Molecular Fingerprint-regulated Cu(Ⅱ) Adsorption in Acidic Soil by Biomass Burning Smoke-derived DOM: Feedstock Specificity and Aging Effects

Purpose Biomass burning smoke-derived dissolved organic matter (BBS-DOM) is annually deposited in massive quantities into terrestrial ecosystems, yet its impacts on heavy metal geochemistry in acidic soils remain poorly characterized. Methods We investigated the 3-month dynamic effects of six BBS-DOMs derived from alfalfa, pinewood, and corn straw combustion on Cu(Ⅱ) adsorption in an acidic soil, combining UV-Vis, EEM-PARAFAC and FT-ICR MS. Results Feedstock-specific bidirectional effects strongly modulated by aging: alfalfa-BBS-DOM consistently promoted Cu(Ⅱ) adsorption, with 4648 L·kg ^− 1 K _d in unaged soil and remaining 7.8 ~ 8.4-fold higher than control throughout incubation; pinewood/corn straw-BBS-DOM initially inhibited or had no significant promotive effect on soil Cu(Ⅱ) adsorption, with K _d increasing by 187.2%~206.8% in the first month but returning to control levels after 3 months. Molecular characterization revealed alfalfa-BBS-DOM was dominated by nitrogen-enriched large humic-like matters (CHON and CHONP compounds), while pinewood/corn straw-BBS-DOM mainly consisted of oxygen-rich polyphenol-like matters dominated (CHO compounds). Mechanistically, these divergent effects arise from the coupled regulation of aqueous-phase complexation and soil-surface interactions on Cu(Ⅱ) adsorption: protonated amino (-NH ₂ ) groups in alfalfa-BBS-DOM inhibit soluble DOM-Cu(Ⅱ) complex formation in the aqueous phase, while negatively charged -SO ₃ ⁻ , -H ₂ PO ₃ ⁻ , and -COO ⁻ groups enable alfalfa-BBS-DOM to strongly adsorb to soil surfaces; the adsorbed alfalfa-BBS-DOM retains these negatively charged functional groups, which attract Cu(Ⅱ) ions. Conversely, -COOH and phenolic-OH groups in pinewood/corn straw-BBS-DOM form soluble aqueous complexes with Cu(Ⅱ). Conclusion This study provides a mechanistic basis for heavy metal risk assessment in wildfire-affected ecosystems.