Jan. 25th, 2011B4730/5730

Plant Physiological Ecology

Photosynthesis I

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

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?

Plant and Environmental Controls Over Photosynthesis

• Within a given CA, plants control supply and demand for CO2– full model of A requires both

• Supply of CO2 determined by stomatal conductance (gs)– Balance transpiration (EL) and A– Environmental controls?

• Demand for CO2 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• CO2 responses reveals some light independent

mechanisms– Parameters: supply, demand, compensation, Rubisco,

RuBP, CO2 and Phosphate• Multivariate controls on response curves

C.m. shade C3, H.v. sun C3, Z.m. sun C4BL blue light, RL red lightBukhov et al 1995 J. Photo. Chem. Bio.

Pinus pinaster, Medlyn et al 2002 PCE

States of Calvin Cycle Photosynthesis• State one-Rubsico limited

– CO2 low– No Vcmax limitation

• State two-RuBP regeneration limited– Light limited– Enzymes of Calvin cycle limited– Increases with increasing CO2

• State three-Triose Phosphate Use (TPU)– Photosynthesis at higher rate than capacity to use

products – Not CO2 or O2 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

– VCmax - maximum carboxylation by Rubisco– J - rate of photosynthetic electron transport– TPU - triose phosphate use– Rd - day respiration– gm-mesophyll conductance

• Parameters adjusted to 25 °C for comparison

– c is scaling constant = 1 at 25 C), ΔHa enthalpy of activation, ΔHd enthalpy of deactivation, ΔS entropy, R is universal gas constant, T is temperature in K

TRH

TS

TRH

c

d

a

e

eParameter

1