Straw decreased N2O emissions from flooded paddy soils via altering denitrifying bacterial community compositions and soil organic carbon fractions.

Straw return is widely applied to increase soil fertility and soil organic carbon storage. However, its effect on N2O emissions from paddy soil and the associated microbial mechanisms are still unclear. In this study, wheat straw was amended to two paddy soils (2% w/w) from Taizhou (TZ) and Yixing (YX), China, which were flooded and incubated for 30 d. Real-time PCR and Illumina sequencing were used to characterize changes in denitrifying functional gene abundance and denitrifying bacterial communities. Compared to unamended controls, straw addition significantly decreased accumulated N2O emissions in both TZ (5071 to 96 mg kg-1) and YX (1501 to 112 mg kg-1). This was mainly due to reduced N2O production with decreased abundance of major genera of nirK and nirS-bacterial communities and reduced nirK and nirS gene abundances. Further analyses showed that nirK-, nirS- and nosZ-bacterial community composition shifted mainly along the easily oxidizable carbon (EOC) arrows following straw amendment among four different soil organic carbon fractions, suggesting that increased EOC was the main driver of alerted denitrifying bacterial community composition. This study revealed straw return suppressed N2O emission via altering denitrifying bacterial community compositions and highlighted the importance of EOC in controlling denitrifying bacterial communities.