Water potential

Water potential is the potential energy of water per unit volume as compared to pure water, which allows to predict the direction of water flow. It is represented by the Greek letter Ψ (psi) and is expressed in units of pressure (pressure is a form of energy), which is typically in pascals (Pa).

Definition

Water potential is a measure of the potential energy in water, specifically, water movement between biotic and abiotic factors. It is defined as the difference in potential energy between a given water sample and pure water (at the same temperature and pressure). When all water in a system is free to move, equilibrium will be reached, with water moving from areas of high Ψ to areas of low Ψ.

Components

Water potential has several components: solute potential (also called osmotic potential), pressure potential, and matric potential.

Solute potential

Solute potential, also called osmotic potential, is negative in a plant cell and zero in distilled water. Typical values for cell cytoplasm are -0.5 to -1.0 MPa.

Pressure potential

Pressure potential (Ψp), typically ranges from 0 to 0.6 MPa, but can reach values of 1.0 MPa.

Matric potential

Matric potential arises from the adhesion of water molecules to the walls of the plant cells and other surfaces.

Measurement

Water potential can be measured using a variety of methods, including gravimetric methodologies and the use of a pressure chamber, psychrometer or tensiometer.

Applications

Water potential plays a crucial role in water distribution in the environment, plant water relations, and soil science.

See also

• Soil plant atmosphere continuum
• Transpiration stream
• Cohesion-tension theory
• Osmosis
• Hydrostatic pressure
• Turgor pressure

References

Water potential Resources
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