Long-term mineral fertilization shaped aboveground plant and belowground bacterial and fungal communities more than cutting frequency in a temperate grassland

Agricultural grassland management intensity strongly influences soil microbial community structure in Europe, though the influence of individual practices, such as fertilization and cutting frequency, requires further investigation. Using a 46 year old field experiment in the Swiss Jura region, we examined how both fertilizer input and cutting frequency influence both soil microbial community structure and functional potential. For community structures of soil bacteria and fungi (determined via genetic metabarcoding) and plants (determined via plant species relevés) the effect of fertilization had a stronger effect than that of cutting frequency. The fatty acid biomarker for arbuscular mycorrhizal fungi (AMF, 16:1ω5), however, responded more to cutting frequency (relative effect size = 87.71 %) than fertilization (relative effect size = −7.90 %). Among bacteria with genes linked to soil phosphorous (P) and nitrogen (N) mobilization, only the abundance of the gcd gene (inorganic P solubilisation) displayed a significant fertilization effect. These findings suggest that long-term mineral fertilizer application is a key driver of differences in microbial community structure in grasslands of contrasting management type, and may influence bacterial P solubilisation capacity. Some microbial groups, such as AMF, appear more sensitive to cutting frequency, possibly due to additional plant re-growth. This study highlights the importance of disentangling agricultural management practices to better predict grassland plant and soil microbial responses to intensification.