Tropical forests have an exceptional capacity to sequester carbon, support biodiversity, and cycle nutrients. Ample soil nitrogen (N) in these forests allows high rates of primary production and rapid regeneration. Nitrogen is regulated by microbial communities, which can be free-living in the soil and leaf litter (asymbiotic) or in symbioses with certain trees. Climate warming is predicted to increase microbial N fixation and may alter the growth of N-fixing trees, which are major N inputs in tropical forests. To investigate the effects of warming on both the asymbiotic and symbiotic components of the N cycle in tropical forests, we analyzed soil and leaf litter samples as well as annual seedling census data from a warming field experiment in Puerto Rico. Amplicon sequencing of the 16S and nifH regions of our samples revealed that microbial community composition was significantly altered by warming. We found that asymbiotic N fixation rates were increased under warming, and this increase in fixation was partially mediated by the change in the N-fixing bacterial community, at least in the leaf litter. Nitrogen-fixing seedlings exhibited a higher growth rate than non-fixers under warming, and this growth advantage was absent under ambient conditions. The growth of N fixers was reduced by a higher proportion of neighboring N fixers, but this competitive effect was only significant under warming. Finally, seedling growth increased following hurricane disturbance before significantly decreasing, possibly because a flux of growth-supporting light and nutrients after the hurricane quickly dissipated. This growth increase and subsequent decrease was significantly exaggerated in N fixers under ambient conditions. These results tentatively indicate that the anticipated increase in N fixation under warming confers N fixers a growth advantage that alters neighborhood growth dynamics and growth response to hurricane disturbance. These effects of warming on both asymbiotic and symbiotic N fixers suggest that warming increases N flux from the atmosphere into this tropical forest, but it remains unclear how the other components of the N cycle are altered, including N mineralization. Future research should aim at understanding how climate change influences the full N cycle in tropical forests.