Nutrient limitation of eco-physiological processes in tropical trees

Tropical forests play a disproportionately large role in the global climate system, yet the extent to which nutrients limit the potential for tropical trees to increase carbon gain as atmospheric carbon dioxide rises is unknown. This review focuses on what is known about tropical tree responses to experimental nutrient addition and how such information is critical for developing a more complete picture of the ability of tropical forest to respond to a changing world. Most of our knowledge of nutrient limitation of eco-physiological processes in tropical trees is derived from stand-scale nutrient addition experiments, in which physiological or growth responses signify limitation by that element. Our knowledge is further supplemented by fertilization studies of individual plants in pots. There is emerging evidence that fine root biomass decreases and maximum photosynthetic rates, water transport capacity and plant growth in tropical trees increase with nutrient addition, but the magnitude of response depends upon the successional status of the species, the size of the individual, light availability and the element in question. The sheer variation in responses of tropical trees to nutrient addition calls for a more complete evaluation across tropical environments.