Linking vegetation types to molecular signatures of dissolved organic matter and their distinct complexation...

Despite the recognized role of vegetation in shaping soil dissolved organic matter (DOM), a systematic understanding of how major vegetation classes (arbors, shrubs, grasses, crops) differentially drive DOM molecular diversity and thereby control heavy metal complexation remains lacking. This study fills this critical gap by employing an integrated multi-spectroscopic and molecular dynamics (MD) simulation approach to comprehensively characterize DOM molecular signatures across four vegetation types and to elucidate their distinct cadmium (Cd) complexation mechanisms. Results reveal that vegetation type fundamentally structures DOM chemistry: arbor-derived DOM is relatively enriched in hydrophilic, oxygen-containing functional groups (e.g., carboxyl) that form dispersed molecular clusters via hydrogen bonding, maximizing carboxyl site accessibility and enhancing Cd complexation capacity (critical coagulation concentration = 12.56 mM). In contrast, grassland DOM contains a higher proportion of hydrophobic aromatic structures that aggregate into compact clusters, increasing steric hindrance and reducing carboxyl accessibility, thereby weakening Cd immobilization (CCC = 10.6 mM). MD simulations further confirm that Cd forms stable inner-sphere coordination primarily with carboxyl-O, with coordination numbers following grassland (1.57) > cropland (1.33) > arbors (1.17) > shrubs (1.0). This work establishes the first mechanistic framework linking vegetation type to DOM molecular diversity and subsequent Cd binding behavior, providing a molecular-level basis for optimizing vegetation design in contaminated soil remediation and improving predictive assessment of heavy metal fate in terrestrial ecosystems.