Root hairs are the most important root trait for rhizosheath formation of barley (Hordeum vulgare), maize (Zea mays) and Lotus japonicus (Gifu)

Abstract

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.

A soil-binding polysaccharide complex released from root hairs functions in rhizosheath formation

“…The role of root hairs in rhizosheath development is well documented, even if the effects of root hair density and length vary between species (Haling et al 2013;Pang et al 2017;Brown et al 2017). While the brb barley genotype morphologically compensated for its lack of root hairs by having greater root mass (Dodd and Diatloff 2016) and length (Burak et al 2021; Fig. 1B here) than the WT, rhizosheath development was still limited with approximately 5-fold less rhizosheath mass per unit root length (Fig.…”

“…2). In contrast, whole root (unfractionated) exudates from brb showed greater soil binding than the WT in the nitrocellulose-based assay (Burak et al 2021). Since low molecular weight metabolites are also likely to contribute to adhesiveness of exudates and can have differing impacts (Naveed et al, 2017), further work is needed to disentangle the contributions of different root exudate fractions to soil-binding.…”

“…Moreover, while root hair length is strongly positively correlated with rhizosheath weight in wheat (Delhaize et al 2012) weaker relationships are detected in other species such as barley (George et al 2014). Limited rhizosheath formation (rather than a complete absence of the rhizosheath) even in root hairless mutants suggests that adhesive factors can also be released from, and/or presented at the surface of, non-root hair cells (Burak et al 2021).…”

“…Previous research has utilised this mutant to study rhizosheath formation, root carbon efflux, nutrient uptake, plant growth and transpiration (e.g. Gahoonia et al 2001;Dodd and Diatloff, 2016;Pausch et al 2016;Carminati et al 2017;Holz et al 2018;Burak et al 2021). Here we assess the capacity of the two genotypes to form rhizosheaths, in conjunction with carbohydrate analyses and glycan antibody-based analyses of released and root-surface polysaccharides.…”

Development of Mechanical Soil Stability In An Initial Homogeneous Loam And Sand Under In-Situ Field Conditions

“…Furthermore, former root channels constitute an important root growth pathway in soil layers with a high mechanical impedance (Han et al, 2015). Both root exudates (Burak et al, 2021, Galloway et al, 2020 and existence of root hairs (Carminati et al, 2017) contribute to the formation of a rhizosheath, which in turn can strengthen soil structure (Wang et al, 2017) and affect both porosity and connectivity of the surrounding pores (Koebernick et al, 2017). In the light of these processes plant growth affects soil structure formation and stabilization by a wide range of interacting mechanisms, which in turn ultimately in uences soil mechanical parameters.…”