HR: 17:00h
AN: B32D-05    [PDF]
TI: Heterotrophs Dominate Soil Respiration From Boreal Black Spruce Forest: Using Isotopes to Partition Sources of Soil CO$_{2}$ Flux
AU: * Schuur, E A
EM: tschuur@ufl.edu
AF: University of Florida, Department of Botany 220 Bartram Hall, Gainesville, FL 32611 United States
AU: Trumbore, S E
EM: setrumbo@uci.edu
AF: University of California, Department of Earth System Science 220 Rowland Hall, Irvine, CA 92697 United States
AB: Most carbon that enters terrestrial ecosystems via photosynthesis is returned to the atmosphere by the process of respiration. Of total ecosystem respiration, 40-80% occurs below ground as soil respiration, a combination of root metabolism (autotrophic respiration) and the decomposition of organic matter (heterotrophic respiration) by soil organisms. While the major factors affecting autotrophic and heterotrophic respiration are known, predictions of soil respiration are limited primarily by the difficulty of measuring these two belowground respiration sources independently. We used radiocarbon measurements to estimate the partitioning of carbon between heterotrophic and autotrophic respiration in three mature black spruce (Picea mariana) forests in interior Alaska. We measured radiocarbon from soil respiration in the field, in laboratory soil incubations, and in the atmosphere. These measurements were combined with a two-pool mixing model in order to estimate partitioning between sources. Soil respiration radiocarbon signatures in the mature forest ranged from +112\permil to +122\permil and differed significantly from soil incubations that ranged from +135\permil to +145\permil. These values were significantly higher than the current atmospheric radiocarbon at +78\permil due to the residence time of carbon in plants and soil. Using soil incubations as an end member for heterotrophic respiration and the atmospheric value for the autotrophic end member, we estimated that 58-72% of soil respiration was derived from heterotrophic decomposition of organic matter. This estimate did not differ among the three stands and is significantly larger than the 50% estimate commonly used in model parameterization.
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
DE: 1040 Isotopic composition/chemistry
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting