Comparison of Psychrometric and Pressure Chamber Techniques for Measurement of Leaf Water Potential

Some commercially made psychrometer chambers for in situ leaf water potential measurements have been evaluated under controlled environmental conditions during the continuous desiccation of sunflower plants in pots. Results have been compared with pressure chamber measure ments. Results indicated that at high soil-water potentials, ψ_ws, the leaf water potential, ψ_wl, was more negative than the xylem sap potential, ψ_wx, but as the soil-water potential decreased, ψ_wx became more negative than ψ_wl. Whereas data obtained with the thermocouple psychrometers are not reproducible under different conditions, the pressure chamber gives fairly consistent results.