HR: 0830h
AN: GC31B-0184    [PDF]
TI: Carbon Dioxide and Water Vapor Fluxes at Reduced and Elevated CO$_{2}$ Concentrations in Southern California Chaparral
AU: * Cheng, Y
EM: ycheng@sunstroke.sdsu.edu
AF: Global Change Research Group, San Diego State University, San Diego, CA 92182 United States
AU: Oechel, W C
EM: oechel@sunstroke.sdsu.edu
AF: Global Change Research Group, San Diego State University, San Diego, CA 92182 United States
AU: Hastings, S J
EM: shastings@sunstroke.sdsu.edu
AF: Global Change Research Group, San Diego State University, San Diego, CA 92182 United States
AU: Bryant, P J
EM: pbryant@sunstroke.sdsu.edu
AF: Global Change Research Group, San Diego State University, San Diego, CA 92182 United States
AU: Qian, Y
EM: qian@sunstroke.sdsu.edu
AF: Global Change Research Group, San Diego State University, San Diego, CA 92182 United States
AB: This research took two different approaches to measuring carbon and water vapor fluxes at the plot level (2 x 2 meter and 1 x 1 meter plots) to help understand and predict ecosystem responses to elevated CO$_{2}$ concentrations and concomitant environmental changes. The first measurement approach utilized a CO$_{2}$-controlled, ambient lit, temperature controlled (CO$_{2}$LT) null-balance chamber system run in a chaparral ecosystem in southern California, with six different CO$_{2}$ concentrations ranging from 250 to 750 ppm CO$_{2}$ concentrations with 100 ppm difference between treatments. The second measurement approach used a free air CO$_{2}$ enrichment (FACE) system operated at 550 ppm CO$_{2}$ concentration. These manipulations allowed the study of responses of naturally-growing chaparral to varying levels of CO$_{2}$, under both chamber and open air conditions. There was a statistically significant CO$_{2}$ effect on annual NEE (net ecosystem exchange) during the period of this study, 1997 to 2000. The effects of elevated CO$_{2}$ on CO$_{2}$ and water vapor flux showed strong seasonal patterns. Elevated CO$_{2}$ delayed the development of water stress, enhanced leaf-level photosynthesis, and decreased transpiration and conductance rates. These effects were observed regardless of water availability. Ecosystem CO$_{2}$ sink strength and plant water status were significantly enhanced by elevated CO$_{2}$ when water availability was restricted. Comparing the FACE treatment and the FACE control, the ecosystem was either a stronger sink or a weaker source to the atmosphere throughout the dry seasons, but there was no statistically significant difference during the wet seasons. Annual average leaf transpiration decreased with the increasing of the atmospheric CO$_{2}$ concentration. Although leaf level water-use efficiency (WUE) increased with the growth CO$_{2}$ concentration increase, annual evapotranspiration (ET) during these four years also increased with the increase of the atmospheric CO$_{2}$ concentrations. These results indicate that chaparral or other similar ecosystems, under future elevated CO$_{2}$ concentrations, might be even more water stressed than they are under current conditions.
DE: 0315 Biosphere/atmosphere interactions
DE: 1600 GLOBAL CHANGE (New category)
DE: 1655 Water cycles (1836)
DE: 1866 Soil moisture
SC: Global Climate Change [GC]
MN: 2003 Fall Meeting