Absorption of15NH4+,15NO3- and15glycine in degraded and non-degraded alpine meadows
Aboveground 15NO3-in the plant community was higher than the concentrations of other N sources in both the undegraded alpine meadow and the degraded alpine meadow ; however, the concentrations of different sources of root15N did not differ in the undegraded alpine meadow, and root 15N labeled as 15glycine was significantly higher than the15NO3- concentration in the degraded alpine meadow (Table 3). Other traits, such as the root to aboveground 15N ratio and root15N absorption efficiency, for the three N sources showed the same pattern as those of the roots; there were no significant differences among the three N sources for the two traits in the undegraded alpine meadows, the root to aboveground 15N ratio for 15glycine and15NH4+ were higher significantly than the15NO3-, and the root15N absorption efficiency for15glycine were higher significantly than the15NH4+ in the degraded alpine meadows (Table 3).
Species richness, aboveground biomass, and belowground biomass showed significantly negative correlations with total plant15N in the undegraded alpine meadow. Species richness and aboveground biomass were significantly positively correlated, and R/S was significantly negatively correlated with total plant15N in the degraded alpine meadow (Supplementary table 1). With respect to plant N stoichiometry, plant root N and root to aboveground N ratio were positively correlated with plant total15N in the degraded alpine meadow (Supplementary table 1).