Multi-trophic communities in river ecosystems: Insights into environmental drivers and assembly mechanisms for ecological management- a case study in the Minjiang River.

Understanding the differences in community structure, assembly processes, and environmental responses among aquatic multi-trophic communities is essential for effective ecological management but remains limited. To fill this gap, we proposed an ecological management framework integrating key drivers, species interactions, and assembly mechanisms across trophic levels, supported by the statistical methods (VPA, PCA, CCA, RDA, Bioenv, SEM) and ecological models (null model, neutral community model, co-occurrence network) using the Minjiang River as a case study. The results indicated that the impact factors that affected the distribution, dominant species and diversities varied significantly among different communities. Salinity and electrical conductivity were important environmental factors other than the concentration of nutrient salts and geographical factors. Moreover, sediment microorganisms, phytoplankton, and periphytic algae communities were mainly controlled by stochastic processes, while water microorganisms, zooplankton, and benthic macroinvertebrates communities were mainly shaped by deterministic processes. Significant interactions were observed among multi-trophic communities. Increased phytoplankton richness reduced the abundance of certain periphytic algae (path coefficient [PaC] = -0.351; p < 0.05), which negatively affected the richness of benthic macroinvertebrates and associated taxa (PaC = -0.288; p < 0.01). Conversely, the richness and composition of benthic macroinvertebrate suppressed the diversity and richness of water microbial community (PaC = 0.413; p < 0.01), which in turn negatively affected the richness of sediment microbial community and specific species (PaC = -0.868; p < 0.001). Based on these findings, a "3W" ecological management framework was proposed. This study elucidated the assembly mechanisms and interactions of aquatic multi-trophic communities, identified key drivers of community dynamics, offering valuable insights for watershed ecological conservation.