Exploring the role of biota and biogenic components for the formation and function of (micro-)aggregates in soil

The here presented cumulative dissertation deals with the initial processes/mechanisms of aggregate formation in soil with a special focus on soil biota. Generally, aggregates are formed by the interaction between (in-)organic soil constituents (e.g., minerals and soil organic matter) and their response to changing environmental conditions. The interactions of these potentially (micro-)aggregate forming materials are influenced by their inherent properties (e.g., surface charge and roughness, particle shape and size, biopolymer composition, molecular weight and size), the prevailing environmental conditions (e.g., pH and electrical conductivity) and external forces (e.g., bioturbation, gravity, water menisci, swelling and shrinking processes). In soil, a three dimensional natural porous medium, aggregation-forming processes are ubiquitous, occurring sequentially as well as simultaneously. Consequently, the identification and investigation of specific aspects of aggregate formation is essential to place them in a high-level context and thus derive consequences on the pedon-scale (e.g., pollutant/nutrient accumulation, evolution of habitat, structure formation and stabilization). This cumulative work includes five publications dealing with the influence of biogenically excreted organic matter on aggregation revealed by lab based in-vitro studies (P2 and P3), numerical simulations dealing with the impact of the balance between particle size and concentration on aggregate morphology and aggregation dynamics (P4 and P5) as well as one comprehensive review article of biogenically triggered aggregation processes in soil (P1).