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

Abstract

Context 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. Aim 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. Methods Two field experiments with monoculture plots were conducted in a common soil. Experiment 1 compared grasses and legumes, using two cultivars of perennial ryegrass (Lolium perenne) that varied in fructan content, along with the legumes white clover (Trifolium repens) and bird’s-foot trefoil (Lotus pedunculatus) that varied in tannin content. Grass treatments received high and low N application levels. Experiment 2 compared the presence/absence of Epichloë strains in ryegrass, tall fescue (Schedonorus phoenix) and meadow fescue (Schedonorus pratensis). Soil microbial communities were analysed by using high-throughput sequencing of DNA isolated from bulk soil cores. Key results 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. Epichloë affected soil microbiota by reducing the abundance of certain fungal phytopathogens, increasing mycorrhizal fungi and reducing N-fixing bacteria. Conclusions Chemical composition of plant cell walls, which differs between grasses and legumes, and presence of Epichloë in grasses were the main drivers of shifts in soil microbial communities. Implications Impacts of farming practices such as mono- or poly-culture, N fertilisation and presence of Epichloë in grasses on soil microbial communities should be considered in pasture management.