Pressure chamber procedures for leaf water potential measurements of cotton

Summary Measurement of leaf water potential ( _l ) with a pressure chamber is usually regarded as a reliable and practical field technique. However, recent evidence indicates that results depend on the measurement techniques employed. Field experiments were conducted to identify the magnitude and sources of error affecting pressure chamber measurements of _l in cotton (Gossypium hirsutum L.) and to develop an accurate and operationally flexible procedure. Water potential of bare cotton leaves was about 0.2 MPa less than aluminum foil wrapped leaves when the elapsed time between excision to chamber pressurization was less than 30 s. The water potential of intact leaves increased 0.3 MPa after 15 s of enclosure in aluminum foil. 5 to 30 min of enclosure were sufficient to reach equilibrium between _l and water potential within the plant stem. Aluminum foil wrapped leaves maintained their _l for 2 h stored in a humid, dark box at 21–28 °C while wet wrapped (cheesecloth) or bare leaf _l increased after one hour because of hydration. An accurate and operationally flexible _l measurement procedure, suitable for large scale sampling, was defined.Contribution from the USDA-ARS, Water Management Research Laboratory, 2021 S. Peach, Fresno, CA 93727 and the Dept. of Land, Air and Water Resources, University of California, Davis, CA 95616, USA