Effects of nitrogen availability on the competitive interactions between an invasive and a native grass from Brazilian cerrado

Background and aims Nitrogen (N) deposition is currently widespread in many ecosystems and often promotes shifts in plant composition towards invasive species. In this study we evaluated how soil N availability affects the competitive interactions between a native Cerrado grass (Aristida riparia) and an invasive African grass (Melinis minutiflora). Methods We evaluated the effects of increased soil N and the presence of another species on the relative growth rate (RGR), relative competition intensity (RCI), shoot N concentration and δ¹⁵N, intrinsic water-use efficiency (iWUE) and N productivity (A) of the two grasses in a glasshouse experiment. Results We found that the presence of M. minutiflora reduces the RGR of A. riparia by 52 % under high N availability, and by 29 % under low N availability. The shoot N and δ¹⁵N patterns of A. riparia when grown together with M. minutiflora indicate that the exotic species interferes with the native species’ N acquisition. However, the lower RGR and iWUE of A. riparia observed only when grown together with M. minutiflora under high N availability suggests that other mechanisms might also limit A. riparia growth. Conclusions We predict that the global trend of N deposition in ecosystems might facilitate the spread of M. minituflora in Cerrado areas.