Elucidating the role of surface alteration and dynamic relocation for the formation and maturation of microaggregates in the soil-parent rock continuum

聚集和聚集是土壤的独特特征之一。结果表明，在亚微米尺度上，固相的空间排列是非随机的。在这个系统中，微团聚体被认为是几乎所有土壤中团聚体结构的基本组成部分，包括那些具有团聚体层次的土壤。土壤微团聚体被定义为小于0.25mm的复合结构，包括胶体大小和纳米颗粒的复合建筑单元以及有机-矿物复合材料。值得注意的是，微聚集体可以作为流动相的悬浮或胶体分散组分存在。因此，它们容易随渗流运移，并可能影响表面和孔隙空间性质。渗流组分与不动表面的相互作用导致的地表变化可能是一个重要的、但基本上尚未被探索的途径，它触发了土壤-母质岩石连续体中微团聚体的形成。在成熟的土壤中，粘土与其他通常结晶性差但活性高的矿物质和有机物的结合是化学非均质土壤悬浮液成核的结果。这两种途径并存，在土-岩过渡带，次生矿物相的风化和形成/蚀变仍处于早期阶段，可以进行研究。微聚集体的稳定性及其相互作用依赖于干湿循环，进而依赖于水合脱水循环。这种与水分相关的动态规律发生在温带地区的土壤中，甚至下至土-母-岩过渡带，表明水力和渗透应力及其历史导致了附着、分离、迁移和积累。通过这个项目，我们打算弥补在理解土壤-母质岩石连续体中微团聚体的形成和稳定性方面的基本知识空白。研究项目包括原位研究（空间-时间方法的黄土土壤层序剖面分析）、体外研究（动态迁移实验）和计算机研究（异聚集数值模拟）。我们重点研究了两个迄今为止被忽视的微聚集体和复合建筑单元的形成途径，即“地球化学继承”和“悬浮异聚集”，从而考虑了上游隔间中复合建筑单元和微聚集体形成物质的动态迁移作用。通过本子项目的研究，我们旨在通过对所产生现象的探索，定量地了解空间和时间上形成途径的相互作用和相互依赖，控制过程和潜在机制。我们改进的理解将最终推动我们在协调项目指导和实现的土壤中微团聚体形成和功能的定量理论框架的发展。

Aggregation and the build-up of aggregates is one of the unique features of soils. It results in a non-random spatial arrangement of the solid phase already at the submicron scale. Within this system, microaggregates are considered the fundamental building blocks for the aggregated structure in almost all soils, including those with an aggregate hierarchy. Soil microaggregates are defined as compound structures smaller <0.25mm, comprising the colloidal-sized and nanoparticulate composite building units and the organo-mineral composites. Noteworthy, microaggregates, may be present as suspended or colloidally-dispersed components of the mobile phase. As such, they are prone to transport with the seepage and may affect the surface and pore-space properties. Surface alteration by interactions of seepage components with immobile surfaces is likely an important, yet essentially unexplored pathway triggering formation of microaggregates in the soil-parent rock continuum. In matured soils, the commonly found associations of clays with other, often poorly crystallized but highly reactive minerals and organic matter is the consequence of nucleation in the chemically heterogeneous soil suspension. Both pathways coexist and can be studied in the soil-parent-rock transition zone were weathering and formation/alteration of secondary mineral phases are still in the early stage. The stability of microaggregates and their interactions are dependent on wetting-drying and in turn by hydration-dehydration cycles. Such moisture-related dynamics regularly take place in soils of the temperate regions even down to the soil-parent-rock transition zone and suggests that the hydraulic and osmotic stress and their history results in attachment, detachment, translocation and accumulation. With this project we intend to close fundamental knowledge gaps in the understanding of the formation and stability of microaggregates in the soil-parent rock continuum. The research program comprises studies in-situ (profile analysis loess pedosequence in a space-for-time approach), in-vitro (dynamic relocation experiments) and in-silico (numerical simulations of hetero-aggregation). We focus on two so far ignored formation pathways of microaggregates and composite building units, i.e. the "geochemical inheritance" and "heteroaggregation from Suspension", thereby considering the role of dynamic relocation of composite building units and microaggregate forming materials from upstream compartments. With the research in this subproject, we aim for a quantitative understanding of the interplay and interdependence of the formation pathways in space and time, the controlling processes and underlying mechanism by the exploration of the resulting phenomena. Our improved understanding will ultimately fuel our endeavor for the development of a quantitative theoretical framework of microaggregate formation and function in soils guided and realized within the coordination project.