N2O emissions from soils under short-term straw return in a wheat-corn rotation system are associated with changes in the abundance of functional microbes

Straw return is an effective conservation tillage measure that improves soil properties, increases crop yields, and is an efficient means of reusing agrobioenergy by-products. Straw return has been shown to affect nitrogen (N) cycling and related functional microbes in agricultural soils. However, the relationship between nitrous oxide (N2O) emissions and N-related functional genes under different straw return strategies in wheat-corn double cropping systems remains elusive. Here, we conducted a short-term field study to investigate the response of N2O emissions driven by N cycling functional genes (bacterial and archaeal amoA genes and nirS, nirK, and nosZ genes) to different straw return patterns in a wheat-corn double cropping system in the North China Plain. Three treatments were established, namely, both wheat and corn straw return (CWSR), only wheat straw mulch return (WSR), and no straw return (NSR). Over the wheat-corn season, the total N2O emissions significantly increased by 31.74% and 12.37% in CWSR and WSR-treated soils, respectively. Straw return increased nitrifying and denitrifying functional gene abundances, thus stimulating N2O emissions. Correlation analysis showed that AOA (r = 0.262, p < 0.05) and AOB (r = 0.703, p < 0.01) were strongly and positively correlated with NO3−-N concentrations, indicating that AOA and AOB were involved in nitrification under straw return. Both nirS (r = 0.287, p < 0.05) and nirK genes (r = 0.252, p < 0.05) were positively correlated with N2O emissions, while nosZ genes (r = −0.266, p < 0.05) were negatively correlated with N2O emissions. Structural equation model (SEM) analysis further revealed that straw return indirectly affected N2O emissions by influencing the abundances of AOB-amoA (r = 0.324, p < 0.05), nirK (r = 0.417, p < 0.05), and nosZ (r = −0.388, p < 0.001) genes. Overall, short-term straw return increased N2O production in a wheat-corn double cropping system, mainly through increased AOB-amoA and nirK gene abundance, which stimulated N2O production, and reduced nosZ gene abundance, which inhibited N2O reduction.