Chemically recalcitrant molecules are the primary components regulating the electron-donating capacity (EDC) of dissolved organic matter.

The electron-donating capacity (EDC) of dissolved organic matter (DOM) plays a central role in regulating environmental redox processes, and is closely governed by the DOM characteristics. As DOM increasingly becomes a focal point in carbon sequestration strategies aimed at mitigating climate change, understanding how its molecular characteristics influence redox functionality is critical. However, the role of DOM chemodiversity, including molecular diversity, functional diversity, and compositional traits, in governing its EDC remains underexplored at the molecular scale. In this study, representative allochthonous, autochthonous, and mixed DOM samples were analyzed using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), UV-Vis spectroscopy, and excitation-emission matrix fluorescence spectroscopy. The EDC was quantified using a decolorization assay based on ABTS reduction. Results showed that EDC was not significantly correlated with overall molecular diversity, but was strongly associated with the relative abundance of polyphenolic, highly aromatic, and unsaturated compounds. These molecules also exhibited greater persistence and formed highly interconnected and thermodynamically constrained transformation networks, indicating a structural trade-off between redox functionality and degradability. This structure-function-persistence relationship implies that changes in DOM stability during carbon sequestration may significantly influence its redox capacity, thereby modulating key environmental processes such as metal cycling, and contaminant fate. By elucidating the molecular-level linkages between DOM chemical traits and electron-donating activity, this study reveals how structural characteristics govern redox functionality, emphasizes the dominant role of composition over diversity in regulating DOM reactivity, and highlights potential ecological risks relevant to carbon stabilization strategies.