HR: 1340h
AN: B43B-1167    [Abstracts]
TI: Thresholds of Carbon Assimilation and Respiration in a California's Oak/Grass Savanna
AU: * Ma, S
EM: sma@nature.berkeley.edu
AF: University of California at Berkeley, 137 Mulford Hall 3114 Baldocchi's Lab Dept of ESPM, Bekerley, CA 94720, United States
AU: Baldocchi, D
EM: baldocchi@nature.berkeley.edu
AF: University of California at Berkeley, 137 Mulford Hall 3114 Baldocchi's Lab Dept of ESPM, Bekerley, CA 94720, United States
AU: Vargas, R
EM: rvargas@nature.berkeley.edu
AF: University of California at Berkeley, 137 Mulford Hall 3114 Baldocchi's Lab Dept of ESPM, Bekerley, CA 94720, United States
AB: Multi-year ecosystem CO₂ fluxes measurement provides us opportunities to understand dynamics and thresholds of carbon assimilation and respiration. Based on eddy-covariance-measured ecosystem carbon assimilation and respiration in a California's oak/grass savanna from 2001 to 2006, we examined the thresholds of these two major processes that control ecosystem carbon uptake. Our preliminary results indicated that year- to-year variations in water supplies (i.e., precipitation) significantly controlled interannual variability in carbon uptake in the savanna ecosystem. Seasonally, grass photosynthesis decreased with decreases in soil moisture, but our results suggested multiple degrading peaks, indicating coupling effects of temperature. On the contrary, tree photosynthesis responded to decreases soil moisture with one significant peak. The thresholds of soil moisture at maximum tree photosynthesis were around 0.1 cm cm^-3. The lowest soil moisture threshold occurred in the dry year, 2004. Annual grass grew during the period when soil temperature was lower than 25^oC, while oak tree was active during the period with soil temperature between 10 to 35^oC. Grass reached maximum photosynthesis at 13.1, 13.7, 16.1, 15.4, and 16.9^oC in the spring of 2002, 2003, 2004, 2005, and 2006, respectively. Under current climate variation, difference of temperature thresholds of grass photosynthesis spanned up to 3.8^oC, and difference of soil moisture thresholds of tree photosynthesis spanned up to 0.11 cm cm^-3. On the other hand, thresholds of ecosystem respiration were coupled with those of photosynthesis responding to interannual variations of soil temperature and moisture. Implications of ecosystem thresholds to global change are also to be discussed.
DE: 0416 Biogeophysics
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting