PLANT PHYSIOLOGY , Vol 106, Issue 1 179-186, Copyright © 1994 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Formation and Stabilization of Rhizosheaths of Zea mays L. (Effect of Soil Water Content)
M. Watt, M. E. McCully and M. J. Canny
Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, Canada K1S 5B6
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 L.) 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 (15-17% water content). 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 function
in nutrient acquisition in dry soils.
