HR: 0800h
AN: H51D-1176    [Abstracts]
TI: Modeling Carbon and Water Vapor Fluxes and Carbon Isotope Discrimination at the Canopy Scale in a Semi-arid Pine Forest.
AU: * Aranibar, J N
EM: aranibar@catalase.stanford.edu
AF: Department of Biology, University of Utah, 257S 1400E, Salt Lake City, UT 84112 United States
AU: Berry, J A
AF: Department of Global Ecology, Carnegie Institution of Washington, 260 Panama St., Stanford, CA 94305 United States
AU: Riley, W J
AF: Earth Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 United States
AU: Bowling, D R
AF: Department of Biology, University of Utah, 257S 1400E, Salt Lake City, UT 84112 United States
AU: Pataki, D E
AF: Department of Biology, University of Utah, 257S 1400E, Salt Lake City, UT 84112 United States
AU: Ehleringer, J R
AF: Department of Biology, University of Utah, 257S 1400E, Salt Lake City, UT 84112 United States
AU: Law, B E
AF: Department of Forest Sciences, Oregon State University, 328 Richardson Hall, Corvallis, OR 97331 United States
AB: Water, energy, and carbon exchange between the biosphere and the atmosphere in forest ecosystems are strongly coupled and affected by stomatal conductance and photosynthesis, which in turn respond to environmental factors such as air humidity, temperature, radiation, and soil water content. In this study, we test biochemical models of photosynthesis, stomatal conductance, and carbon isotope discrimination at canopy scales, using eddy covariance and isotopic data from the AmeriFlux and BASIN networks. Carbon and water vapor fluxes were simulated with an ecophysiologically based model (ISOLSM) driven by half hourly meteorology at the Old Ponderosa flux tower in Metolius (OR). The model was parameterized with half hourly eddy covariance data of carbon, latent and sensible heat fluxes, and foliar carbon isotope ratios (\delta$^{13}$C) from the same site. Carbon isotope discrimination was sensitive to stomatal conductance parameters that also affect estimates of carbon and water vapor fluxes, reducing the parameter space obtained from the eddy flux data. The variability of simulated \delta$^{13}$C was similar to that of observed \delta$^{13}$C, and the relation between vapor pressure deficit (VPD) and simulated \delta$^{13}$C of assimilated carbon was similar to that between VPD and observed \delta$^{13}$C of ecosystem respiration. These simulations support hypotheses of tight atmospheric controls of stomatal conductance, photosynthesis, and carbon isotope discrimination at short time scales, which affect biosphere-atmosphere carbon and water exchange at large spatial scales.
DE: 1818 Evapotranspiration
DE: 1851 Plant ecology
DE: 1615 Biogeochemical processes (4805)
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting