Climate and microbial community composition drive shifts in ecosystem function along three parallel elevational gradients

Mountains are home to steep elevational gradients in environmental factors, biodiversity and ecosystem functionality. Though these gradients are tightly connected, little is known about the relative contribution of environmental and biotic factors in driving elevational changes in ecosystem functionality. Here, we conducted a comprehensive survey of three > 2000 m long elevational gradients within the Hengduan Mountains region (southern China), quantifying key metrics of ecosystem functionality, as well as community composition and species richness of both plants and soil microbes. We found significant elevational patterns of plant and bacterial richness and ecosystem functionality, varying from unimodal (hump‐shaped or U‐shaped) to monotonic (linear) among the three mountains. Unexpectedly, plant and bacterial richness were either negatively or not significantly correlated with key indicators of ecosystem functionality. We further demonstrated that climate and soil pH were the key predictors of ecosystem functionality. Ecosystem functionality was additionally affected by changes of the bacterial species composition. Our results suggest that climate and microbial community composition jointly drive elevational changes in ecosystem functionality, with no clear role for species richness per se. These findings advance our understanding of mountain biogeography and the links between biodiversity and ecosystem function.