Co-incorporation of wheat straw and hairy vetch reduced soil N2O emission via regulating nitrifier and denitrifier structure on the Qinghai plateau

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Introducing green manure is considered a sustainable practice in wheat production on the Qinghai plateau, an ecologically fragile area. However, the regulatory mechanisms governing N2O emission through green manure and wheat straw co-incorporation in nitrifiers and denitrifiers communities remain unclear. Herein, a microcosm experiment was conducted, including no-addition (CK), hairy vetch (VS), wheat straw (WS), and the mixture of hairy vetch and wheat straw (VWS), to investigate soil N2O emission and functional microbes communities. Compared with CK, cumulative N2O emission decreased by 19.1 % and 74.8 % in WS and VWS, whereas it increased by 60.4 % in VS. Residues incorporation increased absolute abundances of denitrifier (narG, nirK, and nosZ genes) by 39 %–139 % than CK. However, the contribution of structures of functional microbes on N2O emission overweighed their absolute abundances. The reduced N2O emission was mainly associated with the decreased relative abundance of M5 and M7 (key ecological cluster, gained from co-occurrence network of narG- and nirK-types denitrifier, dominant genera were Pseudomonas and Bradyrhizobium), and with the increased M13 (from nosZ-type denitrifier, dominant genus was Tardiphaga). In N2O emission peak (the 6th day of incubation), VWS reduced the relative abundance of Pseudomonas by 9.9 % and 11.2 % and Bradyrhizobium by 39.7 % and 49.2 % compared with CK and VS, respectively. Additionally, VWS increased the relative abundance of Tardiphaga by 134.1 % and 172.1 % compared with CK and WS. Our results suggest that wheat straw and hairy vetch co-incorporation is an effective practice to mitigate N2O emission via regulating key denitrifier taxa on the Qinghai Plateau.