HR: 09:25h
AN: B31A-06 INVITED     [PDF]
TI: Nutrient Controls over Soil Organic Matter Turnover: Implications for Land Use Effects on Soil Carbon Storage
AU: * Townsend, A R
EM: alan.townsend@colorado.edu
AF: INSTAAR and Dept. of Ecology and Evolutionary Biology, Box 450 Univ. of Colorado, Boulder, CO 80309 United States
AU: Neff, J C
EM: jason.neff@colorado.edu
AF: Dept. of Geological Sciences, Box 399 Univ. of Colorado, Boulder, CO 80309 United States
AU: Lehman, S J
EM: scott.lehman@colorado.edu
AF: INSTAAR, Box 450 Univ. of Colorado, Boulder, CO 80309 United States
AB: A wide variety of land use changes can significantly alter soil carbon pools, to the extent that feedbacks between shifting land use and atmospheric carbon dioxide may have global importance. Land use changes also frequently alter nitrogen and phosphorus availability, both via direct application of fertilizer, and via indirect biogeochemical responses to a changed environment. Both N and P availability are known to constrain decomposition rates and microbial activity in a range of ecosystems, but the effects of changing N and P levels on the large stocks of soil carbon are poorly known. We used a combination of radiocarbon analyses and soil organic matter fractionation techniques in long-term N and P fertilizer plots located in tundra, grassland and forest ecosystems to show that soil carbon responses to shifting nutrient levels are likely to be highly complex, but also potentially dynamic. For example, increasing N and P availability appears to accelerate decomposition of some soil carbon fractions, while simultaneously increasing stabilization and storage of others. These counteracting responses of the soil C pool often result in no detectable change in total soil C stocks, yet the radiocarbon data clearly show that soil carbon decomposition can be sensitive to shifts in nutrient availability. A number of current models of soil carbon cycling are widely used to simulate and predict soil C responses to changes in land use, but our data suggest that none of these models contains the mechanisms required to simulate the complex relationships between N and P cycling and soil carbon storage.
DE: 0315 Biosphere/atmosphere interactions
DE: 0330 Geochemical cycles
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2003 Fall Meeting