Mitigating nitrogen loss in paddy field microcosms through indigenous arbuscular mycorrhizal fungi assemblage

Whether farmers should consider the role of arbuscular mycorrhizal fungi (AMF) in agriculture is a hotly debated topic. We aimed to investigate the role of indigenous AMF in reducing nitrogen (N) loss from paddy fields via runoff, leaching, NH₃ volatilization, and N₂O emission. We conducted a pot experiment employing a mycorrhiza-defective rice mutant (non-mycorrhizal) as the control, grown in soil containing indigenous AMF. The corresponding AMF treatment used the progenitor of this mutant with the same soil. The plants were fertilized with nitrogen, phosphorus and potassium 6 weeks after sowing. The root colonization was 23% in mycorrhizal rice, and no typical AMF structures were observed in the roots of non-mycorrhizal rice. Our findings indicated that the mycorrhizal system exhibited lower N concentrations of runoff and leachate further compounded by reduced fluxes of N₂O and NH₃. This led to 14% decrease (mycorrhizal rice 111 kg N ha⁻¹; the non-mycorrhizal rice: 129 kg N ha⁻¹) in cumulative N loss within 3 days post-fertilization. While this AMF effect was consistent across the four tested N loss pathways, differences were observed between NH₄⁺-N and NO₃⁻-N in the runoff pathway. Notably, our results revealed no evidence of trade-offs in AMF effect on N loss among the tested pathways. Additionally, mycorrhizal rice had larger shoots and roots than their non-mycorrhizal counterparts. Our study underscores the potential benefits of indigenous AMF in paddy fields for mitigating water pollution and reducing greenhouse gas emission.