PHYSIOLOGICAL ECOLOGY: Plant Adaptations To Their Needs

! Nutrition
! Soil conditions ! Essential nutrients ! Root mutualists

Plant Nutrition: Soil Quality Impacts Plant Vigor

! Two soil factors:
1)! Texture - its general structure 2)! Composition - its organic & inorganic components

! Water
! Water stress ! Role of stomata ! C4 & CAM plants

! Other stresses
! ! ! ! Sunlight Heat Cold Low Oxygen

!Plant defenses & 2 compounds

Plant Nutrition: Topsoil Loss Is Critical

! Mix of rock (inorganic) & organic matter (humus breakdown)
! grasslands accumulate most
! 100t/km2/yr

Plant Nutrition: Topsoil Loss Is Critical

! Mix of rock (inorganic) & organic matter (humus breakdown)
! grasslands accumulate most
! 100t/km2/yr

! Its loss is important

! From 1700-5000 t/km2/yr ! 50,000 km2/ yr of arable land to wind & water erosion, salination, sodification, & desertification.

! Its loss is important

! From 1700-5000 t/km2/yr ! 50,000 km2/ yr of arable land to wind & water erosion, salination, sodication, & desertification.

! Precautions reduce loss ! Role of grazers

World food production faces a serious decline within the century due to climate change

UN FAO !
By the 2080s 5-20% decline in agricultural output globally!

Plant Nutrition: Essential Elements

! 9 Macronutrients
! need large amounts

! Deficiencies are visible

! Main ones are P, K, N
Healthy

IMPORTANT: ! 30-40% decline in India, 20-30% in Africa, with some countries experiencing some gain (mostly temperate countries). Sudan and Senegal could experience collapse: >50% decline!

! 8 Micronutrients
! need small amounts

Phosphate-deficient

Potassium-deficient

Nitrogen-deficient

Plant Nutrition: N has the greatest impact

! Its in:
! proteins ! nucleic acids ! chlorophyll ! enzymes (remember the giant rubisco) ! & more!
Healthy

Lets Talk About Getting Nitrogen

Phosphate-deficient

Potassium-deficient

Nitrogen-deficient

Plant Nutrition: Bacteria Fix Atmospheric N2

! Soils have:
! Nitrogen-fixers making nitrogenous minerals
! ammonia, ammonium & nitrate
N2 Atmosphere Soil N2 Nitrogen-fixing bacteria
NH3 (ammonia) H+ (From soil) NH4+ (ammonium)

Root Mutualists: Rhizobium In Nodules

! Legumes have:
! root nodules w/ Rhizobium ! A mutualistic relationship

! Legumes have:
! root nodules w/ Rhizobium ! A mutualistic relationship
N2
Nitrate and nitrogenous organic compounds exported in xylem to shoot system NH4+

! Crop rotation
! Grow various crops
! that deplete soil N

Denitrifying bacteria

Soil

Nitrifying bacteria

NO3 (nitrate)

! But rotate in a legume

! to refresh soil N

Organic material (humus)

Ammonifying bacteria

Root

Root Mutualists: Mycorrhizal Root/Fungus Mutualism

! Fungus gives plant: ! Plant give fungus:
! Sugars!

EPIPHYTES

Staghorn fern

! ! water & nutrient uptake by ! ! root surface area w/ hyphae

PARASITIC PLANTS
Hosts phloem Dodder Haustoria

Mistletoe - photosynthetic

Dodder - nonphotosynthetic

Indian pipe - nonphotosynthetic

CARNIVOROUS PLANTS

Venus flytrap

Pitcher plants

Sundews

What Youve Learned So Far: Plant Nutrition

! Soils provide nutrients
! So soil loss is important ! Texture
! Mix of rock & organics

PHYSIOLOGICAL ECOLOGY: WHAT PLANTS NEED

! Nutrition
! Soil conditions ! Essential nutrients ! Root symbionts

! Agricultural benefits ! Water

! Adaptations to water stress ! Special role of stomata ! Photosynthesis C4 and CAM plants revisited

! Other stresses
! ! ! ! Sunlight Heat Cold Low Oxygen

! Root Mutualisms
! Rhizobium in legume nodules
! Crop rotation ! soil nitrogen

! Composition
! Esp. P, K, N

! Nitrogen is critical
! Plentiful in air ! Fixed by bacteria
! In soil, make
! ammonia ! ammonium

! Mycorrhizal fungi
! Ecto & endomycorrhizae ! Translocate water/nutrients ! Get sugars

! Nitrate

! Some plants have evolved special nutritional modes

!Plant defenses & 2 compounds

Adaptations to water stress

! Water is an important factor influencing plant growth and development ! Plants exhibit structural and physiological adaptations to water supply ! Well see some in lab

Mesophytes:
moderate water supply temperate forests and grasslands - shade and sun forms.

