HR: 0830h
AN: B31E-0350    [PDF]
TI: Source Contributions to the Carbon Isotopic Signature of Ecosystem Respiration in a Northern Deciduous Forest Ecosystem
AU: * Curtis, P S
EM: curtis.7@osu.edu
AF: Ohio State University, Dept. EEO Biology 318 W. 12th Ave., Columbus, OH 43210 United States
AU: Vogel, C S
AF: University of Michigan Biological Station, 9008 Biological Rd., Pellston, MI 49769 United States
AU: Cruz, J
AF: University of Michigan Biological Station, 9008 Biological Rd., Pellston, MI 49769 United States
AU: Biswas, S
AF: Ohio State University, Dept. EEO Biology 318 W. 12th Ave., Columbus, OH 43210 United States
AU: Grant, M
AF: University of Michigan Biological Station, 9008 Biological Rd., Pellston, MI 49769 United States
AB: Respiratory carbon (R$_{c}$) losses from forests are large and may account for regional differences in annual carbon sequestration. In addition, different sources of R$_{c}$ respond differently to temperature, soil moisture, and current photosynthesis. One of our objectives at the UMBS Forest Carbon Cycle Research Program in northern lower Michigan USA ($45.6\deg$ N, $84.7\deg$ W) is to partition ecosystem respiration (R$_{e}$) among major contributing fluxes and to account mechanistically for annual and interannual variation in R$_{e}$. Previous work based on analyses of the temperature and moisture dependencies of soil, leaf, and bole respiration suggested that over three years (1999-2001), soil respiration contributed $\sim$ 70% of R$_{e}$, with leaves and boles contributing 11% and 19% respectively. With the installation of a ThermoFinnigan Delta$^{Plus}$ XL isotope ratio mass spectrometer at UMBS in early 2003 we have expanded our analyses of R$_{e}$ to include partitioning the isotopic signature of R$_{e}$ into that contributed by the autotrophic and heterotrophic components of soil respiration, and by leaves, branches, and coarse woody debris. Results from Keeling plots taken mid-summer 2003 at 2.5 m above the soil surface showed an ecosystem $\delta^{13}C$ of -24.5$\permil$. Soil respiratory $\delta^{13}C$ taken from soil cuvettes was very similar, at -24.7$\permil$. Corticular photosynthesis in {\it Populus}, the dominant canopy species, caused a shift in branch respiratory $\delta^{13}C$ from -21.5$\permil$ in the dark to -15.2$\permil$ in the light. Respiratory $\delta^{13}C$ from coarse woody debris varied with decay class, but averaged $\sim$ -26$\permil$. Leaf organic matter $\delta^{13}C$ varied with canopy position and species, from $\sim$ -27$\permil$ at the top of the canopy to $\sim$ -30$\permil$ in the shrub layer. We will use these observations as an independent check against our partitioning of R$_{e}$ based on measured component fluxes and to facilitate interpretation of the responses of these ecosystem components to changing environmental conditions.
DE: 0315 Biosphere/atmosphere interactions
DE: 0322 Constituent sources and sinks
DE: 0400 Biogeosciences
DE: 1610 Atmosphere (0315, 0325)
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting