Effects of soil nutrient availability on investment in acquisition of N and P in Hawaiian rain forests

We determined the influence of nutrient availability on the mechanisms used by plants to acquire nitrogen and phosphorus from the soil. Extracellular acid phosphatase production, mycorrhizal colonization, and N and P uptake c apacities were measured in control, N-, and P-fertilized forests in three s ites that varied in nutrient status from N limited to relatively fertile to P limited. Nitrogen fertilization increased extracellular phosphatase acti vity in all sites. Phosphorus additions consistently reduced phosphatase ac tivity, mycorrhizal colonization, and P uptake capacity across sites. Our r esults indicate that these plants efficiently allocate resources to nutrien t acquisition as suggested by an economic model. Investment in acquisition of a nutrient was greatest when that nutrient was limiting to growth, and p lants appeared to allocate excess N to construction of extracellular phosph atases to acquire P This increase in phosphatase production with N fertiliz ation implies that even P-limited systems might respond to N deposition wit h greater productivity.