Community assemblage of free-living diazotrophs along the elevational gradient of Mount Gongga

Mountain systems are unique for studying the responses of species distribution and diversity to environmental changes along elevational gradients. It is well known that free-living diazotrophic microorganisms are important to nitrogen cycling in mountain systems. However, the elevational patterns of free-living diazotrophs and the underlying ecological processes in controlling their turnover along broader gradients are less well documented. Here, we investigated the pattern of diazotrophic diversity along the elevational gradient (1800 m-4100 m) in Mount Gongga of China. The results showed that the alpha -diversity of diazotrophs did not change with the elevation from 1800 m to 2800 m, but decreased at elevations above 3000 m. Such diversity pattern was driven mainly by soil total carbon, nitrogen, and plant richness. Various diazotrophic taxa showed differential abundance-elevation relationships. Ecological processes determining diazotrophic community assemblage shift along the elevations. Deterministic processes were relatively stronger at both low and high elevations, whereas stochastic processes were stronger at the middle elevation. This study also suggested a strong relationship among aboveground plants and diazotrophs, highlighting their potential interactions, even for free-living diazotrophs.