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Plant Photosynthesis: Understanding Energy Balance and Environmental Controls

Explore plant physiology in ecological settings, focusing on energy balance through Eddy Covariance Techniques and the Soil Plant Atmosphere Continuum. Discover the impacts of plant and environmental controls on photosynthesis, diving into SPAC fluxes and Calvin Cycle states. Learn about the Farquhar Model and its parameters in determining photosynthetic limitations. Gain insights into response curves and multivariate controls affecting plant photosynthesis.

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Plant Photosynthesis: Understanding Energy Balance and Environmental Controls

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

  2. Examples of Energy Balance Using Eddy Covariance Techniques Wilson et al. Ag. For. Met. 2002

  3. Picea mariana; Goulden et al. 1997 Baldocchi et al. 1997

  4. 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

  5. SPAC What other fluxes in SPAC besides water? http://www.fsl.orst.edu/~bond/phystalk/Ecohydrology/SPAC%20diagram.jpg

  6. 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

  7. 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

  8. 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.

  9. Pinus pinaster, Medlyn et al 2002 PCE

  10. 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

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

  12. 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

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