3D-organisation of the solid, pore and organic phases in soil microaggregates and its control on mechanical stability

土壤结构是固体(有机和无机物质)和孔隙的复杂空间排列的表现，这些孔隙中充满了不同的水和气体。土壤的过多功能，如养分和水的供应、碳的封存、污染物的转化或土壤作为土壤生物栖息地的功能，都取决于土壤结构。尽管团聚体作为支撑土壤结构相关功能的构建块的重要性，但对初始团聚体的形成仍然知之甚少。在研究单元2179(疯狂土壤：土壤中的微团聚体发展)的框架内，该分项目调查土壤团聚体中涉及的物理关键过程，以支持对团聚体形成的机械理解的发展。本研究采用现代实验方法和分析工具，如X射线层析成像(University Of Kassel)、同步辐射层析成像(Synchrotron Tomography，HASYLAB)、定量三维图像分析和物理化学显微传感等，研究土壤微团聚体形成和周转的动态过程，以获得微团聚体结构及其对生物和非生物过程的影响之间的定量联系。在研究单元的第一阶段，我们将重点放在地形序列(粘土含量梯度)和多同位素标记的微观世界实验上。在此背景下的主要研究问题是土壤结构如何随粘土含量的变化而演变，以及这如何影响物理(水和氧的运输)与生物(微生物活性，EPS)过程的相互作用以及由此产生的微团聚体的机械稳定性(例如，通过创建低熵稳定的结构)。将对3D图像进行分析，以获得形态和结构信息。这将使我们不仅能够量化孔隙空间，而且还能够量化这些构建块的孔隙和固相的空间组织。结果将与微尺度土壤测量获得的物理性质(如氧气微扩散、SOM位置、机械稳定性)相关联，这将加深我们对物理过程在团聚体形成中的作用的理解，并为发展微团聚体形成的机械定量模型(子项目PM)提供输入数据。

Soil structure is the expression of a complex spatial arrangement of solids (organic and inorganic matter) and pores, which are variably filled with water and gas. A plethora of soil functions such as the supply of nutrients and water, sequestration of carbon, transformation of pollutants or simply the functioning of soil as a habitat for soil organisms depend on soil structure. Despite of the importance of aggregates as building blocks that sustain soil structure related functions, initial aggregate formation is still poorly understood. In the frame of the research unit 2179 (Mad Soil: Microaggregate development in Soil) this subproject investigates physical key processes involved in soil aggregation to support the development of a mechanistic understanding of aggregate formation. We study the dynamics of soil micro-aggregate formation and turnover by applying modern experimental approaches and analytical tools such as X-ray tomography (University of Kassel), Synchrotron tomography (HASYLAB), quantitative 3D image analysis and physicochemical microsensing to obtain quantitative links between micro-aggregate architecture und its influence on biotic and abiotic processes leading to aggregate formation. In the first phase of the research unit we will focus on a toposequence (clay content gradient) and a multi-isotope labelled microcosm experiment. The main research question in this context is how soil structure evolves as a function of clay content and how this influences the interaction of physical (water and oxygen transport) with biological (microbial activity, EPS) processes and the resulting mechanical stability of micro-aggregates (e.g. by creating low entropy stable structures). The 3D images will be analyzed to obtain morphological and structural information. This will enable us to quantify not only the pore space, but also the spatial organization of pores and solid phases of these building blocks. The results will be correlated with physical properties obtained from microscale soil measurements (e.g. oxygen microdiffusion, SOM location, mechanical stability) which will enhance our understanding of the role of physical processes in aggregate formation and provide input data for the development of a mechanistic quantitative model of micro-aggregate formation (subproject PM).