HR: 14:25h
AN: B22B-03    [PDF]
TI: Changing sources of respired CO2 with time since fire in a boreal forests
AU: * Czimczik, C I
EM: czimczik@uci.edu
AF: University of California, Department of Earth System Science, Irvine, CA 92697-3100 United States
AU: Trumbore, S
EM: setrumbo@uci.edu
AF: University of California, Department of Earth System Science, Irvine, CA 92697-3100 United States
AB: We compared the carbon isotopic composition of soil CO2 fluxes and potential respiration sources (root and microbial) of 6 forest stands along a chronosequence ranging from 0 to 150 years following stand replacing fire. Study sites are located in the BOREAS Northern Study Area near Thompson, Manitoba, Canada (55N, 98W). The vegetation is dominated by black spruce (Picea mariana), the understorey by mosses. The clay soils have underlying permafrost below 50 to 90 cm. Soil CO2 flux and its carbon isotopic composition was measured using dynamic chambers. Heterotrophic and autotrophic respiration were characterized using in situ and laboratory incubations. Results from a preliminary study in 2001 showed an increasing contribution of heterotrophic respiration with time since fire. Drier conditions in 2003 were associated with dramatically lower CO2 fluxes. We will present isotope data collected in the summer of 2003 and contrast it with our earlier study. In addition to surface fluxes we measured CO2 concentration and isotopic signature of depth profiles along the chronosequence. Radiocarbon signatures in the mineral soil differed significantly from the isotopic signature of surface CO2 fluxes, indicating that the majority of the soil respiration flux is derived from near surface layers.
DE: 1600 GLOBAL CHANGE (New category)
DE: 1610 Atmosphere (0315, 0325)
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting