EFFECTS OF ELEVATED CARBON-DIOXIDE ON PLANT BIOMASS PRODUCTION AND COMPETITION IN A SIMULATED NEUTRAL GRASSLAND COMMUNITY

Using open-top chambers, four prominent species (Lolium perenne, Cynos urus cristatus, Holcus lanatus and Agrostis capillaris) of Irish neutr al grasslands were grown at ambient and elevated (700 mu mol mol(-1)) atmospheric CO2 for a period of 8 months. The effects of interspecific competition on plant responses to CO2 enrichment were investigated by growing the species in a four-species mixture. The results indicate t hat the species differ in their ability to respond to elevated CO2. CO 2-enrichment had the largest effect on the biomass production of H. la natus, but substantial stimulations in biomass production were also fo und for the other three species. The CO2-stimulation of biomass produc tion for H. lanatus was accompanied by increased tillering. In additio n, reductions in specific leaf area were found for all species. Exposu re to elevated CO2 increased the community biomass of the four-species mixture. This increase can be mainly attributed to a significant incr ease in the biomass of H. lanatus at elevated CO2. No statistically-si gnificant changes in species composition of community biomass were fou nd. However, H. lanatus did increase its share of community biomass at each of the harvests, with the other three species, mainly L. perenne , suffering losses in their shares at elevated CO2. The results show t hat: (1) the species varied in their response to elevated CO2; and (2) species composition in natural plant communities is likely to change at elevated CO2, but these changes may occur rather slowly. Much longe r periods of exposure to elevated atmospheric CO2 may be required to p ermit detection of significant changes in species composition. (C) 199 8 Annals of Botany Company.