Vegetation fine-tunes aridity thresholds in soil biodiversity and function worldwide

Aims: Plant-soil interactions regulate the response of terrestrial ecosystem to climate change. Recent work suggests that aridity thresholds control soil biodiversity and function worldwide, which abruptly decreased once crossing specific levels of aridity. However, whether and how different vegetation types regulate these aridity thresholds remains largely unknown. Methods: Here, we used a global dataset published in the literature to investigate how 24 biodiversity and functional ecosystem attributes respond to aridity in different biomes using a global field survey across grasslands, shrublands, and forests. The biodiversity metrics included the richness of soil organisms at multiple trophic levels from bacteria and fungi to protist and invertebrates, the functional metrics linked to a diverse range of ecosystem services from plant productivity and organic matter decomposition to nutrient cycling and plant-microbe interactions. Results: Pervasive nonlinear relationship between aridity and soil biodiversity and functions were observed in all vegetation types, with vegetation fine-tuning aridity thresholds in soil biodiversity and functions worldwide. Specifically, soil biodiversity and functions in forest ecosystems higher aridity index thresholds compared to those in grassland and shrubland, and they are more likely to collapse in response to increasing aridity. Conclusion: Ecosystem functionality in forest may collapse under less arid conditions in response to aridification compared to grassland and shrubland. Our findings highlight the ecosystem-specific vulnerability of soil system to aridification, and suggest that future studies incorporating biome variance into risk estimation will advance our understanding of how climate change may affect the functioning of terrestrial ecosystem in large areas of our planet.