Exogenous dissolved organic matter redirects humic carbon fate at mineral interfaces through pre-contact molecular conditioning

作者：Li Y, Mi G, Cheng J, Zhang M, Liu Y, Ai S, Yang F, Cheng K · 发表于：Water research · 年份：2026 · DOI：10.1016/j.watres.2026.126592

Mineral-associated organic carbon (MAOC) formation is commonly interpreted from the moment organic matter contacts mineral surfaces, emphasizing mineral reactivity, molecular functional groups, or adsorption strength. However, in soils receiving continuous organic inputs, humic precursors may first coexist with exogenous dissolved organic matter (DOM) in pore water and thin water films before mineral contact. Whether this upstream liquid-phase interaction reorganizes humic matter and redirects its subsequent mineral-interface fate remains poorly understood. Here, we introduce the concept of a pre-contact molecular conditioning and examine whether biochar-derived dissolved organic matter (BDOM) reorganizes the humic acid (HA) precursor state before contact with goethite (GOE), montmorillonite (MON), and a goethite-montmorillonite composite (MGA). FT-ICR MS spectrometry revealed that mineral-free co-incubation with BDOM generated a distinct HA-BDOM molecular pool rather than a simple addition of the two endmembers, producing 951 newly detected formulas, increasing O/C (17.97%) and nominal oxidation state of carbon (NOSC, 18.46%), and decreasing double-bond equivalent (DBE, 20.26%), modified aromaticity index (AImod, 15.76%), and (DBE-O)/C (55.41%). This pre-contact conditioning weakened the bulk affinity of HA for Fe-bearing minerals (53.45% on GOE, 63.12% on MGA). The lower first-contact retention did not imply a weaker contribution to MAOC formation. At the MGA interface, pri...