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Feb. 15th, 2011 B4730/5730 Plant Physiological Ecology Whole Plant Carbon Balance I Phaseolus vulgaris; Tcherkez et al Pl Phys. 2003 Hymus et al New Phyt. 2005 (Ehleringer et al., 1991). Water Sources and Water Isotopes (Dawson and Ehleringer, 1991). 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 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 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 Arabidopsis thaliana; Torii Plant Cell Mongraphs 2007 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 Rajabi 2006 in Seibt et al Oecol. 2008 Pinus pinaster; Ogee et al PCE 2010 Fagus sylvatica; Ferrio et al PCE 2009 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 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 Van Bel PCE 2003 Münch Pressure Flow Sevanto et al. PCE 2003 Sevanto et al. PCE 2003