Interacting management effects on soil microbial alpha and beta diversity in Swiss agricultural grassland

Agriculturally managed grasslands are a major land-use type and crucial for global food production. Yet, degradation of grassland soils endangers both soil microbial diversity and food security, as they harbor diverse microbial life integral to ecosystem functioning and therefore ultimately also human wellbeing. Despite its functional significance, the impact of different aspects of grassland management on the soil microbiome remains insufficiently elucidated and limits our ability to maintain this invaluable and insufficiently explored biological resource. This study examined the interacting impacts of grassland management intensity, harvest type (grazing or mowing predominate), and production system (organic vs. non-organic) on soil microbial alpha and beta diversity (community structure) in the context of the local environment using a metabarcoding approach of ribosomal markers across 86 permanent grasslands in Switzerland. The local environment including soil properties and topographical variables explained more of the variance in fungal and prokaryotic diversity than management, which was still significantly related to most microbial diversity measures. Soil prokaryotic and fungal communities were strongly driven by management intensity, and especially in the case of fungal communities, harvest type played an important role - for alpha diversity in the form of an interaction between management intensity and harvest type, for beta diversity in the form of a main effect. Organic farming had only little direct influence on soil microbial communities. Taxa enriched in intensively managed and fertilized grasslands were typically linked to coprophilous and nitrogen-cycling guilds. Grazed grasslands were characterized by high copiotroph to oligotroph ratios. Because the most diverse soil microbiomes in permanent grasslands appear to be driven by management intensity interacting with harvest types, grasslands of differing management regimes are needed to sustain and promote soil microbial diversity at the landscape level.