Understanding the Rhizosheath: Opportunities for Manipulating the Soil Root Interface

Temperate cereals produce a rhizosheath, which is a discrete structure at the root-soil interface consisting of soil particles, root hairs, microorganisms and biological mucilage. The trait was first noted on desert species over 100 years ago and thought to be limited to grass species in the Poales order until recently, when its presence was demonstrated in many orders of flowering plants [Brown et al. (2017) Plant Soil 418:115–128]. Rhizosheath weight can be screened easily and rapidly and has been shown to be related to the ability of plants to tolerate abiotic stresses.

We have demonstrated genotypic variation in this trait in range of crop species, specifically populations of barley. A range of QTLs and candidate genes associated with rhizosheath formation were identified using a population of elite genotypes [George et al. (2014) New Phytologist 203: 195–205]. We will present a validation of these associations in other populations of barley including recombinant chromosome substitution lines and a population of landrace barleys from the highlands and islands of Scotland.

We have also investigated the role of root hair length and mucilage production on rhizosheath formation. We have generated novel insight into the physical conditions at the root soil interface using high resolution synchrotron X-ray tomography [Koebernick et al. (2017) New Phytologist 216: 124–135] and recently performed experiments which will link modifications in the root-soil interface to changes in the microbiome.

Understanding the biophysical nature of the rhizosheath is the first step to engineering the root soil interface and improving our ability to manipulate the function of the rhizosphere. Breeding cereal genotypes for beneficial rhizosheath characteristics is achievable and we have identified potential to do this in many other crop species. Enhancing this trait could contribute to agricultural sustainability in future environments where nutrient availability and water relations may be compromised.