Non-linear Responses of Soil Diazotrophs to Aridity in Xinjiang Grasslands

Although drought strongly affects soil microbial communities and ecosystem functioning, the threshold responses and assembly mechanisms of diazotrophs along aridity gradients remain poorly understood. Here, we investigated diazotrophic communities across 155 grassland sites in Xinjiang, China, spanning a broad natural aridity gradient (1−AI: 0.46–0.88). By integrating segmented regression, null and neutral community models, structural equation modeling, and network stability analysis, we identified critical aridity thresholds and clarified the mechanisms underlying diazotroph community assembly under increasing aridity.