Soil functions are shaped by aridity through soil properties and the microbial community structure

Increasing aridity poses a threat to soil functionality, as it affects the key players -prokaryotes and fungi- responsible for these functions. Studying microbial diversity and functions in soils from different aridity conditions is crucial to understanding potential adaptations and response mechanisms to climate change, which may ultimately affect soil ecosystem multifunctionality. Here, we used a natural humid-to-arid climate gradient to determine: (1) if and how soil functions and microbial communities change across the aridity gradient; and (2) the main drivers of soil function variability along the gradient. We sampled soils (0–10 cm depth) from 12 sites across the Iberian Peninsula and analyzed their prokaryotic and fungal diversity and biomass as well as soil functions (aerobic respiration and extracellular enzyme activities linked to organic carbon, nitrogen and phosphorus degradation), together with soil physicochemical characteristics. Our results showed that increasing aridity resulted in a gradual change in the microbial community structure and a decrease in fungal diversity. However, soil functions did not show clear changes in response to aridity itself. Instead, microbial respiration and enzyme activities depended mainly on the local soil properties (i.e. organic matter quantity and quality, soil texture and pH) rather than on aridity. Overall, results indicated that in long-term climate-adapted soils, microbial functions are primarily driven by soil edaphology with aridity influencing them indirectly by shaping the microbial community composition and the intrinsic soil characteristics.