Impact of multi-species mixtures and edaphic context on soil functioning in sown grasslands: a mesocosm experiment

Background and aims Multi-species grassland mixtures are gaining popularity in managed grasslands to maintain yields under a changing climate, yet their effect on belowground functioning of the soil remains poorly quantified. This study aimed to determine the combined effects of plant community, edaphic context and management intensity on productivity, greenhouse gas (GHG) effluxes and soil microbial functioning. Methods We conducted a full-factorial mesocosm experiment comparing a perennial ryegrass monoculture with a multi-species mixture across two edaphic contexts and three management intensities. Above- and belowground productivity, GHG effluxes (CO ₂ , CH ₄ and N ₂ O) and functional catabolic diversity of soil microbes were analysed using ANOVA, linear mixed models and random forests with SHAP values. Results Multi-species grass mixtures consistently increased yield and belowground carbon inputs compared to monocultures and affected all three GHG effluxes. Both plant community and edaphic context significantly shaped functional microbial diversity, with plant community explaining comparable amounts of variance as the edaphic context. SHAP values further identified threshold values for the effects of soil temperature and moisture on GHG effluxes, going beyond the effects captured by the linear mixed models. Conclusion Our results show that sowing a multi-species grass mixture can consistently enhance belowground soil functioning and can promote the delivery of crucial ecosystem services such as climate regulation, biomass production and nutrient cycling. These findings underline the potential of multi-species grassland mixtures to improve productivity and soil processes future multifunctional grassland systems.