Aridity gradient overrides degradation in shaping the topsoil microbiome of the Tianshan wild fruit forest.

The Tianshan wild fruit forest, a critical relict ecosystem and biodiversity hotspot, is experiencing severe degradation, a process widely assumed to be the primary driver of negative shifts in soil microbial communities. However, in arid regions, the overarching influence of climatic aridity may supersede localized degradation effects, creating a pivotal scientific question: which factor-aridity or degradation-dominantly regulates the soil microbiome in this unique habitat? To address this, we analyzed 360 topsoil samples across degradation and aridity gradients using high-throughput sequencing. The results demonstrate that the aridity index, not degradation level, is the paramount factor shaping microbial community structure, explaining the largest proportion of variation in both bacterial (∼43%) and fungal (∼30%) communities. The ecosystem harbors an exceptionally stable core microbiome, with community assembly predominantly governed by stochastic processes. Notably, alternating wet-dry (dry sub-humid) conditions significantly enhanced the complexity and stability of microbial co-occurrence networks compared to semi-arid or humid regions. Additionally, soil microbes mediated multiple core ecological processes, with nitrogen cycling as the most abundant-dominated by