Nitrogen-fixing legumes are widely used to improve ecosystems. However, N accumulation in biomass, N₂ amounts biologically fixed, and the effects on soil N status are poorly understood for plantations with slow-growing N₂-fixing legume trees in seasonally dry environments. In this study, we assessed these questions in monospecific stands of uninoculated Anadenanthera peregrina (L.) var. peregrina (angico) trees established in the Atlantic Forest biome. Nine experimental plots with a stand density of 1111 tree ha⁻¹ were examined about five to six years after tree planting. N content in the leaves, branches, bark, and wood was estimated using allometric equations and N concentration in the tissues. To assess the N content, the topsoil layer was sampled in each plot and in one pasture area. The annual N₂ fixation rate at the stand scale was estimated by the natural abundance of ¹⁵N, using leaves of angico and a mix of leaves of herbs and shrubs growing in the understory in each plot. N accumulation in aboveground biomass was estimated at 260 kg ha⁻¹ and N allocated in the leaves and branches was four-fold that in the tree stem. N derived from biological N₂ fixation was estimated at 50% on average, with an annual rate of N fixed in the aboveground biomass of 22 kg ha⁻¹ year⁻¹. Soil N storage was similar between A. peregrina stands and the pasture area at six years after planting. Long-term gains of N₂ fixation may be greatly improved by the adoption of breeding programs for this slow-growing species and the use of an adequate rhizobium strain.

固氮豆类被广泛用于改善生态系统。但是，对于季节性干燥环境中固定有N _2的豆科植物生长缓慢的人工林，人们对生物量中的N积累，N ₂的生物量固定以及对土壤N状况的影响了解得很少。在这项研究中，我们评估了未接种的Anadenanthera peregrina（L.）var的单特异性林分中的这些问题。在大西洋森林生物群系中建立的peregrina（angico）树。九个实验地块的林分密度为1111树ha ^-1植树大约五到六年后进行了检查。叶片，树枝，树皮和木材中的N含量是使用异速方程和组织中的N浓度估算的。为了评估氮含量，在每个样地和一个牧场中对表土层进行了采样。在每个样地的林下层中，使用安吉科的叶子以及草本和灌木的叶子的混合物，通过自然丰富的¹⁵ N估算了林分规模下的年度N ₂固定率。地上生物量中的氮累积量估计为260 kg ha ^-1，而在叶和枝中分配的氮是在树茎中的四倍。源自生物N _2的N固定平均估计为50％，固定在地上生物量中的N的年比率为22 kg ha - ¹ 年^-1。种植六年后，百日草林和牧场之间的土壤氮储量相似。通过为这种缓慢生长的物种采用育种程序并使用适当的根瘤菌菌株，可以大大提高N ₂固定的长期收益。