The components and aromaticity of dissolved organic matter derived from aquatic plants determine the CO2 and CH4 emission potential

Abstract

Lakes are integral to the carbon cycle through the processing of dissolved organic matter (DOM). However, the specific contributions of various aquatic plants to carbon emissions during their decomposition remain inadequately understood. In this study, decomposition experiments were performed on three aquatic plants—algae, Phragmites australis (PA), and Potamogeton crispus L. (PC)—using advanced techniques, including FT-ICR-MS and metagenomics, to investigate the mechanisms of carbon dioxide (CO₂) and methane (CH₄) emissions. The results indicate that algae exhibit a substantial potential for CO₂ emissions, with emissions reaching up to 2193 μmol·g^–1. Conversely, PA contributes the highest CH₄ emissions, reaching up to 2397 μmol·g^–1. Factors such as the protein-like content and aromaticity of DOM molecules significantly influence emission levels. DOM with lower aromaticity undergoes easier decomposition in the first 6 days, leading to increased CO₂ production. Elevated C/N and C/P ratios in plants enhance the abundance of methanogenic bacteria and genes. Surplus carbon will be mineralized under anaerobic conditions, giving rise to mineralization of organics to CH₄. These findings elucidate the mechanisms underlying CO₂ and CH₄ emissions during the decomposition of different aquatic plants and provide valuable insights for lake water environment management.