HR: 1340h
AN: B23D-1592    [Abstracts]
TI: Effects of Soil Water on Soil Surface CO2 Fluxes and the Carbon Budget of a Deciduous Forest
AU: * Wilson, T B
EM: Tim.Wilson@noaa.gov
AF: NOAA/ATDD/ORAU, 456 South Illinois Avenue, Oak Ridge, TN 37830, United States
AU: Meyers, T P
EM: Tilden.Meyers@noaa.gov
AF: NOAA/ATDD/ORAU, 456 South Illinois Avenue, Oak Ridge, TN 37830, United States
AU: Heuer, M
EM: Mark.Heuer@noaa.gov
AF: NOAA/ATDD/ORAU, 456 South Illinois Avenue, Oak Ridge, TN 37830, United States
AB: The CO2 flux from the soil surface is an important component of the carbon budget in a forest stand. The soil surface CO2 may contribute about 20 percent of the photosynthesis uptake by the forest with the remainder coming from the atmosphere. Since such a large fraction of the total CO2 flux above the forest canopy may originate in the soil, the contribution of soil surface CO2 flux must therefore be considered in using field measurements of CO2 fluxes to evaluate models for predicting the components of photosynthesis. The CO2 flux at the floor of a deciduous forest seems to depend on soil temperature, soil water content, amount of litter, and the photosynthesis capacity of the forest. An important way to understand these factors is to use fast response and accurate instrument to measure soil CO2 fluxes. We used a prototype soil chamber to measure soil CO2 fluxes at two locations in an oak forest in the NOAA-ATDD GEWEX flux tower network in TN, and the results from the measurement were used to evaluate the performance of a soil-plant-atmosphere model important as a gap- filling tool. Soil surface CO2 flux is the result of largely respiration by the soil biomass consisting of plant roots and dead plant materials. The respiration in vegetation environments depends on the capacity and types of vegetation, as well as on the mineralization of the organic matter by soil microbial activity, which provides nutrients for plant growth and development. In our case of the deciduous forest with large litter cover at floor below the canopy, CO2 flux may be produced by chemical reaction between rainwater and the top organic soil layer. During and immediately after rainfall, the CO2 dissolved in rainwater seems to be released from the warm soil relative to the rainwater. Similarly, CO2 may be released from the soil when rainwater displaces gas in the soil pore space. This physical interaction was observed at two flux tower sites in the oak forest reservation in Oak Ridge, TN. The soil chamber measurements reported strong increases in the hourly soil CO2 flux from low values of below 0.1 mg m-2 s-1 for dry soil conditions to values as high as 0.4 mg m-2 s-1 following rainstorm, suggesting that the soil CO2 flux is sensitive to soil water content. The fraction of the CO2 flux in the deciduous forest attributable to respiration seems to vary from 20 to 80 percent related to time of day and year and rainfall.
DE: 0428 Carbon cycling (4806)
DE: 4806 Carbon cycling (0428)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting