In structured soils, earthworm burrows, root channels, shrinkage cracks, and interaggregate spaces form complex macropore networks relevant for preferential transport, turnover processes, and root growth. Macropore walls are often coated with organomineral material, which determine physicochemical properties such as wettability, sorption, and the cation exchange capacity (CEC). The objective here was to identify volume‐averaged mean macropore coating properties of larger intact soil cores (∼7,500 cm³) from Bt horizons of Luvisols developed from loess and glacial till. The quantification of organic C (OC) content and CEC of macropore surfaces was based on three‐dimensional images of X‐ray computed tomography (XRCT) of 231‐μm voxel resolution and a vesselness procedure to distinguish between biopores and cracks. Macropore surface areas were combined with millimeter‐scaled data of OC contents and CEC of macropore coating material. The surface of macropores that accounted for 5.6 % (loess‐Bt) and 4.6 % (till‐Bt) of the samples’ volumes represented approximately one‐third of the OC content and CEC of the bulk soil. Among the macropores, surfaces of larger biopores contributed most to OC content of the soil cores. The contribution of coated cracks and pinhole fillings to OC content was larger for the till‐Bt than for the loess‐Bt. Locally higher OC contents and CEC values emphasize the role of macropore surfaces in Bt horizons of Luvisols as geochemical hotspots and for mass exchange, especially during preferential flow and transport. Volume‐based coating properties may help improving macroscopic‐scale two‐domain flow and transport models.

中文翻译：

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Bt层中大孔表面有机碳含量和阳离子交换容量的体积相关定量

在结构化土壤中，worm的洞穴，根部通道，收缩裂缝和集聚空间形成了复杂的大孔网络，这些网络与优先运输，周转过程和根系生长有关。大孔壁通常涂有有机矿物材料，这些材料决定了物理化学性质，如润湿性，吸附性和阳离子交换容量（CEC）。此处的目的是确定较大完整土壤芯（〜7,500 cm ^3）的体积平均平均大孔涂层性能）从黄土和冰川直至卢比索的Bt地平线。大孔表面有机C（OC）含量和CEC的定量是基于231μm体素分辨率的X射线计算机断层扫描（XRCT）的三维图像以及用于区分生物孔和裂缝的疏松程序。大孔的表面积与大孔涂料的OC含量和CEC的毫米级数据结合在一起。大孔表面占样品体积的5.6％（黄土-Bt）和4.6％（耕作-Bt），约占散装土壤中OC含量和CEC的三分之一。在大孔中，较大的生物孔表面对土壤核心的OC含量贡献最大。直到Bt，涂层裂缝和针孔填充对OC含量的贡献要大于黄土-Bt。局部较高的OC含量和CEC值强调了Luvisols的Bt层中大孔表面作为地球化学热点和物质交换的作用，尤其是在优先流动和运输过程中。基于体积的涂层特性可能有助于改善宏观的两域流动和传输模型。