DFG Research Unit 2179

MAD Soil - Microaggregates: formation and turnover of the structural building blocks of soils

Within the soil aggregate system, microaggregates are supposed to be of primary importance, as they are strongly linked with essentially all processes which control interaction, transport and turnover of soil constituents. As such, they are intimately connected with the major energy and biogeochemical cycles. During pedogenesis, microaggregates are formed by a complex interplay of physical, chemical and biological aggregation mechanisms, the quantitative role of which, although progressively more investigated, is still poorly understood. Soil microaggregates are generally all compound soil structures <250 µm, which are composed of mineral and organic components arranged in a heterogeneous but rather unknown pattern. Soil microaggregates are considered the fundamental building blocks for aggregate structure in almost all soils, including soils with an aggregate hierarchy where they are the subunits for increasingly larger aggregates. Although soil properties and functions are to a large degree controlled by the formation of an aggregate structure, still very little is known about the rates and underlying deterministic or stochastic controls on soil microaggregate formation in space and in time. Yet, this knowledge is mandatory to functionally link the microarchitecture of soils to fluid flow and transport processes, activity of soil microorganisms, the turnover and interactions of elements, as well as to the stability of the soil microaggregates themselves.