Global environmental dependences of soil biodiversity and functions are modified by water availability thresholds

Global soil biodiversity and functions are threatened by water availability thresholds. However, the role of these thresholds in modulating the environmental drivers of soil biodiversity and functions remains poorly understood. Analyzing a global dataset of 383 sites across major terrestrial biomes, we found that water availability threshold (measured by aridity index) reorganizes the relative importance of climate, vegetation, and soil properties in regulating soil biodiversity and functions. In less arid regions, vegetation and soil properties jointly explained the primary patterns of soil biodiversity and functions. Conversely, after crossing such water availability threshold toward more arid conditions, climate became the dominant controlling factor, outpacing other environmental variables. Notably, this water-induced shift in environmental dependence was more pronounced for soil multidiversity than for soil multifunctionality. Our findings highlight the critical role of water availability thresholds in shaping the environmental factors that govern soil biodiversity and ecosystem functions, providing valuable insights into potential ecosystem transformations in the context of on-going global aridification.