Interactions between earthworm species and soil type influence the porosity of earthworm casts

Earthworms significantly influence soil structure and associated ecosystem services, but the effect of different earthworm species and soil types on the physical organization of casts remains poorly understood. This study aims to shed light on the importance of earthworm species, soil type and their interactions in shaping cast microstructure. Using a microcosm experiment and X-ray microtomography image analysis, we examined the porosity and pore connectivity of casts produced by nine different temperate earthworm species in two contrasting soil types (Alluviosol and Cambisol). Our results showed that generally casts were characterized by lower overall porosity (reduced by 39–86% in Cambisol and 14–64% in Alluviosol) and pore connectivity (up to 76% lower in Cambisol) than control aggregates formed without earthworm activity, but they showed higher bioporosity (up to 50%). Both, earthworm species and soil type influenced pore properties, and the interaction of both explained most of the variability. In addition, we found no clear link between ecological categories of earthworms and the cast pore characteristics, highlighting the difficulty of generalizing species effects on cast microstructural properties. These results call for more nuanced approaches in future research to better predict earthworm effects on physical soil properties and resulting ecosystem services, considering both species-specific traits and their interactions with different soil environments.