Roses

Maple trees: genus Acer

Mesophytic grasses

Hydrophytes:
wet habitats, wet soil, sometimes partially submerged. Water lily, Elodea

Structural adaptations of hydrophyte leaves and plants

! Air sacks in leaves (for floatation) ! Stomata on the upper side of the leaf (often) and almost always open ! Thin cuticle (dont need to prevent water loss) ! Leaves often flat for surface area ! Less rigid structure (water holds them up)

La jacinthe d' eau (Eichhornia crassipes) Water Lily: Nymphaeaceae, basal angiosperms Waterlettuce (Pistia stratiotes)!

Xerophytes:
seasonal or persistent drought - arid and semiarid. Cactus, succulents ! ! ! !

Structural adaptations of xerophyte leaves

Small leaves (reduced surface area) Thick cuticle and epidermis Stomata on underside of leaves Stomata in depressions (protected from wind) or buried in hairs ! Reflective leaves ! Hairs

Saguaro Cactus!
Carnegiea gigantea!
(Cereus giganteus)!

BOOJUM TREE (Idria columnaris)!

Halophytes: salty soils - makes water

osmotically unavailable to them - resemble xerophytes. Pickleweed, mangroves

Pickle weed: Salicornia virginica

Oleander: stomatal crypts on the underside of the leaves

Common Sea-lavender (Limonium serotinum)

Red mangrove: Rhizophora mangle

Batis maritima

The stomata
! Stomata help regulate the rate of transpiration (water loss), in part through stomatal morphology and placement ! Stomatal density is under both genetic and environmental control ! Desert plants (xerophytes) have lower stomatal densities than water lilies (hydrophytes)

Environmental control of stomatal density

! During development, light intensities and = stomatal densities What might that mean??? Studies show that CO2 leads to of stomata which leads to an transpiration. This has implications for cooling, xylem flow etc. CO2 levels

! Guard cells take in water and buckle outward due to cellulose microfibrils, opening the stoma ! They close when they become flaccid

Transpiration
! Plants can wilt if too much water is lost ! Higher rates of photosynthesis can lead to increased sugar production ! Transpiration also results in evaporative cooling: prevent the denaturation of enzymes involved in photosynthesis and other metabolic processes
20 !m

The role of potassium in stomatal opening

! Changes in turgor pressure that open and close stomata result primarily from the reversible uptake and loss of potassium ions by the guard cells ! These are driven by active transport of H+ = membrane potential ! Accumulation of K+ (lowers water potential) results in water gain through osmosis - opens stoma ! Stomata are usually open during the day and closed at night: minimizes water loss when photosynthesis is not possible

! The stomata of xerophytes

! Are concentrated on the lower leaf surface ! Are often located in depressions that shelter the pores from the dry wind
Cuticle Upper epidermal tissue

Lower epidermal tissue

Trichomes (hairs)

Stomata

100 m

Cues for stomatal opening and closing

OPENING: ! Redlight receptors in Chlorophyll and Bluelight receptors in Xanthophyll stimulate the proton pumps=uptake of potassium ! Depletion of CO2 in leaf as photosynthesis begins ! internal clock: circadian rhythm (approximately 24 hours) ! Environmental stresses can cause stomata to close during the day ! ! ! ! ! CLOSING: Darkness ABA (Abscisic Acid, a hormone) High internal CO2 concentration Circadian rhythm.

Stomatal opening
! Proton pumps activate to pump H+ out of the cell ! This triggers gated inward specific K+ channels to open. K+ moves down its electrochemical gradient ! Cl- diffuses in to balance the positive charge of the K+ ! It is the accumulation of the ions that lowers the water potential of the cells, causing water to move inward, swelling the guard cells and opening the stomatal pore.

