Grassland ecosystems are vital for ecosystem services such as biodiversity and soil health, yet intensification has caused soil degradation, biodiversity loss, and reduced functioning. This PhD project investigates how increasing plant diversity in grassland restoration can improve soil health and resilience. It integrates three work packages (WPs): WP1, a field experiment on an equine farm in Trévol, France, will test species-rich reseeding on soil structure, biotic activity, and microbial biodiversity. WP2 will assess long-term management and plant diversity effects across ~50 Swiss grasslands from the ALL-EMA network, focusing on soil organic carbon, nutrient stratification, and structure under varied regimes. WP3 will use greenhouse experiments with manipulated species richness to explore root-driven mechanisms shaping pore networks, water dynamics, and nutrient cycling. Advanced methods (X-ray imaging, soil physics, molecular tools) will be applied across WPs. Outcomes will deliver actionable insights into biodiversity-based strategies to regenerate soils, enhance multifunctionality, and promote resilient agricultural landscapes.