Root-pore interactions and their role in shaping rhizosphere structure and rhizosheath development

Much research has evaluated rhizosphere structure as distinct from bulk soil, often attributing these differences to root-induced changes. However, the role of inherent root growth preferences and their interactions with existing soil pore networks remains underexplored. This study investigates the relative contributions of root-induced changes and root growth preferences in shaping rhizosphere porosity gradients and their relationship to rhizosheath development.

Using repeated X-ray computed micro-tomography (µCT), we analyzed rhizosphere macroporosity in intact and sieved soils. For the first time, we distinguished between changes driven directly by root activity and those arising from the inherent reuse of pre-existing macropores. Our findings demonstrate that root growth preferences, such as the utilization of large macropores, are the dominant factor shaping rhizosphere structure. In contrast, direct root-induced changes, including compaction and pore rearrangement, contributed minimally to overall rhizosphere porosity, particularly in intact soils.

We also examined rhizosheath development, traditionally being considered as a representative subsample of the rhizosphere. Contrary to conventional assumptions, our results revealed no correlation between rhizosheath mass and root-soil contact or rhizosphere soil volume derived from µCT analysis. Instead, rhizosheath formation was primarily associated with roots growing into macropores and actively modifying their surroundings. Roots exploring dense soil matrices or biopores showed minimal rhizosheath development.

This study underscores the importance of root growth preferences in rhizosphere structure development and challenges existing assumptions about the relationship between rhizosheath and rhizosphere properties. Our findings highlight the necessity of conducting rhizosphere research in soils with intact structure to fully capture the complex interactions between roots and soil.