Abstract:
To investigate the response patterns of plant communities in the semiarid mountain grasslands of Yili, Xinjiang, to short-term nitrogen application, this study examined the Tohulasu Grassland in the Yili River Valley. Four nitrogen application rates (N1: 50 kg·hm⁻²·a⁻¹, N2: 100 kg·hm⁻²·a⁻¹, N3: 150 kg·hm⁻²·a⁻¹, and N4: 200 kg·hm⁻²·a⁻¹) were compared with a control group. Over one growing season, the effects of different nitrogen inputs on community aboveground biomass, community composition, and species diversity were analyzed to elucidate the key pathways through which short-term nitrogen application enhances aboveground biomass. Nitrogen application exerted a unimodal effect on aboveground biomass, with N3 treatment yielding the optimal result, a 52.08% increase relative to the control. The biomass of the dominant species, Dactylis glomerata, increased by 132.12% relative to the control. There were significant increases in community height and cover, but not in community density. Nitrogen application caused significant alteration in species diversity patterns: the importance value of D. glomerata increased by 65.01% under the N3 treatment relative to the control, whereas the importance value of the primary associate species, Trifolium repens, decreased by 65.54% under the N4 treatment relative to the control. Overall, community diversity first decreased and then increased as the nitrogen application rate increased, with the lowest diversity observed under the N3 treatment. Mantel tests revealed that species diversity was regulated primarily by the biomass of subdominant species and the density of dominant companion species. Structural equation modeling indicated that nitrogen application exerted significant, positive, and direct effects only on dominant and subdominant species. Overall, a nitrogen rate of 150 kg·hm⁻²·a⁻¹ was most effective for vegetation restoration in the semiarid mountain grasslands of Yili, Xinjiang.
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