HR: 1340h
AN: B13B-1184    [Abstracts]
TI: Carbon Isotope Composition of Ecosystem Respired Carbon Dioxide in Three Boreal Forest Ecosystems: Measurements and Model Calculations
AU: * Cai, T
EM: tiebo.cai2@uleth.ca
AF: University of Lethbridge, Department of Biological Sciences 4401 University Drive, Lethbridge, AB T1K 3M4, Canada
AU: Flanagan, L B
EM: larry.flanagan@uleth.ca
AF: University of Lethbridge, Department of Biological Sciences 4401 University Drive, Lethbridge, AB T1K 3M4, Canada
AB: We conducted measurements of seasonal and inter-annual variation in the carbon isotope composition of ecosystem respired CO₂ (δ_R) in aspen, black spruce and jack pine dominated ecosystems in northern Saskatchewan during 2004-2006 as part of the Fluxnet-Canada Research Network. All three sites showed relatively small variation (approximately -26 to -29 per mil) in δ_R values during the entire study. The measurements were strongly correlated with modeled δ¹³C values of ecosystem respired CO₂. The model calculated leaf CO₂ assimilation, stomatal conductance and chloroplast CO₂ concentration separately for sunlit and shaded leaves within multiple canopy layers, and, therefore, allowed us to estimate canopy photosynthetic ¹³C discrimination. All three sites showed variation in canopy ¹³C discrimination in response to environmental conditions in a manner consistent with well-known leaf-level studies. Specifically, ¹³C discrimination was positively correlated with soil moisture and negatively correlated with photon flux density, air temperature and vapor pressure deficit. As a consequence a strong diurnal pattern was observed for ¹³C discrimination. The measured δ_R values also varied in response to environmental conditions in a manner consistent with well-known leaf-level studies of photosynthetic ¹³C discrimination, but with a dampened response caused by the contribution of heterotrophic respiration, which had a constant δ¹³C value. These results indicate that the stable isotope composition of respired CO₂ is a useful ecosystem-scale tool to study constraints to photosynthesis and acclimation of ecosystems to environmental stress.
DE: 0400 BIOGEOSCIENCES
DE: 0428 Carbon cycling (4806)
DE: 0476 Plant ecology (1851)
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting