Biodiversity and ecosystem multifunctionality under environmental stress: from a continental-scale survey to a microcosm approach

Understanding the relationship between biodiversity and ecosystem functioning under increasing environmental stress is essential for predicting and mitigating global change impacts on terrestrial ecosystems. Here, we combined a Europe-wide soil survey with controlled microcosm experiments to assess how global change drivers (applied either alone or in combination) alter soil biodiversity and its capacity to sustain key ecosystem functions, such as greenhouse gas emissions, litter decomposition, and plant productivity.At the continental scale, we relied on ca. 400 soil samples collected across 27 European countries representing the main land cover types in Europe (i.e., grasslands, woodlands, and croplands), as well as the main climatic regions (temperate and mediterranean). Each site was characterised in terms of soil properties, climatic variables (temperature, precipitation), and DNA-based microbial diversity (bacterial and fungal metabarcoding). For each site, we integrated multiple environmental stressors (e.g., climatic anomalies, soil pollutants) and explored how they relate to soil biodiversity and other soil health components (e.g., microbial biomass) using general additive models (GAMs) and feature-importance analysis (Random Forest). To mechanistically complement field patterns, we performed microcosm experiments manipulating microbial diversity and exposing soils to co-occurring stressors, including pesticides and antibiotics. We found that reductions in microbial diversity strongly impaired multiple soil functions, including litter decomposition, carbon-substrate utilisation, acid phosphatase activity, and plant growth. We also found that exposure to multiple pesticide residues altered the biodiversity–functioning relationship: it reduced fungal richness and weakened its contribution to decomposition and plant productivity. Finally, we observed the lowest plant productivity (biomass and number of plants) in microcosms with co-occurring stressors (pesticides and antibiotics).Together, our findings demonstrate that global change negatively impacts soil biodiversity at large scales and that multiple co-occurring stressors (e.g., pesticides and antibiotics) can decouple biodiversity from ecosystem functioning. These results underscore the urgency of protecting soil biodiversity to safeguard ecosystem resilience under intensifying global change.