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<p>Dissolved organic matter (DOM) critically influences biogeochemical processes in soil, aquatic, and sedimentary environments. However, the coupled impacts and mechanisms of mineral adsorptive fractionation and biodegradation on DOM dynamics remain poorly understood. In this study, soil-derived DOM was fractionated by goethite at pH 4.5 and 6.5, and subsequently incubated for 63 days with native microbes. Changes in DOM composition were analyzed via UV–vis, fluorescence spectroscopy and FT-ICR MS, while bacterial communities were tracked using 16S rRNA sequencing. Results showed that&#xa0;goethite preferentially adsorbed aromatic, high-molecular-weight compounds, enriching labile components like proteins and aliphatics in solution, with greater fractionation at lower pH. The greater the mineral fractionation, the greater the extent or rate of biodegradation and the higher the diversity of dominant bacterial classes. Specifically, pH 6.5 fractionation enhanced biodegradation and sustained microbial activity by concentrating labile and moderately labile components and retaining a pool of accessible substances, achieving the highest DOC loss. In contrast, pH 4.5 fractionation concentrated labile DOM pool, leading to rapid depletion. Microbial communities exhibited distinct metabolic successions, shifting from protein/lipid degradation to humic-like substances as labile fractions were consumed. <i>Gammaproteobacteria</i> and <i>Actinobacteria</i> were primarily responsible for degradation of labile DOM fractions (e.g., proteins); bacterial classes like <i>Alphaproteobacteria</i>, <i>Acidimicrobiia</i>, and <i>Planctomycetes</i> tended to utilize humic-like substances (e.g., lignins), which in turn promoted their growth. This study elucidates the mechanisms by which pH-dependent iron oxide fractionation and microbial degradation synergistically govern DOM molecular fate and microbial ecology, providing direct implications for predicting carbon dynamics in iron-rich aquatic and terrestrial systems.</p> Graphical Abstract <p></p>

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Iron oxide fractionation alters the biodegradability of dissolved organic matter: molecular dynamics and microbial interactions

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年5月1日

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  • Yuzhen Liang,
  • Tongxin Liu,
  • Zishan Cen,
  • Zhenqing Shi

摘要

Dissolved organic matter (DOM) critically influences biogeochemical processes in soil, aquatic, and sedimentary environments. However, the coupled impacts and mechanisms of mineral adsorptive fractionation and biodegradation on DOM dynamics remain poorly understood. In this study, soil-derived DOM was fractionated by goethite at pH 4.5 and 6.5, and subsequently incubated for 63 days with native microbes. Changes in DOM composition were analyzed via UV–vis, fluorescence spectroscopy and FT-ICR MS, while bacterial communities were tracked using 16S rRNA sequencing. Results showed that goethite preferentially adsorbed aromatic, high-molecular-weight compounds, enriching labile components like proteins and aliphatics in solution, with greater fractionation at lower pH. The greater the mineral fractionation, the greater the extent or rate of biodegradation and the higher the diversity of dominant bacterial classes. Specifically, pH 6.5 fractionation enhanced biodegradation and sustained microbial activity by concentrating labile and moderately labile components and retaining a pool of accessible substances, achieving the highest DOC loss. In contrast, pH 4.5 fractionation concentrated labile DOM pool, leading to rapid depletion. Microbial communities exhibited distinct metabolic successions, shifting from protein/lipid degradation to humic-like substances as labile fractions were consumed. Gammaproteobacteria and Actinobacteria were primarily responsible for degradation of labile DOM fractions (e.g., proteins); bacterial classes like Alphaproteobacteria, Acidimicrobiia, and Planctomycetes tended to utilize humic-like substances (e.g., lignins), which in turn promoted their growth. This study elucidates the mechanisms by which pH-dependent iron oxide fractionation and microbial degradation synergistically govern DOM molecular fate and microbial ecology, providing direct implications for predicting carbon dynamics in iron-rich aquatic and terrestrial systems.

Graphical Abstract