Plant Identity Impacts the Soil Microbiome More Than Interspecific Interactions in Intensively Managed Grasslands

ABSTRACT Plants and soil microbes are intricately linked, and agricultural production relies heavily on microbially mediated ecosystem services. However, the effects of plant diversity (richness, relative abundance and composition) on soil microbial community diversity and function are still unclear. To better inform agricultural grassland management, it is essential to understand these relationships in intensively managed systems. Between May and September 2019, we conducted a field experiment on an established, intensively managed agricultural grassland to investigate the effect of plant diversity on soil microbial abundance, community composition and nitrogen cycling functional capacity. We systematically manipulated sown plant diversity comprising six forage species at a lower level of chemical nitrogen application, and we included a high chemical N treatment on an L. perenne monoculture as a reference level for conventional productive grassland management. Using Diversity‐Interactions (DI) modelling, we measured the effects of plant richness, relative abundance and composition on soil microbial community gene abundance and nitrogen cycling functional capacities, finding limited effects of plant identity and even weaker effects of interspecific interactions. Where differences in identity effects occurred, the plant species involved were not consistent across responses. In a separate multivariate community analysis, soil microbial community composition was found to be significantly affected by plant species composition, and this was more evident in fungal communities than in prokaryotic communities. There were no differences in microbial community composition between L. perenne monocultures receiving a high and lower nitrogen application; however, the high nitrogen L. perenne had a different microbial community structure than some other plant communities at lower nitrogen. Overall, our study found weak effects of plant diversity on several measures of microbial diversity and function in intensively managed agricultural grasslands.