H2S emission by the crop (Bloem et al., 2004a). In
ity. H2S may be released prior or after cysteine for- the laboratory it was possible to stimulate leaves to
mation (Giovanelli, 1990), but the question is still emit H2S at 1000 times higher rates than under field
open which enzymes catalyze the release of H2S. conditions (Filner et al., 1984). When sulfate was
Another possible mechanism, which induces the fed to intact roots of whole plants, the increase in
H2S emission by plants could be the involvement in the H2S emission was usually much lower (Rennen-
the natural defense system of crop plants against berg and Filner, 1982, 1983; Filner et al., 1984).
fungal infections (Haneklaus et al., 2004). Apparently, the root system constitutes a barrier for
Conditions determining the H2S emission by the influx of sulfate into the plant, and hence pre-
plants are physiological factors such as the growth vents an immediate release of H2S from excessive
stage (Seykia et al., 1982a; Rennenberg and Filner sulfate in the soil (Rennenberg and Lamoureux,
1983; Filner et al., 1984; Lakkineni et al., 2003) and 1990). In some experiments the H2S emissions were
metabolic activity of the plant tissue, but also nutri- stimulated by injuring the roots, but for the same
tional and environmental factors (Fall et al., 1988; reason as in case of the cut leave these results are
Rennenberg 1991; Schröder 1993; Lakkineni et al., also not suitable to calculate the H2S emissions by
2003). Generally, the emission of S gases increases plants under natural conditions.
with temperature and illumination (Lamb et al., Although it is generally assumed that H2S can be
1987; Seykiya et al., 1982b; Fall et al., 1988). The reliably determined using cryogenic trapping with
strategy to dispose of excess S depends on a concen- gas chromatographic analysis, slight variations of
tration gradient for H2S between plant and atmos- the analytical procedure may result in significant
phere. The presence of high atmospheric H2S con- losses of H2S (Rennenberg, 1991). Despite these
centrations prevents H2S emission, so that it is not analytical problems that have to be overcome, the
surprising that H2S fumigation resulted in a rapid determination of H2S emissions from intact plants in
accumulation of thiols, including cysteine in the dependence on the S supply and infections with
plant tissue (Rennenberg, 1991; De Kok et al., fungal diseases will be a milestone for addressing
1998). key metabolites involved in SIR. The role of S nutri-
Data for the natural release of gaseous S- tion and fungal infections for the potential release of
compounds reported in literature vary over a wide H2S emissions was shown in field experiments with
range (Seykia et al., 1982a, b, c; Rennenberg and Brassica napus L. (Bloem et al., 2004b). For in-
Filner 1982, 1983, 1984; Filner et al., 1984; Fall et stance, the activity of the H2S releasing enzyme L-
al., 1988; Schröder 1993; Collins 1996; Lakkineni et cysteine desulfhydrase significantly increased in
al., 2003). Filner et al., (1984) calculated a world- infected plant tissue and, to a lower extent in plants
wide S emission from plants of 7.4 Tg S yr-1, while with a higher S nutritional status. (Bloem et al.,
Winner et al. (1981) came to a value of 54 Tg S yr-1. 2004b).
Globally, Crutzen (1983) calculated the annual S
emissions of H2S, DMS and methylmercaptan from
agricultural fields to be in the range of < 4 Tg S yr–1. Surface ozone concentrations
One reason for the large discrepancies observed for
S emissions are analytical problems. H2S measure- H2S emissions by plants may degrade toxic sur-
ments are difficult to conduct if emissions are low, face ozone and thus be of high ecological signifi-
because analytical systems need to be extremely cance (Schnug 1997). Surface ozone concentrations
sensitive so that there is only a few data available increased in rural areas over the last decade on an
that provides information about the release of gase- average by 1.8 g m-3 yr-1 (Figure 1). At the same
ous S compounds in the low range (Wilson et al., time plant S concentrations declined at a constant
1978; Seykia et al., 1982b; Lakkineni et al., 1990; rate of 0.45 mg yr-1 (Figure 1; Schnug, 1993,
Bloem et al., 2004a). Another problem of H2S Schnug, 1997).
measurements is that most experiments were con- Assuming that: a) H2S emissions from plants de-
ducted under artificial conditions, e.g. with cut plant cline linearly together with the S supply (Collins
parts that were fed with concentrated S solutions 1996, Rennenberg 1984) at a rate of 0.57 nmol m-2
(Wilson et al., 1978; Seykia et al., 1982b; Rennen- h-1 (calculated from the data of Schnug and Hanek-
berg and Filner 1983). Therefore such estimates laus 1994); b) crops have an average leaf area index
need to be treated carefully. The metabolism of liv- of 1; c) crops assimilate and reduce S during an av-
Landbauforschung Völkenrode, Special Issue 283, 2005 159

erage of 100 days a year and 10 h a day; and d) H2S Schnug et al., 1995b; Haneklaus et al., 1999; Bloem
degrades O3 in a 1:1 ratio; then up to 75% of the et al., 2004). H2S is highly fungi-toxic (Pavlista,
observed increase of surface ozone could be attrib- 1995) and therefore a relationship between increas-
uted to the decrease in the total amount of S-turn- ing H2S emissions and the resistance of crops
over in the “green part” of the ecosystem (Schnug, against pests and diseases is likely (Seykia et al.,
1997). 1982c; Beauchamp et al., 1984; Schröder 1993). All
these findings clearly show that extensive field
measurements are required to evaluate the impact of
different nutritional conditions and fungal diseases
on the emission of H2S. It is the aim of a joint re-
search project financed by the DFG (German Re-
search Foundation) to determine the release of H2S
in relation to the S nutritional status of agricultural
crops and to answer the question whether such rela-
tionship is involved in SIR. The identification of the
mechanisms causing SIR will be an important mile-
stone for a sustainable agricultural production as the
input of fungicides could be minimized or com-
pletely waived (Haneklaus et al., 2004). Consumers
are increasingly concerned about the contamination
of foodstuff with pesticide residues and conse-
quently markets for plant production from farming
systems avoiding such contaminations are expand-
ing (Schnug, 1997). Thus, SIR may become an im-
Figure 1: portant strategy to efficiently combat pathogens in
Atmospherical surface ozone concentrations and total
sustainable farming systems, favorably organic
sulfur in younger, fully developed leaves of field grown
Brassica napus varieties in northern Germany from 1980- farming. An important advantage of SIR compared
1992 (Schnug 1993). to pesticides is that the resistance will not be rapidly
broken by new pathotypes (Haneklaus et al., 2004).
And an indirect effect of an increased release of H2S
These figures here are only an estimate and may could be the detoxification of toxic surface ozone
change depending on the actual input parameters, concentrations by which oxidative stress would be
but they still outline the important function of S as- lowered outside the organism (Schnug, 1993, 1997).
similation and reduction in ecosystems. Despite the
significance of these findings for air quality, higher
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emission of hydrogen sulfide from plants. Plant Physiol
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JD, Krouse HR (1981) Rates of emission of H2S from
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Zhao F, McGrath SP (1996) Importance of sulphur in UK
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162 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants
Landbauforschung Völkenrode, Special Issue 283, 2005 163

