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 N2O and NH3 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 (N126S), N-126 + 30% organic fertilizer substitution (N126O), and N-126 + 15% straw +15% organic fertilizer substitution (N126SO). Straw or organic fertilizer addition decreased annual N2O emissions by 6.29%-15.41% and significantly lowered total NH3 emissions by 6.42%-15.39% relative to the N-180, with the N126SO treatment achieving the greatest emission reduction. Mechanistic analysis suggests that straw and organic fertilizer suppress the activity of ammonia monooxygenase and AOB, thereby constraining N2O 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 N2O to N-2 and reducing net denitrificationderived N2O emissions. Furthermore, Straw and organic fertilizer significantly lowered NH4+-N concentrations relative to the N180 treatment, limiting substrate availability for NH3 volatilization. Notably, accelerated NO3--N consumption by nirK and nirS may trigger a substrate feedback effect that enhances nitrifier activity, thereby promoting NH4+ oxidation and depleting the NH4+ pool available for NH3 emission. Random forest analysis identified Ochrobactrum and Devosia in nirK, and Zeimonas, Ramlibacter, and Lautropia in nirS strongly influenced N2O and NH3 emissions. Nitrosospira sp. Nsp41 in AOB was identified as a predictor to N2O emissions. These findings provide mechanistic insights into how straw and organic fertilizers regulate gaseous nitrogen transformations in dryland soils.