Bacterial and environmental factors had alternatively dominant effects on ecosystem multifunctionality of river–lake continuum: A rate-focused study

• Bacterial α-diversity distributed nonlinearly along the river–lake continuum. • Rates of change of ecological factors captured turning points in their dynamic shift. • Bacterial and environmental factors had alternatively dominant effects on EMF. Aquatic ecosystems play crucial roles in maintaining biodiversity and supporting key ecosystem functions. Microbial communities are key components of aquatic ecosystems and sensitive to environmental changes. However, the links between microbial community and aquatic ecosystem function under changing conditions remain unclear. In this study, a field survey was conducted in a river–lake continuum within the Poyang Lake basin to investigate the spatial dynamics and interrelationships between bacterial communities, environmental factors and ecosystem multifunctionality (EMF) from a rate-based perspective. Results revealed that the trophic states of water increased from headwater to lake, whereas the qualities of sediment exhibited fluctuating patterns. Bacterial α-diversity and EMF distributed nonlinearly along the river–lake continuum. Rate-of-change (RoC) analyses, based on first-order derivatives, identified turning points for bacterial α-diversity and EMF. Those turning points were captured by changes in RoCs above or below zero along the river–lake continuum. Lags were observed between the RoCs and the spatial values of bacterial α-diversity and EMF. An integrated coupling index (CI), a ratio of the combined RoCs of bacterial and environmental factors in water and sediment, varied continuously along the river–lake continuum. The dynamic of CI and Spearman correlation analyses showed that bacterial and environmental factors had alternatively dominant effects on EMF spatially. Partial least squares path modeling analysis revealed that land-use primarily had indirect effects on EMF by mediating bacterial and environmental factors. This study advances a dynamic-based approach to assess bacteria-environment-ecosystem EMF relationships based on RoCs in aquatic ecosystems.