The capacity of soil as a carbon (C) sink is mediated by interactions between organic matter and mineral phases. However, previously proposed layered accumulation of organic matter within aggregate organo–mineral microstructures has not yet been confirmed by direct visualization at the necessary nanometer-scale spatial resolution. Here, we identify disordered micrometer-size organic phases rather than previously reported ordered gradients in C functional groups. Using cryo-electron microscopy with electron energy loss spectroscopy (EELS), we show organo–organic interfaces in contrast to exclusively organo–mineral interfaces. Single-digit nanometer-size layers of C forms were detected at the organo–organic interface, showing alkyl C and nitrogen (N) enrichment (by 4 and 7%, respectively). At the organo–mineral interface, 88% (72–92%) and 33% (16–53%) enrichment of N and oxidized C, respectively, indicate different stabilization processes than at organo–organic interfaces. However, N enrichment at both interface types points towards the importance of N-rich residues for greater C sequestration.

土壤作为碳 (C) 汇的能力是由有机质和矿物相之间的相互作用调节的。然而，先前提出的有机矿物聚集体微观结构中有机物的分层积累尚未通过必要的纳米级空间分辨率的直接可视化得到证实。在这里，我们识别出无序的微米级有机相，而不是之前报道的 C 官能团中的有序梯度。使用冷冻电子显微镜和电子能量损失光谱（EELS），我们展示了有机-有机界面与纯有机-矿物界面的对比。在有机-有机界面处检测到单位数纳米尺寸的 C 形式层，显示烷基 C 和氮 (N) 富集（分别增加 4% 和 7%）。在有机-矿物界面，N 和氧化碳分别富集 88%（72-92%）和 33%（16-53%），表明与有机-有机界面不同的稳定过程。然而，两种界面类型的氮富集表明富氮残基对于更大的碳封存的重要性。