Sulfur status of Chinese soils and response of Chinese cabbage to sulfur fertilization in
the Beijing area
Liping Yang1,2, Ineke Stulen2 and Luit J. De Kok2

Abstract1 practices has resulted in a sustained increase in

2
crop production in the last decades. This had led
During recent years sulfur deficiency has become a to increased removal of nutrients from agricultural
major problem in agricultural crops throughout China, ecosystems. The sulfur input to soil has decreased
due to an imbalance of sulfur in relation to N, P and K due to the use of low sulfur-containing fertilizers.
in the fertilizers. One-fourth of the tested Chinese soils In the past fertilizers such as ammonium sulfate,
appeared to be sulfur deficient. Pot experiments at single superphosphate, potassium sulfate and
locations in the Beijing area showed that shoot bio- farmyard manure were used. At present these fer-
mass production of Chinese cabbage was significantly tilizers are often replaced by low sulfur or sulfur-
enhanced upon sulfur fertilization of the soil. A level free fertilizers such as complex fertilizers (like
of fertilization of 15-30 kg S ha-1 was sufficient to get N15P15K15), DAP (diammonium phosphate) and
optimum yield. However, the level of fertilization in urea. For example, the share of ammonium sulfate
other regions in China might have to be adjusted to the production in the total nitrogen fertilizers produc-
level of local atmospheric sulfur deposition. tion in China dropped from 100% in the 1950s to
44.9% in the 1960s, 6% in the 1970s and 0.7% in
Key words: Chinese cabbage, plant nitrogen, plant the 1990s. The N/S ratio in the fertilizers used in
nutrients, N/S ratio, plant sulfur, available soil sulfur, China increased from 1.0 in 1960 to 8.8 in 1990
sulfur deficiency, sulfur dioxide, sulfur nutrition (Liu, 1995). Recently, China has improved the
balance of N, P and K in fertilizers, however, the
importance of S and other micronutrients is often
Introduction ignored. As a consequence in several regions, sul-
fur has become a limiting factor for optimal yield
Sulfur is the fourth major nutrient after N, P and K and quality of crops. In order to get insight into
for agricultural crops and is essential for growth and the sulfur status of Chinese agricultural soils,
physiological functioning of plants. Sulfur is needed more than 18,000 samples from all over the coun-
for the synthesis of the amino acids cysteine and me- try and about 900 samples from the Beijing and
thionine, which are of great significance in the struc- Tianjin areas were analyzed.
ture, conformation and function of proteins and en- Chinese cabbage is a common and widely
zymes. Furthermore, it is incorporated into several grown vegetable throughout the country, espe-
other metabolites, as thiols (glutathione), sulfolipids cially in northern China, since it has a high yield
and secondary sulfur compounds (alliins, glucosi- and relatively short growing period. For instance,
nolates, phytochelatins), which play an important role winter Chinese cabbage usually has a yield of
in the physiology of plants and in the protection and 100-120 ton ha-1 in the Beijing and Tianjin areas.
adaptation of plants against stress and pests (De Kok With the current high production levels, an ade-
et al., this issue). Sulfur fertilization is not always op- quate supply of nutrients must be available for
timal, which might negatively affect both crop yield optimum plant growth and production. However,
and quality. It has been recognized that currently sul- Chinese farmers tend to apply more nitrogen fer-
fur deficiency is one of the major plant nutrient tilizer than is needed for optimal yield, whereas
stresses in crops throughout the world (Schnug, 1991; often insufficient phosphate and potassium are
McGrath and Zhao, 1996; Schnug and Haneklaus, applied. In addition, the significance of the secon-
1998; Zhao et al., 1999). In China sulfur deficiency dary nutrients and micronutrients are ignored,
has also become apparent and now occurs frequently resulting in loss of potential yield and income
(Wang et al., 2001; Cui and Wang, 2003; Zhao et al., from production of this vegetable. Responses to
2003; Li and Liu, 2004; Meng et al., 2004). The use of sulfur fertilization were reported for some leaf
high yielding varieties, increased cultivation intensity, vegetables and Chinese cabbage in China (Chen et
and an overall improvement of cultural management al., 2000; Liu et al., 2003).
In general, Chinese cabbage is grown in the
vicinity of cities and here yield and quality might
1
Soil and Fertilizer Institute, Chinese Academy of Agricul- be negatively affected by air pollution (Zheng et
tural Sciences (CAAS), 100081, Beijing, China al., 1996). Coal is still the principle source of en-
2
Laboratory of Plant Physiology, University of Groningen, ergy in China and its combustion results in high
P.O. Box 14, 9750 AA Haren, The Netherlands levels of the air pollutants SO2, NOx, and acid
164 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

Table 1:
Levels of available nutrients in fluviogenic soil from Changping County, Beijing, China and the critical levels for the differ-
ent nutrients.
Organic
pH matter Nutrients (mg l-1)
(%)
Ca Mg K N P S B Cu Fe Mn Zn
Soil test results 8.1 1.09 2204 244 53 12 15 0.5 0.46 2.5 8.0 4.1 1.7
Critical levels 400 121 78 50 12 12 0.20 1.0 10 5.0 2.0

