Long-term CO2 enrichment of a pasture community: Species richness, dominance, and succession

The present study addresses responses of a pasture community to CO2 enrichment in situ. It focused on two levels of organization. We examined changes in both community properties and species-specific responses during long-term exposure to high CO2 concentration. The underlying hypothesis is that CO2 enrichment could change community composition. At the community level, we observed higher species richness and lesser dominance under enriched than ambient CO2. Two species were apparently central in explaining our results, Agropyron repens and Plantago major. The cover of this first species increased only under ambient CO2. Conversely, the cover of the latter species decreased under ambient CO2 but remained stable under enriched CO2. Species were pooled into dicots and monocots to examine space acquisition. Changes in monocot cover through time were more tightly coupled with that of dicots under ambient than high CO2. Enrichment with CO2 appeared to have a positive effect on the early-successional species, preventing the complete dominance by late-successional species. In fact, under elevated CO2 early- and late-successional species were coexisting. Therefore, our results suggest the possibility that succession patterns might be altered by CO2 enrichment apparently because enriched CO2 stimulates the growth of dicots.