Formation and Stabilization of Rhizosheaths of Zea mays L. (Effect of Soil Water Content)

Abstract

Field observations have shown that rhizosheaths of grasses formed under dry conditions are larger, more coherent, and more strongly bound to the roots than those formed in wet soils. We have quantified these effects in a model system in which corn (Zea mays 1.) primary roots were grown through a 30-cm-deep prepared soil profile that consisted of a central, horizontal, "dry" (9% water content) or "wet" (20% water content) layer (4 cm thick) sandwiched between damp soil (15-1 7% water cqntent). Rhizosheaths formed in dry layers were 5 times the volume of the subtending root. In wet layers, rhizosheaths were only 1.5 times the root volume. Fractions of the rhizosheath soil were removed from individual roots by three successive treatments; sonication, hot water, and abrasion. Sonication removed 50 and 90% of the soil from rhizosheaths formed in dry and wet soils, respectively. After the heat treatment, 35% of the soil still adhered to those root portions where rhizosheaths had developed in dry soil, compared with 2% where sheaths had formed in wet soil. Root hairs were 4.5 times more abundant and were more distorted on portions of roots from dry layers than from wet layers. Drier soil enhanced adhesiveness of rhizosheath mucilages and stimulated the formation of root hairs; both effects stabilize the rhizosheath. Extensive and stable rhizosheaths may fundion in nutrient acquisition in dry soils.

Surface tension and viscosity of axenic maize and lupin root mucilages

“…Indeed, the largest, most coherent soil ' rhizosheaths' are formed on the roots of grasses in dry soil (Watt, McCully & Canny, 1994). However, sheath formation requires fully hydrated mucilage to permeate the surrounding soil particles which are then bonded to the root and each other as the mucilage dries.…”

How Do Real Roots Work? (Some New Views of Root Structure)

“…Rhizosheath development is the result of an interplay between the plant, the soil, and rhizobacteria, the complexities of which we are just beginning to appreciate. We now know that the aggregation of soil particles in the rhizosheaths is caused partly by the mucilage released from the root cap, together with cap cells that remain alive all along the rhizosheath (Vermeer and McCully, 1982;Watt et al, 1994). These root-cap products, formed as long as the apical meristem remains active (Fig.…”

“…They do not stick to the first centimeter or so of the root, which is covered by a special temporary pellicle layer (Abeysekera and McCully, 1993), but they lodge in the soil and root hair zone. This cap-derived mucilage, together with mucilages from bacteria specific to this region of the root, help to glue the soil to the root (Watt et al, 1994). Root hairs become much distorted in the sheath-forming region, and the soil is anchored at these distortions (Fig.…”

Effect of exo-polysaccharides producing bacterial inoculation on growth of roots of wheat (Triticum aestivum L.) plants grown in a salt-affected soil

“…However, significance and role of roots of the plants in improving fertility and crop productivity of the salt-affected soils have mostly been remained unexplored (Munns, 2002). Most of the nutrients and water taken up by plants are passed through the interfacial region, the rhizosheaths (RS); the soil adhered strictly to the roots of the crop plants (McCully and Canny, 1988;Watt et al, 1994). Intimate association of plant roots to the soil in this region not only enables plants to harness nutrients from the soil but it also provides source of C supply (in the form of root exudates) to the soil microbes that are involved in cycling, mineralization and availability of the soil nutrients to the growing plants (Nannipieri, et al, 2003).…”