Environmental drivers of aquatic macrophyte composition and beta diversity of Southern Amazonian River Basins

Abstract We investigated the effects of environmental temporality (temporary and permanent aquatic systems) and vegetation type on the beta diversity of aquatic macrophytes across major river basins in southern Amazonia. We analyzed aquatic macrophyte diversity across hierarchical basin scales, partitioning beta diversity into turnover and nestedness components, and related community composition to environmental temporality, vegetation type, and spatial structure. A regional checklist was compiled and classified by vegetation type and hydrographic level across the Tapajós, Xingu, Madeira, Araguaia, and Upper Paraguai basins. Floristic similarity was highest between the Tapajós and Xingu basins (48%) and lowest between Araguaia and all other basins (< 10%). Beta diversity increased with spatial scales, mainly driven by species turnover in Tapajós, Xingu, and Madeira basins. Temporary aquatic environments exhibited lower species similarity within and among basins, reflecting their dynamic and heterogeneous nature. These patterns were consistent across different vegetation types, indicating that hydroperiod has a stronger influence on species composition than surrounding terrestrial vegetation. Overall, aquatic macrophyte assemblages in southern Amazonian basins are compositionally distinct and strongly structured by the permanence of aquatic environments. Temporary systems emerge as key determinants of regional beta diversity of macrophytes, underscoring their ecological importance and vulnerability to hydrological changes.