HR: 1340h
AN: B43B-0155    [Abstracts]
TI: Reduced Atmospheric CH4 Consumption by Temperate Forest Soils Under Elevated CO2
AU: * Dubbs, L E
EM: dubbs@email.unc.edu
AF: University of North Carolina- Chapel Hill, UNC-CH Dept. ESE 104 Rosenau Hall, Chapel Hill, NC 27599 United States
AU: Whalen, S C
EM: steve\_whalen@unc.edu
AF: University of North Carolina- Chapel Hill, UNC-CH Dept. ESE 104 Rosenau Hall, Chapel Hill, NC 27599 United States
AU: Fischer, E N
EM: efischer@email.unc.edu
AF: University of North Carolina- Chapel Hill, UNC-CH Dept. ESE 104 Rosenau Hall, Chapel Hill, NC 27599 United States
AB: Models project that atmospheric CO$_2$ concentrations, by the end of the present century, will exceed the preindustrial concentration by up to 250%. The regional and global impact of this projected concentration increase on other biogeochemical cycles is uncertain. We recently reported in a two year study a 17 (year 2) to 30% (year 1) decrease in atmospheric CH$_4$ consumption by soils in CO$_2$-enriched plots in a temperate loblolly pine (Pinus taeda) forest, although the reason for the decline was unclear. Consumption by upland soils is the only terrestrial sink for atmospheric CH$_4$, which is second only to CO$_2$ in terms of radiative forcing. Forest ecosystems occupy about half of the Earth's terrestrial surface. A sustained CO$_2$-induced negative feedback on forest soil CH$_4$ consumption could lead to a 25% reduction (7.5 Tg CH$_4$ yr$^-1$) in the current upland soil sink of $\sim$30 Tg yr$^-1$. However, CO$_2$-enriched tundra ecosystems showed down regulation in at least the photosynthetic response after 3 yr of fertilization and it is uncertain whether decreased atmospheric CH$_4$ consumption represents a transient or sustained response of forest-soil systems to elevated CO$_2$. We report here the early results of our efforts to determine the duration and underlying causes for the decline in atmospheric CH$_4$ consumption in a CO$_2$-enriched forest. Reduced CH$_4$ consumption persisted in elevated CO$_2$ plots, which showed declines of 13% (year 3) and 34% (year 5, to date), relative to unenriched controls. This decline may be related to the rate of supply of CH$_4$ to the subsurface zone of oxidation, as soil moisture was significantly higher in CO$_2$-enriched plots. A single experiment to date showed that changes in the chemical composition of leachate from aboveground plant material had no impact on the CH$_4$ oxidizing community, as rates of CH$_4$ consumption by soil samples amended with throughfall from CO$_2$-enriched and control plots were not significantly different.
DE: 1615 Biogeochemical processes (4805)
DE: 0315 Biosphere/atmosphere interactions
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting