Drivers and mechanisms that contribute to microbial -diversity patterns and range sizes in mountains across a climatic variability gradient

Microbial communities are highly diverse, yet the mechanisms underlying microbial community assembly are not well understood. Janzen's mountain passes hypothesis proposed that climatic barriers and dispersal limitation shape communities to a greater extent in mountains with lower climatic variability and overlap, permitting higher levels of species coexistence. Here, we investigate changes in microbial community dissimilarities, distributional range sizes and ecological processes along elevational gradients in three montane ecosystems representing a climatic variability gradient. We found that climate, climatic variability and spatial distance play dominating roles in affecting microbial beta-diversity patterns and range sizes along elevational gradients. Janzen's mountain passes hypothesis can be applied to microbial community assembly: mountains with lower climatic variability and higher climatic difference between elevations exhibited higher beta-diversity, higher endemism, lower range sizes and steeper distance-decay trends. However, microbial communities experience clear climate-driven limited range sizes and dispersal processes, and show typical endemic patterns, in all mountain ecosystems. Our results emphasize the importance of dispersal and climatic niche processes in shaping montane biodiversity. As a result, changes in climate may significantly impact soil biodiversity in montane ecosystems by altering the effects of dispersal limitation and climatic variability on bacterial and fungal community composition along elevational gradients.Keywords: community assembly, dispersal limitation, beta-diversity, montane biodiversity, microbial community