rain. The impact of acid deposition on agricultural The data of atmospheric SO2 concentrations in
crops and forests in southern China has been reviewed Beijing were provided by the Beijing Environ-
by Feng (2000). Despite the potential toxicity of sul- mental Protection Bureau and were also measured
furous air pollutants they also may contribute to the by the national standard method (GB/T 15262:
plants´ sulfur fertilization. For instance, one of the Ambient air – Determination of sulfur dioxide –
primary causes of sulfur deficiency in North America Formaldehyde absorbing – Pararosaniline spec-
and Western Europe is attributed to the ongoing reduc- trophotometry).
tion of atmospheric sulfur deposits as the consequence For the experiments a fluviogenic soil was taken
of strict regulations on industrial sulfur emissions from Changping County, Beijing; it is the main
(Schnug, 1991; McGrath et al., 1996). This is sup- soil type in the Beijing and Tianjin areas. The soil
ported by laboratory experiments, which have shown was air-dried for a few days and sieved through a
that dependent on the atmospheric level and the pe- 2 mm screen. Available nutrients and adsorption
dospheric sulfur suply of plants, SO2 may act both as characteristics were determined by ASI Soil
toxin and nutrient (De Kok et al., 1998, 2000; De Kok Analysis Methods. From the obtained data it was
and Tausz, 2001; Yang et al., 2003). It remains to be evident that the soil had a high pH, high levels of
questioned to what extent SO2 pollution in the vicinity plant available Ca, Mg and Cu and low levels of
of Chinese cities is toxic or contributes to sulfur fer- plant available N, P, K, S, Fe, Mn and Zn (Table
tilization of Chinese cabbage. The current paper pre- 1). Two cultivars of Chinese cabbage (Brassica
sents results of pilot experiments with two cultivars of pekinensis, cv. Kasumi F1, Nickerson-Zwaan, the
Chinese cabbage, which were grown in pots with local Netherlands and cv. Beijing 3, China) were used
soil with and without additional sulfur fertilization at in the experiments.
two sites in the Beijing area. In the summer of 2002 the response of Chinese
cabbage to sulfur fertilization was tested at the
two experimental sites. Plants were fertilized with
Material and methods nutrients at levels more than adequate for maxi-
mum growth but much less than those considered
Soil testing to be toxic or out of balance with other plant nu-
ASI Soil Analysis Methods (PPI/PPIC Beijing Of- trients and conditions. The levels of the various
fice, 1992; Portch and Hunter, 2003) for available soil nutrients were added to the soil according to “a
sulfur test was adopted. Available soil sulfur was ex- Systematic Approach to Soil Fertility Evaluation
tracted by 0.08 M calcium phosphate and measured by and Improvement”, and were based on soil test
the turbidimetric procedure for SO42--S in the PPIC- results and sorption studies (data not shown). The
CAAS Corporative Soil and Plant Analysis Labora- nutrients were added as follows: 50 mg N l-1 soil,
tory. If the level of available soil sulfur is lower than 234 mg K l-1 soil, 55 mg P l-1 soil, 0.4 mg B l-1 soil,
12 mg l-1, the soils are considered to be sulfur defi- 20 mg Fe l-1 soil, 28 mg Mn l-1 soil, 5 mg Zn l-1
cient. Soils containing sulfur levels ranging from 12 to soil and 66 mg S l-1 soil. The latter represents an
24 mg l-1 are potentially sulfur deficient. At these soil equivalent to a level of sulfur fertilization of
sulfur levels supplemental sulfur fertilization is re- approx. 130 kg ha-1 and is referred to in the fig-
quired to obtain optimal crop yield and quality. If ures as +S. In part of the pots no sulfur was added;
available sulfur is higher than 24 mg l-1, the soils are referred to as -S. The nutrients were added as a
considered to be sulfur sufficient. solution and mixed thoroughly with the soil. The
soil was watered to field capacity and 15-20 seeds
Response of Chinese cabbage to sulfur fertilization at were sown in each pot (with 800 ml air-dried
two sites in the Beijing area soil), and then thinned to 4 plants per pot after
emergence. All treatments were irrigated by a
Two experimental sites were selected; one at central system of capillary irrigation (1.5 g NH4NO3 per 5
Beijing inside the 3rd Ring Road (site A) and one at the liters of de-ionized water) at the bottom of the pot
outskirts of Beijing outside the 6th Ring Road (site B). in order to maintain a soil moist content close to
Landbauforschung Völkenrode, Special Issue 283, 2005 165

field capacity. The plants in pots were placed under a level), while 18% (14% in Beijing and Tianjin) of
plastic transparent foil in order to provide protection the soils contained available sulfur levels ranging
against heavy rainfall in summer. After 20 days the from 12 to 24 mg l-1, which might be considered
first harvest of the plants was carried out and two to be potentially sulfur deficient (Table 2). The
plants in the diagonal corner in each pot were har- data demonstrated that sulfur deficiency of soils is
vested. The second harvest was carried out after 28 a widespread problem in China and that in these
days. areas additional sulfur fertilization is required for
In the summer of 2003 the response of Chinese cab- optimal crop yield and quality.
bage to various levels of sulfur fertilization was tested
at one of the experimental sites (site A). The same SO2 pollution levels in Beijing
cultivars of Chinese cabbage were used. The same soil The atmospheric SO2 concentration in Beijing
as used in the first experiment and the basal nutrients has substantially decreased during recent years.
at the optimum levels were added, except S (see This can be ascribed to the great effort to reduce
above). Sulfur was applied as K2SO4 at levels of 0, 15, air pollution levels in the city. The change in use
30, 60, 90 and 120 kg S ha-1 which was calculated by of coal to natural gas as energy source and a
20 cm cultivated layer and 1.2 g cm-3 soil bulk density stricter regulation of pollutant emissions have
of this soil (so the applied rate was 0.0, 6.3 12.5, 25.0, resulted in a strong decrease of SO2 emission over
37.5, 50.0 mg S kg-1 soil in the pot experiments). The the period of 1998 to 2002 (Figure 1). The natural
soil was watered to field capacity and 20 seeds were gas supply in the city was more than 1.8 billion m3
sown in each pot (containing 1 kg air-dried soil) and in 2002, which was about 6 times higher than in
thinned to 2 plants per pot after emergence. During the 1998. The use of high quality and lower-sulfur
experiment period all pots were watered with the same coals was 8 million ton in 2002, which was 4-fold
amount (50-100 ml) of NH4NO3 solution (2.0 g higher than in 1998. SO2 annual mean concentra-
NH4NO3 per 5 liters of deionized water) every day. tion has decreased from 120 µg m-3 in 1998 to 67
There were 5 replicates in each treatment of the 6 fer- µg m-3 in 2002. During 2002 and 2003, the atmos-
tilization levels of sulfur. The pots were put under a pheric SO2 levels were monitored at the experi-
plastic shed, which provided the plants protection mental sites during the experimental period and
against heavy rainfall in summer. The plants were the daily mean concentrations in Beijing are
harvested after 28 days. shown in Table 3 and Figure 2. SO2 concentra-
The fresh and dry (80 °C, 24 hours) weight of shoots tions in Beijing in the summer time were about 20
was measured after harvest. Total nitrogen was deter- µg m-3.
mined with the Kjeldahl method according to Barneix
et al. (1988). Analysis of the total S content was car- Impact of sulfur fertilization on Chinese cabbage
ried out as described by Durenkamp and De Kok
(2002). Sulfate was determined after HPLC separation Sulfur fertilization of the fluviogenic soil from
according to Tausz et al. (1996). The content of P, K, the Beijing and Tianjin areas had a substantial
Zn, Mn, Fe, Ca and Mg of the shoots were determined impact on Chinese cabbage and resulted in a sig-
after H2SO4-H2O2 digestion (Lu, 1999). nificant increase of the shoot fresh weight produc-
tion of two cultivars of Chinese cabbage (Figure
3). The fresh weight of the shoot of Beijing 3 was
Results and discussion significantly higher upon sulfur fertilization at
both harvests. However, an increase in shoot
The status of available soil sulfur weight of Kasumi F1 upon sulfur fertilization was
only observed at day 28. This indicated that the
During recent years a total of 18,183 soil samples local cultivar Beijing 3 had a higher sulfur de-
from China (and 923 samples from Beijing and Tian- mand than Kasumi F1 (Figure 3). There were no
jin) were analyzed. From the data on available soil differences in plant growth within the same treat-
sulfur it is obvious that 24% (27% in Beijing and ment for either harvesting day or experimental
Tianjin) of the soils tested were S deficient, with site.
available sulfur levels less than 12 mg l-1 (the critical

