Drought and soil nutrients effects on symbiotic nitrogen fixation in seedlings from eight Neotropical legume species

Symbiotic nitrogen fixation is a dominant source of nitrogen to many terrestrial ecosystems, and thus may influence their responses to global change. High legume species diversity and abundance are thought to lead to high rates of symbiotic nitrogen fixation in Neotropical forests. However, how changes in water and nutrient availability will affect symbiotic nitrogen fixation have only recently been explored, even as droughts begin to increase in severity and frequency in the Neotropics.  To explore these effects, we grew eight species of Neotropical woody legume seedlings in a shadehouse for four months while manipulating soil water, phosphorus and molybdenum availability. Overall, drought reduced nodule biomass, nitrogenase activity (acetylene reduction g-1 nodule), and acetylene reduction per seedling by 33%, 27%, and 41%, respectively, but reduced seedling biomass by only 18%.  Species varied in the manifestation of drought effects. For example, drought reduced the probability that ...