HR: 0830h
AN: B51D-0993    [PDF]
TI: Transpiration: A Test of Optimality Hypothesis
AU: * Wang, J
EM: jfwang@mit.edu
AF: Massachusetts Institute of Technology, Parsons Lab, Dept of Civil and Environmental Engineering, 15 Vassar Street, Cambridge, MA 02139 United States
AU: Bras, R L
EM: rlbras@mit.edu
AF: Massachusetts Institute of Technology, Parsons Lab, Dept of Civil and Environmental Engineering, 15 Vassar Street, Cambridge, MA 02139 United States
AU: Lerdau, M
EM: manuel.lerdau@sunysb.edu
AF: State University of New York, Stony Brook, Ecology and Evolution Dept., 650 Life Sciences Bldg., South Loop Rd., SUNY, Stony Brook, NY 11794-5245 United States
AU: Salvucci, G D
EM: gdsalvuc@bu.edu
AF: Boston University, Boston University, Geography Department, Stone Science Bldg, Rm 461, 675 Commonwealth Avenue, Boston, MA 02215 United States
AU: Wofsy, S
EM: wofsy@fas.harvard.edu
AF: Harvard University, Division of Engineering and Applied Science, Department of Earth and Planetary Science, 29 Oxford St., Cambridge, MA 02138 United States
AB: The argument is that the fundamental mechanisms behind bare soil evaporation are also responsible for plant transpiration except that stomata affect the exchange of water vapor between the evaporating surface and the atmosphere. It is hypothesized that the system of liquid water in leaf tissues and the water vapor in the atmosphere tries to evolve towards a potential equilibrium as quickly as possible by maximizing transpiration. In the proposed theory, CO$_2$ flux is used as a non-parametric equivalent of stomatal conductance as CO$_2$ and water vapor diffuse in and out of leaves through the same path. It is further assumed that stomatal aperture is directly controlled by guard cell turgor (or leaf water potential). Transpiration is formulated as a function of leaf temperature, leaf water potential/stomatal conductance (or CO$_2$ flux as the surrogate), and sensible heat flux (characterizing transport mechanism) at a given level of radiative energy input. Optimization of transpiration constrained by the energy balance equation leads to vanishing derivatives of transpiration with respect to leaf temperature and CO$_2$ flux. Effect of vapor pressure deficit on transpiration is also investigated. Preliminary tests using field experimental measurements lead to encouraging evidence in support of the hypothesis. It is found that transpiration is fairly insensitive to atmospheric humidity as suggested by several earlier studies.
DE: 0315 Biosphere/atmosphere interactions
DE: 1815 Erosion and sedimentation
DE: 1818 Evapotranspiration
DE: 1836 Hydrologic budget (1655)
DE: 1878 Water/energy interactions
SC: Biogeosciences [B]
MN: 2003 Fall Meeting