HR: 13:55h
AN: B43F-02    [Abstracts]
TI: Seasonality and Interannual Variability of Carbon Uptake and Respiration in a California Oak Savanna
AU: * Ma, S
EM: sma@nature.berkeley.edu
AF: University of California at Berkeley, 137 Mulford Hall #3114, Berkeley, CA 94720 United States
AU: Baldocchi, D
EM: baldocchi@nature.berkeley.edu
AF: University of California at Berkeley, 137 Mulford Hall #3114, Berkeley, CA 94720 United States
AU: Xu, L
EM: LXu@licor.com
AF: LI-COR Biosciences, Environmental Products, Lincoln, NE 68504 United States
AB: Estimating terrestrial carbon sink with large-scale modeling research requires understanding the physiological and ecological processes associated with the carbon uptake and respiration of ecosystems and their variability in seasons and years. This study was conducted in an oak/grass savanna ecosystem in California, USA. The savanna ecosystem consists of blue oak trees ( Quercus douglasii) in the overstory and annual C₃ grasses in the understory. Fluxes of CO₂ were measured above the canopy (overstory) and the grasses (understory) from 2001 to 2005 with two eddy covariance systems. Under typical Mediterranean Climate, net ecosystem exchange of CO₂ (NEE), ecosystem respiration (R_eco), and gross primary production (GPP) in this savanna ecosystem had a distinctive dry-wet seasonal pattern. Leaf area index, leaf nitrogen concentration, and leaf carbon stable isotope discrimination reflected the responses of leaf to the seasonality and interannual variability. Light- use efficiency, the ratio of GPP to absorbed photosynthetically active radiation (aPAR), was not consistent within a year or from year to year, indicating that photosynthesis process was constrained with low temperature during the beginning of the wet season and limited by precipitation during the summer drought. Annual NEE, R_eco, and GPP above the canopy varied significantly between years, varying from -108 - 133 gC m^-2, 780 - 988 gC m^-2, and 646 - 963 gC m^-2, respectively. The difference of interannual R_eco was 1.2 times of that of interannual GPP. There was a tight relationship between annual NEE and the precipitation during the period with daily mean temperature varying between 10 - 20°C, equivalent to precipitation during March and April. The longer the period lasted, the higher carbon uptake occurred. Estimated annual NEE from 1949 - 2005 in the savanna ecosystem varied between ~-400 - 200 gC m^-2.
DE: 4806 Carbon cycling (0428)
SC: Biogeosciences [B]
MN: Fall Meeting 2005