Contrasting signatures of vegetation-mediated environmental filtering under different hydrological contexts in a tailwater and a natural wetland.

Aquatic bacterial communities underpin wetland water purification, yet it remains unclear how vegetation-mediated environmental filtering is expressed under contrasting tailwater-fed and natural wetland contexts. To address this gap, we integrated 16S rRNA gene sequencing and multivariate statistical analyses to systematically investigate a tailwater wetland (QL) and a natural wetland (YA). In YA, bacterial community differentiation was more pronounced among vegetated zones. Conversely, in QL, continuous tailwater inputs and more active water movement were associated with a less persistent expression of local environmental differences among vegetation zones and weaker community differentiation among vegetation types. Nevertheless, vegetated and unvegetated zones remained clearly distinct, suggesting that signatures consistent with vegetation-mediated environmental filtering were still detectable in QL and were also reflected in predicted functional potential. Differences in conductivity, pH, and nitrogen availability were associated with bacterial community variation between QL and YA. Stochastic processes played a relatively stronger role in QL, whereas YA showed more pronounced habitat dependence and selective retention. Co-occurrence subnetworks were denser in QL but more modular and exhibited stronger small-world organization in YA. Overall, the contrasting hydrological conditions observed in QL and YA were associated with differences in how vegetation-mediated local environmental filtering was expressed through bacterial community differentiation. These findings provide ecological insights for informing tailwater wetland management and conserving natural wetlands.