Use of X‐ray microcomputed tomography for characterizing earthworm‐derived belowground soil aggregates

• Published in: European journal of soil science Vol. 72; no. 3; pp. 1113 - 1127
• Main Authors: Le Bayon, Renée‐Claire, Guenat, Claire, Schlaepfer, Rodolphe, Fischer, Franziska, Luiset, Alexandre, Schomburg, Andreas, Turberg, Pascal
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-05-2021; Wiley Subscription Services, Inc
• Subjects: Aggregates; Allolobophora chlorotica; belowground casts; Components; Computed tomography; Controlled conditions; earthworms; Lumbricus rubellus; Lumbricus terrestris; mesocosm; Oligochaeta; Organic matter; Parameters; Resolution; Signatures; Soil; Soil aggregates; Soil properties; Soil structure; Spatial discrimination; Spatial distribution; Spatial resolution; Species; Tomography; X‐ray microcomputed tomography
• ISSN: 1351-0754; 1365-2389
• DOI: 10.1111/ejss.12950

Soil structure is closely linked to biological activities. However, identifying, describing and quantifying soil aggregates remain challenging. X‐ray micro computed tomography (X‐ray μCT) provides a detailed view of the physical structure at a spatial resolution of a few microns. It could be a useful tool to discriminate soil aggregates, their origin and their formation processes for a better comprehension of soil structure properties and genesis. Our study aims to (a) determine different X‐ray μCT‐based aggregate parameters for differentiating earthworm casts belowground (earthworm aggregates) from aggregates that are not formed by earthworms (non‐earthworm aggregates), and (b) to evaluate if these parameters can also serve as specific “tomographic signatures” for the studied earthworm species. For this purpose, we set up a microcosm experiment under controlled conditions during 8 weeks, including three species of earthworms tested separately: the epigeic Lumbricus rubellus, the anecic Lumbricus terrestris and the endogeic Allolobophora chlorotica. Our results show that X‐ray μCT analysis helps distinguish earthworm aggregates from non‐earthworm ones using (a) the relative volume of the components within aggregates and (b) the volumetric mass of aggregates and their global volume. In particular, the volume ratio of mineral grains within the aggregates is significantly different according to earthworm species. So, X‐ray μCT is a powerful and promising tool for studying the composition of earthworm casts and their formation. However, future research is needed to take into account the shapes and spatial distribution of the aggregates' components, in particular the different states of organic matter decomposition.
Highlights
Can earthworm belowground casts be differentiated from other soil aggregates using X‐ray μCT?
The use of X‐ray μCT for characterizing soil aggregates at a spatial resolution of a few microns.
A combination of X‐ray μCT variables discriminates earthworm casts from non‐earthworm aggregates.
X‐ray μCT, used alone, is relevant for defining species‐specific signatures of earthworm casts.