Light fuels while nitrogen suppresses symbiotic nitrogen fixation hotspots in neotropical canopy gap seedlings

Mature neotropical lowland forests have relatively lower symbiotic nitrogen fixation (SNF) rates compared with secondary forests. Canopy gap formation may create transient SNF hotspots in mature that increase overall these ecosystems, as canopy gaps are pervasive across the landscape and increasing frequency. However, what environmental conditions driving upregulation is unknown. In a field experiment to test potential controls on SNF, we grew 540 nitrogen-fixing legume seedlings (Pentaclethra macroloba, Zygia longifolia, Stryphnodendron microstachyum) under manipulated light soil availability intact at La Selva Biological Station, Costa Rica. Seedling biomass, nodule (g N seedling−1 h−1) were 4-, 17- 42-fold higher, respectively, than forest. Nitrogen additions decreased but had stronger positive effect. Upregulation of was driven by increased plant growth not disproportionate allocation. These data provide evidence driven, part, availability, demonstrating driver spatial heterogeneity. This further suggests dynamics important for understanding biogeochemistry