Mechanisms of carbon sequestration via interactions between dissolved organic matter (DOM) and bacteria during floating-leaf macrophyte decline

Given the global decline in aquatic vegetation, the fate and ecological effects of persistent plant-derived dissolved organic matter (DOM) in shallow lakes remain poorly understood. Through mesocosm experiments combined with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and ecological network analysis, we show that bacterial communities mediate DOM migration and transformation while the floating-leaved macrophyte Trapa bispinosa shifts from health to decay stages, thereby modulating lake carbon storage and eutrophication risk. As T. bispinosa declined, substantial amounts of total nitrogen (TN) and total phosphorus (TP) were released back into the aquatic ecosystem. This transition from plant health to decay, characterized by higher chromophoric DOM content (a355) and greater DOM aromaticity (SUVA254), coincided with the accumulation of recalcitrant DOM. Concurrently, bacterial diversity and niche breadth declined, whereas anaerobic biomarkers such as Campylobacterota and Desulfobacterota became enriched. Ongoing DOM release was consistent with MCP-like processing, whereby microbes such as Polynucleobacter and Rhodobacterales transformed low-molecular-weight, labile compounds (e.g., proteins and lipids) into recalcitrant forms (e.g., lignin-like and tannins). Our findings elucidated the fate and transformation of plant-derived DOM during macrophyte decline and its interactions with bacterial communities, providing a scientific basis for the management and restoration of floating-leaved plants in shallow lakes.