High‐resolution synchrotron imaging shows that root hairs influence rhizosphere soil structure formation

Abstract

Summary In this paper, we provide direct evidence of the importance of root hairs on pore structure development at the root–soil interface during the early stage of crop establishment.This was achieved by use of high‐resolution (c. 5 μm) synchrotron radiation computed tomography (SRCT) to visualise both the structure of root hairs and the soil pore structure in plant–soil microcosms. Two contrasting genotypes of barley (Hordeum vulgare), with and without root hairs, were grown for 8 d in microcosms packed with sandy loam soil at 1.2 g cm−3 dry bulk density. Root hairs were visualised within air‐filled pore spaces, but not in the fine‐textured soil regions.We found that the genotype with root hairs significantly altered the porosity and connectivity of the detectable pore space (> 5 μm) in the rhizosphere, as compared with the no‐hair mutants. Both genotypes showed decreasing pore space between 0.8 and 0.1 mm from the root surface. Interestingly the root‐hair‐bearing genotype had a significantly greater soil pore volume‐fraction at the root–soil interface.Effects of pore structure on diffusion and permeability were estimated to be functionally insignificant under saturated conditions when simulated using image‐based modelling.

Imaging microstructure of the barley rhizosphere: particle packing and root hair influences

“…This study has contrasting findings to previous work where root hairs were observed to increase detectable porosity (Koebernick et al ., ) and many studies that observed significant increases in macroporosity due to the presence of roots (Whalley et al ., ; Feeney et al ., ). However, the current study used soil sieved to < 250 μm, whereas previous research used soil sieved to < 2 mm (e.g.…”

“…However, the current study used soil sieved to < 250 μm, whereas previous research used soil sieved to < 2 mm (e.g. Feeney et al ., ; Helliwell et al ., ; Koebernick et al ., ). Our smaller particle size and the resulting packing condition produced a soil environment more typical of intra‐aggregate structure.…”

“…Individual syringe barrels were clustered in groups of seven and connected to a three‐dimensional (3D) printed seedling assembly as described in Koebernick et al . (). This housed a larger compartment of soil where the seed was planted, with an array of small funnels at the base that directed growing roots into the connected syringe barrels.…”

“…The greatest porosity gradient was observed in the youngest roots and it decreased with root maturation. Similar observations were made in an experiment comparing the rhizosphere soil structure of a root hair‐deficient barley mutant with its wildtype parent (Koebernick et al ., ). While the hairless mutant exhibited decreased air‐filled porosity at the soil–root interface, wildtype roots showed a significantly greater air‐filled porosity at the immediate root surface.…”

Plant roots redesign the rhizosphere to alter the three‐dimensional physical architecture and water dynamics

“…(), who observed limited root hairs in 3D soil volumes using μCT; Koebernick et al . (), who observed the impact of root hairs on rhizosphere soil structure formation; and MacFall et al . (), who observed spatially heterogeneous water uptake around a single root using MRI.…”