Responses of communities of tropical tree species to elevated CO₂ in a forest clearing

Abstract

Communities of ten species of tropical forest tree seedlings from three successional classes were grown at ambient and elevated CO₂ in large open-top chambers on the edge of a forest in Panamá. Communities grew from 20 cm to approximately 2 m in height in 6 months. No enhancements in plant biomass accumulation occurred under elevated CO₂ either in the whole communities or in growth of individual species. Reductions in leaf area index under elevated CO₂ were observed, as were decreases in leaf nitrogen concentrations and increases in the C:N ratio of leaf tissue. Species tended to respond individualistically to elevated CO₂, but some generalizations of how successional groupings responded could be made. Early and mid-successional species generally showed greater responses to elevated CO₂ than late-successional species, particularly with respect to increases in photosynthetic rates and leaf starch concentrations, and reductions in leaf area ratio. Late-successional species showed greater increases in C:N ratios in response to elevated CO₂ than did other species. Our results indicate that there may not be an increase in the growth of regenerating tropical forest under elevated CO₂, but that there could be changes in soil nutrient availability because of reductions in leaf tissue quality, particularly in late-successional species.