Molecular shifts in dissolved organic matter and microbial community assembly during vegetation restoration in karst ecosystems

Dissolved organic matter (DOM), as one of the most active components of soil organic matter, influences fundamental biogeochemical processes in soils. However, in ecologically vulnerable karst regions, how vegetation restoration drives the co-evolution of DOM molecular composition and microbial communities remains unclear. This study employed Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and high throughput sequencing to investigate the dynamics of soil DOM molecular composition and microbial communities along a typical karst vegetation restoration chrono sequence. The results indicate that with vegetation restoration, both the molecular aromaticity and oxidation state of DOM increased, accompanied by a relative enrichment of lignin-like compounds and a decrease in bioavailability, thereby promoting the formation of a more stable soil carbon pool. Microbial analysis showed that bacterial assembly was stochastic while fungal assembly was deterministic, with fungi being more sensitive to environmental changes. Network analysis indicated that more protein-like components were closely associated with bacteria, while recalcitrant lignin-like components were more strongly linked to fungi. These findings elucidate the microbial mechanisms underpinning vegetation restoration driven soil carbon stabilization at the molecular level, highlighting the critical role of DOM molecular composition and microbial communities in carbon sequestration within karst ecosystems.