Root-induced recovery of compacted subsoil under perennial grassland mixtures using ingrowth soil cores

Biological tillage by roots has been proposed as a sustainable strategy for subsoil structural recovery following compaction; however, the potential of perennial grassland mixtures remains insufficiently quantified. This study evaluated two well-established perennial grassland mixtures (three vs twelve species) using field-incubated ingrowth soil cores. Two root-contact conditions were imposed: direct root contact ( DCR ; roots allowed into cores) and isolated root contact ( ICR ; roots excluded by mesh). X-ray µCT was used to analyze the total CT-detectable pore space (CTtotal ) and vertically continuous biopores ( VCBio ), before and after incubation. Following incubation, soil physical characteristics, root intensity, arbuscular mycorrhizal fungi ( AMF ) biomarkers ( PLFA and NLFA C16:1ω5), and glomalin-related soil protein ( GRSP-EE ) were measured, followed by destructive assessment of structural quality. VCBio was more sensitive to root-induced structural changes than CTtotal . In DCR twelve-species mixture, macroporosity ( mv rel ) and macropore length density ( ρ L ) derived from VCBio increased with incubation by 39% and 52%, respectively, while total macropore volume ( mv CT ) within the 0.24–0.5 mm diameter class increased 2.50 times with incubation. No significant increases in mv rel , ρ L , mv CT from CTtotal were found. The DCR twelve-species mixture exhibited greater increases in CT-derived parameters than the DCR three-species mixture, indicating stronger biological subsoiling potential. This coincided with higher concentrations of AMF biomarkers PLFA and NLFA than all other treatments. Air-filled porosity and visual structural quality showed significant treatment effects. These results indicate that early subsoil recovery under perennial grassland mixtures is driven by changes in VCBio , with AMF biomarkers and soil physical characteristics responding at different rates.