Effect of aridity on the -diversity of alpine soil potential diazotrophs: insights into community assembly and co-occurrence patterns

Microbial diversity plays a vital role in the maintenance of ecosystem functions. However, the current understanding of mechanisms that shape microbial diversity along environmental gradients at broad spatial scales is relatively limited, especially for specific functional groups, such as potential diazotrophs. Here, we conducted an aridity-gradient transect survey from 60 sites across the Tibetan Plateau, the largest alpine ecosystem of the planet, to investigate the ecological processes (e.g., local species pools, community assembly processes, and co-occurrence patterns) that underlie the beta-diversity of alpine soil potential diazotrophic communities. We found that aridity strongly and negatively affected the abundance, richness, and beta-diversity of soil diazotrophs. Diazotrophs displayed a distance-decay pattern along the aridity gradient, with organisms living in lower aridity habitats having a stronger distance-decay pattern. Arid habitats had lower co-occurrence complexity, including the number of edges and vertices, the average degree, and the number of keystone taxa, as compared with humid habitats. Local species pools explained limited variations in potential diazotrophic beta-diversity. In contrast, co-occurrence patterns and stochastic processes (e.g., dispersal limitation and ecological drift) played a significant role in regulating potential diazotrophic beta-diversity. The relative importance of stochastic processes and co-occurrence patterns changed with increasing aridity, with stochastic processes weakening whereas that of co-occurrence patterns enhancing. The genera Geobacter and Paenibacillus were identified as keystone taxa of co-occurrence patterns that are associated with beta-diversity. In summary, aridity affects the co-occurrence patterns and community assembly by regulating soil and vegetation characteristics and ultimately shapes the beta-diversity of potential diazotrophs. These findings highlight the importance of co-occurrence patterns in structuring microbial diversity and advance the current understanding of mechanisms that drive belowground communities.IMPORTANCERecent studies have shown that community assembly processes and species pools are the main drivers of beta-diversity in grassland microbial communities. However, co-occurrence patterns can also drive beta-diversity formation by influencing the dispersal and migration of species, the importance of which has not been reported in previous studies. Assessing the impact of co-occurrence patterns on beta-diversity is important for understanding the mechanisms of diversity formation. Our study highlights the influence of microbial co-occurrence patterns on beta-diversity and combines the drivers of community beta-diversity with drought variation, revealing that drought indirectly affects beta-diversity by influencing diazotrophic co-occurrence patterns and community assembly. Recent studies have shown that community assembly processes and species pools are the main drivers of beta-diversity in grassland microbial communities. However, co-occurrence patterns can also drive beta-diversity formation by influencing the dispersal and migration of species, the importance of which has not been reported in previous studies. Assessing the impact of co-occurrence patterns on beta-diversity is important for understanding the mechanisms of diversity formation. Our study highlights the influence of microbial co-occurrence patterns on beta-diversity and combines the drivers of community beta-diversity with drought variation, revealing that drought indirectly affects beta-diversity by influencing diazotrophic co-occurrence patterns and community assembly.