Environmental and Spatial Structuring of Aquatic Macrophyte Metacommunities Across River Networks and Associated Freshwater Systems

ABSTRACT Aquatic macrophytes are key structural and functional components of freshwater ecosystems, yet the processes shaping their community composition across spatial scales remain incompletely understood. Less attention has been paid to macrophyte metacommunity organisation across heterogeneous freshwater landscapes composing both lotic and lentic system types. Here, we investigate how environmental filtering and spatial structuring are jointly associated with aquatic macrophyte community composition within a regional metacommunity context. Using abundance‐based community data from a nationwide freshwater network encompassing lotic and lentic systems, we analysed macrophyte assemblages using non‐metric multidimensional scaling (NMDS), distance decay relationships, variation partitioning, beta diversity decomposition, and local contribution to beta diversity (LCBD). Macrophyte communities exhibited continuous compositional variation, with substantial overlap among freshwater ecosystem types. Community similarity declined significantly with increasing geographic distance, with steeper distance decay relationships observed in lotic systems than in reservoirs, indicating stronger spatial structuring within river networks. Beta diversity was high and dominated by species turnover rather than nestedness, with nearly complete turnover in lotic systems and a modest nestedness component in reservoirs. LCBD analysis identified spatially widespread sites contributing disproportionately to regional compositional heterogeneity. Together, these results indicate that aquatic macrophyte metacommunities are associated with both environmental heterogeneity and spatial structuring, rather than being explained by a single dominant process. Differences among freshwater ecosystem types are likely linked to contrasts in hydrological connectivity, environmental gradients, and landscape configuration. By examining rivers, reservoirs, and natural lakes within a single regional framework, this study highlights how hydrological context influences spatial structuring and compositional turnover in aquatic macrophyte communities and demonstrates the value of large‐scale monitoring networks for metacommunity research.