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底土有机碳变异性、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，强调由于大的固体表面质量比，物理，化学和生物过程的界面特性的相关性。然而，目前大多数被忽视的是固体界面的重要性，可能会增加空间和时间的异质性土壤。因此，委员会认为，仍然需要回答的是，哪些土壤特定因素控制着底土中的碳收支，以及捕获稳定机制的相应尺度是什么。子项目P4的一个创新要素是开发流动池土壤取样技术，以评估小尺度土壤性质和过程，并将三维运输过程减少到准二维。d，它允许土壤异质性和感兴趣的过程之间的直接联系。流动池采样提供了在一个框架（即8 x 12 cm）内同时采样多达5个未扰动土壤切片作为三明治的选项。由于单个夹层的厚度很小（5至10 mm），因此未受干扰的样品可用作准重复样品。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。通过串联不同深度的流动单元，可以模拟虚拟土壤剖面，并分析DO13 C溶液渗透的深度依赖性穿透行为。使用单个流动池，物理，化学和生物特性可以映射到原状土颗粒界面。两个中心问题得到解决：（i）是否和如何热点的微生物活动有关的物理或物理化学性质的孢子空间和（ii）什么是具体的物理和界面之间的相互作用，土壤和根系特别注重根阶段（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进行评估的润湿性测量（座滴接触角测定，环境扫描电镜冷凝实验），而土壤有机质的含量和质量，即衍生的DRIFT映射的疏水性指数，通过校准的MIR光谱评估。将测量生物学参数（呼吸、胞外酶活性、14C标记葡萄糖的衰减），以将界面特性与相应的生物学反应联系起来。将与其他项目密切合作，在3个不同母体材料的地点对流动池进行取样。总体而言，本研究的目的是提供新的见解的评估和小规模的结构和界面异质性的SOM稳定化过程中结构较少的森林底土的相关性。

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.