Table 2:
The status of available sulfur (mg l-1) in the selected soil.
Min. Mean Max. <12 12-24 24-48 >48 Number of samples
% of total selected samples
China 0 40 820 24 18 28 30 18,183
Beijing and Tianjin 0 55 262 27 14 16 43 923
166 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

20 1 40
N at ura l g as su pp ly
18
H ig h qu alit y a nd lo w s ulfu r co nt ent co al 1 20
16 A nnua l a vera ge co nc ent rat io n o f s ulfu r dio xid e
Gas (10 m ); Coal (10 ton)

14 1 00
6

SO2 (ug m )
12

-3
80
10
3

60
8
8

6 40
4
20
2
0 0
19 9 8 1 999 2 00 0 2 0 01 20 0 2

Y ear

Figure 1:
Energy supply and SO2 concentration change in recent years. Data from Beijing Environment Monitoring Station.

Sulfur fertilization resulted in an increase of the total Table 3:

sulfur, which was mainly due to a higher sulfate con- SO2 concentrations at two experimental sites in the
tent of the plants (Figure 3). The organic sulfur con- Beijing area in 2002. SO2 concentration was measured
tent was also increased upon sulfur fertilization for every day at site A and twice a week at site B during the
both harvests at the different sites. experiment period (for information on sites see Material
and methods).
SO2 (µg m-3)
Mean Range
Site A 17 2-34
Site B 17 9-32

Sulfur fertilization only slightly increased total

nitrogen content of Beijing 3 for both harvests,
whereas that of Kasumi F1 was hardly affected
(Figure 3). The N/S ratio in non-sulfur fertilized
Figure 2: plants was much higher than that of the sulfur-
SO2 concentrations (daily mean) in Beijing during the ex- fertilized plants in both cultivars especially after
perimental period. Data from Beijing Environment Monitor- 28 days when shoot growth was reduced (Figure
ing Station. 3). The ratio of N/S was between 15 to 20 in the
sulfur-fertilized plants.

Table 4:
Effect of sulfur fertilization on P, K, Ca, Mg, Fe, Zn and Mn content of shoots of two cultivars of Chinese cabbage. Plants were
grown at site A for 28 days. Data represent the mean of 3 measurements with 8 plants in each (r SD). Different letters (a, b) indi-
cate significant differences at p ” 0.05 between different treatments.

P K Ca Mg Fe Zn Mn
(%) (%) (%) (%) (mg kg-1) (mg kg-1) (mg kg-1)
Beijing 3 -S 0.42 ±0.04a 2.67 ±0.22a 2.9 ± 0.2a 0.33 ±0.02a 294 ± 53a 47 ± 7a 51 ± 4a
+S 0.39 ±0.06a 3.81 ±0.53b 2.5 ± 0.2a 0.34 ±0.02a 302 ± 21a 64 ±13b 72 ±13b
Kasumi F1 -S 0.42 ±0.01a 2.48 ±0.05a 2.8 ± 0.1a 0.32 ±0.03a 293 ± 53a 40 ± 6a 45 ± 8a
+S 0.53 ±0.05b 3.32 ±0.16b 3.2 ± 0.2b 0.38 ±0.02b 376 ± 60b 65 ±10b 65 ± 6b
Landbauforschung Völkenrode, Special Issue 283, 2005 167

Kasumi F1 Beijing 3
25 d d
Fresh weight of shoot
-1
(g plant ) 20

c
15
b bc c c
b
10
ab b b
5
a a a
a a
0

d
200 c
DW)

d d c
d c c
Total S

150 c
-1

b
(Pmol g

100 b
b
a a
a a
50

120 d
DW)

d
Sulfate

90 cd b b
-1

cd b b
(Pmol g

b
c
60
a a
30 b b a
a
0

120 c
DW)

c c
Organic S

c c
90 c c c
-1

b
(Pmol g

b b b
60
a
a
a a
30

4 c d
DW)

a b bc
a a a b
Total N

3 a a ab b b
-1

a
(mmol g

a
2

0
c
c c
60 c
c c
N/S

40
b b
a a a a b b
20 a a

0
-S +S -S +S -S +S -S +S
20-d 28-d 20-d 28-d

Figure 3:
Response of growth, sulfur and nitrogen metabolites of two cultivars of Chinese cabbage to sulfur fertilization at two sites in
the Beijing area. Plants were grown in the fluviogenic soil for 20 and 28 days at site A (open bars) and site B (dotted bar, see
Material and methods). Without sulfur fertilization (-S) and with 66 mg SO42--S l-1 soil (+S). The fresh weight of shoots (g)
represents the mean of 12 measurements with 2 plants in each (± SD). Total S, total N, and sulfate content (µmol g-1 DW) of
the shoot represent the mean of 3 measurements with 8 plants in each (±SD) at day 20 and the mean of 4 measurements with
6 plants in each (± SD) at day 28. The organic sulfur content was derived by subtracting the sulfate content from that of the
total S content. Different letters indicate significant differences at p ” 0.05 between (+S) and (-S) treatments.
168 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

