Enclosure restoration regulates epiphytic microbial communities involved in carbon sequestration in a restored urban lake: A new insight from the stability of dissolved organic matter

Microbial transformation of dissolved organic matter (DOM) critically regulates aquatic carbon sequestration through DOM stabilization. Submerged macrophyte enclosure restoration is considered an effective strategy for ameliorating eutrophic urban lakes; however, its effects on DOM biogeochemical stability and associated microbial drivers remain unclear. This investigation employed a multidisciplinary approach integrating DOM source tracking, molecular characterization, and leaf-epiphytic multitrophic microbiome analysis in a vegetated enclosure-restored urban lake. The results showed, compared to non-enclosure areas, enclosure areas exhibited enhanced DOM stability characterized by elevated aromaticity (SUVA₂₅₄: 70.9%), hydrophobicity (SUVA₂₆₀: 71.3%), and humification (HIX: 7.4%), coupled with 10.7% reduction of terrestrial anthropogenic input. FT-ICR MS analysis further uncovered a 2.9-fold enrichment in aromatic compounds (such as lignin and tannin) concomitant with depletion of labile compounds (lipids: 2.2% versus 8.2%; carbohydrates: 4.3% versus 12.3%) in enclosure compared to non-enclosure areas. Concurrently, enclosure restoration restructured epiphytic microbial communities and enriched functional microbes involved in C/N/S cycling processes, with Mantel test analysis demonstrating significant microbial-DOM covariation. Furthermore, reactomics analysis identified key enzymatic processes (such as dehydrogenation and functional group transfer) potentially driving DOM stabilization. Additionally, network analysis not only revealed distinct co-occurrence patterns of the epiphytic microbes and DOM properties but also showed stronger trophic interaction within the enclosure areas. These findings advanced empirical insights into DOM biogeochemistry and epiphytic microbial roles in driving DOM stabilization, providing novel linkages between aquatic carbon sequestration mechanisms and ecological engineering applications for urban lake restoration.