Diversity and syntaxonomy of aquatic macrophyte communities in floodplain lakes of the Middle Ob River (Tomsk Carbon Polygon, Western Siberia)

The floodplain of the Ob River, one of the largest wetland systems in Eurasia, plays a significant role in the regional carbon cycle, yet its aquatic macrophyte communities remain poorly studied. This work presents the first comprehensive study of the diversity and syntaxonomy of aquatic macrophyte communities in three floodplain lakes of the Middle Ob River, located within the "Kaybasovo" Carbon Polygon. Field studies conducted in the summer and autumn of 2025 included geobotanical surveys and bathymetric mapping. We recorded 40 species of aquatic and semi-aquatic vascular plants from 19 families, with the core of the flora represented by hydrophytes and helophytes (77.5%). The most species-rich families were Cyperaceae, Potamogetonaceae, and Araceae. Syntaxonomic analysis revealed five associations of aquatic vegetation, belonging to the classes Lemnetea and Potamogetonetea. The dominant communities were Stratiotetum aloidis and Nymphaeo albae-Nupharetum luteae. The flora is characterized by a stable core of 12 species common to all lakes, formed by ecologically plastic taxa adapted to the dynamic hydrological regime of the floodplain. The high alpha-diversity (23–29 species per lake) significantly exceeds that of the main river channel, highlighting the importance of floodplain lakes as local biodiversity hotspots. The obtained data provide a baseline for future monitoring of these aquatic ecosystems in the context of climate change and the functioning of carbon polygons.