BayCEER Workshop 2026

Soil structure turnover and POM redistribution driven by soil fauna revealed by X-ray CT derived particle–pore relationships

Faunal activity is a major driver of soil structure turnover, influencing the spatial organisation and accessibility of soil organic matter. However, quantitative comparisons of how functionally distinct soil fauna reorganise mineral and organic particles relative to pore space remain limited. We examined how three earthworm species with contrasting ecological strategies (Eisenia fetida, Lumbricus terrestris, and Aporrectodea caliginosa), the enchytraeid Enchytraeus albidus, and the ant Lasius niger reorganise soil structure and particulate organic matter (POM). We combined X-ray µCT with garnet particles as inert tracers of structural redistribution. Particle–pore distances were normalised to the soil matrix–pore distance to quantify structural turnover. Maize POM particles placed at the soil surface served as tracers of spatial incorporation and occlusion, while POM morphology indicated transformation.

POM was consistently positioned closer to pore space than garnet across all fauna groups. However, neither POM nor garnet exhibited consistent displacement relative to controls when averaged across entire subsamples or enchytraeid microcosms. In contrast, pronounced spatial reorganisation emerged within individual biogenic structures. Across all three earthworm species, both POM and garnet were located farther from pore space in cast-associated structures than in burrow-associated regions, while POM consistently remained closer to pore space than garnet. Additionally, POM object size and morphology showed species- and depth-dependent responses.

Bioturbation drives pronounced local reorganisation within biogenic structures, while the persistent spatial separation between POM and an inert mineral tracer indicates that physical restructuring and organic-matter organisation are related yet distinct processes. X-ray µCT-derived particle–pore relationships provide a quantitative framework for assessing how soil fauna reorganise soil structure and organic matter across spatial scales.