Integrating bacterial generalist and specialist dynamics into the assessment of tidal-gate-regulated coastal rivers:...

Freshwater salinization caused by sea-level rise poses a continuous threat to the ecosystem multifunctionality (EMF) of coastal rivers. Although tidal gates can mitigate seawater intrusion and stabilize salinity conditions, anthropogenic hydrological regulation reduces the effectiveness of traditional abiotic indicators in identifying EMF changes. Therefore, it is necessary to identify more sensitive indicators under salinity stress for EMF changes. This study selected a tidal-gate-regulated coastal river to assess how bacterial generalist-specialist strategies influence EMF changes under salinity gradients. At the basin scale, environmental heterogeneity was pronounced, and EMF decreased markedly. Salinity was a key driver influencing EMF and bacterial community composition. Increasing salinity differentially shaped the stochastic assembly of generalists and specialists, resulting in contrasting patterns in community structure, diversity, and predicted metabolic potential. Threshold model indicated that EMF and bacterial community composition rather than environmental parameters, shifted within the EA salinity range. The critical point for the metabolic abundance changes of generalists and specialists occurred earlier than that of EMF. This pattern can be attributed to sediment accumulation in EA caused by the construction of tidal gates. Salinity primarily affected the metabolic abundance of bacteria, with a negative correlation for generalists and a positive correlation for specialists, leading to inconsistent effects on EMF. This study demonstrated that bacterial taxonomy plays a key role in identifying and regulating EMF changes under salinity stress, and emphasized the importance of using the ecological attributes of generalists and specialists as an early-warning tool, which is crucial for addressing future climate changes.