The complex interplay between physical, chemical and biological processes determines the three-dimensional arrangement of mineral, organic and biotic materials in soils, shaping the soil structure and micro-environments and habitats in soils. This leads to a wealth of structures at all scales, starting with composite building units like the organo-mineral associations and micro-aggregates (smaller than 250 µm), which are thought to be ubiquitous and fundamental building blocks for larger aggregates, continuing into gradients of water, exudates and nutrients across the rhizosphere of living roots, and ending at continuous biopores (e.g. earthworm burrows or root channels) that may stretch across the entire soil profiles.

A vast variety of biotic (bioturbation, secretion, rhizodeposition, etc.) and abiotic (wetting/drying cycles, chemical reactions, etc.) processes form and modify soil structure, while at the same time the soil architecture regulates and controls these processes. Little is known about these feedback mechanisms and the rates of aggregate formation and turnover. Quantitative understanding of these processes and interactions is impaired by limited information on the spatial heterogeneity within micro-aggregates, across the rhizosphere and in other microhabitats. The way forward might be provided by a combination of non-invasive imaging techniques, carefully designed experiments, and spatially resolved, coupled models of water and matter fluxes, element cycling, patterns formation of organic or inorganic compounds and the emergence of microhabitats in soil. The session will provide the platform for scientist from different disciplines to discuss fundamental and methodological advances related to:
• Composition and turnover of micro-aggregates as well as their controlling role for the different environments they form in.
• Water and element fluxes across the soil and the soil-root interface from the pore scale to the soil profile.
• Biogeochemical processes associated with microbial activity in hotspots like the rhizosphere as well as in disperse zones of soil.
• Vadose zone hydrology, soil aeration and related two-phase flow problems and how they are governed by microscale heterogeneity.
• Changes in soil structure, soil biota and their interactions due to root growth, atmospheric boundary conditions, land use management, etc.