ROOT AND CANOPY

REGULATION
• Better canopy management is conducive for
flowering, fruit set, carbohydrate flow to fruits,
increased xylem drive of solutes, fruit firmness,
colour and thereby quality.
• Restriction on the canopy may be overcome by
managing the soil to create a more suitable
medium for root growth
Approaches
- To modify the root system itself to enable it to
capture more of the limiting resources
• To adjust the canopy characteristics so that it
utilises those resources more efficiently
• Through genetic improvement and by cultural
means
• What size and distribution of root system is
required to avoid restriction on the canopy
• Which cultural practices provide the level of
control scale of changes to root growth
• How roots acquire water and nutrients from
different soil horizons how roots regulate
growth, activity and life span of the canopy
 Growth

Crop growth can be defined in terms of the

production of biomass. This involves the net fixation
of CO2 and the assimilation of mineral nutrients, such
as N, P and S, for the synthesis of more complex C
molecules.

Growth could be considered in terms of relationship between

sources, where metabolites are synthesised or nutrients are
absorbed, and sinks where they are utilised to create new
tissues.

-
• Photosynthesising leaves and absorbing roots
provide sources and the growing tissues
provide the sinks.

- The coordination between root and shoot

growth is compatible with the maintenance
of a constant source-sink relationship during
the period of exponential vegetative growth.
Morphological Relationship
Dicotyledonous species
• The root system of most dicotyledonous plants
develops from the radicle, which is the root pole of the
embryonic axis.
• The secondary transporting tissues- the xylem and
phloem are the primary pathways by which roots and
shoots are related. They are the primary routes by
which materials are moved from one tissue to another,
and the structural basis of root-shoot interconnection.
• Xylem – root to Aerial part(shoot)
• Phloem- Leaves(shoot) to storage organ, growing
part (root)
The radicle is the first part of a seedling (a growing plant embryo) to
emerge from the seed during the process of germination. The radicle
is the embryonic root of the plant, and grows downward in the soil
(the shoot emerges from the plumule). Above the radicle is the
embryonic stem or hypocotyl, supporting the cotyledon(s).
 Lateral transfer of water across stem tissues
• with divided root system water transferred
from one side to another through the stem in
grape
Monocotyledonous species

• Inmonocots, root axes (except for the radicle)

originate at nodes and comprise two root
systems: the seminal one, which arises from
primordia associated with nodes in the
embryo, and the crown or adventitious root
system, which comes from primordia
associated with nodes of foliar primordia.
• Each root axis is associated with a particular
part of the canopy
 Root primordia

A primordium ( plural: primordia) in embryology, is defined as

an organ or tissue in its earliest recognizable stage of
development. A primordium is the simplest set of cells capable
of triggering growth of the would-to-be organ and the initial
foundation from which an organ is able to grow.
 Seminal (Seed) Root
System

Seminal (seed) roots originate from the scutellar node

located within the seed embryo and are composed of
the radicle and lateral seminal roots.
 Nodal Root
System

Nodal roots develop sequentially from individual nodes

above the mesocotyl, beginning with the lowermost node
in the area of the young seedling known as the "crown".
•

Root/ Shoot ratio

- Annual crop plants show high root/shoot ratios during
germination and stand establishment
- young seedlings almost always begin with a high root/shoot
ratio.
- This ratio generally shifts during the growing season in
favour of shoot production.
Perennial Plants
- both growth and maintenance respiration were greater in the
roots than in the shoots.

Homeostasis
- There is a general tendency for any species to maintain a
characteristic relationship between root and shoot dry weight.
When part of either root or shoot is removed, the plant tends to
compensate in such a way as to return to a root/shoot ratio
characteristics of the species.
 CO2 – Assimilating organs, stems, and roots (as a
percentage of total Biomass) in various plant functions

Plant type CO2 Shoot Root Root/shoot

assimilatin (%) (%) Ratio
g organs
(%)
Evergreen 1-2 80-90 10-20 0.11
trees
Deciduous 1-2 80 20 0.25
trees

The homeostasis observed in root/shoot ratios of most

plants results from a functional equilibrium between
these two parts of the plants
Genetic influences on root-shoot relationships
- late varieties of potato have larger root system
- late varieties of potato have higher root shoot ratio

Hormonal effect
- caulocaline supplied by roots needed for shoot growth
- growth controlled by several groups of hormonal sub
- synthesis of cytokinin , gibberellin , ABA – roots
- synthesis of auxin- shoots
- stress signal
• Environmental factors
Temperature
Variation in temperature, however, directly affect both
roots and shoot in a number of ways - through affecting the
absorption of nutrients and water, through modifying the
balance of growth substances or by influencing the
temperature of the apical meristem of the shoot.
• Shoots subjected to large didrnal temp fluctuation
• Translocation of carbohydrate from shoot to root decreases
as root temp decreases
• Root zone temp effects
- Leaf elongation rate controlled by soil temperature
- impact of poor nutrient uptake and water stress when roots
are cold
 Light Intensity

Competition between leaves and roots for

carbohydrates increases when the supply is
restricted by low light intensity.
Root shoot ratio

Temperatur Soil N levels (g/kg)

e
0 0.035 0.175 0.315
(oC)
14 0.39 0.33 0.31 0.24

22 0.47 0.43 0.40 0.23

30 0.56 0.45 0.40 -

 Water status

• Roots are subjected to transient flooding

which shoots rarely experience
• Roots restricted with high water tables
• When adequate mineral and water supply by
unflooded soil, low root/shoot ratio sufficient
• Xylem continuity provide rapid
communication of water status from one part
to another
 Nutrients

• High N level reduces size of the root system compared to shoots

• If the increased supply of nitrogen leads to greater growth,
the actual weight of roots usually increases, not as greatly as that
of shoots
- Greatest increment of growth obtained when supply of nutrients
is above that which leads to physiological symptoms of deficiency
- increased phosphate reduces root/shoot ratio
-Fertilizers stimulate shoot growth than root growth
- Continuous circulation of amino acids and certain cations K, Mg
in the phloem and xylem
 Canopy management
• Canopy management aims at more
distribution sunlight to convert light energy
into chemical energy of the plant(Dry matter
gain). There should have leaves to intercept
light .
• DM = (RAD X % INT X PH) - RESP
Where DM = Dry Matter
RAD=Active radiation to initiate photosynthesis. Normally only
50% of solar light radiations are active radiations taped by
plants. Hardly 37-75% of this active radiation is actually used
by the plants.
% INT =Percentage of light intercepted by leaves of the crop or
plant. This is never more than 40% of the solar light avail
PH = Photosynthetic index or conversion capacity of the plant
to convert light energy to chemical energy and the actual
biomass production ratio
RESP=Respiratory carbon loss. It is estimated at 15 % usually.
 Light interception
• Increased tree density, provides more leaf
area than the available land area and thus
better light interception
• Reduced row distances, increased height north
to south planting rows help better light
interception
• High Density Planting
• Dwarfing root sticks
 Pruning

• allow maximum light interception and is

important for shape, Size of the fruit, leaf
arrangement & photosythsis
• summer pruning in apple helps in water
conservation; calicium retention