Kasumi F1 Beijing 3
40
Fresh weight of shoot

30 b b b b
c c
(g plant )

c c
-1

ab b
a
20 a

10

0
200
b b
ab ab b b b b
160 b
(Pmol g DW)

ab a
Total S

120
a
-1

80

40

0
a a b
a a a b ab
4 a a a a
(mmol g DW)
Total N

3
-1

0
a
40
ab ab b ab
30 b a ab b b
N/S

b b
20

10

0
0 30 60 90 120 0 30 60 90 120 150

Sulfur fertilization (kg ha-1)

Figure 4:
Effect of different levels of sulfur fertilization on growth, total S, total N and N/S ratio of two cultivars of Chinese cabbage.
Sulfur was applied as K2SO4 at levels of 0, 15, 30, 60, 90 and 120 kg S ha-1 which was calculated by 20 cm cultivated layer
and 1.2 g cm-3 soil bulk density of this soil (so the applied rate was 0.0, 6.3 12.5, 25.0, 37.5, 50.0 mg S kg-1 soil in the pot
experiments, see Material and methods). Data of the fresh weight of shoot represent the mean of 5 measurements with 2
plants in each (± SD). Total S and total N content of the shoot represent the mean of 3 measurements with 2 plants in each (±
SD). Different letters indicate significant differences at p ” 0.05 between different treatments.

Upon 28 days of sulfur fertilization the levels of Optimizing of sulfur fertilization for Chinese cab-
other plant nutrients in shoots was also affected (Table bage
4). The levels of P, K, Fe, Mg, Zn, Ca and Mn in It was evident from the previous results that the
shoots of Chinese cabbage cv. Kasumi F1 were levels of sulfur in the fluviogenic soil from Bei-
slightly enhanced upon sulfur fertilization. In cv. Bei- jing and Tianjin were not sufficient for optimal
jing 3 sulfur fertilization only resulted in an enhance- growth of Chinese cabbage. In order to assess
ment of the levels of K, Zn, Mn. optimal sulfur fertilization plants were grown on
Landbauforschung Völkenrode, Special Issue 283, 2005 169

soil fertilized with 0, 30, 60, 90 and 120 kg S ha-1 Conclusions

(Figure 4). The shoot fresh weight increased by 50 %
when 30 kg S ha-1 sulfur fertilizer was applied for Bei- Sulfur fertilization of soils is necessary to obtain
jing 3 and was not further affected at higher levels of optimal yield in various areas in China. For in-
sulfur fertilization. There were no differences in shoot stance the present data showed that in the Beijing
biomass production at 30, 60, 90 and 120 kg S ha-1. area a level of sulfur fertilization of 15-30 kg S
For Kasumi F1, sulfur fertilization at 15 kg ha-1 was ha-1 was needed to get optimal biomass production
sufficient for optimal shoot biomass production. of Chinese cabbage. However, the level of fertili-
Sulfur fertilization resulted in a slight increase of the zation in other regions in China might have to be
total S content in both cultivars of Chinese cabbage adjusted to the level of local atmospheric sulfur
and an increase of the total N content in Beijing 3 deposition.
(Figure 4). As a consequence the N/S ratio in shoots of
Kasumi F1 decreased from 38 in the non-fertilized to
29 in the fertilized plants (Figure 4). Likewise, the N/S Acknowledgements
ratio of Beijing 3 decreased from 29 to 24-25.
It has been suggested that the N/S ratio could be This study was funded by the Netherlands
used as a diagnostic tool to determine plant sulfur de- Foundation for the Advancement of Tropical Re-
ficiency, based on an assumed direct interaction be- search (NWO-WOTRO).
tween nitrogen and sulfur assimilation in plants (Zhao
et al., 1996; Thomas et al., 2000; Blake-Kalff et al.,
2002; Randall et al., 2003). However, one should be References
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Society, York, UK teraction, Signaling. Backhuys Publishers, Leiden, pp
Meng C, Lu X, Cao Z, Hu Z (2004) Effect of sulfur fertilizer 363-365
on yields of rice and oil rape and the critical values of soil Zhao FJ, Hawkesford MJ, Warrilow AGS, McGrath SP,
available sulfur. Plant Nutr Fert Sci 10:218-220 (in Chi- Clarkson DT (1996) Responses of two wheat varie-
nese) ties of sulfur addition and diagnosis of sulfur defi-
PPI/PPIC Beijing Office (1992) Systematic Approach for ciency. Plants Soil 181:317-327
Soil Nutrient Evaluation. China Agricultural Scientech- Zhao FJ, Hawkesford MJ, McGrath SP (1999) Sulphur
nology Press, Beijing, pp 54-70 (in Chinese) assimilation and effects on yield and quality of
Portch S, Hunter A (2003) A Systematic Approach to Soil wheat. J Cereal Sci 30:1–17
Fertility Evaluation and Improvement. Modern Agricul- Zhao S, Hu S, Li W, Du J (2003) Effect of sulfur on
ture & Fertilizers - PPI/PPIC China Program Special Pub- grain protein content and storage protein content in
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Landbauforschung Völkenrode, Special Issue 283, 2005 171

The role of sulfur fertilizers in balanced fertilization

Yiming Zhou1, Defang Wang1, Jinghua Zhu1, Qingshan Liu2 and Ming Xian Fan3

Abstract1 suburban type agricultural production in metropolis.

