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, Cynosurus cristatus, Holcus lanatus and Agrostis capillaris ) of Irish neutral grasslands were grown at ambient and elevated (700 μmol mol -1 ) atmospheric CO 2 for a period of 8 months. The effects of interspecific competition on plant responses to CO 2 enrichment were investigated by growing the species in a four-species mixture. The results indicate that the species differ in their ability to respond to elevated CO 2 . CO 2 -enrichment had the largest effect on the biomass production of H. lanatus , but substantial stimulations in biomass production were also found for the other three species. The CO 2 -stimulation of biomass production for H. lanatus was accompanied by increased tillering. In addition, reductions in specific leaf area were found for all species. Exposure to elevated CO 2 increased the community biomass of the four-species mixture. This increase can be mainly attributed to a significant increase in the biomass of H. lanatus at elevated CO 2 . No statistically-significant changes in species composition of community biomass were found. 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 CO 2 . The results show that: (1) the species varied in their response to elevated CO 2 ; and (2) species composition in natural plant communities is likely to change at elevated CO 2 , but these changes may occur rather slowly. Much longer periods of exposure to elevated atmospheric CO 2 may be required to permit detection of significant changes in species composition.