What was done
Semi-natural grassland communities, characteristic of the Irish lowlands, were grown in pots placed within open-top chambers and fumigated for eight months at atmospheric CO2 concentrations of 350 and 700 ppm to study the effects of elevated CO2 on community biomass and species composition.  Each community consisted of a four-species mixture composed of the C3 grasses: Lolium perenne, Holcus lanatus, Agrostis capillaris, and Cynosurus cristatus.

What was learned
Elevated CO2 increased the biomass of all four grasses in a species-specific manner, with Holcus lanatus and Cynosurus cristatus exhibiting the largest and smallest growth responses of 41 and 19%, respectively.  At the community level, these individual positive growth responses to atmospheric CO2 enrichment contributed to a 26% increase in total biomass.  Additionally, even though elevated CO2 had no significant effects on species composition, it caused Holcus lanatus to slightly increase its share of community biomass, at the expense of the other species, due to its strong individual growth response.

What it means
As the CO2 content of the atmosphere increases, it is likely that these lowland grass ecosystems common to Ireland and north-western Europe will display increased biomass production while maintaining their species richness.  Thus, rising atmospheric CO2 levels should do little to affect competition between C3 grasses in these communities, thereby preserving their compositional biodiversity.