Water availability to plants depends on surface tension, soil structure

1
Water availability to plants depends on surface
tension, soil structure
Different soil types, with different particle
sizes (and size distributions) have different
soil water availability
loam
From Ricklefs, R.E. Ecology, 3rd Ed., W.H.
Freeman
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Biologically relevant properties of light
3
Different plant pigments absorb light in
different parts of electromagnetic spectrum--and
reflect colors that they dont absorb
chlorophylls green, carotenoids yellow-red
4
Water tends to absorb longer wavelengths, scatter
shorter ones thus greens penetrate deepest
Surface plant such as green alga (Ulva) thus has
pigments like terrestrial plants deeper water
red alga (e.g., Porphyra) absorbs most
efficiently in the green wavelengths
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Biologically relevant properties of air

• Air less viscous, less buoyant than water
  (organisms move easily thru it, but need more
  support)
• Composed of different substances 78 N2, 21 O2,
  0.03 CO2, traces of CH4, N2O, etc.
• Diffusion of gases much more rapid in air than
  water
• O2 diffuses rapidly in air (solubility 0.21
  cm3/cm3 air) slowly in water (solubility 0.01
  cm3 O2 /cm3 water)
• O2 often limits organisms in water-saturated
  environments, especially where decay organisms
  (heterotrophs like bacteria) take up O2
• This leads to anoxic conditions (like
  sulfur-stink of mucks in Lafitte Park)
• CO2, by contrast, is rare, often limiting, in air
  (0.03) dissolves readily in water (carbonic
  acid, bicarbonate)

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Many plants tend to have great difficulty getting
enough CO2, when stomata are open enough to
transpire water this is particular problem in
desert environments (see next lecture)
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• Reduction reaction less favorable energetically
  than oxidation--former requires energy from sun
  via chlorophyll molecules as energy-absorbers
• energy of living things stored in reduced carbon
  bonds, e.g., carbohydrates

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Respiration is reverse of photosynthesis

• Respiration involves coupled oxidation
  reduction (redox) half reactions, the reverse of
  those in photosynthesis
• O2 4e- C4 CO2 Reduction half-reaction
  (oxygen is reduced by gain of electrons)
• CH2O C4 H2O 4e- Oxidation half-reaction
  (carbon is oxidized)
• Coupled together CH2O O2 CO2 H2O
• Overall reaction is favorable (net release of
  energy) because reduction of oxygen (top step)
  releases more energy than reduction of carbon
  and oxidation of carbon (bottom step) releases
  more energy than reduction of oxygen requires

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Temperatures of living things

• Temperatures of living things determined by range
  of temperatures at which water is in liquid phase
• Few organisms can survive temperatures gt 45ºC,
  because of protein denaturation at high
  temperatures
• Some organisms can exist at higher temperatures
  due to particularly heat-stable proteins
• Most organisms cannot tolerate body (cell)
  temperatures below freezing, because of damage to
  cells from ice crystals
• Some organisms can exist at slightly lower
  temperatures using antifreezes such as salts,
  glycerol
• Increased temperature sets higher rate of
  chemical reactions (2-4 times increase in rate
  per 10ºC)

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Physiological ecology adaptations to the
physical environment

• Selected adaptations to physical environment
• Plant adaptations for CO2 uptake, water use
  efficiency
• Animal adaptations for water conservation
• Animal adaptations for gas, heat exchange
• Tradeoffs involved in adaptations

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Plant adaptations to hot, dry environments (e.g.,
deserts)

• Gas exchange challenges faced by plants

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Plant adaptations to hot, dry environments (e.g.,
deserts)

• Gas exchange challenges faced by plants
• Water loss
• Water diffusion gradient steeper than CO2
  gradient
• High metabolic rates
• Shortage of soil water
• Herbivory

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• Increase osmotic potential of roots to pull
  water from soil particles

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• Increase heat dissipation from leaves by
  increasing surface area (recall flux equation) by
  small leaf sizes

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• Reduce transpiration water loss
• Drop leaves in drought (e.g., tropical dry forest
  trees)

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• Reduce transpiration water loss
• Waxy cuticle

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Stomata on leaves control water loss, gas exchange
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• Reduce transpiration water loss
• Recessed hair-filled cavities)

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• Reduce heat absorption--leaves perpendicular to
  sun

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Reduce heat absorption by leaf surfaces using
dense hairs (e.g., pubescent leaves of
Enceliopsis, a desert perennial)
21

• Spines both reflect light, protect precious
  tissues

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Important set of adaptations for water
conservation involve photosynthesis

• C3 plants the norm in cool, moist climates
• C4 plants adapted to hot, dry climates because of
  efficiency of CO2 uptake
• CAM plants are another fundamental variation on
  C4 plants, also adapted to hot, dry climates

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C3 plant anatomy and biochemistry
Example Geranium
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C4 plant anatomy and biochemistry
Examples Sorghum vulgare (pictured), sugar cane
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C4 photosynthesis has advantages, costs

• Advantages
• CO2 in high concentration
• Water loss reduced
• Costs and tradeoffs
• Recovering PEP from Pyruvate expensive
• Less leaf tissue devoted to photosynthesis
• Not beneficial in cool climates

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Illustration of tradeoffs of C4, C3 plants with
temp., CO2 concentration
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CAM photosynthesis separates cycles diurnally
Example Sedum obtusatum
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Review of variations on theme of
photosynthesis

• Adaptations involve multiple levels of
  organization
• Tradeoffs evident--no one adaptation best in all
  environments specialization comes with costs
• Plant adaptations to desert environments
  illustrate modification of flux components area,
  conductance, gradient

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Animals also modify components of flux equation
to obtain materials--e.g., countercurrent
exchange mechanisms

• Countercurrent circulation in fish allows
  concentration of O2 from water into blood stream
• Blood flows across gill lamellae (of gill
  filaments) in vessels that flow opposite to
  direction of water flowing across gills
• This countercurrent maintains a concentration
  gradient for absorption of O2 throughout gills
• According to physical laws O2 diffuses from areas
  of higher concentration to lower

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Anatomy of countercurrent circulation in fish
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Theory of counter-current flow mechanism
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Concurrent flow, by contrast, would not allow
concentration of O2 in blood of fish
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Some birds use countercurrent mechanism to cool
extremities, so as to minimize gradient (and thus
minimize heat loss) to cold environment heat
flows from artery to vein along length of leg, to
conserve heat proximal to body
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Kangaroo rats of SW deserts illustrate variety of
mechanisms to minimize water loss

• Minimize water-loss gradient by nocturnal
  activity-- illustrates importance of behavior
• Large surface area of nasal passages conserves
  H2O
• Inhalation of hot, dry air evaporates H2O, cools
  surfaces
• Exhalation of moist, warm air condenses on cooled
  surfaces, retains water
• Large small intestines resorb water efficiently

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Conclusions

• Physiological adaptations covers a huge
  topic--weve just skimmed surface with a few
  examples
• Re-emphasizes the constraints imposed by physical
  environment
• Every specialization comes with costs
• Jack of all trades is master of none
• Corollaries A master of one is master of no
  others and theres no free lunch
• Adaptations can be observed at many levels of
  organization--e.g., biochemistry, cell and tissue
  anatomy, whole-organism anatomy and behavior
• Most organisms have many, diverse adaptations to
  physical environment