Eutrophication driven macrophyte-derived organic matter decomposition to methane emission relates to co-metabolism effect in freshwater sediments

Abstract

Lakes and wetlands play pivotal roles in global organic matter storage, receiving significant inputs of organic material. However, the co-metabolic processes governing the decomposition of these organic materials and their impact on greenhouse gas emissions remain inadequately understood. This study aims to assess the effects of mixed decomposition involving macrophytes and cyanobacteria on carbon emissions. A series of microcosms was established to investigate the decomposition of macrophyte residues and algae over a period of 216 days. A two-component kinetic model was utilized to estimate methane (CH4) production rates. Gas isotope technology was employed to discern the contributions of CH4 produced by macrophyte residues or algae. Quantitative PCR and analysis of 16S rRNA gene amplicons were employed to assess changes in functional genes and microbial communities. There were significant differences in the cumulative carbon release from the decomposition of different plant types due to the addition of carbon sources. After adding algae, the cumulative emission of CH4 increased significantly. The δ13C–CH4 partitioning indicated that CH4 originated exclusively from the fresh organic carbon of macrophyte residues, while it shifted to algae source after adding algae. The synergistic effect of the mixed decomposition on the CH4 emissions was greater than the sum of the individual decompositions. The microbial community richness was higher in the single plant residue treatment compared to the mixed treatment with algae addition, while microbial evenness in the sediment increased steadily in each treatment. Our findings emphasize the pronounced co-metabolic effect observed during the mixed decomposition of macrophytes and cyanobacteria.