Non-destructive assessment of the effects of elevated CO 2 on plant community structure in a calcareous grassland

Abstract

Calcareous grassland was exposed to ambient or elevated CO 2 using a Screen-Aided CO 2 Control (SACC) system starting in March 1994. The effects of elevated CO 2 on plant community structure were studied using the point intercept method. Measurements were made in March 1994 prior to the start of CO 2 exposure and again in June 1994 at peak plant biomass. There were no significant differences in the initial structure of the communities based on their assigned CO 2 treatments in March. After 9 weeks of exposure of the community to elevated CO 2, the total number of intercepts per plot was not significantly different between CO 2 treatments; however, Carex flacca and Cirsium acaule had marginally significant (P=0.055 and P=0.06) increases in the % sward of the community at elevated CO 2 (number of intercepts for a single species divided by the total number of intercepts for all species). Measurements of leaf extension in Carex flacca showed that at least part of the increase in % sward at elevated CO 2 could be explained by greater leaf length per plant (P=0.02). These measurements and other experiments with calcareous grassland species and communities suggest that rising atmospheric CO 2 concentrations will probably alter the structure of calcareous grassland communities.