Fe-controls on soil microaggregate structure, stability, and composition

胶体和纳米级的有机和矿物颗粒是土壤微团聚体形成的基本成分;然而，它们在初始团聚体（核）形成中的作用及其作为胶结剂的功能还不清楚。通过该提案，我们的目标是阐明胶体和纳米颗粒对土壤微团聚体形成、组成和结构的作用。我们将结合使用最先进的方法来分析土壤微团聚体的尺寸分布，它们在低微米到纳米级的构建单元，它们的总组成和空间组成，以及它们的结构。使用的方法包括SPLITT、AF 4、DLS、MALS（粒度分级）与ICP-MS和OCD（总元素组成）、TEM/SEM-EDX（空间元素组成）或SAXS/USAXS和气体吸附技术（孔隙率）联用。这些方法将被应用到土壤样品的拓扑序列和多同位素标记的微团聚体从中央微观实验的土壤中分离出来。从这些样品中分离出的土壤微团聚体将通过物理和化学处理进行分解，并重新团聚，以分析亚基特征对土壤微团聚体形成的影响。获得的土壤微团聚体及其亚基将使用上述方法进行分析，以揭示土壤微团聚体的核心，其胶结剂，OM封存，以及OM和Fe-物种对团聚体形成和孔隙度的作用。孔隙率数据将与SP 7收集的较大孔隙的X射线CT获得的孔隙率数据进行补充。此外，将与SP 6合作收集胶体和纳米颗粒组成对微生物活性的影响。获得的粒度分布数据将提供给PM，以帮助开发一个机械定量模型。

Colloidal and nanosized organic and mineral particles are essential ingredients for soil microaggregate formation; however, their role for initial aggregate (nucleus) formation and their function as cementing agent is not well understood. With this proposal we aim to elucidate the role of colloids and nanoparticles for soil microaggregate formation, composition, and architecture. We will use a combination of state-of-the-art methods to analyze the size distribution of soil microraggregates, their building units on the low micron- to nanoscale, their total and spatial composition, as well as their architecture. Methods used include SPLITT, AF4, DLS, MALS (size fractionation) coupled to ICP-MS and OCD (total elemental composition), TEM/SEM-EDX (spatial elemental composition), or SAXS/USAXS and gas-adsorption techniques (porosity). These methods will be applied to soil samples obtained from the toposequence and to the multi-isotope labeled microaggregates isolated from soils from the central microcosm experiments. Soil microaggregates isolated from these samples will be disaggregated by physical and chemical treatments, and reaggregated to analyze the influence of subunit-characteristics on soil microaggregate formation. Obtained soil microaggregates and their subunits will be analyzed using the methods described above to reveal the nucleus of soil microaggregates, their cementing agents, OM sequestration, and the role of OM and Fe-species on aggregate formation and porosity. Porosity data will be complemented with porosity data obtained by X-ray CT for larger pores as collected by SP7. In addition, the influence of colloidal and nanoparticular composition on microbial activity will be gathered in collaboration with SP6. The obtained size distribution data of will be given to PM to help developing a mechanistic quantitative model.