Stomatal closure
! A build up of ABA causes Cl- anions to move towards the cell wall, and the closure of the inward specific K+ channels and opening of outward specific K+ channels. ! K+ moves out of the cells, again down its electrochemical gradient. ! This increases water potential in the cell, and water will follow the K+ out, collapsing the guard cells and closing the pore

PHYSIOLOGICAL ECOLOGY: WHAT PLANTS NEED

! Nutrition
! Soil conditions ! Essential nutrients ! Root symbionts

! Water
! Adaptations to water stress ! Special role of stomata ! Photosynthesis C4 and CAM plants revisited

! Other stresses
! ! ! ! Sunlight Heat Cold Low Oxygen

!Plant defenses & 2 compounds

Figure 10.5 An overview of photosynthesis: Cooperation of the light reactions and the Calvin cycle (or C3 Cycle) (Layer 3)

Figure 10.17 The thylakoid membrane.

Figure 10.18 The Calvin cycle (Layer 3)

Calvin Cycle
! Begins with Rubisco catalyzing reaction of 3 CO2 and 3 RuBP to form 6 3-carbon compounds ! Energy from ATP and NADPH is used to re-arrange 3-carbon compound into higher energy G3P ! G3P used to build glucose, other organic molecules ! Cyclic process: one G3P (of 6) released each pass through cycle, rest (5) regenerate (3) RuBP

Rubisco
! The key enzyme in the Calvin Cycle or C3 pathway ! Worlds most abundant enzyme! ! Contains lots of Nitrogen ! Catalyzes two competing and opposite reactions

Photosynthesis and photorespiration

Normal

reaction:

Photorespiration:

non-

productive and wasteful:

Photosynthesis and photorespiration

! O2 has an inhibitory effect on photosynthesis ! Competition between O2 and CO2 on the Rubisco enzyme

Some plants solve this problem with a CO2-concentrating mechanism: The C4 photosynthetic pathway
! Increases [CO2]:[O2] around Rubisco, essentially eliminating photorespiration ! Downside: it takes extra energy to do this, therefore

! A higher ratio of O2 to CO2 favors photorespiration (which, unlike normal respiration, produces no chemical energy) ! Result: Decreased efficiency of photosynthesis, esp. at high temperatures

! Only beneficial at high temperatures

Big Bluestem-a C4 plant

Figure 10.19 C4 leaf anatomy and the C4 pathway Light reactions (and O2 production) only in mesophyll

C4 pathway
! Physically separates light reactions (O2 production) and Calvin cycle ! CO2 first fixed into a 4-carbon compound in mesophyll by an enzyme that does not catalyze a reaction with O2 ! 4-carbon compound transported to bundlesheath cell ! CO2 enters Calvin cycle in bundle-sheath cell, where oxygen concentration is low ! Energetically costly

C4 plants fix CO2 in the mesophyll using the enzyme PEP Carboxylase, which has a much higher affinity for CO2 than does Rubisco. CO2 is then shunted into the isolated bundle-sheath cells to join the Calvin Cycle. Calvin cycle (and Rubisco) only in bundle-sheath cells.

Advantages of C4 pathway at higher temperatures

1. More efficient use of light energy

Advantages of C4 pathway at higher temperatures

2. Higher Water Use Efficiency (WUE)
Net Photosynthesis (!mol m-2 s-1)
50 40 30 20 10 0 0 160 320 480 640

C4 C3

(from Pearcy & Ehleringer 1984)

Leaf Conductance (mmol m-2 s-1)

Advantages of C4 pathway at higher temperatures

3.! Higher Nitrogen Use Efficiency (NUE)

Ecological advantages for C4 plants

! At higher temperatures, C4 plants:
! Use light more efficiently ! Use water more efficiently ! Use nitrogen more efficiently

Why?
Less Rubisco is needed per gram of leaf

! Examples: !! In North American tallgrass prairie, C3 grasses

dominate during cool seasons, while C4 grasses dominate the summer season In grasslands of South Africa, C4 grasses dominate, except at higher altitudes

Question: how might litter quality differ between C4 and C3 plants?

!!

Another ecological challenge for plants: dry air. Solution: CAM photosynthesis
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C3

Net Photosynthesis (!mol m-2 s-1)

50 40 30 20 10 0

The advantage of C4 plants at high temps is negated at high [CO2]!

