Bacterial and fungal communities along temperature and aridity gradients are linked with soil functions across global biomes

Changes in temperature and water availability under global warming will alter soil bacterial and fungal community structures and thus ecosystem functioning across the globe. We sampled large-scale temperature and aridity gradients across Greenland, Europe, Spain, the Swiss Alps and South Africa to understand microbial long-term adaptation to climatic conditions in soils and to predict microbial responses to climate change. We found that bacterial communities from South African soils were distinct from those in European and Greenlandic soils, largely explained by high relative abundances of Firmicutes. Conversely, fungal communities additionally differed between European and Greenlandic soils and thus seem to be more affected by oceans acting as geographical barrier compared to bacteria. Interestingly, bacterial communities in hyperarid soils from Northern Greenland clustered with hyperarid soils from Southern Spain and South Africa indicating that these communities share taxa adapted to low water availability despite their distinct geographical origin and temperature regimes. Within regional gradients in Europe and Greenland microbial community structures sequentially shifted along the gradients of temperature and aridity, whereas in the South African gradient soil physicochemical properties such as pH and texture that were not related with aridity were important drivers of microbial community structures. Shifts in fungal and bacterial community structures along climatic gradients occurred in parallel with changes in microbial functions, such as extracellular enzyme activities, greenhouse gas fluxes as well as abundances of functional genes involved in soil carbon and nitrogen cycling. Collectively, our results suggest that alterations in microbial community structures along climatic gradients, which serve as a proxy for climate change over time, translate into an alteration in ecosystem services provided by the community members. Moreover, at the global scale our study indicates that bacterial communities are mainly controlled by environmental conditions whereas fungal communities are more influenced by geographic barriers.