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Jan. 25th, 2011B4730/5730
Plant Physiological Ecology
Photosynthesis I
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Wilson et al. Ag. For. Met. 2002
Examples of Energy Balance Using Eddy Covariance Techniques
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Baldocchi et al. 1997
Picea mariana; Goulden et al. 1997
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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
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SPAC
http://www.fsl.orst.edu/~bond/phystalk/Ecohydrology/SPAC%20diagram.jpg
What other fluxes in SPACbesides water?
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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
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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
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C.m. shade C3, H.v. sun C3, Z.m. sun C4BL blue light, RL red lightBukhov et al 1995 J. Photo. Chem. Bio.
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Pinus pinaster, Medlyn et al 2002 PCE
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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
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Sharkey et al. PCE 2007; incorporates newest material to Farquhar model
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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