HR: 10:50h
AN: B41E-03    [PDF]
TI: Disequilibrium of $^{13}$CO$_{2}$ fluxes between photosynthesis and respiration in North American temperate forest biomes
AU: * Lai, C
EM: lai@biology.utah.edu
AF: Department of Biology, University of Utah, 257S, 1400E, Salt Lake City, UT 84112 United States
AU: Ehleringer, J
EM: ehleringer@biology.utah.edu
AF: Department of Biology, University of Utah, 257S, 1400E, Salt Lake City, UT 84112 United States
AU: Schauer, A
EM: schauer@biology.utah.edu
AF: Department of Biology, University of Utah, 257S, 1400E, Salt Lake City, UT 84112 United States
AU: Tans, P
EM: Pieter.Tans@noaa.gov
AF: Climate Monitoring and Diagnostics Laboratory, National Oceanic and Atmospheric Administration,, 325 Broadway, Boulder, CO 80303 United States
AU: Hollinger, D
EM: davidh@hypatia.unh.edu
AF: USDA Forest Service, Northeastern Research Station, P.O. Box 640, Durham, NH 03824 United States
AU: Paw U, K
EM: ktpawu@ucdavis.edu
AF: 4. Department of Land, Air and Water Resources, University of California, University of California, Davis, CA 95616 United States
AU: Wofsy, S
EM: wofsy@fas.harvard.edu
AF: Division of Engineering and Applied Science and Department of Earth and Planetary Science, Harvard University, Harvard University, Cambridge, MA 02138 United States
AB: We report the first weekly dataset of seasonal and interannual variability in $\delta^{13}$C of CO$_{2}$ fluxes from dominant forest ecosystems in the US. We observed large variations in the $\delta^{13}$C of respired biosphere-atmosphere fluxes ($\delta^{13}$C$_{R}$) across 3 temperate coniferous and deciduous forest ecosystems (-24.9 $\pm$ 0.4 to -31.3 $\pm$ 0.6 per mil). Values of $\delta^{13}$C$_{R}$ were significantly correlated with growing-season soil water availability. By analyzing daytime flask measurements collected at the top of canopies, we estimated an annual mean, flux-weighted $\delta^{13}$C of net ecosystem CO$_{2}$ exchange fluxes ($\delta^{13}$C$_{net}$). Combining $\delta^{13}$C$_{R}$ and $\delta^{13}$C$_{net}$, along with eddy-covariance measured fluxes, we estimated regional discrimination against $^{13}$C during photosynthesis ($\Delta_{A}$) for these 3 forest ecosystems. Our approach allows for examination of the interannual correlations between gross primary production fluxes and $\Delta_{A}$ that could potentially modulate atmospheric 13C budget. The results showed that C$_{3}$ forests in temperate regions in the U.S. exhibited a slight isotopic disequilibrium ($<$ 1 per mil) on an annual basis, despite significant seasonal variations in respired $\delta^{13}$CO$_{2}$ values ($>$ 3 per mil). Such subtle isotopic disequilibrium however, when associated with enormous one-way gross fluxes, can effectively affect atmospheric $^{13}$C budget.
DE: 0315 Biosphere/atmosphere interactions
DE: 0614 Biological effects
DE: 1040 Isotopic composition/chemistry
DE: 1600 GLOBAL CHANGE (New category)
DE: 3322 Land/atmosphere interactions
SC: Biogeosciences [B]
MN: 2003 Fall Meeting