Natural pasture community response to enriched carbon dioxide atmosphere

We examined the response of a pasture community in southern Quebec (Canada) to long-term exposure of enriched atmospheric CO(2) conditions. The study was conducted using open-top growth chambers directly placed on top of the natural pasture community. To investigate the change in the overall species composition in time and space, we used canonical correspondence analysis, a direct ordination method. Over the three years, the overall community responded significantly to enriched CO(2). The analyses show that, after three years, CO(2) was the most important environmental variable affecting the species composition. Initially the presence of the wall of the chambers influenced the composition but CO(2) became more important by the third year. Soil and air temperatures only slightly influenced the community composition. The first two axes of the canonical correspondence analysis explained a large proportion of the variation in the three years and these trends appeared to increase with time. Species such as Agropyron repens appeared to be positively influenced by the presence of the wall (slightly warmer conditions). However, the analyses suggest that Phleum pratense and Trifolium repens, for example, were favored by the increase in atmospheric CO(2). The variation in species composition in enriched versus ambient CO(2) chambers suggests that the effect of the environmental factors, particularly CO(2), were important in affecting the rate and pattern of succession. Furthermore, the temporal increase in importance of the variable CO(2) in the present analyses indicates that there might be a time-lag in response to atmospheric enrichment.