HR: 0800h
AN: B51C-0960    [Abstracts]
TI: Altered Seasonality and Magnitude of Rainfall Affects Soil Respiration and Nitrous Oxide Fluxes in California Annual Grassland
AU: * Chou, W W
EM: wchou@nature.berkeley.edu
AF: University of California - Berkeley, Department of Environmental Science, Policy and Management, 151 Hilgard Hall MC #3110, Berkeley, CA 94720 United States
AU: Silver, W L
EM: wsilver@nature.berkeley.edu
AF: University of California - Berkeley, Department of Environmental Science, Policy and Management, 151 Hilgard Hall MC #3110, Berkeley, CA 94720 United States
AU: Jackson, R D
EM: rdjackson@wisc.edu
AF: University of Wisconsin - Madison, Department of Agronomy 1575 Linden Drive, Madison, WI 53706 United States
AU: Allen-Diaz, B
EM: ballen@nature.berkeley.edu
AF: University of California - Berkeley, Department of Environmental Science, Policy and Management, 151 Hilgard Hall MC #3110, Berkeley, CA 94720 United States
AB: Currently, climate models do not agree on how rising concentrations of CO$_{2}$ and other greenhouse gases will affect rainfall in California. Changes in moisture regime will likely alter rates of carbon (C) loss via soil respiration, as well as fluxes of N$_{2}$O. Moisture availability can also affect plant productivity in highly seasonal environments. We examined the consequences of wetter conditions in an annual grassland in the Sierra foothills of northern California by extending the duration of the wet season by about 5 weeks and augmenting total annual rainfall by approximately 50 %. Discrete wet-up events took place prior to the onset of natural rains (early October 2003) and early in the drought period (May 2004). Soil respiration, N$_{2}$O and CH$_{4}$ effluxes, N mineralization, and above- and belowground plant production were measured in treatment and control plots over a one-year period. Soil CO$_{2}$ fluxes for the first treatment year, though large, were not statistically different between wet and control plots (1078 \pm148 g C m$^{-2}$ and 1006 \pm138 g C m$^{-2}$, respectively). The combined wet-up events comprised 17 % of the soil respiration over the 12-month period in treated plots, about twice as much C released by control plots during the same time interval. Aboveground biomass was similar between wetted and control plots (415 \pm45 g m$^{-2}$ y$^{-1}$ and 374 \pm36 g m$^{-2}$ y$^{-1}$, respectively), while root biomass increased significantly with wetting during the first year of treatment (179 \pm23 g m$^{-2}$ y$^{-1}$ and 111 \pm13 g m$^{-2}$ y$^{-1}$ for treatment and control plots, respectively). The additional biomass C gained in treatment plots (53 g C m$^{-2}$) partly offset the greater losses from respired C observed in treatment plots (72 g C m$^{-2}$). Nitrous oxide emissions were low to negligible during the year with the exception of the time directly following wet-up, when N$_{2}$O emissions averaged over 78\pm13 ng N cm$^{-2}$ h$^{-1}$. Our first year of water manipulation in annual grasslands suggests that increased water availability via early and late rainfall events releases large pulses of CO$_{2}$, increases belowground C inputs, and increases N$_{2}$O emissions.
DE: 1866 Soil moisture
DE: 1600 GLOBAL CHANGE (New category)
DE: 1615 Biogeochemical processes (4805)
DE: 0315 Biosphere/atmosphere interactions
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting