Soil potential nitrification rate and influencing factors in the riparian wetlands of the Third Drainage Ditch in Ningxia

Nitrification is a key process in the soil nitrogen cycle of riparian wetlands, and the potential nitrification rate (PNR) can reflect the potential capacity and rate of soil nitrification. To explore the PNR and its influencing factors in the riparian wetland soils of the Third Drainage Ditch in Ningxia, soil samples were collected from 12 representative riparian wetland sites along the ditch in March, June and August 2023. Soil physicochemical properties and PNR were measured, and the abundances of nitrification-related functional genes were determined using quantitative PCR (qPCR). The relationships between PNR and soil physicochemical properties as well as the abundances of nitrification functional genes were analyzed. The results showed that the PNR in the riparian wetland soils of the Third Drainage Ditch ranged from 0.025 to 0.266 mg/kg/h, following a trend of August>June>March, with higher values observed in the downstream section compared to the midstream and upstream sections. The abundances of both AOA amoA and AOB amoA functional genes peaked in August, however, AOA amoA dominated in the Helan County section, whereas AOB amoA dominated in the Pingluo County and Huinong District sections. PNR was significantly positively correlated with soil total nitrogen, ammonium nitrogen, organic carbon, and the abundances of AOA amoA and AOB amoA. Ammonium nitrogen indirectly influenced PNR by affecting the abundances of AOB amoA and AOA amoA. This study elucidates the spatiotemporal variations and influencing factors of the nitrification process in the riparian wetland soils of the Third Drainage Ditch in Ningxia, and provides a scientific basis for the environmental management of drainage ditches.