Macrophyte restoration alters sedimentary organic matter-microbes-environment interactions and enhances carbon...

Lake eutrophication is a widespread challenge, and macrophyte reconstruction has been shown as an effective strategy for restoring shallow eutrophic lakes. However, the impacts of macrophyte on the sedimentary carbon sequestration and underlying mechanisms remain poorly understood. Here, we conducted a year-long field investigation to compare carbon dynamics in macrophyte-restored and unrestored areas within a typical urban lake, analyzing physicochemical properties, organic matter composition, and microbial community structure. Compared to the unrestored areas, macrophyte-restored areas showed ∼80% higher total sedimentary carbon, along with lower sediment pH and increased aromaticity (SUVA₂₅₄) and humification (HIX) of both water-soluble and alkaline-extractable organic matter. In addition, sediments in the restored areas supported a higher microbial richness and a microbial community more enriched in Alphaproteobacteria. Partial least squares-path modeling revealed that enhanced carbon sequestration by macrophyte restoration was primarily driven by shifts in sedimentary organic matter composition. Reduction in labile substrates (e.g., peptides and protein-like components), coupled with lower sediment pH, shifted the microbial community toward taxa associated with enhanced carbon persistence (Alphaproteobacteria). Overall, our results demonstrate that macrophyte restoration enhances sediment carbon sequestration through initiating shifts in sedimentary organic matter composition that subsequently restructure organic matter-microbe-environment interactions. This study provides direct evidence that macrophyte restoration, as a nature-based solution widely applied in shallow eutrophic lakes, can contribute to carbon sequestration beyond its well-recognized role in water quality improvement.