Uneven distributions of unique species promoting N niche complementarity explain the stability of degraded alpine meadow

Alpine meadow degradation, usually involving decreased soil N and patchy landscapes, is challenging for natural restoration. However, the mechanism underlying plant species coexistence during degradation is unclear. In this study, we evaluated plant N niche complementarity in degraded alpine meadows by a 15N-labeling (15NO3-, 15NH4+ and 15N-glycine) experiment. At the community level, the degraded alpine meadow showed larger root and all plant 15N concentrations and preferred glycine over NO3- compared with the undegraded alpine meadow. At the species level, dominant species in the undegraded alpine meadow consistently preferred NO3-. For the degraded alpine meadow, generalist species, common to both meadows, showed diverse preferences, while unique species generally preferred glycine, among which the uneven distribution could reduce glycine competition. We observed that differentiation in N sources and the uneven distribution of unique species may explain the stability of degraded alpine meadows. Our results suggested that plant spatial distribution could be powerful for community stability and emphasized the importance of considering fine-scale perspectives in studies of niche theory. This study have important implication for restoration of degraded alpine meadows.