Enriched ammonium induced by fairy ring fungi promotes the growth of grasses and sedges relying on soil microbial functions

Fairy rings in grasslands formed by basidiomycetes fungi are characterized by a green belt with luxuriant plants and soil nutrients. However, the way in which the fairy ring fungi enhance plant-available nutrients and subsequently influence plant growth remains poorly understood. We conducted an observational study involving 30 fairy rings in alpine grasslands to investigate the effects of fairy ring fungi on plant biomass, available nutrients, and soil microbial functions. Furthermore, a glasshouse experiment was performed to test the differential response of five plant species to increased ammonium nitrogen (NH₄ ⁺-N) induced by fairy ring fungi. We found that fairy ring fungi enhanced soil NH₄ ⁺-N accumulation, which might be due to increases in the relative abundance of specific bacteria and N-acquiring enzyme activities. Meanwhile, fairy ring fungi increased the abundance of genes related to N fixation and mineralization, but decreased the abundance of a nitrification gene. Furthermore, the observed 82% greater shoot biomass on the fairy ring as compared to outside it was mainly attributed to grasses and sedges, which were promoted by the increased NH₄ ⁺-N concentration. Our findings reveal a novel mechanism by which fairy ring fungi stimulate the microbial capacity to convert available nutrients, thereby reshaping plant composition in alpine grasslands.