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Seasonal Variations in the Proportions of Suberized and Unsuberized Roots of Trees in Relation to the Absorption of Water

Paul J. Kramer and Henry C. Bullock
American Journal of Botany
Vol. 53, No. 2 (Feb., 1966), pp. 200-204
Stable URL: http://www.jstor.org/stable/2440089
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Seasonal Variations in the Proportions of Suberized and Unsuberized Roots of Trees in Relation to the Absorption of Water
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Abstract

Growing root tips usually constituted less than 1 per cent and mycorrhizal roots less than 6 per cent of the total root surface under a 34-year-old pine stand. Growing root tips usually constituted less than 1 per cent of the total root surface under a yellow poplar stand, although one sample taken in May contained 9 per cent of unsuberized roots. The water permeabi ity of various types of roots was measured under a pressure gradient of 31 cm of mercury. It differed widely among individual roots, ranging from an average of 6.6 mm3/cm2/hr for suberized pine roots 1.33 mm in diameter, to 36.6 mm3 for suberized pine roots 3 mm in diameter, and 178 mm3/cm2/hr for unsuberized roots grown in water culture. Water intake through a group of unsuberized roots grown in soil averaged 37.4 mm3/cm2/hr. The permeability of yellow poplar roots varied even more, ranging from essentially zero to 30,000 mm3/cm2/hr. It is concluded that the major part of water absorption in pine occurs through suberized roots, some through mycorrhizal roots, and relatively little through growing root tips. Likewise, in yellow-poplar most of the water probably enters through suberized roots. Further study is needed of the role of suberized roots in water and salt absorption.

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