Jan. 20, 2011
B4730/5730
Plant Physiological Ecology
Biotic and Abiotic Environments
Photosynthesis, O2 and H2O
• Plants face two major problems
– 1) whenever stomata open to allow CO2 to diffuse to
the locations of carbon fixation, H2O invariably leaves
– 2) Rubisco fixes both CO2 and O2
• Transpiration loss of H2O from plants
– Stomatal physiology tries to maximize photosynthesis
while minimizing transpiration
– Stomatal closure decreases CO2 concentrations and
increases O2 concentrations promoting O2 fixation
• Photorespiration fixation of O2 by Rubisco
– Photorespiration requires light
– Photorespiration produces no ATP
– Photorespiration uses organic material from the
Calvin cycle
Alternative Pathways of
Photosynthesis
• Three major photosynthetic pathways based on
which molecule first incorporates CO2
– 1) C3 plants fix CO2 into 3-PGA (3 carbon)
– 2) C4 plants initially fix CO2 into a 4 carbon molecule
before passing it to the Calvin cycle
– 3) CAM plants initially fix CO2 into organic acids
• C4 and CAM photosynthetic pathways minimize
transpiration and photorespiration at the cost of
additional energy for carbon fixation
– Temporal or spatial separation
– Light reactions same for all pathways
Defining Environment
• Environment of plants is anything outside
of the plant body that influences the plant
– Response to present environment due to
adaptations/acclimations to previous
environments
• Biotic and abiotic environmental
interactions
– Both positive and negative
– Stress never completely alleviated
Spheres of Plants
• Atmosphere
– Plants respond to and change the atmosphere
– Climate and atmosphere, atmospheric cycles
• Hydrosphere
– Heat transfer from water evaporation
– Water and climate
• Lithosphere
– Any lithosphere with biological activity is soil
– Soil properties and plant response to environment
intimately linked
• Ecosphere combines all of the above and
biological interactions
– Rhizosphere most neglected
Atmospheric structure
http://www.ux1.eiu.edu/~cfjps/1400/atmos_origin.html
Boundary Layers
• Turbulence is nonparallel, disorderly flow of a
fluid
– Turbulence intensity is standard deviation of flow
divided by mean flow
– Increasing turbulence means more fluid moves by
eddies
• Boundary layers formed by shearing stresses at
some surface
– Boundary layers form at any solid/liquid interface
– Flow must go to zero at interface
Visualizing Boundary Layers
http://www.cartage.org.lb/en/themes/Sciences/Physics/Mechanics/FluidMechanics/RealFluids/BoundaryLayers/BoundaryLayers.htm
Radiation Fundamentals
• Total amount of radiation received by a body on
earth is a combination of short and longwave
radiation
• Amount of energy from radiation is a function of
the wavelength
– Wien’s displacement law
– Planck’s law
– Stephan-Boltzman law
• Shortwave radiation is received directly from the
sun from high temperatures
• Longwave radiation is given off by bodies on
earth
Energy emitted by the sun and
earth
Oke et al. 1987
Atmospheric Effects on Radiation
Landsberg and Gower 1997
Oke et al. 1987
Leaf Energy Budgets
• The energy budget of a leaf determines its leaf
temperature
• TL-TA = (RN-λEL)/(ρ·cp·gT)
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–
–
–
–
–
–
–
TL is leaf temperature
TA is air temperature
λ latent energy of evaporation
EL transpiration per unit leaf area
ρ is air density
cp is the heat capacity of air
gT is the total conductance to water vapor
Metabolic heat generation is generally ignored but
can be substantial in certain species
Impact of canopy structure on
temperature and photosynthesis
Smith and Carter 1988
Triangles Abies lasiocarpa
Diamonds or squaredot Picea engelmannii
Squares Pinus contorta
Radiation Balance
• Radiation balance requires conservation of
energy
• RN=(1-α)RS+(RLi+RLo) + G
– RN is net radiation
– α is albedo
– RS is solar radiation
– RL is longwave radiation (i) incoming
(o) outgoing
– G is storage
Impact of Vegetation on Albedo
Landsberg and Gower 1997
Partitioning of Net Radiation
• Net radiation and physical and
physiological controls on water loss
determine the temperature of a stand of
vegetation
• RN + G = λE + H
– G is heat storage
– λE is the latent energy or heat of vaporization
– H is the sensible energy or heat
Examples of Energy Balance Using
Eddy Covariance Techniques
Wilson et al. Ag. For. Met. 2002
Picea mariana; Goulden et al. 1997
Baldocchi et al. 1997
Fluxes
• Molecules move from high concentration to low
concentration
– Entropy
• Flux is the amount substance moving across a
planar front per unit time
• Flow is the total amount of substance moving
per unit time
• Ficke’s first and second laws describe fluxes
• Flux density is proportional to the driving force
– Diffusion coefficient changes flux per driving force
• Diffusion coefficient can be converted to
resistance or conductance to flux
– Resistances sum directly in series
– Conductances sum inversely in series
Plants respond to environment with
fluxes
• Plant fluxes
– Mass
– Energy
– Momentum
• Soil Plant Atmosphere Continuum (SPAC)
defines where fluxes occur
– subcellular to global
• Deriving flux equations; connecting anatomy
– Photosynthesis
– Transpiration
• Importance of scale
SPAC
What other fluxes in SPAC
besides water?
http://www.fsl.orst.edu/~bond/phystalk/Ecohydrology/SPAC%20diagram.jpg