In order to achieve the goal of agricultural produc-
A survey on the nutrient content of soils in the Tian- tion with high yield, improving crop quality and
jin area in the north of China, showed that 30% of increasing farmer’s income, balanced fertilization is
total farmland area was sulfur and potassium defi- necessary. Therefore we arranged the following
cient. Deficiency occurred mainly in cinnamon soil, studies.
chao cinnamon soil and partly chao soil in Ji and
Baodi counties. Results collected from field trials on
rice, wheat and corn showed that deficiency of S or Material and methods
K caused a reduction in grain yield ranging from 6 -
24%. Combined S and K fertilization resulted in The selection of experiment fields and the condi-
substantial increases in crop production. Fertiliza- tion of soil nutrients
tion of the soils of 12 trials with Chinese cabbage,
garlic, scallion, chili, green turnips and carrot with We arranged field experiments mainly in Ji and
NPK, adding 60 - 120 kg ha-1 sulfur, increased Baodi counties in cinnamon and Chao soils where
yields by 16.0 - 36.4% with a large of value/cost soil sulfur and potassium contents are lower than
ratio of 12.3 - 28.7, and high vegetable quality. In other districts (Figure 1 and 2).
nutrient management, S combined with other nutri-
ents has to become a common fertilizer practice to Analysis methods
guarantee optimal crop production. Ca(H2PO4).H2O extraction and BaSO4 contrast
turbid ratio method was used for analyzing available
Keywords: Sulfur, potassium, grain, vegetables sulfur content in soil, and other nutrients analysis by
using Systematic Approach of Soil Nutrient Status
(Dowel and Porch, 1988). The commix of HNO3and
Introduction HCLO3 was used to digest plant and BaSO4 contrast
turbid ratio method was used for analyzing plant
The Tianjin area is located in North China, which total S EDTA titration was used for SO42- in irriga-
is facing the Bohai Sea eastwards and backing Yan- tion water.
shan Range northwards. It comprises a total land
area of 11,920 square km2 and 4,893 km2 of it is Treatment and fertilizer application
used as farmland. The area has total population of
Winter wheat, corn, cotton and vegetables sensi-
over 10,000,000 distributed over 12 districts and
tive to sulfur fertilizer including cabbage, Chinese
counties. The staple grain crops cultivated in the
cabbage and three pungent crops (garlic, scallion
Tianjin area are wheat, maize and rice. The area is
and chili) were selected as testing crops in field tri-
also an important basis of vegetable production. In
als. With various S application rates (60 - 120 kg ha-
addition to farmland, there are forests, various fruit 1
), the effect of combination of S and K or other
trees and cash crops planted in the Tianjin area.
nutrient on crops yield was examined with the treat-
In addition to the soil potassium depletion, since
ments of NP (or NPS), NPK, and NPKS etc. Urea,
the 1980s sulfur deficiency of soils has become a
DAP and potassium chloride were used as nitrogen,
major problem due to a replacement of high-sulfur-
phosphorus and potassium source respectively. All of
containing fertilizers by sulfur-free or low-sulfur-
the P, S and K were applied as basal at seeding time.
containing fertilizers, a decrease in organic manure
For nitrogen, 40 percent was applied as basal dressing
fertilization and the use of high yield crops (Liu
and the rest was applied as top dressing at two times.
Chongqun and Hu Sinong, 1993; Zhou Yimin and
Crop yield was measured on each plot. Soils samples
Jing Haichun, 1995).
were taken by soil auger from the cultivable layer (0 -
Developing high quality crop and vegetable pro-
20 cm).
duction and ensuring the supply to urban consump-
tion are the foremost tasks facing the urban-

1
Tianjin Soil and Fertilizer Institute, Tianjin 300192,
China,
2
Agri-Technical Demon Station of Ji county, China
3
The Sulphur Institute, Washington DC, USA
172 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

197

234

131
201

159
134

78
26
21
16

Cinnamon Chao soil Humid Salinity Coastal

soil Chao soil Chao soil solonchak

Available K Available S

Figure 1: Figure 2: The mean contents of available S and K in the

The main soil types, the average contents of available S different soil types.
and K, and the number of trials in different districts of
Tianjin, China.
China, and has been growing in large areas in Tianjing.
Chinese cabbage has also a high demand for both sul-
Results and discussion fur and potassium.
Seven field trials on Chinese cabbage were arranged
The role of sulfur fertilizers in balanced fertilization at Baodi and Ji County respectively, from 2000 though
of staple crops 2003. The results are presented in Table 2. It was
From 1994 to 2000, we conducted the field trials on shown that compared with farmer’s routine treatment
rice, wheat and corn with various combinations of (only NP) the treatment of NPK (in 2000, 2003)
NPKS. The results are shown in Table 1. It indicated increased yield by 7.9 - 13.7%. Based on NPK, add-
that in most cases, the deficiency of S or K resulted in ing 60 - 120 kg ha-1 sulfur, Chinese cabbage yield
yield reduction in certain degrees. Sulfur deficiency were increased by 16.9 - 26.4%. Clearly, sulfur fer-
led to 6 -16% yield reduction. The combination use of tilization promoted potassium use efficiency. It also
S and K produced the best results. Therefore, in fertil- increased the effect of phosphorus on Chinese cab-
izer nutrient management, S combined with other nu- bage yield (in 2001). In Figure 3 it is shown that
trients has become one of the necessary measures in adding 104 kg ha-1 phosphorus the yield of Chinese
sound crop production. cabbage increased by 18% compared to no P treat-
ment with a value : cost ratio of 16; based on NPK
Effect of sulfur fertilizers on yield of Chinese cab- treatment, adding S 60 kg ha-1, though the Chinese
bage cabbage yield increased by 5%, but value : cost ratio
was boosted to 19. It means a small amount of sulfur
Chinese cabbage is the major vegetable grown in fertilizer input produced high economic return to
Tianjin. Due to its high yield and quality for food, it farmers.
has become one of the important vegetables in North
Landbauforschung Völkenrode, Special Issue 283, 2005 173

Table 1:
Effect of S and K fertilization on yield of corn, rice and wheat.
Relative
Mean yield
No. Sites Crop Treatment yield
(kg ha-1)
(%)
N275P215S60 7878 89
Maozhuang, NingHe
1 Rice N275P215K150 8231 93
County
N275P215K150S60 8885 100
N225P173S60 6120 83
2 Mongeying, Ji County Wheat N225P173K135 7380 100
N225P173K135S60 7380 100
N102P69S60 3462 83
3 Dongerying, Ji County Corn(Shendan 7) N102P69K90 3509 84
N102P69K90S60 4166 100
N135P1380S60 6270 88
4 Dongerying, Ji County Corn (Yedan13) N135P138K150 6495 91
N135P138K150S60 7110 100
N205P138S60 7823 88
Haogezhuang, Baodi
5 Corn (Shendan 7) N205P138K90 8327 94
County
N205P138K90S60 8867 100
N205P138S60 5670 76
Haogezhuang, Baodi
6 Corn (Yedan 13) N205P138K90 6405 86
County
N205P138K90S60 7455 100

