Document: YUF-3-66-35

Ecosystem carbon flux under elevated CO₂ by CO₂ LT Chambers in southern California chaparral.

CHENG, Y.* ¹, W.C.OECHEL* ¹, S.HASTINGS ¹, J.MAJOR ¹, P.BRYANT ¹, I.IBANEZ ² and J.VERFAILLIE ¹

San Diego State University, San Diego, CA 92182 USA ¹
Duke University, Durham, NC 27708 USA ²

Abstract:
Ecosystem carbon flux was studied under six different CO₂ treatments by CO₂ LT (CO₂ controlled, Natural Lit, Temperature controlled) null balance chambers in Southern California chaparral dominated by Adenostoma faciculatum H. & A. between 1996 and 1999. By using the chamber technique, we measured net ecosystem flux directly and continuously. Net CO₂ flux was processed using the null-balance chamber system algorithms, and modeled using non-linear curve fitting techniques and meteorological data. The annual net ecosystem carbon flux under different CO₂ treatments was accumulated from daily carbon flux values. After three-years of exposure, an increase of CO₂ from 250 PPM to 750 PPM increased rates of gross primary production (GPP) by 56%, which is equal to 537 gC/m²/y. The CO₂ effect on the ecosystem during these three years was variable. The results showed that the effect of elevated CO₂ on net CO₂ exchange of chaparral is inversely correlated with water availability. Although elevated CO₂ stimulated leaf-level photosynthesis and decreased transpiration and conductance regardless of water availability, whole-ecosystem rates of net CO₂ flux and evapotranspiration were not significantly altered by elevated CO₂ when water availability was high. A significant negative effect (p = 0.028) of CO₂ on soil respiration was detected by in situ measurement. Plant growth and LAI measurement didn't show the significant effect of different CO₂ treatment, the chaparral ecosystem above ground response to the environment is very slow, which might mask the CO₂ effect temporally.

Keywords: elevated CO2, carbon flux, Chaparral

This abstract is being presented at: 10:30 AM in session:
Poster Session #18: Elevated CO₂.