C4
700 ppm CO2 350 ppm CO2 200 ppm CO2

! In dry climates, water is lost from the stomata when they are open to obtain CO2 ! One solution to this problem: Open stomata only at night, when its cooler & moister, and store the captured CO2 until daytime: CAM photosynthesis ! Found in many succulent plants (e.g. ice plant), many cacti, pineapples, and many other species in hot dry climates

-10 0 100 200 300 400 500 600

Intercellular CO2 (ppm)

Figure 10.20 C4 and CAM photosynthesis compared

Other adaptations to environmental stresses

! Dry conditions lead to suppression of shallow roots, promotion of deep roots ! Aerial roots (pneumatophores) ! Apoptosis (ethylene) leading to air pockets acting as snorkels ! Salt secretion (halophytes) ! Heat shock proteins - preventing denaturation ! Antifreeze -high solute (eg. sugars) concentrations

Crassulacean Acid
Spatial separation of carbon fixation from the Calvin cycle

Temporal separation of carbon fixation from the Calvin cycle

! Photorespiration can be a bad thing ! The C4 pathway helps at high Adaptations to water temperatures, but not stress high CO2! ! Mesophytes, Role of stomata ! The CAM hydrophytes ! Regulate water loss photosynthetic halophytes, and and CO2 uptake pathway works in dry xerophytes have conditions specific adaptations ! Density and placement are to water availability important ! Stomata open and close with specific cues

What Youve Learned So Far: Water, heat and CO2

C4 and CAM photosynthesis

Plant physiological ecology

Plant defenses and secondary compounds
! ! ! ! Allelopathy Defenses against herbivory Plant secondary compounds Competing with neighbors: revisiting allelopathy

Ecological factors influencing plant growth and development

! Fall into two broad categories: physical and chemical (abiotic factors), including ! Biological (biotic) factors including competition, herbivory, symbiosis ! Competition can involve chemicals (allelopathy)

Allelopathy: chemical warfare

Eucalyptus (blue) forest

Chara

Forms of defense against herbivores:! Trichomes, spines etc.!

Bull-horn Acacia species (Americas, Africa!

Pseudomyrmex ants! (in central America)! Obligate mutualism?! Ant mutualists! (especially African acacias)! First defense = Physical structures.! Second defense = Chemical poisons.! Poisons! Secondary compounds! Secondary metabolites! Derived from offshoots of the biochemical pathways that produce primary metabolites like amino acids.!

Ant acacias lack alkaloid! defenses present in species! lacking ant mutualists ! Ants are extremely aggressive! predators! What about pollination?! (Willmer 1997)!

Plant secondary compounds ! !--> In 1999, $400million for St. Johns wort in the U.S.! !(an antidepressant).!

Plant secondary compounds!

Phenolics!
Phenol unit!

Terpenes !
Taxol - Pacific Yew, Cancer

8000+ kinds, 4500 avonoids! Flavonoids: in fruits! !Anthocyanin pigments! Herbivore deterrents:! Lignans: in grains and veggies (prevent cancer)! Tannins: in leaves and unripe fruits ![oak family]! Capsaicin: in chili peppers.! !Function--to deter mammals from eating seeds.! Have receptors in mucous membranes --> PAIN.! vs.! Do NOT have receptors.! !But does act as a laxative -->Improves dispersal.!

25,000 different kinds! Fragrances! !(Aromatherapy)! Insect-deterrents! !Citronella! !Pyrethrum! Sagebrush! Mint family!

Peppermint ! (menthol)! Oregano! Basil! Catnip!

Plant secondary compounds!

Alkaloids!
Caffeine!

12,000+ types! Nitrogen-containing compounds! Anti-herbivore and anti-pathogen defenses! !Active on nervous system! !Most psychoactive drugs! !Toxic in high doses! Medicinal uses: morphine, quinine, codeine! Nicotine, caffeine!

What is different about this cactus?! Heroin--! From the opium poppy! Peyote cactus (Lophophora)! !No spines!! !Chemical defense instead of mechanical defense! !(25 different alkaloids)!

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How come all plants dont make all possible poisons?!

Allelopathic effects
! Most often inhibit seed germination or seedling growth ! May act directly on competing plants, or inhibit their growth via effects on soil microbes (eg mycorrhizae) or nutrient availability ! Proving importance of allelopathy in nature can be tricky

Cost of defense --! TRADEOFFS: No free lunch! Either you put energy into producing poison, or! you put energy into something else (e.g. competing with your neighbor or making lots of offspring.)!

Identifying allelopathy in nature

! Step 1: isolate presumed allelochemicals, prove that they inhibit seedling germination in the lab (relatively easy) ! But:
! what are concentrations of these chemicals in nature? ! How do you distinguish allelopathy from simple competition in the field? ! Indirect effects

How to compete with neighbors

! Grow faster (above ground) and monopolize light resources ! Grow faster (below ground) and monopolize soil resources ! Poison them - allelopathy

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