Table 2:
Effect of S, K and P fertilization on yield of Chinese cabbage in 2000-2003.
Increase in Increase
Average
No. Sites Year Variety Treatment yield income
ton ha-1
( %) (103 $ ha-1)
N120P104 74.2 0 2.6
7 Bangjun, Baodi district Beijing3 N120P104K90 84.4 13.7 3.0
N120P104K90S60 93.8 26.4 3.3
2000
N160P52 74.5 0 2.6
Niudaokou, Baodi
8 Tianjin55 N160P52K90 80.3 7.9 2.8
district
N160P52K90S60 87.1 16.9 3.1
N450K135S60 74.4 0 1.6
9 Shiqiao, Baodi district 2001 Qiulv75 N450P104K135 83.3 5.1 1.8
N450P104K135S60 87.6 17.8 1.9
N300P173S120 107.6 0 2.0
10 Anding, Baodi district Beijing3 N300P173K90 119.0 10.6 2.5
N300P173K90S120 137.3 27.6 2.8
2002
N360P200S120 96.6 0 1.9
11 Liangsq, Ji county Beijing3 N360P200K150 111.1 14.9 2.2
N360P200K150S120 127.1 31.6 2.8
N360P225 113 0 5.3
12 Mongq1, Ji county Qiulv75 N360P225K300 123 8 5.6
N360P225K300S120 128 19 5.9
2003
N360P225 87 0 3.6
13 Mongq2, Ji county Beijing3 N360P225K300 97 8.9 3.9
N360P225K300S120 114 25.2 4.6

At harvest time we investigated the effect of K thickness, and plant weight improved clearly over
mixed with S on yield and quality of Chinese cab- farmer’s routine fertilization, with 2 - 3.3 cm, 3.2 -
bage. The results (See Table 3) showed that effect of 3.3 cm, and 0.9 - 1kg respectively.
NPK, NPKS on Chinese cabbage plant height, stem A field trial was conducted to compare two Chi-
174 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

Table 3:
Effect of S and K fertilization on Chinese cabbage cv. Beijing3 (n = 18).
Treatment Plant height (cm) Stem thickness (cm) Plant weight (kg)
N120P104 42.5 38.0 2.9
N120P104K90 43.8 40.2 3.6
N120P104K90S60 44.6 41.3 3.9

Table 4:
Effect of S and K fertilization on garlic.
Treatment Plant high Fresh weight (no garlic Diameter of a Weight of a garlic head
(with garlic shooting) shooting/a plant) garlic head
(cm) (g) (cm) (g)
N150P120 42 32.4 3.87 20.1
N150P120S60 48 39.3 4.11 22.9
N150P120 K112 47 34.2 4.04 21.9
N150P120 K1120S60 51 44.3 4.25 23.7

Table 5:
Effect of S and K fertilization on scallion.
Plant height Length of white stem Fresh weight of a plant Diameter of stem
Treatment
(cm) (cm) (g) (cm)
N180P110 83.3 26.8 80 1.9
N180P110 K90 88.1 27.4 112 1.9
N180P110 K90S60 87.3 27.7 129 2.2

Table 6:
Effect of S and K fertilization on scallion yield.
Scallion yield (kg ha-1) Average Yield
Treatment
1 2 3 (kg ha-1 ) increase (%)
N180P110 35445 36645 36870 36320 0
N180P110 K90 40800 41460 39240 40500 11.5
N180P110 K90S60 45525 41010 44955 43830 20.7

nese cabbage varieties response to sulfur fertilizer in Effect of S fertilizer, and combination of S and K on
2003. The result showed that applying the same garlic, scallion and chili yields and quality
quantity of S fertilizer increased Chinese cabbage Garlic, scallion and chili are sensitive crops to
Qiulv75 yield by 16.3%, but by 10.6% on Beijing 3 sulfur, and have high sulphur demand. In order to
compared to NPK treatment. This result illuminated evaluate the response of these crops to sulfur fertil-
the differences between Chinese cabbage varieties in izer, five field trials were conducted from 2000
response to sulfur. It indicates that when applying S through 2003 in Baodi county (site no.14,15,16,17,
fertilizer we should concern with the varieties sensi- respectively). The results of garlic were shown in
tivity to S to get higher benefit from S fertilization. Table 4 and Figure 3. The data in Figure 3 illustrate
that comparing with NP treatment, adding S in-
creased garlic yield by 16%, resulted in a high
value : cost ratio of 25. But for K, the yield increase
and VCR was 7% and 6.3, respectively. It means
garlic is more sensitive to S than K in this region.
The treatment of combined application of NPKS
resulted in the highest VCR on garlic with impres-
sive yield increasing. It indicated that NPKS bal-
anced fertilization is the way to get high yield, im-
prove crop quality and increase farmer’s income
Figure 3: The results of scallion and chili were showed in
Effect of P and S fertilization on Chinese cabbage yield Table 5, 6, 7, 8. The scallion yield in NPK treat-
(black bars) and value cost ratio (gray bars) ment was 4185 kg ha-1 higher than NP treatment, or
Landbauforschung Völkenrode, Special Issue 283, 2005 175

