HR: 0800h
AN: B11A-0996    [Abstracts]
TI: The carbon isotopic composition of heterotrophically-respired CO₂ flux from soil organic matter
AU: * Wynn, J G
EM: jonathan.wynn@st-andrews.ac.uk
AF: University of St. Andrews, School of Geography & Geosciences, St. Andrews, KY16 9AL United Kingdom
AU: Bird, M I
EM: michael.bird@st-andrews.ac.uk
AF: University of St. Andrews, School of Geography & Geosciences, St. Andrews, KY16 9AL United Kingdom
AU: Harden, J W
EM: jharden@usgs.gov
AF: U S Geological Survey, 345 Middlefield Rd ms 962, Menlo Park, CA 94025 United States
AU: Pruett, L
EM: lpruett@usgs.gov
AF: U S Geological Survey, 345 Middlefield Rd ms 962, Menlo Park, CA 94025 United States
AB: CO₂ flux from soil to atmosphere combines CO₂ derived from root metabolism (autotrophic respiration) and soil organic matter decomposition (heterotrophic respiration). A major challenge to biogeochemistry is the separation of soil respiration into these components and the evaluation of how each is controlled by environmental conditions and will respond to environmental change. Laboratory studies of the carbon isotopic composition of soil-respired CO₂ produced during incubation provides an opportunity to separate heterotrophic respiration and study the controls on its isotopic composition during the course of long-term incubation experiments. We have developed and utilized methods using the carbon isotopic composition of laboratory respired CO₂ to determine the relative contribution of different decomposing substrates to heterotrophic CO₂ flux. We will present stable and radiocarbon isotope measurements of heterotrophic CO₂ respiration from organic matter collected from soils over a wide range of environmental controls, and discuss how various factors may influence the contribution of different components to heterotrophic CO₂ respiration. Incubation studies of soil organic matter from the Lower Mississippi Basin, and a moisture gradient in Alaska indicate that heterotrophic respiration progressively consumes older and more humified components of organic matter (at a decreased rate) in the absence of fresh input from biomass. Results of 4-year incubations of soil organic matter from a continental-wide data set from Australia indicate a pronounced difference in turnover time of C3- and C4-derived soil organic matter. These results have significant implications for modeling the soil to atmospheric flux, and responses of the size, isotopic composition and turnover time of the soil organic carbon pool to environmental change.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0486 Soils/pedology (1865)
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
SC: Biogeosciences [B]
MN: Fall Meeting 2005