PHYSIOLOGICAL ECOLOGY:
Plant Adaptations To Their Needs
Plant Nutrition:
Soil Quality Impacts Plant Vigor
• 
•  Nutrition
•  Other stresses
•  Water
–  Water stress
–  Role of stomata
–  C4 & CAM plants
–  Soil conditions
–  Essential nutrients
–  Root mutualists
– 
– 
– 
– 
Sunlight
Heat
Cold
Low Oxygen
Two soil factors:
1)  Texture - its general structure
2)  Composition - its organic &
inorganic components
• Plant defenses & 2° compounds
Plant Nutrition:
Topsoil Loss Is Critical
•  Mix of rock (inorganic) &
organic matter (humus
breakdown)
Plant Nutrition:
Topsoil Loss Is Critical
•  Mix of rock (inorganic) &
organic matter (humus
breakdown)
•  grasslands accumulate most
•  grasslands accumulate most
•  100t/km2/yr
•  100t/km2/yr
•  Its loss is important
•  Its loss is important
•  From 1700-5000 t/km2/yr
•  50,000 km2/ yr of arable land
to wind & water erosion,
salination, sodification,
& desertification.
•  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 2080’s 5-20%
decline in agricultural
output globally
Plant Nutrition:
Essential Elements
•  9 Macronutrients
–  need large amounts
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
•  Deficiencies are visible
–  Main ones are P, K, N
Healthy
–  need small amounts
Phosphate-deficient
Potassium-deficient
Nitrogen-deficient
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Plant Nutrition:
N has the greatest impact
•  It’s in:
–  proteins
–  nucleic acids
–  chlorophyll
–  enzymes (remember
the giant rubisco)
–  & more!
Healthy
Let’s Talk About Getting
Nitrogen
Phosphate-deficient
Potassium-deficient
Nitrogen-deficient
Plant Nutrition:
Bacteria Fix Atmospheric N2
•  Soils have:
Root Mutualists:
Rhizobium In Nodules
•  Legumes have:
–  Nitrogen-fixers making
nitrogenous minerals
•  Legumes have:
–  root nodules w/ Rhizobium
–  A mutualistic relationship
–  root nodules w/ Rhizobium
–  A mutualistic relationship
•  ammonia, ammonium & nitrate
N2
N2
Atmosphere
Soil
N2
Soil
Nitrogen-fixing
bacteria
NH3
(ammonia)
H+
(From soil)
NH4+
(ammonium)
Denitrifying
bacteria
•  Crop rotation
Nitrate and
nitrogenous
organic
compounds
exported in
xylem to
shoot system
–  Grow various crops
•  that deplete soil N
–  But rotate in a legume
NH4+
Nitrifying
bacteria
NO3–
(nitrate)
•  to refresh soil N
Ammonifying
bacteria
Organic
material (humus)
Root
EPIPHYTES
Root Mutualists:
Mycorrhizal Root/Fungus Mutualism
•  Fungus gives plant:
•  Plant give fungus:
–  ⇑ water & nutrient uptake
by
–  ⇑ root surface area w/ hyphae
Staghorn fern
PARASITIC PLANTS
–  Sugars!
Host’s phloem
Dodder
Haustoria
Mistletoe - photosynthetic
Dodder - nonphotosynthetic
Indian pipe - nonphotosynthetic
CARNIVOROUS PLANTS
Venus’ flytrap
Pitcher plants
Sundews
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What You’ve Learned So Far:
Plant Nutrition
•  Soils provide nutrients
–  So soil loss is important
–  Texture
•  Mix of rock & organics
•  Agricultural benefits
•  Nutrition
•  Root Mutualisms
–  Rhizobium in legume nodules
–  Composition
–  Crop rotation ⇑ soil nitrogen
•  Esp. P, K, N
–  Mycorrhizal fungi
•  Nitrogen is critical
–  ammonia
–  ammonium
–  Nitrate
–  Soil conditions
–  Essential nutrients
–  Root symbionts
•  Ecto & endomycorrhizae
•  Translocate water/nutrients
•  Get sugars
–  Plentiful in air
–  “Fixed” by bacteria
•  In soil, make
PHYSIOLOGICAL ECOLOGY:
WHAT PLANTS NEED
•  Some plants have
evolved ‘special’
nutritional modes
Adaptations to water stress
•  Water is an important factor influencing
plant growth and development
•  Plants exhibit structural and physiological
adaptations to water supply
•  We’ll see some in lab…
•  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
Mesophytes:
moderate water supply
temperate forests and grasslands - shade and sun
forms.
Maple trees: genus Acer
Roses
Mesophytic grasses
Hydrophytes:
wet habitats, wet soil, sometimes partially
submerged. Water lily, Elodea
La jacinthe d' eau (Eichhornia crassipes)
Water Lily: Nymphaeaceae, basal
angiosperms
Waterlettuce (Pistia stratiotes)
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 (don’t need to prevent water
loss)
•  Leaves often flat for surface area
•  Less rigid structure (water holds them up)
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Xerophytes:
Structural adaptations of
xerophyte leaves
seasonal or persistent drought - arid and
semiarid. Cactus, succulents
Saguaro Cactus
Carnegiea gigantea
(Cereus giganteus)
• 
• 
• 
• 
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
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
The stomata
•  Stomata help regulate the rate of transpiration (water
loss), in part through stomatal morphology and
placement
Common Sea-lavender
(Limonium serotinum)
Red mangrove: Rhizophora mangle
Batis maritima
Environmental control of stomatal density
•  During development, light intensities and
=
stomatal densities
•  Stomatal density is under both genetic and
environmental control
What might that
mean???
•  Desert plants (xerophytes) have lower stomatal densities
than water lilies (hydrophytes)
Studies show that
CO2 leads to of
stomata which
leads to an
transpiration. This
has implications for
cooling, xylem flow
etc.
CO2 levels
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•  Guard cells take in water and buckle
outward due to cellulose microfibrils,
opening the stoma
Transpiration
•  Plants can wilt if too much water is lost
•  They close when they become flaccid
•  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 µm
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
•  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
•  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
Lower epidermal
tissue
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.
Trichomes
(“hairs”)
Stomata
100 µm
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.
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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
Figure 10.5 An overview of photosynthesis: Cooperation of the light reactions
and the Calvin cycle (or C3 Cycle) (Layer 3)
Figure 10.18 The Calvin cycle (Layer 3)
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 10.17 The thylakoid membrane.
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
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Rubisco
•  The key enzyme in the Calvin Cycle or
“C3 pathway”
Photosynthesis and photorespiration
‘Normal’
reaction:
•  World’s most abundant enzyme!
•  Contains lots of Nitrogen
•  Catalyzes two competing and opposite
reactions
Photosynthesis and photorespiration
•  O2 has an inhibitory effect on
photosynthesis
•  Competition between O2 and
CO2 on the Rubisco enzyme
‘Photorespiration:
non-
productive and
wasteful:
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
Figure 10.19 C4 leaf anatomy and the C4 pathway
Light reactions (and O2 production) only in mesophyll
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.
•  Only beneficial at high
temperatures
Big Bluestem-a “C4 plant”
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
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Advantages of C4 pathway at
higher temperatures
Advantages of C4 pathway at
higher temperatures
2. Higher Water Use Efficiency (WUE)
Net Photosynthesis (µmol m-2 s-1)
1. More efficient use of light energy
50
40
C4
C3
30
20
10
0
0
160
320
480
640
Leaf Conductance (mmol m-2 s-1)
(from Pearcy & Ehleringer 1984)
Advantages of C4 pathway at
higher temperatures
Ecological advantages for C4
plants
•  At higher temperatures, C4 plants:
3.  Higher Nitrogen Use
Efficiency (NUE)
–  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
 
Question: how might litter quality
differ between C4 and C3 plants?
In grasslands of South Africa, C4 grasses
dominate, except at higher altitudes
Another ecological challenge for plants:
dry air. Solution: CAM photosynthesis
C3
The advantage
of C4 plants at
high temps is
negated at high
[CO2]!
Net Photosynthesis (µmol m-2 s-1)
60
•  In dry climates, water is lost from the stomata
when they are open to obtain CO2
50
C4
40
30
700 ppm CO2
20
200 ppm CO2
350 ppm CO2
•  One solution to this problem: Open stomata only
at night, when it’s cooler & moister, and store the
captured CO2 until daytime: CAM photosynthesis
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•  Found in many succulent plants (e.g. ice plant),
many cacti, pineapples, and many other species
in hot dry climates
0
-10
0
100
200
300
400
500
600
Intercellular CO2 (ppm)
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Figure 10.20 C4 and CAM photosynthesis compared
Crassulacean Acid
•  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
Temporal
separation of
carbon
fixation from
the Calvin
cycle
Spatial
separation of
carbon
fixation from
the Calvin
cycle
What You’ve Learned
So Far:
Water, heat and CO2
Other adaptations to
environmental stresses
Plant physiological ecology
C4 and CAM
photosynthesis
–  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
Plant defenses and secondary compounds
• 
• 
• 
• 
Allelopathy
Defenses against herbivory
Plant secondary compounds
Competing with neighbors: revisiting allelopathy
Ecological factors influencing plant growth and
development
Allelopathy:
chemical warfare
•  Fall into two broad categories: physical and
chemical (abiotic factors), including …
•  Biological (biotic) factors including
competition, herbivory, symbiosis
•  Competition can involve chemicals
(allelopathy)
Eucalyptus (blue) forest
Chara
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Bull-horn Acacia species (Americas, Africa
Forms of defense against herbivores:
Trichomes, spines etc.
Pseudomyrmex ants
(in central America)
Obligate mutualism?
Ant mutualists (especially African acacias)
Ant acacias lack alkaloid
defenses present in species
lacking ant mutualists First defense = Physical structures.
Second defense = Chemical poisons.
Poisons
“Secondary compounds”
“Secondary metabolites”
Ants are extremely aggressive
predators
Derived from offshoots of the
biochemical pathways that
produce “primary
metabolites” like amino acids.
Plant secondary compounds --> In 1999, $400million for St. Johns wort in the U.S.
(an antidepressant).
What about pollination?
(Willmer 1997)
Plant secondary compounds
Phenolics
Phenol unit
Terpenes 8000+ kinds, 4500 flavonoids
Taxol - Pacific Yew, Cancer
25,000 different kinds
Fragrances
(Aromatherapy)
Insect-deterrents
Citronella
Pyrethrum
Sagebrush
Mint family
Flavonoids: in fruits
Anthocyanin pigments
Herbivore deterrents:
Lignans: in grains and veggies (prevent cancer)
Tannins: in leaves and unripe fruits
[oak family]
Peppermint (menthol)
Oregano
Basil
Catnip
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.
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 don’t make all possible poisons?
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
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…
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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