increasing by 11.5%. However, the NPKS treatment

produced 7515 kg/ha more than NPK treatment, and Yi el d, t / ha
25 24
increasing production by 20.7% (seeing Table 6). 25 I ncr ease, % 23
Chili was harvested in Oct. 2000, when the price VCR
of 1st class dry chili was 1.82$ kg-1. The output of 20 VCR( S)
NPS treatment was 1879 kg/ha, 367 kg ha-1 higher 16
than NP treatment. The output of NPKS was 2063 15
12
kg/ha, 552 kg ha-1 higher than NP treatment. Using
the local first class dry chili price, the treatment of 10 7. 1 7
6. 1 6. 5 6. 3 7. 5
NPS increased income by 665 $ ha-1, but treatment
of NPKS increased more than 1000 $ ha1, compared 5
with NP. With the NPKS balanced fertilization on
scallion and chili, high quality, output, and income 0
NP NPS60 NPK112 NPK112S60
are obtained.
In order to evaluate the effects of combined K and
S on scallion seed yield, we arranged field trials at
Shiqiao Village, Baodi District. The result is shown Figure 4:
in Table 9. Comparing with normal farmers’ prac- Effect of S and K fertilization on garlic yield.
tice (CK), the K application increased scallion seed
yield by 15.0%, for the S2 application the maximal
yield reached 717kg ha-1, an increase of 39.6% in Conclusions
yield and 1438 $ha-1 in income. It showed that
treatment of NPKS2 have the highest volume in
Based on the results collected from field trials
plant weight, weight of head, and diameter of head
conducted in Tianjing from 2000 to 2003, it can be
in four treatments, which produced the highest out-
concluded that: sulfur and potassium deficiencies
put. It indicated that in this region the proper
were identified in about 30% of total farmland area,
amount of application sulfur fertilizer should be
and mainly distributed in cinnamon soil, chao cin-
more than 100 kg ha-1 for scallion seed production.
namon soil and partly chao soil in Ji and Baodi
county. Deficiency of S or K cause grain yields re-
Effects of combined of K and S application on green
duction by 6% - 24% in rice, wheat and corn produc-
turnips and carrot yield
tions in these areas, combination use of S and K pro-
The green turnips field trials were arranged at duced highest yield.
Caijiafang Village, Wuqing (site no. 18). From the Adding 60 - 120 kg ha-1 sulfur to NPK recommen-
field survey that was conducted in the mid-growth dation increased Chinese cabbage yields by 16.9 -
period, potassium and sulfur deficiency had affected 26.4% in seven field trials. Results of garlic, scallion,
growth of green turnips. The leaves of green turnips and chili also showed that adding S60kg/ha in-
showed different degrees of nutrient deficiency creased yields by 16 - 19.5% over NP treatment, and
symptoms. Based on the results collected from the NPKS combined application increased yields by 20.
field trials at harvesting time (Table 10), adding 60 - 36.4% over NPK treatment, with high vegetable
kg S ha-1 increased yield by 28.7% over NPK treat- quality. Results of green turnips and carrot field
ment, with the higest value : cost ratio of 28.7. trials showed that comparing with NPK treatment,
While adding K increased yield by 24.9% over NPS, adding S 60-120 kg ha-1 increased yield by 17.6 -
with value to cost ratio of 27.1. 28.8% with maximum value : cost ratio of 12.3 -
The carrot field trials were arranged at Shen- 28.7.
grenzhuang Village, Baodi District (site no. 19) and
the result was shown in Table 11. The carrot bio-
logic character evaluation on 40 carrot plants
showed that the treatment of NPKS have the higher References
values in total fresh weight/per pant, fresh
weight/per carrot, the carrot length and thickness Dowel S., Porch S. (1988) A systematic approach for
than treatment of either NP or NPK, resulting in the determining soil nutrient constrains and establishing
highest yield in all treatments. Compared with balanced fertilizer recommendations for sustained high
yields. In: CAAS (eds) Proceedings of the Soil Interna-
farmer’s routine treatment (NP) applying 90 kg ha-1 tional Symposium on Balanced Fertilization. Chinese
K2O increased carrot yield by 9.5%; adding 120 kg - Agricultural Science and Technolgy Press, Beijing, pp
1
ha S increased carrot yield to 24.7 ton ha-1, with 8-12
income of 1048 $ ha-1 and value : cost ratio of 12.3.
176 L.J. De Kok and E. Schnug (eds.), Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

Table 7:
Effect of combined of S and K fertilization on chili shape.
Treatment Plant height Plant weight Number of chili Chili weight Number of ill Number of green
(cm) (kg) per plant (g) chili per plant chili per plant
N150P90 81.6 0.173 40.1 1.90 8.1 5.4
N150P90S60 82.8 0.181 44.7 2.08 7.4 4.4
N150P90 K90 79.0 0.196 42.6 2.05 5.2 3.5
N150P90 K90S60 82.4 0.216 50.8 2.11 4.5 3.4

Table 8:
Effect of S fertilization on yield of first class chili.
Yield of first class chili Increase by S fertilization rate
Treatment
(kg ha-1) (%)
N150P90 1512 0
N150P90S60 1879 19.5
N150P90 K90S60 2063 36.4

Table 9:
Effect of combined of K and S fertilization on scallion seed production (kg ha-1) in 2001.
Repeat Increasing
Treatment Increasing Increasing Response Response
Aver- income
I II III amount % to K % to S %
age ($ ha-1)
N180P104 490 520 530 513 0 0 0 0 -
N180P104K90 590 570 610 590 77 531 15.0** 15 0
N180P104K90S60 670 690 650 670 157 1105 30.5** - 13.6**
N180P104K90S120 721 713 716 717 203 1438 39.6** - 21.5**
LSD 0.05 = 35.3*; LSD 0.01 = 53.5**

Table 10:
Effect of combined K and S fertilization on yield of green turnips (ton ha-1).
Repeat Response Response to S Value cost
Treatment Average
I II III IV to K (%) (%) ratio
N206P173S60 53.0 54.7 49.9 52.8 52.6 0 - 27.1
N206P173S60K112 66.7 67.0 63.7 65.5 65.7 24.9** 28.8** 28.7
N206P173K112 50.8 52.9 49.0 51.4 51.0 - 0 23.3
LSD 0.05 = 2.97*; LSD0.01 = 4.49**

Table 11:
Effect of combine K and S fertilization on yield of carrots.
Repeat (kg 667 m-2) Income in-
Yield increase
Treatment I II IV Average crease Value cost ratio
(%)
($ ha-1)
N180P90 21.3 19.5 926 21.3 21.0 0 926 9.0
N180P90K150 23.4 23.0 981 23.1 23.0 9.5* 981 11.9
N180P90K150S120 23.4 24.2 1048 24.5 24.7 17.6** 1048 12.3
LSD 0.05 = 1.79*; LSD 0.01 = 2.71**

Liu C, Hu S (1993) Soil sulfur status and sulfur fertilizer ricultural Science and Techology Press, Beijing, pp 74-
requirements in China. Proceedings of the International 80
Symposium on the Role of Sulfur, Magnesium and
Micronutrients in Balanced Plant Nutrition Chengdu
Ccience and Technology University Publishing Com-
pany, pp 19-29
Zhou Y, Jing H (1995) Soil nutrient balance and potash
effects in Tianjin. In: Xie J et al. (eds) Soil Potassium
Fertility and Management in North China. Chinese Ag-
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Joachim Riedel und Ulrich Sommer (2005)
Vergleichende Analyse verschiedener Vorschläge zur Reform der Zuckermarktordnung

283 Luit J. De Kok and Ewald Schnug (eds.) (2005) 11,00€

Proceedings of the 1st Sino-German Workshop on Aspects of Sulfur Nutrition of Plants

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