Arbuscular mycorrhizal fungi decrease soil nitrate by accelerating mulberry uptake and dissimilatory nitrate reduction to ammonium

Karst landforms, characterized by their shallow and nutrient-poor soils, are susceptible to nitrate leaching loss, leading to environmental pollution and health risks. This study investigates the role of arbuscular mycorrhizal fungi (AMF) in mitigating deep soil nitrate accumulation through enhanced mulberry uptake and dissimilatory nitrate reduction to ammonium (DNRA). A 4-month symbiotic experiment with mulberry ( Morus alba L.) and two AMF species ( Funneliformis mosseae and Rhizophagus intraradices ) was conducted. We found that AMF treatments significantly reduced soil nitrate levels by 10.5 %-58.9 %, while increased soil ammonium by 35.9 %-63.3 %, and enhanced mulberry nitrogen accumulation by 5.2 %-17.8 %. Microbial community analysis revealed significant shifts in nitrogen-cycling microorganisms, with Proteobacteria , Acidobacteria , and Actinobacteria as dominant phyla. AMF inoculation slowed nitrification and denitrification in deeper soil layers while accelerating DNRA, as evidenced by changes in the abundance of nirK / nirS and nrfA / nrfH genes. Structural equation modeling underscored the significant feedback effects of plants and soil nitrogen-cycling microorganisms under AMF influence. This study provides novel insights into the ecological benefits of mycorrhizal symbiosis in managing soil nitrogen dynamics. • Mycorrhizal symbiosis can mitigate nitrate leaching loss. • AMF slowed nitrification and denitrification in deeper soil layers while accelerating DNRA. • The effects of AMF on soil inorganic nitrogen are attributed to nitrogen accumulation in mulberry and the soil nitrogen cycle.