Mitigation of soil N₂O emissions by decomposed straw based on changes in dissolved organic matter and denitrifying...

The return of decomposed straw represents a less explored potential option for reducing N₂O emissions. However, the mechanisms underlying the effects of decomposed straw return on soil N₂O mitigation are still not fully clear. Therefore, we used a helium atmosphere robotized continuous flow incubation system to compare the soil N₂O and N₂ emissions from four treatments: CK (control: no straw), WS (wheat straw), IWS (wheat straw decomposed with Irpex lacteus), and PWS (wheat straw decomposed with Phanerochaete chrysosporium). All the treatments have been fertilized with the same amount of KNO₃. Furthermore, we also analyzed i) the chemodiversity of soil dissolved organic matter (DOM), ii) the nirS, nirK, and nosZ gene copies and relative abundances of denitrifying bacterial communities (DBCs), and iii) the specific linkages between N₂O emissions and DOM and DBC. The results showed that the WS, IWS and PWS treatments increased N₂O emissions compared to the CK treatment. However, applying decomposed straw to soil, especially straw treated with P. chrysosporium, effectively decreased the soil N₂O and increased N₂ emissions compared to WS and IWS. Moreover, the IWS and PWS treatments increased the CHO composition, but they decreased the CHON and CHOS compositions of heteroatomic compounds of DOM compared with the WS and CK treatments. Furthermore, the WS, IWS and PWS treatments all significantly increased the nirS and nosZ gene copies compared with the CK treatment. Additionally, compared with the other treatments, the PWS treatment significantly shaped the DBC and led to a higher relative abundance of Pseudomonas with nirS and nosZ genes. Meanwhile, Network analysis showed that the mitigation of N₂O was closely related to particular DOM molecules, and specific DBC taxa. These results highlight the potential for decomposed straw amendments to mitigate of soil N₂O emissions not only by changing soil DOM but also mediating the soil DBC.