Electrical resistance measurements of water potential in avocado and white spruce

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Abstract
Simultaneous measurements of electrical resistance (or impedance (Z)) and water potential were made on avocado Persea americana Mill. in the laboratory and on white spruce Picea glauca (Moench) Voss in the field. A significant correlation was found between electrical impedance (corrected to standard temperature of 20.degree. C) and water potential of nearby leaves as measured by either pressure bomb or thermocouple psychrometer. When the resistance measurements were expressed as a percent of the measured maximum resistance reading the correlation with water potential was very nearly linear (correlation coefficient: P. americana Mill., 0.98; P. glauca (Moench) Voss, 0.94). This relationship also seems to hold in Helianthus annuus L. The application of electrical resistance measurement techniques to these 2 plant systems was shown to be a simple, nondestructive method of monitoring the water potential of such systems. The linear correlation between water potential and electrical resistance held whether the technique was applied on a tree at a fixed position through daily cycles, at different positions vertically up a tree, or under various degrees of hydration in a pressure bomb.

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