Quantification of small-scale physicochemical and microbiological properties of intact macropore surfaces in structured soils

在结构性土壤中，水和活性溶质可以优先通过较大的集合体间孔隙、裂缝和生物孔。这些结构的表面通常被土壤有机质（SOM）和粘土物质覆盖，并可以被微生物定植，从而促进周转过程，例如碳和从底土释放。结构表面的物理化学和几何性质影响着土壤的优先流动以及不同流动域（大孔隙和土壤基质）之间的水和质量交换。由于这些表面的易损性和复杂的结构，使这些表面特性的参数化变得复杂。迄今为止，从完整的结构表面获得的参数仅涉及土壤有机质的潜在润湿性和结构的粗糙度。该项目的想法是通过对这些大孔结构的空间排列的三维分析来推断土壤层结构表面的二维确定特性，从而估计结构表面特性对Bt-Horizons中优先流动和周转过程的影响。本项目扩展的目的是定量分析黄土和冰川坡耕地上发育的Luvisols bt层完整结构表面的小尺度物理化学和微生物特性。第一个项目（LE 3177/1-1）的结果将通过以下工作包进行扩展：(i)将使用x射线计算机断层扫描（µCT）对优先流动期间可能可用的整个大孔隙系统进行三维量化。在染料示踪实验的帮助下，实际可用的大孔（在特定流动事件中活跃）将被确定，以评估优先流动的表面结构的空间相关性。小尺寸和大尺寸样品的微CT测量组合将确保考虑所有大孔尺寸。不同土壤含水量对土壤结构特征的影响将通过比较饱和和非饱和土壤水分条件的数据来评估。（ii）完整结构表面的物理化学性质（OC含量，SOM组成，CEC，微生物活性）将在漫反射模式下使用红外光谱进行二维量化（DRIFT制图）。使用完整的结构表面对DRIFT光谱进行校准，将确保利用DRIFT作图光谱预测元素含量和表面参数的有效绝对值。（iii）利用酶谱法和DRIFT制图技术表征土壤微生物的空间分布及其丰度和活性，旨在识别微生物热点，解释SOM组成的局部小尺度差异，并评估结构表面对底土碳周转的重要性。

In structured soils, water and reactive solutes can preferentially move through larger inter-aggregate pores, cracks, and biopores. The surfaces of these structures are often coated by soil organic matter (SOM) and clayey material and can be colonized by microorganisms, which promote turnover processes, e.g., carbon and release from subsoils. The physico-chemical and geometrical properties of structural surfaces influence the preferential flow through soils as well as the water and mass exchange between the different flow domains (macropores and soil matrix). A parametrization of these surface properties is complicated by the vulnerability and complex structure of these surfaces. Parameters from intact structural surfaces were obtained to date only concerning the potential wettability of the soil organic matter and the roughness of the structures. The idea of this project is to extrapolate the two-dimensionally determined properties of structural surfaces for soil horizons by the help of three-dimensional analyses of the spatial arrangement of these macropore structures and thereby to estimate effects of structural surface properties on preferential flow and turnover processes in Bt-Horizons. The objective of this project extension is the quantification of small-scale physico-chemical and microbial properties of intact structural surfaces from Bt-horizons of Luvisols developed on loess and glacial till. Results from the first project (LE 3177/1-1) will be extended by the following work packages:(i) The entire macropore system potentially available during preferential flow will be quantified three-dimensionally using x-ray computer tomography (µCT). The actually available macropores (active during specific flow events) will be determined by the help of dye tracer experiments in order to assess the spatial relevance of surface structures for preferential flow. The combination of µCT measurements of small- and large-sized samples will ensure the consideration of all macropore sizes. Effects of different soil water contents on the soil structure characteristics will be assessed by comparing data from saturated and unsaturated soil water conditions.(ii) The physico-chemical properties of intact structural surfaces (OC content, SOM composition, CEC, microbial activity) will be two-dimensionally quantified using infrared spectroscopy in the diffuse reflectance mode (DRIFT mapping). The use of intact structural surfaces for the calibration of the DRIFT spectra will ensure the prediction of valid absolute values of elemental contents and surface parameters by the help of DRIFT mapping spectra. (iii) The characterization of the spatial distribution of soil microorganisms and their abundance and activities by the help of zymography and DRIFT mapping aims to identify microbial hot spots, to explain local small-scale differences in the SOM composition, and to assess significances of structural surfaces with respect to carbon turnover in subsoils.