The effect of soil nutrient availability on resource allocation in tropical tree species

Tropical tree communities are diverse in both their taxonomic composition and in their functional strategies for resource use and acquisition. Soil resources influence productivity of tropical forests and the distributions of tree species across edaphically heterogeneous landscapes. My dissertation evaluates functional variation among tropical trees in nutrient use, and the implications of this functional diversity of tropical forest nutrient and carbon cycling. Through a comparison forest litterfall patterns along a natural fertility gradient and experimental nutrient addition, I show that responses of forest productivity to nutrient availability are difficult to predict across space from environmental parameters alone due to turnover in forest functional composition. Evaluation of wood and foliar nutrient allocation along a soil fertility gradient demonstrates that tree species vary enormously both within and among soil habitats in the allocation of soil-derived nutrients to both foliar and woody biomass. I investigated the function of wood nitrogen and phosphorus repositories by conducting a sapling defoliation experiment, finding that wood P reserves are a dynamic pool reflecting both P in the soil and the demand for P allocation to leaves. Finally, I found that soil phosphorus availability is strongly correlated with the frequency of multiple stemmed trees across a regional forest plot network, indicating that reserves of soil derived nutrients influence the survival of trees after damage. By uncovering the importance of wood nutrient storage in forest ecosystem and community dynamics, this dissertation highlights a novel mechanism by which soil fertility influences the structure and function of tropical forests