Molecular-level insights into the reshaped redox characteristics of wildfire-impacted soil dissolved organic matter:...

Global wildfires significantly reshape soil dissolved organic matter (DOM), yet the molecular-level mechanisms governing its redox characteristics and induced pollutant dynamics remain unclear. The study comprehensively deciphered the linkages of molecular diversity in pyrogenic DOM (PyDOM) to the electron-donating capacity (EDC) and electron-accepting capacity (EAC), exploring their role in regulating the generation of hydroxyl radical (•OH) in the dark. By leveraging mediated electrochemical characterization and Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), the highly heterogeneous molecular compositions across the PyDOMs can be divided into three representative redox groups. Results showed that the EDC pool was closely associated with N-containing aliphatic, polyphenols and highly unsaturated phenolic compounds, with EAC pool being primarily composed of CHO-containing compounds of polyphenols and highly unsaturated phenolic compounds, among which the EAC-related molecules exhibited significantly higher molecular weights (MW) than those driving EDC. Crucially, two distinct molecular organization modes were revealed: the EDC demonstrated a significant shift in contributions from multi-source components across differential MWs, whereas EAC maintains a high structural consistency, reflecting its stable reliance on oxygen-rich aromatic conjugates. Wildfires regulate redox capacity by reshaping the composition and abundance of these characteristic molecular groups, further inducing a significant positive correlation between the EDC and •OH formation potential, which implied the impact of post-wildfire on the long-term pollutant dynamics and biogeochemical cycling. This study establishes a mechanistic linkage of wildfire-reshaped organic carbon pools to their redox traits, offering new insights into assessing post-fire environmental impacts.