Jan. 20, 2011B4730/5730

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

Oke et al. 1987

Landsberg and Gower 1997

Leaf Energy Budgets

• The energy budget of a leaf determines its leaf temperature

• TL-TA = (RN-λEL)/(ρ·cp·gT)

– 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 lasiocarpaDiamonds or squaredot Picea engelmanniiSquares 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

Wilson et al. Ag. For. Met. 2002

Examples of Energy Balance Using Eddy Covariance Techniques

Baldocchi et al. 1997

Picea mariana; Goulden 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

http://www.fsl.orst.edu/~bond/phystalk/Ecohydrology/SPAC%20diagram.jpg

What other fluxes in SPACbesides water?