Microbial Communities and Environmental Factors Interact to Regulate Soil Respiration Under Nitrogen Addition Conditions in Alpine Meadows in Northwest China

Alpine meadow ecosystems are highly sensitive to global change, yet the response mechanisms of soil respiration (Rs) to nitrogen deposition remain unclear. This research employed a gradient nitrogen addition experiment (0, 5, 10, 15, 20 g·m^-2·a^-1) in an alpine meadow ecosystem in Northwest China to determine the major factors regulating soil respiration responses. High nitrogen inputs (N15 and N20) significantly elevated Rs by 31.96% and 29.21% relative to the control (<i>p</i> < 0.05). Nitrogen addition significantly increased soil ammonium nitrogen (NH₄⁺-N) content, as well as the activities of cellobiohydrolase (CBH) and peroxidase (POD). Microbial community structure shifted with nitrogen addition, showing increased relative abundance of Actinobacteriota (14-25%) and Basidiomycota (13-26%). Functional prediction analysis revealed that high nitrogen treatments enhanced bacterial carbon metabolism functions such as fermentation and ureolysis, while enriching fungal functional guilds like Wood Saprotroph and Arbuscular Mycorrhizal fungi. Partial Least Squares Path Modeling (PLS-PM) indicated that nitrogen addition indirectly drives changes in Rs by regulating physicochemical factors (e.g., NH₄⁺-N), which subsequently influence microbial community composition, functional potential, and key enzyme activities. These findings elucidate the factors influencing soil respiration under varying nitrogen addition levels, providing a theoretical basis for assessing soil carbon cycling in alpine meadows under global change scenarios.