Different grazing intensities affect soil nitrogen cycling by altering microbial nitrogen metabolism in alpine wetlands

Grazing significantly affects soil nitrogen cycling in eastern Qinghai-Tibet Plateau alpine wetlands. Grazing did not alter soil microbial α-diversity, but shifted community composition via metagenomic analysis. Moderate and heavy grazing reduced soil total and active nitrogen contents by 53.8%-92.0% vs. light grazing, significantly decreased abundances of nitrification genes (amoA and hao) and ammonium assimilation gene (glnA), while increased dissimilatory nitrite reduction to ammonium gene (nirB) by 142.1%. A nitrification bottleneck from impaired nitrification drove active nitrogen decline, and structural equation modeling identified nitrogen cycle gene abundance as the key driver. This study reveals microbial nitrogen cycling mechanisms and provides a scientific basis for sustainable grazing management in alpine wetlands.