Enrichment of nosZ-type denitrifiers by arbuscular mycorrhizal fungi mitigates N2 O emissions from soybean stubbles

Abstract

Hotspots of N₂ O emissions are generated from legume residues during decomposition. Arbuscular mycorrhizal fungi (AMF) from co-cultivated intercropped plants may proliferate into the microsites and interact with soil microbes to reduce N₂ O emissions. Yet, the mechanisms by which or how mycorrhizal hyphae affect nitrifiers and denitrifiers in the legume residues remain ambiguous. Here, a split-microcosm experiment was conducted to assess hyphae of Rhizophagus aggregatus from neighbouring maize on overall N₂ O emissions from stubbles of nodulated or non-nodulated soybean. Soil microbes from fields intercropped with maize/soybean amended with fertilizer nitrogen (SS-N1) or unamended (SS-N0) were added to the soybean chamber only. AMF hyphae consistently reduced N₂ O emissions by 20.8%-61.5%. Generally, AMF hyphae promoted the abundance of N₂ O-consuming (nosZ-type) denitrifiers and altered their community composition. The effects were partly associated with increasing MBC and DOC. By contrast, AMF reduced the abundance of nirK-type denitrifiers in the nodulated SS-N0 treatment only and that of AOB in the non-nodulated SS-N1 treatment. Taken together, our results show that AMF reduced N₂ O emissions from soybean stubbles, mainly through the promotion of N₂ O-consuming denitrifiers. This holds promise for mitigating N₂ O emissions by manipulating the efficacious AMF and their associated microbes in cereal/legume intercropping systems.