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Axial Resistance to Water Flow of Intact Cotton Taproots
Author(s) -
Yamauchi Akira,
Taylor Howard M.,
Upchurch Dan R.,
McMichael Bobbie L.
Publication year - 1995
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1995.00021962008700030009x
Subject(s) - xylem , taproot , hagen–poiseuille equation , water flow , water transport , chemistry , botany , soil science , flow (mathematics) , environmental science , mathematics , biology , geometry
Abstract A knowledge of root hydraulic resistance is required for the application of water flow models of the plant‐soil system. An attempt was made to estimate axial resistance of intact cotton ( Gossypium hirsutum L. cv. Tamcot CAMD‐E 107‐5A) taproots to water flow by direct and simultaneous measurement of water flow rate and of the gradient in xylem water potential. Fiscus's root psychrometer was modified and used for the measurement of xylem water potential. The measurements were made in rigidly controlled, constant temperature environments, and under conditions in which no water was available for the portion of the taproot where xylem water potential gradient was measured, but water was available distal to that portion. The water uptake rate was simultaneously measured while water was supplied at a constant head. Axial resistance to water flow along a cotton taproot of 70‐ to 120‐d‐old plants was on the order of 1 mg −1 water m −1 root s MPa, which is near the lower limit of published values for cotton and other species. Axial resistance was also calculated from the measured xylem vessel diameters based on the Poiseuille‐Hagen equation. Measured axial resistance values were ≈ 20 times those calculated using the Poiseuille‐Hagen equation. It required as long as 34 d for the water potential inside the psychrometer chamber to equilibrate with that of the root xylem. Drying the root substantially increased the radial resistance and thereby increased the time required for equilibration. Modifications to the described experimental apparatus and procedure will be required.