Organic matter stabilization processes in subsoils: Impact of small-scale physical heterogeneity of soil particle interfaces

降解物与基质之间的空间分离被认为是控制土壤有机碳变异、稳定性和动态的主要因素。土壤中的过程发生在固体颗粒表面，由于固体表面质量比大，强调了物理、化学和生物过程的界面特性的相关性。然而，目前人们往往忽视了固体界面对土壤时空异质性的影响。因此，究竟是哪些土壤因子控制着地下土壤的碳收支，以及捕获稳定机制的尺度是什么，仍然需要回答。子项目P4的一个创新元素是开发一种流动池土壤采样技术，以评估小尺度土壤特性和过程，并将三维运输过程减少到准二维，从而允许土壤异质性和感兴趣的过程之间的直接联系。流动池取样提供了在一个框架内（即8 x 12厘米）取样的选择，同时多达5个未受干扰的土壤切片作为三明治。由于单层夹层厚度小（5 ~ 10mm），未受干扰的样品可以用作准重复。将采用两种方法将界面特性与化学和生物过程联系起来，以确定生物热点。采用不同深度的流池级联，通过连接的流池模拟虚拟土壤剖面，分析渗透DO13C溶液的深度相关突破行为。使用单流细胞，可以在未受干扰的土壤颗粒界面上绘制物理，化学和生物特性。解决了两个核心问题：(i)微生物活动的热点是否以及如何与孢子空间的物理或物理化学性质相关；（ii）土壤与根之间的具体物理和界面相互作用是什么，特别关注根期（根密度，形态）和根际润湿性。为了回答这些问题，将与伙伴项目密切合作，绘制各种参数。界面的物理化学行为是通过润湿性测量（无基滴接触角测定，ESEM冷凝实验）来评估的，而土壤有机质含量和质量，即由DRIFT-mapping得出的疏水性指数，是通过校准的MIR光谱来评估的。生物参数（呼吸、外酶活性、14C标记葡萄糖的衰变）将被测量，以将界面特性与各自的生物反应联系起来。流动细胞将在3个地点取样，采用不同的母材，与其他项目密切合作。总体而言，本研究旨在为结构松散的森林底土中SOM稳定过程的小尺度结构和界面异质性的评估及其相关性提供新的见解。

The spatial separation between degraders and substrate is considered as a major factor controlling subsoil organic carbon variability, stability and dynamics. Processes in soils take place at solid particle surfaces, emphasizing the relevance of interfacial properties for physical, chemical and biological processes due to large solid-surface to mass ratios. However, mostly ignored is at present the importance of the solid interfaces that may enhance spatial and temporal heterogeneity in soils. Accordingly, it still needs to be answered which soil-specific factors are governing the carbon budget in subsoils and what the respective scales for capturing stabilizing mechanisms are.One innovative element of subproject P4 is the development of a flow cell soil sampling technique to assess small-scale soil properties and processes and to reduce 3-dimensional transport processes to quasi 2-d which allows a direct link between soil heterogeneity and processes of interest. Flow cell sampling provide the option to sample within one frame (i.e. 8 x 12 cm) simultaneously up to 5 undisturbed soil slices as a sandwich. Due to the small thickness of a single sandwich layer (5 to 10 mm), undisturbed samples can be used as quasi-replicates. Two approaches will be made to link interfacial properties with chemical and biological processes in order to identify biological hot spots. Using a cascade of flow cells of different depths, a virtual soil profile will be simulated by connected cells and depth-dependent breakthrough behavior of infiltrating DO13C solution can be analyzed. Using single flow cells, physical, chemical, and biological properties can be mapped on the undisturbed soil particle interfaces. Two central questions are addressed: (i) whether and how are hotspots of microorganisms activity related to either physical or physicochemical properties of the spore space and (ii) what are the specific physical and interfacial interactions between soil and roots with special focus on root stage (root density, morphology) and rhizosphere wettability. To answer these questions, mapping of various parameters will be done in close cooperation with partner projects. Physicochemical behavior of the interfaces is assessed by wettability measurements (sessile drop contact angle determination, ESEM condensation experiments), whereas soil organic matter content and quality, i.e. hydrophobicity index derived by DRIFT-mapping,is assessed by calibrated MIR spectroscopy. Biological parameters (respiration, exo-enzyme activity, decay of 14C labeled glucose) will be measured to relate interfacial properties with respective biological responses. Flow cells will be sampled on 3 sites with different parent material in close cooperation with other projects. Overall, this study aims to offer new insights on the assessment and the relevance of small-scale structural and interfacial heterogeneity for SOM stabilization processes in less structured forest subsoils.