Jan. 25 th, 2011 B4730/5730 Plant Physiological Ecology Photosynthesis I

Wilson et al. Ag. For. Met Examples of Energy Balance Using Eddy Covariance Techniques

Baldocchi et al Picea mariana; Goulden et al. 1997

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?

Plant and Environmental Controls Over Photosynthesis Within a given C A, plants control supply and demand for CO 2 –full model of A requires both Supply of CO 2 determined by stomatal conductance (g s ) –Balance transpiration (E L ) and A –Environmental controls? Demand for CO 2 determined by mesophyll biochemistry –Limited by amount of RuBP, Rubsico, ATP, & NADPH –Farqhuar model with fluorescence combines all of above Leaf vs. whole plant limitations

Use of Environmental Response Curves in Photosynthesis Response curves help propose and test physiological mechanisms in ecology Light response reveals some light dependent mechanisms –Parameters: quantum yield, saturation, compensation, curvature CO 2 responses reveals some light independent mechanisms –Parameters: supply, demand, compensation, Rubisco, RuBP, CO 2 and Phosphate Multivariate controls on response curves

C.m. shade C3, H.v. sun C3, Z.m. sun C4 BL blue light, RL red light Bukhov et al 1995 J. Photo. Chem. Bio.

Pinus pinaster, Medlyn et al 2002 PCE

States of Calvin Cycle Photosynthesis State one-Rubsico limited –CO 2 low –No Vcmax limitation State two-RuBP regeneration limited –Light limited –Enzymes of Calvin cycle limited –Increases with increasing CO 2 State three-Triose Phosphate Use (TPU) –Photosynthesis at higher rate than capacity to use products –Not CO 2 or O 2 limited Actual A rate is which of three states is limiting –Farqhuar et al (1980) model used to determine which one

Sharkey et al. PCE 2007; incorporates newest material to Farquhar model

Farquhar Model Overview Five parameters from Farquhar model –V Cmax - maximum carboxylation by Rubisco –J - rate of photosynthetic electron transport –TPU - triose phosphate use –R d - day respiration –g m -mesophyll conductance Parameters adjusted to 25 °C for comparison –c is scaling constant = 1 at 25 C), ΔH a enthalpy of activation, ΔH d enthalpy of deactivation, ΔS entropy, R is universal gas constant, T is temperature in K