Mineral-associated soil organic matter (SOM) is critical for stabilizing organic carbon and mitigating climate change. However, mineral-SOM interactions at the molecular scale, particularly synergetic adsorption through organic–organic interaction on the mineral surface known as organic multilayering, remain poorly understood. This study investigates the impact of organic multilayering on mineral-SOM interactions, by integrating macroscale experiments and molecular-scale simulations that assess the individual and sequential adsorption of major SOM compounds–lauric acid (lipid), pentaglycine (amino acid), trehalose (carbohydrate), and lignin onto soil minerals. Ferrihydrite, Al-hydroxide, and calcite are exposed to SOM compounds to determine adsorption affinities and binding energies. Results show that lauric acid has 20–40 times higher K_d than pentaglycine, following the order K_d(ferrihydrite) > K_d(Al-hydroxide) ≫ K_d(calcite). Molecular-scale simulations confirm that lauric acid has a higher binding energy (30.8 kcal/mol) on ferrihydrite than pentaglycine (6.0 kcal/mol), attributed to lipid hydrophobicity. The lower binding energy of pentaglycine results from its hydrophilic amide groups, facilitating partitioning into water. Sequential experiments examine how the first layer of lipid or amino acid affects the adsorption of carbohydrate/lignin, which show little or no individual adsorption affinities. Macroscale results reveal that lipid and amino acid adsorption induce ferrihydrite particle repulsion increasing reactive surface area and enhancing carbohydrate/lignin adsorption independently and synergistically through organic multilayering. Molecular-scale results reveal that amino acid adsorbed on ferrihydrite interacts more readily with lignin macroaggregates (preformed in solution) than with individual lignin units, indicating organic multilayering via H-bonding. These findings reveal the molecular mechanisms of SOM-mineral interactions, crucial for enhancing soil carbon stabilization.

中文翻译：

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土壤有机质组分与矿物相互作用的协同效应


矿物伴生土壤有机质 （SOM） 对于稳定有机碳和缓解气候变化至关重要。然而，分子尺度上的矿物-SOM 相互作用，特别是通过矿物表面的有机-有机相互作用产生的协同吸附（称为有机多层）仍然知之甚少。本研究通过整合宏观实验和分子尺度模拟来评估主要 SOM 化合物——月桂酸（脂质）、五甘氨酸（氨基酸）、海藻糖（碳水化合物）和木质素对土壤矿物质的单独和顺序吸附，从而调查有机多层对矿物-SOM 相互作用的影响。水化铁、氢氧化铝和方解石暴露于 SOM 化合物中，以确定吸附亲和力和结合能。结果表明，月桂酸的 K_d 比五甘氨酸高 20-40 倍，顺序为 K_d（水铁酸盐） > K_d（氢氧化铝）≫ K_d（方解石）。分子尺度模拟证实，月桂酸对水铁酸盐的结合能 （30.8 kcal/mol） 高于五甘氨酸 （6.0 kcal/mol），这归因于脂质疏水性。五甘氨酸的较低结合能是由其亲水性酰胺基团产生的，有助于分流到水中。连续实验检查了脂质或氨基酸的第一层如何影响碳水化合物/木质素的吸附，这些脂质或木质素显示出很少或没有单独的吸附亲和力。宏观结果表明，脂质和氨基酸吸附通过有机多层独立和协同地诱导水铁酸盐颗粒排斥、增加反应表面积并增强碳水化合物/木质素吸附。 分子尺度结果表明，吸附在水铁矿上的氨基酸比与单个木质素单元更容易与木质素大聚集体（在溶液中形成）相互作用，表明通过 H 键形成有机多层。这些发现揭示了 SOM 与矿物相互作用的分子机制，这对增强土壤碳稳定性至关重要。