HR: 1340h
AN: B23D-1595    [Abstracts]
TI: Plant and Microbial Controls on Soil Respiration in a Western Forest
AU: * Serio, D
EM: dserio@uci.edu
AF: Dept. of Earth System Science, University of California, Irvine, CA 92697, United States
AU: Carbone, M
EM: mcarbone@uci.edu
AF: Dept. of Earth System Science, University of California, Irvine, CA 92697, United States
AU: Trumbore, S
EM: setrumbo@uci.edu
AF: Dept. of Earth System Science, University of California, Irvine, CA 92697, United States
AB: We are using a combination of method to quantify controls on plant and microbial sources of soil respiration over the course of a year at the San Jacinto Mountains James Reserve in Southern California. High frequency autochamber flux measurements are combined with monitoring of air and soil temperature and moisture conditions to monitor diel and seasonal variations in flux. A total of eight autochambers are deployed in this seasonally dry, montane (2370 m) chaparral/mixed hardwood and conifer forest. Partitioning between autotrophic and heterotrophic sources is accomplished by trenching (in April 2007) around four of the chambers to a depth of 60 cm to remove the autotrophic component, and a mass balance approach using radiocarbon measurements of respired CO2 and its root and microbial sources. The climate at this site is characterized by a winter wet season and a long (April-November) dry season, punctuated by occasional summer thunderstorm activity. When soil and surface litter are moist in the wet season, temperature (2cm) is the major correlate for soil respiration. Isotope mass balance partitioning in March shows that 37 +/- 16 per cent of the total respiration is from sources with the radiocarbon signature of root respiration. As the ecosystem enters the dry season, soil respiration fluxes decline to low levels, the amplitude of the diel cycle decreases. Fluxes in this period are anti- correlated with temperature and more closely follow fluctuations in air relative humidity and litter moisture. By July, there was little difference in either soil respiration fluxes or the isotopic signature of respired CO2 between the trenched and untrenched plots, suggesting that less than 12 per cent of the respired CO2 is from root respiration sources. We will update these data to include the effects of anticipated summer moisture events. Overall the combination of frequent measurements of soil respiration with isotopic and experimental manipulation provides a framework for developing models that separate effects of temperature, moisture and season on autotrophic and heterotrophic respiration sources.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
DE: 0438 Diel, seasonal, and annual cycles (4227)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting