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Feb. 1 st , 2011 B4730/5730 Plant Physiological Ecology

Feb. 1 st , 2011 B4730/5730 Plant Physiological Ecology. Photosynthesis I. Filled crop, open broadleaf, crosses conifers Medlyn et al. PCE 2002. Light Dependent Reactions. Three fates of photon striking reaction center Heat, fluorescence, photochemistry

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Feb. 1 st , 2011 B4730/5730 Plant Physiological Ecology

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  1. Feb. 1st, 2011B4730/5730Plant Physiological Ecology Photosynthesis I

  2. Filled crop, open broadleaf, crosses conifers Medlyn et al. PCE 2002

  3. Light Dependent Reactions • Three fates of photon striking reaction center • Heat, fluorescence, photochemistry • Linear electron flux (LEF) goes from PSII to PSI to drive H+ pmf, • Cyclic flux around PSI • Low light, efficiency maximized • High light, energy dissipation maximized

  4. Baker et al. PCE 2007

  5. Chlorophyll Fluorescence • Absorption (photochemistry), heat, and fluorescence all occur in competition with incoming light • Light absorbed different wavelength than light fluorescing • Light always lost, so all measurements relative • Add to 1 • Measurements made with modulated light • Allows measurement in the field with background light levels • Kautsky effect is rise in fluorescence when leaves go from dark to light conditions • Electrons from PSII to QA, • if QA reduced; reaction center closed • fluorescence when reaction center closed • Quenching causes fluorescence to fall after initial burst • Photochemical quenching-light induction • Nonphotochemical quenching (NPQ)-heat and zeaxanthin cycle

  6. Measuring Fluorescence • F rate of fluoresce • ’ indicates light acclimated (“adapted”) measurements • Fo background fluorescence in dark, Fo’ in light • Fm maximal rate in dark or Fm’ in light • Occurs when QA is maximally reduced • Fv variable fluorescence from dark, Fv’ light • Demonstrates primary photochemistry

  7. Interpreting Fluorescence • Fv/Fm intrinsic quantum yield of PSII • Fv’ = F’-Fm’ • Quantum yield of PSII • ΦPSII = Fv’/Fm’ • Photochemical (qP) and nonphotochemical quenching (NPQ) • qP = (F’m – F’o)/(Fm – Fo) • NPQ = 1 – (F’m – F’o)/(Fm – Fo) • J = ΦPSII · Iabs · β · PPFD • β = 0.5 equal distribution PSII & PSI • Relative without Iabs

  8. Nicotiana tabacum; Kramer et al Photo. Res. 2004 qp puddle model PSII open qL lake model PSII open

  9. Wang & Kellomaki New Phyt. 1997, Pinus sylvestris • Control N & amb CO2, b) Control N & elev CO2, • c) High N & amb CO2, d) High N & elev CO2 • ΔF=Fq’

  10. Fs is steady state Fluorescence (F’) Closed circle F’m amb CO2 Closed triangle Fs amb CO2 Open circle F’m elev CO2 Open triangle Fs elev CO2

  11. Leipner et al Env. Exp. Bot. 1999 Maize

  12. Mesophyll conductance • Flux of CO2 to stroma (Cc) limited by gs, gm and gb • Recent work has shown gm to be variable and important • Low gm reduces CC underestimate VCmax • Cc=Ci-A/gm • Estimate gm with curve fitting • Estime gm with fluorescence and A

  13. Hedera helix; Pons et al J Exp Bot 2009

  14. Many species; Sc= surface area of chloroplasts exposed to intercellular airspace; Evans et al J Exp Bot 2009

  15. Limitations to the Farquhar/Fluorescence model of Photosynthesis • No gene expression controls • Connection to hormones, whole plant controls • Longer time scales • Stomatal physiology almost a black box • Scale of leaf patchiness violates homogeneity • Light dynamics problematic • Respiration models are crude

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