Cluster of Dominant Species and Grazing Jointly Influence the Soil Nitrogen and Phosphorus Cycling in Alpine Grasslands

This study systematically analyzes the multi-layered regulatory mechanisms of grazing on soil nitrogen and phosphorus cycling functions, based on the combined effects of different grazing strategies and plant community spatial patterns in alpine grasslands. A controlled mixed grazing experiment with moderate intensity was conducted on a livestock system adaptive management platform in the region surrounding Qinghai Lake on the Qinghai–Tibet Plateau, China. The experimental treatments included yak-only grazing (YG), Tibetan sheep-only grazing (SG), mixed grazing of yak and Tibetan sheep (MG), and no grazing (CK). The study quantitatively assessed the soil microbial nitrogen and phosphorus cycling functional genes in the rhizosphere of dominant species, including the Carex alatauensis and Potentilla acaulis, under different grazing intensities. The aim was to explore the effects of grazing strategy and clusters of dominant species on soil nitrogen and phosphorus cycling and their regulatory mechanisms. The results of this study show that, in the nitrogen cycle, grazing led to a decrease in total nitrogen (TN) content and an increase in ammonium nitrogen content in the dominant species communities. The MG treatment significantly enhanced the abundance of key nitrogen metabolism genes, such as ureC and gs. In the phosphorus cycle, most grazing treatments increased total phosphorus content, but changes in available phosphorus were variable among plant clusters. The MG and SG treatments significantly increased the abundance of functional genes such as aphA, ugpB, and phnW. Compared to the relatively stable soil nitrogen and phosphorus content, the abundance of functional genes exhibited significantly higher variability across different grazing treatments. The clusters of Potentilla acaulis maintained nutrient stability by enhancing nitrogen assimilation and phosphorus uptake, while the clusters of Carex alatauensis promoted ammonium nitrogen accumulation through a conservative strategy. The results indicate that grazing influences nitrogen and phosphorus availability by altering nutrient input and disturbance modes, while plant clusters optimize cycling through differential regulation of microbial functional genes in the community. Both factors jointly regulate nitrogen and phosphorus cycling in Alpine Grassland soils. Mixed grazing exhibited significant advantages in promoting nitrogen retention, enhancing phosphorus activation, and improving plant-microbe interactions, reflecting a comprehensive facilitation of nutrient cycling stability in alpine grasslands. These findings provide important theoretical insights for nutrient cycling management and sustainable grazing practices in alpine grasslands.