The influence of plant species on soil nitrogen (N) dynamics was investigated in lowland Amazonia, Brazil under plantations of tree species with varied phenologies, resource requirements, and chemical characteristics in fine litter. Seasonal N dynamics were studied in replicated stands of Pinus caribaea var. hondurensis Barrett & Golfari, Euxylophora paraensis Hub., Carapa guianensis Aubl., a Leguminosae combination (Dalbergia nigra Fr. All., Dinizia excelsa Ducke, Parkia multijuga Benth.), and native forest in the Curuá-Una Forest Reserve, Pará, Brazil. Textural, mineralogical, and chemical soil properties at 1 m depth under the plantations and the forest indicated that initial soil properties were similar. Net annual N mineralization ranged from 195 kg ha−1 (P. caribaea) to 328 kg ha−1 (forest), and was related to fine root N contents in the surface root mat (R2 = 0.96, p = 0.01). Net annual N mineralization was also inversely related to within-stand nitrogen-use efficiency (R2 = 0.81, p = 0.04). These results suggest that tree species or groups of species with varied N-use efficiencies altered soil N transformation rates in a predictable manner.