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

Abstract

Alpine meadow degradation, usually involving decreased soil nitrogen (N) and patchy landscapes, is a challenge for natural restoration. However, the mechanism underlying plant species coexistence under degradation is unclear. In this study, we evaluated plant N niche complementarity in degraded alpine meadows on the Qinghai–Tibet Plateau using a 15N-labeling (15NO3−, 15NH4+, and 15N-glycine) experiment. At the community level, the concentration of 15NO3− in the degraded alpine meadow was 1.5 times higher than that in the undegraded alpine meadow; both alpine meadows had a significant preference for NO3− (60.72 % and 66.84 % for the degraded and undegraded alpine meadows, respectively), and the degree of glycine preference was significantly higher in the degraded alpine meadow (30.77 %) relative to the undegraded alpine meadow (21.85 %). At the species level, dominant species in both alpine meadows consistently preferred NO3−; the generalist species that can be found in both meadows and unique species of the two alpine meadows generally showed NO3− preferences, while the other plant species that were unevenly distributed in the degraded alpine meadow tended to show increased utilization of glycine, which could reduce N competition. We observed that differentiation among N sources and the uneven distribution of unique species may explain the stability of degraded alpine meadows. Our results suggested that uneven distributions of plants could have strong impacts on community stability and highlighted the importance of considering fine-scale analysis in studies of niche theory. This study has important implications for the restoration of degraded alpine meadows.