Root−soil contact as a driver of rhizosphere structure development and root traits in two contrasting soil textures

Characterizing the interplay between the root−soil contact, root traits, and the densification of the rhizosphere is of particular importance to better understand the biophysical interactions of plant roots with the soil environment. In this work, we aimed to characterize the interaction between these properties, and how it varied with soil texture and structure, with high resolution (10 µm) X-ray CT scanning. We investigated a fine-textured loam with a deformable soil matrix and a coarse-textured sand with rigid grains, with various degrees of compaction, structure heterogeneity, and fraction of fine particles. In loam, the median root−soil contact increased with the soil bulk density and ranged from 57 to 69%. For the compressible loam, there was a positive correlation between the root−soil contact and the peak of soil density close to the roots ( r = 0.49). In sand, the median root−soil contact ranged from 39 to 52%, and increased when roots deformed themselves to penetrate zones of dense packing of sand grains. In summary, our results show that in compressible soils, roots deform the surrounding soil matrix, whereas in non-compressible soils, the roots themselves undergo deformation as they grow into the soil. Our study provides important insights on the interaction between root and soil properties and root−soil contact, with consequences for plant performance and rhizosphere studies.