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 lanatusandAgrostis capillaris) ofIrish neutral grasslands were grown at ambient and elevated(700 µmol mol^-1) atmospheric CO₂for a period of 8 months.The effects of interspecific competition on plant responsesto CO₂enrichment were investigated by growing the species ina four-species mixture. The results indicate that the speciesdiffer in their ability to respond to elevated CO₂. CO₂-enrichmenthad the largest effect on the biomass production ofH. lanatus,but substantial stimulations in biomass production were alsofound for the other three species. The CO₂-stimulation of biomassproduction forH. lanatuswas accompanied by increased tillering.In addition, reductions in specific leaf area were found forall species. Exposure to elevated CO₂increased the communitybiomass of the four-species mixture. This increase can be mainlyattributed to a significant increase in the biomass ofH. lanatusatelevated CO₂. No statistically-significant changes in speciescomposition of community biomass were found. However,H. lanatusdidincrease its share of community biomass at each of the harvests,with the other three species, mainlyL. perenne, suffering lossesin their shares at elevated CO₂. The results show that: (1)the species varied in their response to elevated CO₂; and (2)species composition in natural plant communities is likely tochange at elevated CO₂, but these changes may occur rather slowly.Much longer periods of exposure to elevated atmospheric CO₂maybe required to permit detection of significant changes in speciescomposition.Copyright 1998 Annals of Botany Company Carbon dioxide (CO₂) enrichment, competition, Lolium perenne,Cynosurus cristatus, Holcus lanatus, Agrostis capillaris, biomass, specific leaf area, tillering.