Background and aims Rhizosheaths are defined as the soil adhering to the root system after it is extracted from the ground. Root hairs and mucilage (root exudates) are key root traits involved in rhizosheath formation but to better understand the mechanisms involved, their relative contribution should be distinguished. Methods The ability of three species [barley (Hordeum vulgare L.), maize (Zea mays L.), and Lotus japonicus (Gifu)] to form a rhizosheath in a sandy loam soil was compared to their root hairless mutants [bald root barley (brb), maize root hairless 3 (rth3), and root hairless 1 (Ljrhl1)]. Root hair traits (length and density) of wildtype (WT) barley and maize were compared along with exudate adhesiveness of both barley and maize genotypes. Furthermore, root hair traits and exudate adhesiveness from different root types (axile versus lateral) were compared within the cereal species. Key results Per unit root length, rhizosheath size diminished in the order of barley > L. japonicus > maize in WT plants. Root hairs significantly increased rhizosheath formation of all species (3.9fold, 3.2fold, and 1.8fold for barley, L. japonicus, and maize respectively) but there was no consistent genotypic effect on exudate adhesiveness in the cereals. While brb exudates were more and rth3 exudates were less adhesive than their respective WTs, maize rth3 bound more soil than barley brb. Although both maize genotypes produced significantly more adhesive exudate than the barley genotypes, root hair development of WT barley was more extensive than WT maize. Thus, the greater density of longer root hairs in WT barley bound more soil than WT maize. Root type didn’t seem to affect rhizosheath formation, unless these types differed in root length. Conclusions When root hairs were present, greater root hair development better facilitated rhizosheath formation than root exudate adhesiveness. However, when root hairs were absent, root exudate adhesiveness was a more dominant trait.

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Although plant canopies are widely recognized to protect the soil and help mitigate soil erosion, recent research has shown that the majority of soil scour prevention can be attributed to the roots. Because roots are more difficult and time‐consuming to measure than shoots, research in this area has largely been limited to understanding the influence of large roots and/or whole root systems, and there is little understanding on how smaller root traits, such as root hairs, contribute to the root system's ability to mitigate soil erosion. Therefore, this study subjected a root hairless mutant (brb) of barley (Hordeum vulgare L. cv. Pallas) and its wild‐type (WT) genotype to simulated rainfall. The results showed that increasing root presence significantly reduced soil erosion, but the impact of root hairs was less clear. Soil detachment significantly decreased as root length density increased, with no apparent genotypic difference in this relationship. The brb root systems produced significantly thinner (0.8‐fold) roots and a higher percentage (1.1‐fold) of fine roots, with both traits previously associated with increased ability to mitigate soil erosion. However, brb mesocosms produced a similar quantity of eroded soil to WT mesocosms, suggesting that root hairs in WT plants could have compensated for their root systems' reduced ability to mitigate soil erosion.Highlights It is not known whether root hairs affect a root system's ability to mitigate soil erosion. Soil yield following simulated rainfall was compared for a root hairless mutant (brb) and its WT. Root traits of brb favoured erosion mitigation, but brb and WT mesocosms eroded to the same degree.

Roots reinforce soil by acting as soil pins, dissipating shear stresses and anchoring the soil in place. By protruding into the soil and binding to soil particles, root hairs increase root-soil contact and aid root anchorage. However, it is not yet known whether this ability to anchor roots affects the root system's ability to reinforce soil. Using a laboratory box shearing rig, this study explores whether root hairs affect soil shear resistance. The force required to shear soil columns permeated with roots lacking root hairs (barley brb and maize rth3 mutants) are compared to columns permeated with hairy roots (their respective wild types, WT) using unplanted soil columns as controls. Known root traits (e.g. root length density, root surface area density, average diameter, percentage of fine roots, and root tensile strength) were measured to ensure that differences in shear resistance could be attributed to the presence/absence of root hairs. All rooted columns required more force to shear than their respective unplanted columns but the thicker, stronger maize roots were more effective at soil reinforcement than the more numerous but weaker barley roots. After the maximum growth period, root hairs appeared to have a consistent and significant impact on peak shearing force. However, the WT root systems also produced greater root surface area density. As the rate at which peak shearing force increased with increasing root surface area density was similar for roots with and without root hairs, the increased peak shearing force of the WT columns cannot be attributed to resistance supplied by the presence of root hair but rather to a more prolific root system. Therefore, it was concluded that root diameter and root tensile strength most influenced root reinforcement of soil and as such, the relatively minute root hairs had negligible effects compared to their parent roots.

Root exudates and rhizosheaths of attached soil are important features of growing roots. To elucidate factors involved in rhizosheath formation, wild type (WT) barley (Hordeum vulgare L. cv. Pallas) and a root hairless mutant, bald root barley (brb), were investigated with a combination of physiological, biochemical and immunochemical assays. When grown in soil, WT barley roots bound ∼5-fold more soil than brb per unit root length. High molecular weight (HMW) polysaccharide exudates of brb roots had less soil-binding capacity than those of WT root exudates. Carbohydrate and glycan monoclonal antibody analyses of HMW polysaccharide exudates indicated differing glycan profiles. Relative to WT plants, root exudates of brb had reduced signals for arabinogalactan-protein (AGP), extensin and heteroxylan epitopes. In contrast, the root exudate of 2-week old brb plants contained ∼25-fold more detectable xyloglucan epitope relative to WT. Root system immunoprints confirmed the higher levels of release of the xyloglucan epitope from brb root apices and root axes relative to WT. Epitope detection with anion-exchange chromatography indicated that the increased detection of xyloglucan in brb exudates was due to enhanced abundance of a neutral polymer. Conversely, brb root exudates contained decreased amounts of an acidic polymer, with soil-binding properties, containing the xyloglucan epitope and glycoprotein and heteroxylan epitopes relative to WT. We therefore propose that, in addition to physically structuring soil particles, root hairs facilitate rhizosheath formation by releasing a soil-binding polysaccharide complex.