Effects of elevated CO2 on foliar chemistry of saplings of nine species of tropical tree.

This study examined the effects of elevated CO2 on secondary metabolites for saplings of tropical trees. In the first experiment, nine species of trees were grown in the ground in open-top chambers in central Panama at ambient and elevated CO2 (about twice ambient). On average, leaf phenolic contents were 48% higher under elevated CO2. Biomass accumulation was not affected by CO2, but starch, total non-structural carbohydrates and C/N ratios all increased. In a second experiment with Ficus, an early successional species, and Virola, a late successional species, treatments were enriched for both CO2 and nutrients. For both species, nutrient fertilization increased plant growth and decreased leaf carbohydrates, C/N ratios and phenolic contents, as predicted by the carbon/nutrient balance hypothesis. Changes in leaf C/N levels were correlated with changes in phenolic contents for Virola (r=0.95, P<0.05), but not for Ficus. Thus, elevated CO2, particularly under conditions of low soil fertility, significantly increased phenolic content as well as the C/N ratio of leaves. The magnitude of the changes is sufficient to negatively affect herbivore growth, survival and fecundity, which should have impacts on plant/herbivore interactions.