Download Feb. 15

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