Plant species, nitrogen status and endophytes are drivers of soil microbial communities in grasslands

<p dir="ltr"><b>Context</b>: There is concern that the introduction of ‘novel’ plant germplasm/traits could outpace our capacity to measure and so assess their impacts on soil microbial communities and function.</p><p dir="ltr"><b>Aim</b>: This study aimed to investigate the effects of plant species/functional traits, nitrogen (N) fertilisation and endophyte infection on grassland soil microbial communities within a short time span of 2 years.</p><p dir="ltr"><b>Methods</b>: Two field experiments with monoculture plots were conducted in a common soil. Experiment 1 compared grasses and legumes, using two cultivars of perennial ryegrass (<i>Lolium perenne</i>) that varied in fructan content, along with the legumes white clover (<i>Trifolium repens</i>) and bird’s-foot trefoil (<i>Lotus pedunculatus</i>) that varied in tannin content. Grass treatments received high and low N application levels. Experiment 2 compared the presence/absence of <i>Epichloë</i> strains in ryegrass, tall fescue (<i>Schedonorus phoenix</i>) and meadow fescue (<i>Schedonorus pratensis</i>). Soil microbial communities were analysed by using high-throughput sequencing of DNA isolated from bulk soil cores.</p><p dir="ltr"><b>Key results</b>: Higher abundance of ligninolytic fungi was found in grass soils and pectinolytic fungi in legume soils. Levels of N fertilisation and fructan in ryegrass had only minor effects on soil fungal communities. By contrast, N fertilisation or fixation had a strong effect on bacterial communities, with higher abundance of nitrifiers and denitrifiers in high-N grass soils and in legume soils than in low-N grass soils. <i>Epichloë</i> affected soil microbiota by reducing the abundance of certain fungal phytopathogens, increasing mycorrhizal fungi and reducing N-fixing bacteria.</p><p dir="ltr"><b>Conclusions</b>: Chemical composition of plant cell walls, which differs between grasses and legumes, and presence of <i>Epichloë</i> in grasses were the main drivers of shifts in soil microbial communities.</p><p dir="ltr"><b>Implications</b>: Impacts of farming practices such as mono- or poly-culture, N fertilisation and presence of <i>Epichloë</i> in grasses on soil microbial communities should be considered in pasture management.</p>