Abstract
Water movement between roots and soil can be limited by incomplete root–soil contact, such as that caused by air gaps due to root shrinkage, and can also be influenced by rhizosheaths, composed of soil particles bound together by root exudates and root hairs. The possible occurrence of air gaps between the roots and the soil and their consequences for the hydraulic conductivity of the root–soil pathway were therefore investigated for the cactus t Opuntia ficus-indica, which has two distinct root regions: a younger, distal region where rhizosheaths occur, and an older, proximal region where roots are bare. Resin-embedded sections of roots in soil were examined microscopically to determine root–soil contact for container-grown plants kept moist for 21 days, kept moist and vibrated to eliminate air gaps, droughted for 21 days, or droughted and vibrated. During drought, roots shrank radially by 30% and root–soil contact in the bare root region of nonvibrated containers was reduced from 81% to 31%. For the sheathed region, the hydraulic conductivity of the rhizosheath was the least limiting factor and the root hydraulic conductivity was the most limiting; for the bare root region, the hydraulic conductivity of the soil was the least limiting factor and the hydraulic conductivity of the root–soil air gap was the most limiting. The rhizosheath, by virtually eliminating root–soil air gaps, facilitated water uptake in moist soil. In the bare root region, the extremely low hydraulic conductivity of the root–soil air gap during drought helped limit water loss from roots to a drier soil.
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References
Bristow C E, Campbell G S, Wullstein L H and Neilson R 1985 Water uptake and storage by rhizosheaths of Oryzopsis hymenoides: a numerical simulation. Physiol. Plant. 65, 228–232.
Caldwell M M 1976 Root extension and water absorption. In Water and Plant Life. Problems and Modern Approaches. Ecological Studies, Volume 19. Eds. O L Lange, L Kappen and E-D Schulze. pp 63–85. Springer-Verlag, Berlin.
Caldwell M M and Richards J H 1989 Hydraulic lift: water efflux from upper roots improves effectiveness of water uptake by deep roots. Oecologia 79, 1–5.
Faiz SMA and Weatherley P E 1982 Root contraction in transpiring plants. New Phytol. 92, 333–343.
Fernández C J and McCree K J 1991 Simulation model for studying dynamics of water flow and water status in plants. Crop Sci. 31, 391–398.
Herkelrath W N, Miller E E and Gardner W R 1977 Water uptake by plants: II. The root contact model. Soil Sci. Soc. Am. J. 41, 1039–1043.
Huang, B, North G B and Nobel P S 1993 Soil sheaths, photosynthate distribution to roots, and rhizosphere water relations for Opuntia ficus-indica. Int. J. Plant Sci. 154, 425–431.
Huck M G, Klepper B and Taylor H M 1970 Diurnal variations in root diameter. Plant Physiol. 45, 529–530.
Kooistra M J, Schoonderbeek D, Boone F R, Veen B W and Van Noordwijk M 1992 Root-soil contact of maize, as measured by a thin-section technique II. Effects of soil compaction. Plant Soil 139, 119–129.
McCully M E 1995 Water efflux from the surface of field-grown grass roots. Observations by cryo-scanning electronmicroscopy. Physiol. Plant. 95, 217–224.
McCully M E and Canny M J 1988 Pathways and processes of water and nutrient movement in roots. Plant Soil 111, 159–170.
Moran C J, McBratney A B and Koppi A J 1989 A rapid method for analysis of soil macropore structure. I. Specimen preparation and digital binary image production. Soil Sci. Soc. Am. J. 53, 921–928.
Nobel P S and Cui M 1992a Shrinkage of attached roots of Opuntia ficus-indica in response to lowered water potentials–predicted consequences for water uptake or loss to soil. Ann. Bot. 70, 485–491.
Nobel P S and Cui M 1992b Prediction and measurement of gap water vapor conductance for roots located concentrically and eccentrically in air gaps. Plant Soil 145, 157–166.
North G B and Nobel P S 1992 Drought-induced changes in hydraulic conductivity and structure in roots of Ferocactus acanthodes and Opuntia ficus-indica. New Phytol. 120, 9–19.
North G B and Nobel P S 1994 Changes in root hydraulic conductivity for two tropical epiphytic cacti as soil moisture varies. Am. J. Bot. 81, 46–53.
North G B and Nobel P S 1996 Radial hydraulic conductivity of individual root tissues of Opuntia ficus-indica (L.) Miller as soil moisture varies. Ann. Bot. 77, 133–142.
North G B and Nobel P S 1997 Root–soil contact for the desert succulent Agave deserti Engelm. in wet and drying soil. New Phytol. 135, 21–29.
Nye P H 1994 The effect of root shrinkage on soil water inflow. Phil. Trans. R. Soc. London, Ser. B. 345, 395–402.
Veen B W, Van Noordwijk M, de Willigen P, Boone F R and Kooistra M J 1992 Root-soil contact of maize, as measured by a thin-section technique III. Effects on shoot growth, nitrate and water uptake efficiency. Plant Soil 139, 131–138.
Wang N, Zhang H and Nobel P S 1997 Phloem-xylem water flow in developing cladodes of Opuntia ficus-indica during sink-to source transition. J. Exp. Bot. (In press).
Wang X-L, Canny M J and McCully M E 1991 The water status of the roots of soil-grown maize in relation to the maturity of their xylem. Physiol. Plant. 82, 157–162.
Wullstein L H, Bruening M L and Bollen WB 1979 Nitrogen fixation associated with sand grain root sheaths (rhizosheaths) of certain xeric grasses. Physiol. Plant. 46, 1–4.
Young IM 1995 Variation in moisture contents between bulk soil and the rhizosheath of wheat (Triticum aestivum L. cv. Wembley). New Phytol. 130, 135–139.
Young D R and Nobel P S 1986 Predictions of soil-water potentials in the north-western Sonoran Desert. J. Ecol. 74, 143–154.
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North, G.B., Nobel, P.S. Drought-induced changes in soil contact and hydraulic conductivity for roots of Opuntia ficus-indica with and without rhizosheaths. Plant and Soil 191, 249–258 (1997). https://doi.org/10.1023/A:1004213728734
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DOI: https://doi.org/10.1023/A:1004213728734