Microbially mediated mitigation of N2O and NH3 emissions under combined straw and organic fertilizer management in a wheat-maize rotation system

Partial substitution of synthetic fertilizer with straw or organic fertilizer improves soil quality, yet how it regulates gaseous nitrogen emissions, particularly through modulation of nitrifier and denitrifier microorganisms and enzyme activities, remains unclear. This study analyzed straw and organic fertilizer substitution's effects on N 2 O and NH 3 emissions in the North China Plain, and the potential underlying mechanisms. The treatments included: a control (N 0 ), synthetic fertilizer (180 kg N ha −1 , N 180 ), 70% N 180 (N 126 ) + 30% straw substitution (N 126 S), N 126 + 30% organic fertilizer substitution (N 126 O), and N 126 + 15% straw +15% organic fertilizer substitution (N 126 SO). Straw or organic fertilizer addition decreased annual N 2 O emissions by 6.29%–15.41% and significantly lowered total NH 3 emissions by 6.42%–15.39% relative to the N 180 , with the N 126 SO treatment achieving the greatest emission reduction. Mechanistic analysis suggests that straw and organic fertilizer suppress the activity of ammonia monooxygenase and AOB, thereby constraining N 2 O production via nitrification. Concurrently, these amendments increase SOC and DOC, stimulating activity of denitrifying genes nirS and nirK . Critically, the concurrent upregulation of nosZ , rapidly converting N 2 O to N 2 and reducing net denitrification-derived N 2 O emissions. Furthermore, Straw and organic fertilizer significantly lowered NH 4 + -N concentrations relative to the N 180 treatment, limiting substrate availability for NH 3 volatilization. Notably, accelerated NO 3 − -N consumption by nirK and nirS may trigger a substrate feedback effect that enhances nitrifier activity, thereby promoting NH 4 + oxidation and depleting the NH 4 + pool available for NH 3 emission. Random forest analysis identified Ochrobactrum and Devosia in nirK , and Zeimonas , Ramlibacter , and Lautropia in nirS strongly influenced N 2 O and NH 3 emissions. Nitrosospira sp. Nsp41 in AOB was identified as a predictor to N 2 O emissions. These findings provide mechanistic insights into how straw and organic fertilizers regulate gaseous nitrogen transformations in dryland soils. • Multiple nitrogen sources increase DOC and SOC, but reduce NH 4 + -N and NO 3 − -N. • Multiple nitrogen sources suppress AOB while promoting denitrifying bacteria. • AOB, nirK , and nirS regulate gaseous nitrogen emissions in drylands. • N 126 SO treatment minimizes gaseous N loss and maximizes NUE.