Enchytraeids: Small but important ecosystem engineers

Enchytraeids (Annelida Oligochaeta), small burrowing organisms found worldwide, are known to influence soil structure, though their specific effects on pore space are not well quantified. In this study, we evaluated how the burrowing activities of Enchytraeus albidus and Enchytraeus crypticus affected the X-ray imaged porosity of soil over a 40- day period using two different soils (loamy and silty-clay-loamy soil) sieved to 2 mm and packed at two bulk densities (0.8 and 1 g cm−3). Our findings revealed that while enchytraeids had minimal impact on X-ray imaged porosity, they played a key role in reshaping the soil’s internal structure, increasing pore connectivity and homogenizing pore size distribution. This was evident through a reduction in the number of smaller pores and a shift toward larger pore sizes. The overall pore structure became more uniform, with enchytraeids promoting a shift in the dominant pore sizes. These structural changes were particularly pronounced in loosely compacted soils, where enchytraeids contributed to greater network complexity, as well as in the soil with a higher clay content, which is more conducive to aggregation. This suggests that enchytraeids have a significant role in modifying soil physical properties, especially in conditions where the soil is loosely compacted. X-ray microtomography is a promising tool for studying at the mesopore scale, and further studies are needed to better characterize the bioturbation activity of enchytraeids.