Increased nitrogen deposition alleviated the competitive effects of the introduced invasive plant Robinia pseudoacacia on the native tree Quercus acutissima

Background and aims Increasing atmospheric nitrogen (N) deposition and biological invasion have become major concerns with global environmental change. This study aimed to determine the effects of an exotic species on a native one under increasing N deposition. Methods We conducted a greenhouse experiment in which the exotic species Robinia pseudoacacia and the native species Quercus acutissima were grown inmixture and monocultures under four levels of simulated N deposition (0, 3, 6, 12 g m(-2) year(-1)). After 12 weeks of treatment, plant growth, leaf physiological traits and soil chemical properties were determined. Results With its strong capability for nutrient absorption and carbon assimilation, R. pseudoacacia dominated in competition. R. pseudoacacia reduced the growth of Q. acutissima, but the relative competition index decreased with increasing N deposition. At the end of the experiment, the soil available phosphorus (P) in mixture was significantly lower than that in the monoculture of Q. acutissima, while the soil available N in the two cultivations did not show obvious differences. Conclusions Increased N deposition alleviated the competitive effects of R. pseudoacacia on Q. acutissima. In the future, besides N, increased P availability should also be considered in the interaction between the two species.