Drivers and mechanisms that contribute to microbial β-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 β-diversity
patterns and range sizes along elevational gradients. Janzen’s mountain
passes hypothesis can be applied for microbial community assembly:
mountains with lower climatic variability and higher climatic difference
between elevations exhibited higher β-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.