Secondary and managed plantation forests comprise a rapidly increasing portion of the humid tropical forest biome, a region that, in turn, is a major source of nitrous oxide (N₂O) emissions to the atmosphere. Previous work has demonstrated reduced N₂O emissions in regenerating secondary stands compared to mature forests, yet the importance of species composition in regulating N₂O production in young forests remains unclear. We measured N₂O fluxes beneath four native tree species planted in replicated, 21-yr-old monodominant stands in the Caribbean lowlands of Costa Rica in comparison with nearby mature forest and abandoned pasture sites at two time points (wetter and drier seasons). We found that species differed eight-fold in their production of N₂O, with slower growing, late-successional species (including one legume) promoting high N₂O fluxes similar to mature forest, and faster growing, early successional species maintaining low N₂O fluxes similar to abandoned pasture. Across all species, N₂O flux was positively correlated with soil nitrate concentration in the wetter season and with soil water-filled pore space (WFPS) in the drier season. However, the strongest predictor of N₂O fluxes was fine-root growth rate, which was negatively correlated with N₂O emissions at both time points. We suggest that tree-specific variation in growth habits creates differences in both N demand and soil water conditions that may exert significant control on N₂O fluxes from tropical forests. With the advent of REDD+ and related strategies for fostering climate mitigation via tropical forest regrowth and plantations, we note that species-specific traits as they relate to N₂O fluxes may be an important consideration in estimating overall climate benefits.