Submitted to: Annual Goldschmidt Conference
Publication Type: Abstract Only
Publication Acceptance Date: 6/2/1997
Publication Date: N/A
Technical Abstract: In this study, we evaluate the efflux of soil during the 1995-1996 winter wheat FACE (Free-Air CO2 Enrichment) experiment at Maricopa, Arizona. To determine whether soil respiration is enhanced under FACE conditions, we measured soil respiration rates with a custom-made chamber attached to a portable gas exchange system, and isotopic composition of the evolved CO2. To distinguish soil CO2 produced by decomposition of original organic matter from that produced by root respiration, we measured the C isotopic composition of wheat plants, soil C, and in situ soil CO2. The del 13C is a useful tracer for FACE C because the tank gas used in the experiment is much lighter than background air. The CO2 flux from FACE plots was roughly doubled from that of control plots, and the results suggest this increase is due mainly to enhanced microbial decomposition rather than to increased root respiration. Although organic matter is being added to FACE soils at a higher rate than to control soils, increased decomposition rates may diminish the possibility of long-term sequestration. Incubation experiments on soil collected after years 1 and 2 of the current FACE wheat experiment should provide further evidence for the possibility of sequestering C from FACE plots in the soil.