Jan. 20, 2011 B4730/5730 Plant Physiological Ecology Biotic and Abiotic Environments

Photosynthesis, O 2 and H 2 O Plants face two major problems –1) whenever stomata open to allow CO 2 to diffuse to the locations of carbon fixation, H 2 O invariably leaves –2) Rubisco fixes both CO 2 and O 2 Transpiration loss of H 2 O from plants –Stomatal physiology tries to maximize photosynthesis while minimizing transpiration –Stomatal closure decreases CO 2 concentrations and increases O 2 concentrations promoting O 2 fixation Photorespiration fixation of O 2 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 CO 2 –1) C 3 plants fix CO 2 into 3-PGA (3 carbon) –2) C 4 plants initially fix CO 2 into a 4 carbon molecule before passing it to the Calvin cycle –3) CAM plants initially fix CO 2 into organic acids C 4 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

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

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 Landsberg and Gower 1997

Leaf Energy Budgets The energy budget of a leaf determines its leaf temperature T L -T A = (R N -λE L )/(ρ·c p ·g T ) –T L is leaf temperature –T A is air temperature –λ latent energy of evaporation –E L transpiration per unit leaf area –ρ is air density –c p is the heat capacity of air –g T 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 R N =(1-α)R S +(R Li +R Lo ) + G –R N is net radiation –α is albedo –R S is solar radiation –R L 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 R N + 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 Examples of Energy Balance Using Eddy Covariance Techniques

Baldocchi et al 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 What other fluxes in SPAC besides water?