Rangeland -- plant response to elevated CO{sub 2}. Progress report, 1993

Abstract

Plots of a tallgrass prairie ecosystem were exposed to ambient and twice-ambient CO{sub 2} concentrations in open-top chambers and compared to unchambered ambient CO{sub 2} plots during the entire growing season from 1989 through 1992. Relative root production among treatments was estimated using root ingrowth bags which remained in place throughout the growing season. Latent heat flux was simulated with and without water stress. Botanical composition was estimated annuallyin all treatments. Open-top chambers appeared to reduce latent heat flux and increase water use efficiency similar to elevated CO{sub 2} when water stress was not severe, but under severe water stress, chamber effect on water use efficiency was limited. In natural ecosystems with periodic moisture stress, increased water use efficiency under elevated CO{sub 2} apparently would have a greater impact on productivity than photosynthetic pathway. Root ingrowth biomass was greater in 1990 and 1991 on elevated CO{sub 2} plots compared to ambient or chambered-ambient plots. In 1992, there was no difference in root ingrowth biomass among treatments.