Chapter 19 - Pressure chambers

Abstract

This chapter tells how to measure plant water potential using pressure chambers. Most pressure chambers are based on a design developed by Scholander at the Scripps Institute of Oceanography in the 1960s. His pressure chamber is described. Measurements made with it are compared to measurements made with thermocouple psychrometers because measurements made with thermocouple psychrometers are the standard ones. They are based on sound physics using the Kelvin equation. One of the first scientists to compare measurements made with the Scholander pressure chamber and thermocouple psychrometers was John Boyer, and his comparisons are presented. Advantages and disadvantages of the Scholander pressure chamber are given. Another method, aside from the Scholander pressure chamber, used to determine water potential with pressure chambers is described. It is the pump-up pressure chamber in which pressure is created by pumping the instrument as one would a bicycle pump. Appendices give biographies of Scholander and Boyer.