Short rotation coppices (SRCs) are a promising alternative for environmental-friendly biomass production. However, "profound understanding of nitrogen (N) uptake and allocation dynamics and their interaction with biomass production of individual tree species is required for their sustainable management. In-situ N-15 soil pulse labeling of the widely applied willow cv. Tordis and poplar cv. Max 1 allowed tracing their uptake of N-min and to evaluate the effect of N nutrition on their growth. A pulse of either (NH4NO3)-N-15 or (NH4NO3)-N-15 was applied to the soil of four replicate trees of each species in a pot experiment. Leaf, twigs, stem, root were analyzed to quantify the uptake and allocation of N-15 after labeling. Summarizing all compartments of poplar, almost all of (NO3-)-N-15 (97%) from the N soil pool could be recovered, but only a third of the (NH4+)-N-15 (34%). In contrast, willow incorporated exactly the same amount of N-15 (49%) from both tracers i.e. showing no preference for a certain Nmin species. Poplar did not only have the higher Nmin uptake but also showed a higher total biomass (12.2 g.tree(-1)) production than willow (10.2 g.tree(-1)) in first 56 days, which goes along which its higher allocation of N into leaves. We conclude that the poplar cv. Max 1 might be a better choice for biomass production, especially at arable sites with high N contents as well as for protecting from all negative impacts of non-closed N cycles as typical for classical agricultural managed sites (e.g. nitrate leaching or N2O emissions). (C) 2017 Elsevier Ltd. All rights reserved.