Do root hairs of barley and maize roots reinforce soil under shear stress?

Abstract

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.

Direct Shear Strength on the São Francisco River Bank, Northeastern Brazil, With or Without Roots of Different Native Species

“…The premise that roots grow perpendicularly to the shear surface (Burak, Dodd, & Quinton, 2021;Meijer, Muir Wood, Knappett, Bengough, & Liang, 2019) could not be verified. In fact, the presence of roots allows a mobile slice of the sample to easily slide along the root, permitting the shear force to act with no resistance from the soil-soil friction; similar findings were presented by Campagnolo et al (2018); Pollen and Simon (2010).…”

Comparative phenomics of root architecture and anatomy in Phaseolus species

“…Interestingly, the expression of root hair density and length differed between the greenhouse and roll‐ups (Table 1), likely due to both environmental and developmental influences. Although the growth conditions were controlled in each environment, differences in the age of roots as well as other abiotic factors such as nutrient availability, moisture content, and mechanical damage during the washing process may influence root hair phenotypes (Nestler et al., 2016; Burak et al., 2021). Contrastingly, the number of basal roots and whorls were stable between measurements in seedlings and mature plants, and Spearman rank correlations demonstrated that environment did not substantially alter the ranking of basal root number and basal root whorls among entries (Table 1).…”

Options to reduce ranges in critical soil nutrient levels used in fertilizer recommendations by accounting for site conditions and methodology: A review

“…The observed differences in critical soil P levels among crops is not only associated with differences in rooting systems but also in the ability of crops to deal with water and nutrient stresses during the growing season (Brouder and Volenec 2008). Burak et al (2021) found that barley had longer roots than maize; however, the maize had wider roots. Crops with more intensive rooting systems allow therefore lower critical soil nutrient levels than crops where the nutrient uptake is limited by soil diffusion.…”