Mechanisms and responses of nitrogen transformations mediated by microbial communities in constructed tailwater wetlands to salinity stress

The long-term salinity stress may affect the nitrogen transformation processes and microbial community assembly patterns in constructed wetlands treating tailwater, influencing their operational effectiveness. In this study, we employ 16S rRNA gene sequencing, combined with multivariate ecological and statistical methods, to investigate interactions between bacterial community diversity and nitrogen transformation genes in constructed tailwater wetlands under salinity stress. The results revealed that long-term salinity stress led to reduced microbial diversity and increased community heterogeneity. Additionally, salinity stress led to decreased functionality of microbial community, intensified competition, and elevated expression of functional genes. Furthermore, as predicted by PICRUSt2, long-term salinity stress resulted in overall inhibition of community nitrogen conversion functions, while short-cut nitrification-denitrification processes played a bigger part in ni-trogen conversion. Moreover, the symbiotic nitrogen fixation process was promoted, while the competing dissimilatory nitrate reduction process was inhibited. Salinity can greatly explain the apparent differences in microbial communities and nitrogen transformation potential in saline constructed wetland systems compared to common wetlands. These findings provide novel insights into the mechanisms underlying nitrogen trans-formation processes in constructed tailwater wetlands under long-term salinity stress and important implications for redesign and renovations of constructed wetlands.