SP2

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. The project elucidates the role of colloids and nanoparticles for soil microaggregate formation, composition, and architecture. We 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 are 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 are 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.