Exploring the relationship between soil structure and soil functions via pore-scale imaging

Biogeochemical and structural heterogeneities at the pore-scale govern processes in soil in many ways. They are therefore of key importance for understanding soil functioning. Prominent examples are the stabilization of soil organic matter due to reduced bioavailability in aggregated soil structure, preferential transport of nutrients and contaminants along macropores, highly localized greenhouse gas emission around a few hotspots of microbial activity like particulate organic matter and the formation of the rhizosphere as a complex system composed of plant roots, soil and associated microorganisms.All of these processes have in common that the underlying relevant mechanisms are fairly well understood in artificial systems with reduced degrees of heterogeneity, like soil suspensions, glass beads, micromodels with known structure and so on. However, the far more complex pore architecture of undisturbed soils leads to emergent system behavior which needs to be addressed when studying these structure-mediated processes. The opaque nature of soils predestines the use of non-invasive imaging techniques for exploring how biogeochemical and structural heterogeneities are shaping soil functions. Such imaging techniques and subsequent image analyses are now widely used to study soils. While previously many properties were defined only by averaged bulk parameters, pore-scale imaging reveals details at smaller scales and provides spatial information, in two, three or even more dimensions including time or multispectral data.This virtual special issue presents fourteen contributions that employ pore scale imaging in order to highlight the role of soil structure on soil functions or reversely the effect of soil processes on soil structure or report methodological advancements in pore scale imaging. In this editorial we briefly outline the different conceptions of soil structure, demonstrate the relevance of soil structure for various soil functions with a specific example and review the different avenues along which recent advances in pore scale imaging of soil have been made, before we briefly categorize and summarize the contributions to this virtual special issue.