Structural characteristics and environmental impact factors of submerged macrophytes communities during the natural restoration period of urban lakes with different trophic levels

Abstract Research on the dynamics and driving mechanisms of submerged macrophytes communities during the natural restoration period of lakes with different trophic level remains relatively scarce. This study aims to investigate the structural characteristics of submerged macrophytes communities and their coupling relationships with environmental factors in urban lakes of varying trophic states in Wuhan during a natural restoration phase. Six lakes in Wuhan (comprising two mesotrophic, two light-eutrophic, and two medium-eutrophic lakes) were selected as study areas. Simultaneous monitoring of submerged macrophytes and aquatic environmental factors was conducted from August 2023 to April 2024. The results showed that a total of eight submerged macrophytes species were recorded, with Vallisneria natans, Myriophyllum spicatum, and Hydrilla verticillata identified as dominant species. As trophic levels decreased, the species richness, biomass, and diversity indices of submerged macrophytes significantly increased, whereas community structure became more stable. PCoA analysis revealed distinct community differentiation among lakes with different trophic states. The trophic levels of the lakes determined the key environmental factors influencing submerged macrophytes: biomass in mesotrophic lakes was primarily associated with water temperature (WT) and turbidity (Turb); in light-eutrophic lakes, the dominant factors shifted to chemical oxygen demand and nitrate; in medium-eutrophic lakes, Turb and dissolved oxygen exerted strong constraints. Plant co-occurrence network analysis indicated that interspecific interactions within the community appeared to be dominated by competition, which may result in a relatively loose network structure. Random forest models identified nitrogen as the core driver. Structural equation modeling further confirms that nutrients exert a direct negative effect on submerged macrophytes biomass by increasing Turb and chlorophyll a (path coefficient = −0.629), while WT exhibits a positive effect (0.454). This study enhances our understanding of the response patterns of submerged macrophyte communities in urban lakes during natural recovery to trophic levels and environmental factors, highlighting the key roles of nitrogen control and improved physico-hydrological conditions in promoting the recovery of submerged macrophytes. These findings provide theoretical support for adaptive management strategies in the ecological restoration of eutrophic lakes.