PARENT SESSION
Friday, August 11, 8:00-11:30 am
COS 105 - Nutrient cycling
Chickasaw, Mezzanine Level, Cook Convention Center
Presiders: D Bryant
Controls over foliar N:P ratios in tropical rain forests.
Cleveland, Cory *,1, Townsend, Alan2, Asner, Greg3, Bustamante, Mercedes4, 1 INSTAAR: An Earth and Environmental Systems Institute, Boulder, CO, USA2 INSTAAR & Department of Ecology and Evolutionary Biology, Boulder, CO, USA3 Department of Global Ecology, Stanford, CA, USA4 Departamento de Ecologia, Brasilia, Brasil
ABSTRACT- Observed correlations between foliar nutrient concentrations and soil nutrient availability in terrestrial ecosystems have led to the use of foliar nutrients as an index of nutrient status, and as predictors of broad-scale patterns in ecosystem processes. In addition, a growing interest in ecological element stoichiometry has fueled several analyses of foliar N:P ratios within and across ecosystems. Such studies have observed high plant N:P ratios in tropical forests relative to higher latitude ecosystems, supporting the suggestion that tropical forests are generally N-rich and P-poor. However, while these broad generalizations may have merit, their simplicity masks the enormous environmental heterogeneity of tropical forests; such variation includes dramatic differences in soil fertility and climate, as well as the highest plant species diversity of any biome. Here, we present original data on foliar N and P concentrations from 150 mature, canopy tree species in Costa Rica and Brazil, combined with data from a comprehensive new literature synthesis to explore the major sources of variation in foliar N:P values within the tropics. We found no relationship between N:P ratios and either latitude or mean annual precipitation within tropical latitudes alone. There was, however, evidence of seasonal controls; in a rain forest site in Costa Rica, foliar N:P values differed by 25% between the wet and dry season. N:P ratios did vary with soil P availability and/or soil order, but there was substantial overlap across coarse divisions in soil type. In addition, perhaps the most striking feature of the data set was significant variation at the species-level. Taken as a whole, our results imply that the dominant influence on foliar N:P ratios in the tropics is species variability, and that unlike marine systems, and perhaps some other terrestrial biomes, the N:P stoichiometry of tropical forests is not well constrained.
Key words: nutrient cycling, tropical rain forest, foliar element ratios