Measuring the Water Status of Plants and Soils

Abstract

Why measure the water status of plants and soils? A little thermodynamics. The value of thermodynamic equilibrium. Additional readings. Pressure chamber. Principles of the method. Pressure chamber theory. Types of pressure chambers. How to make measurements. Working with plant tissue. Meauring the components of the water potential precautions. Pressure chamber manufacturers. Thermocouple psychrometer. Principles of the method. Theory of psychrometry. How thermocouples work. Tipes of thermocouple psychrometers. How to make measurements. Working with plant tissue. Working with soils. Measuring the components of the water potential. Precaution. Psychrometer manufacturers. Water potentials (osmotic potentials) of sucrose solutions. Pressure probe. Principles of the method. Pressure probe theory. Using the probe. How to make measurements. Precautions. Building a pressure probe. Measuring the water status of plants and soils: some examples. Practical benefits of thermodynamic equilibrium. Large tensions demonstrated in the apoplast. Single cell and tissue measurements compared. Temperature, membrane transport, and cell walls. Importance of growth. Growth-induced water potentials. Growth at low water potentials. Turgor measured with a pressure chamber. Varietal differences in midday water potential under field conditions. Osmotic adjustment. Water relations of reproductive tissues.