Interactions between neighboring native and alien species are modulated by nitrogen availability.
Plant competitive superiority has long been hypothesized to play a key role in the process of plant invasion, which is also affected by global change components such as anthropogenic nitrogen (N) deposition. To explore mutual interactions between alien and native plants at different N available levels, a pot experiment was carried out at a common garden in northern China. Two alien plants (Lolium perenne and Medicago sativa) and four native species (Agropyron cristatum, Elymus dahuricus, Astragalus adsurgens, and Avena fatua) were monocropped and intercropped alternately, under low (0.28 mg day-1) and high (0.84 mg day-1) N available levels. Results demonstrated N enrichment produced higher biomass of both alien and native plants, and species identity of the neighbor modified the growth responses of both native and alien plants to N enrichment. The alien grass L. perenne increased the biomass of native grass E. dahuricus at high N enrichment level. The alien legume M. sativa promoted the growth of native grasses A. cristatum and A. fatua at high N enrichment level, and promoted the growth of native grass E. dahuricus at low N enrichment level. The native legume A. adsurgens increased the growth of the alien grass L. perenne at low N enrichment level, and increased the growth of the alien legume M. sativa at high N enrichment level. Both alien and native legume species showed positive interactions and thus promoted plant growth. Considering the positive effects of the alien legume M. sativa on the growth of native plants and itself, the introduction of M. sativa could be beneficial for biomass production of plant communities and management of degraded temperate grasslands.