Arbuscular mycorrhizal fungi mediate soil N dynamics, mitigating NO emissions and N-leaching while promoting crop N uptake in green manure systems.

Arbuscular mycorrhizal fungi (AMF), as symbionts of the plant root system, play a pivotal ecological role in soil nutrient dynamics. However, the mechanisms by which AMF mediates nitrogen (N) transformation at the soil-crop interface, particularly under green manure management, remain insufficiently understood. This study investigates these mechanisms through a long-term field experiment, employing four green manure management practices during the flowering stage of common vetch: tillage with total green manure incorporation (TG), no-tillage with total green manure mulching (NTG), aboveground biomass removal with root incorporation (T), and aboveground biomass removal with no-tillage (NT), alongside a conventional tillage control without green manure (CT). Results indicate that NTG notably enhanced AMF abundance and dominant species, attributed largely to increases in soil available N, microbial biomass carbon (MBC), and soil pH. AMF colonization rates in maize roots peaked at 69.7 % under NTG. Additionally, soil mineral N was 17.7 % higher under NTG than TG, with aggregate N concentration increasing by 72.4 %. A strong positive correlation emerged between aggregate N and AMF colonization rates. NTG also significantly elevated nos Z gene abundance and nitrous oxide (NO) reductase activity while lowering the (nir K +nir S) / nos Z ratio. Optimized root architecture under NTG was similarly correlated with AMF colonization, supporting N retention and uptake. Structural equation modeling further confirmed that aggregate N and root structure were primary contributors to reduced N leaching, while root architecture enhanced maize N uptake and NO reductase activity. The increase in nos Z and NO reductase reductase significantly reduced NO emissions. In summary, no-tillage with green manure mulching effectively mitigated N loss and improved crop N uptake by enhancing AMF abundance and colonization.