Plant Water Potential Gradients Measured in the Field by Freezing Point

Abstract

A portable freezing point meter was used in the field to measure the water potential gradients in sunflower (Helianthus annuus), beans (Phaseolus vulgaris), corn (Zea mays), wheat (Tritium aestivum), pumpkin (Cucurbita pepo), potato (Solanam tuberosum), alfalfa (Medicago sativa), and sugarbeets (Beta vulgaris). The measurements were made between daybreak and sunrise, and again during the middle of the afternoon on days when the potential evapotranspiration varied between 6.5 and 8.0 mm of water.The gradients varied from a maximum of 0.2 bar per cm in a wheat, down to an undetectable value for pumpkin. Although most of the soil in the root zone was kept at potentials above -1 bar, the bulk of the root tissue had water potentials of -5 to -10 bars. Differences in water potential between shaded and unshaded leaves, and between leaf tissue and guttation fluid suggested a similar drop of several bars between xylem elements and the surrounding leaf tissue in some plant species. The implications of such drops are discussed with respect to plant water transport equations and pressure cell potential measurements.

Effect of Moisture Stress on Leaf Water Potential and Relative Leaf Water Content in Wheat (Triticum aestivum L.)

“…These include gravimetric techniques to measure leaf water content or saturation deficit (Dedio, 1975), water potential (Sojka et al, 1979;Keim and Kronstad, 1981), water retention (Winter et al, 1988) and other. Nevertheless, leaf water potential have widely and successfully been used to asses the water stress intensity/resistance in different crop species like wheat (Rascio et al, 1987;Entz and Fowler, 1990), rice (O'Toole and Moya, 1977;Tomar and O'Toole, 1982), corn (Cary and Fisher, 1971), alfalfa (Brown and Tanner, 1981), sunflower (Boyer, 1968), sorghum and cotton (Grimes and Yamada, 1982) and different stages of plant growth (Singh et al, 1989). Relative leaf water content is another physiological parameter used by many scientists as a good predictor of drought stress (Schonfeld et al, 1988;Shimshi et al, 1982;.…”

Measurement of Total and Osmotic Potentials in Lucerne and Sunflower Tissues using Thermocouple Psychrometers

“…While measurements of water potential and associated equilibration times have been reported for sunflower leaves (Boyer, 1972), there are no known reports of techniques for water potential measurement applicable to the capitulum and root tissue. Lucerne water potential measurements are sparse, and have been limited to the pressure chamber (Cary and Fisher, 1971;Sheehy et al, 1979;Brown and Tanner, 1983) and leaf dew-point hygrometers (Brown and Tanner, 1981) with no reports of measurement by thermocouple psychrometers. Besides clarifying equilibration times, the importance of a delay between excising the leaf and sealing it in the sample chamber (Walker et al, 1983) was therefore assessed.…”