Root-soil contact as a driver of rhizosphere structure and plant performance traits in contrasting soil structures

Abstract

Root-soil contact is a key factor in determining resource acquisition in soils; however its influence on the rhizosphere structure and the emerging plant traits are poorly understood. The present study aims to provide a comprehensive understanding of the coupled dynamics between plant roots and soil structure, with an emphasis on root-soil contact as a main explanatory variable. 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. Over 21 days, we grew maize plants under well-watered conditions and monitored plant performance traits. After the growth period, we extracted undisturbed soil samples and scanned them with high resolution (10 μm) X-ray CT to characterize root-soil contact and root morphology. Our results show that in compressible soils, roots deform the surrounding soil matrix and induce rhizosphere compaction, whereas in non-compressible soils, the roots undergo deformation as they grow into zones with pores narrower than themselves. Increased root-soil contact did not result in increased plant transpiration or shoot biomass. Our study underscores the complex role of root-soil contact in shaping resource acquisition, and highlights the need to better understand the thresholds at which root-soil contact becomes limiting and how this depends on soil texture. It also emphasizes the influence of soil structure on root development and shows promising avenues for future work aimed at linking pore-scale heterogeneity and gas diffusion to root growth.