Natural drivers of soil pore-structure recovery in compacted intact cores: a 30-month burial experiment in forest and grassland

Soil structure can recover after compaction through the combined action of roots, soil fauna, microbial activity, and physical wetting-drying and freeze-thaw processes. We investigated the extent to which such natural processes restore pore architecture in compacted sandy loam soil cores buried for approximately 30 months under contrasting vegetation types. Intact sandy loam cores (20 cm height × 20 cm diameter) with an initial bulk density of 1.7 g cm^-3 were extracted from compacted headlands of an agricultural field near Copenhagen, Denmark, using perforated cores that allowed root and faunal entry. The pore network was characterised at field-moist conditions prior to burial using X-ray computed tomography (CT), quantifying tortuosity, macroporosity, macropore density, and pore network skeleton and branching properties. Four replicate cores each were buried at 30 cm depth in a forest and a grassland site, both located in the same region and characterised by sandy loam soils. After 30 months, the cores were retrieved and rescanned using the same CT protocol. Changes in pore metrics were assessed relative to initial conditions to evaluate structural recovery. In parallel, microbial biomass, enzyme activity, organic matter content, pH, and other soil properties were measured at all sites to support interpretation of biological and biogeochemical drivers. The results are used to assess the capacity of natural processes to restore pore structure in compacted soils and to identify key mechanisms controlling recovery under different land use.