Distinctive Microbial Processes and Controlling Factors of Nitrous Oxide Emission in an Agricultural River Network: Perspective in Riparian Zone Type and Season

The emission of nitrogen oxides (N₂O) in rivers is an important source of potent greenhouse gases. However, the mechanism at the interface between rivers and riverbanks remains unclear. This study quantified N₂O emissions from natural and artificial riparian zones across seasons and explored the microbial mechanisms affecting N₂O production and consumption in an intensive agricultural river network in China. Significant seasonal variability in N₂O emission rates was observed (<i>p</i> < 0.05), with mean values of 0.56 ± 0.09 mmol·m^-2·h^-1 in autumn and 1.13 ± 0.32 mmol·m^-2·h^-1 in spring. In spring, emissions from natural riparian zones (1.38 ± 0.28 mmol·m^-2·h^-1) were significantly higher than those from artificial riparian zones (0.89 ± 0.05 mmol·m^-2·h^-1). All wind-based models significantly overestimated N₂O emissions (<i>p</i> < 0.05) due to inflated IPCC emission factors (EF_5r), exceeding measured values by 1.76-3.09 times. Dissolved organic carbon and nitrite nitrogen were identified as key environmental drivers of N₂O emissions. Nitrogen fixation and ammonification accounted for 82.3% of N₂O production. Network analysis revealed a dominant microbial niche containing nitrifiers, sulfate-reducing bacteria, and carbohydrate-degrading taxa. Partial least squares path modeling indicated that riparian zone type altered DOC and NO₂^- availability, regulated <i>nifH</i> and <i>ureC</i> gene abundances, and enhanced N₂O production. These findings underscore the importance of riparian-zone-specific microbial regulation of riverine N₂O emissions and demonstrate the necessity of refining EF_5r estimates for agricultural river networks.