Distinct nitrous oxide emissions from various flooded paddy soils after nitrate fertilization: Identification of key...

Nitrogen fertilizers are widely used in agricultural soils and are one of the significant sources of greenhouse gas nitrous oxide (N₂O) emitted through the denitrification process. However, the driving factors and underlying mechanisms of N₂O emissions from different soils after nitrate (NO₃^--N) fertilization via denitrification remain unclear. Herein, NO₃^--N fertilizer was applied into four different types of soils from Southern China with distinct physicochemical properties, and N₂O emissions were measured through the anaerobic incubation experiment. Results showed that there were significant differences in N₂O emissions among different types of soils, with a 43-fold difference between the highest and lowest N₂O emissions. Soil pH, DOC, and Fe(Ⅱ) were the core factors determining the differences in N₂O emissions for different types of soils. Specifically, in Gaoqiao (GQ) soil, the low pH and high concentrations of DOC and Fe(Ⅱ) stimulated the growth of microorganisms carrying denitrification functional genes (nirK and nirS), such as Clostridium, Desulfosporosinus, and Fonticella. This led to a decrease in the nosZ/(nirK + nirS) ratio and substantial accumulation of N₂O. In contrast, the higher pH and lower concentrations of DOC and Fe(Ⅱ) in Wanshan (WS) paddy soil were conducive to the growth of microorganisms carrying the nosZ gene, such as Flavisolibacter, Mesobacillus, and norank_f__Vicinamibacteraceae, improving the nosZ/(nirK + nirS) ratio and decreasing N₂O emissions. The differences in soil pH, DOC, and Fe(II) among different types of soils affect the composition of bacteria carrying denitrification functional genes, thereby influencing N₂O emissions. Overall, the present study systematically elucidated the influencing factors and mechanisms of N₂O emissions from different types of paddy soils and provided an important reference for lowering N₂O emissions from agricultural soils.