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Plant Physiological Ecology: Understanding Whole Plant Carbon Balance

Explore the intricate processes of gas exchange, stomatal conductance, water use efficiency, and phloem properties in plant physiology. Learn about environmental influences and mechanisms governing plant carbon balance.

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Plant Physiological Ecology: Understanding Whole Plant Carbon Balance

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  1. Feb. 15th, 2011B4730/5730Plant Physiological Ecology Whole Plant Carbon Balance I

  2. Phaseolus vulgaris; Tcherkez et al Pl Phys. 2003

  3. Hymus et al New Phyt. 2005

  4. (Ehleringer et al., 1991).

  5. Water Sources and Water Isotopes (Dawson and Ehleringer, 1991).

  6. Gas Exchange • Gas exchange of whole plant passes through stomatal and nonstomatal surfaces • Bark, lenticels • Cuticles • Conductances summed in series and parallel • Stomates are one of the most active physiological response plants have to environment

  7. Derivation of Stomatal Conductance • Stomatal conductance = gs=Dj nast /(δst + rst) • m s-1 (usually mm s-1) • Easiest measurement from water exchange • Molecular diffusion coefficient = Dj • m2 s-1 • (2.4 x 10-5) for water at STP • Ratio of stomata area to leaf area = nast • Unitless • 0.02 mesic example • Depth of stomatal pore = δst • m • 20 x 10-6 m mesic example • Radius of stomata rst • m • 5 x 10-6 m mesic example

  8. Conversion of Stomatal Conductance Units • Units of m s-1 are mostly used by meteorologist, physiologist and ecologist like mol m-2 s-1 • Conversion to mol m-2 s-1 uses ideal gas law • Equations in front of book, account for Pressure and Temperature change • Stomatal parameters • Stomatal Density (# mm-2 ) • Stomatal Index (stomatal area/epidermal area) • Index is less sensitive to CO2 levels than density

  9. Arabidopsis thaliana; Torii Plant Cell Mongraphs 2007

  10. Water Use Efficiency • Water use efficiency is the ratio of CO2 uptake to H2O loss • WUE = A/E = Ca (1-(Ci/Ca))/1.6VPD • VPD effect often neglected • Be careful of ratio effects • Water use efficiency increases with water stress and light • A vs. EL at different light levels • gs vs. A changes with plant functional types • Ci/Ca is related to water use efficiency (intrinsic) • 18O may help with relative A to gs contribution

  11. Rajabi 2006 in Seibt et al Oecol. 2008

  12. Pinus pinaster; Ogee et al PCE 2010

  13. Fagus sylvatica; Ferrio et al PCE 2009

  14. Phloem Properties • Sieve elements retain minimal metabolic function to facilitate transport • Increasing loss of metabolic function with evolution • No nucleus • Surrounding parenchyma have increased metabolic function • Companion cells in angiosperms • Rapid plugging of wounded sieve elements precluded functional studies until recently • Phloem specific protein

  15. Sources and Sinks • Munch hypothesis that osmotic forces drive sugar transport • Active loading of phloem at sources • Moves water from xylem to phloem • Active unloading of phloem at sinks • Moves water from phloem to xylem • Pressure gradient maintained between sources and sinks • Environmental controls largely unknown • Sugar signals • mRNA transport • Girdling studies • pressure waves and osmotica

  16. Van Bel PCE 2003

  17. Münch Pressure Flow Sevanto et al. PCE 2003

  18. Sevanto et al. PCE 2003

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