Three Tibetan grassland plant species tend to partition niches with limited plasticity in nitrogen use

摘要

Aims Niche complementarity theory explains how species coexist by using different resources. Two pathways to partition resource have been demonstrated: classical niche differentiation and plasticity in resource use. We aimed to determine N-uptake patterns in three Tibetan Plateau grassland species, and to examine how N-partitioning is driven by neighbor interactions. Methods We conducted a transplantation experiment using ten plant communities, each comprising a different combination of Kobresia humilis, Stipa aliena, and Saussurea superba. Soil was sprayed uniformly with a mixture of (NH4)(2)SO4, KNO3, and glycine (C2H5NO2) (1:1:1 by mass of N, each containing one form of N-15) after growing for 45 days. Results Across three species, the N-uptake pattern was NO3- > NH4+ > glycine (NO3-: 58.47%; NH4+: 26.91%; glycine: 14.62%). Neighbor presence had species-specific effects on N-15 recovery. Kobresia humilis took up more N-15-NO3- when it was in competition with other species, whereas Stipa aliena and Saussurea superba took up more N-15-NH4+ and N-15-glycine, respectively. Conclusions Plasticity in N resource utilization of the three species was limited. The species competed for N resources proportionally to the availability of these sources, and tended to partition niches. These findings provide important insights into how plant species grow together in alpine grasslands.