The Meaning of Matric Potential

Abstract

The commonly used equation, Ψ = P - π + τ, which describes the partitioning of plant water potential, ψ, into components of hydrostatic pressure, P, osmotic pressure, π, and matric potential, τ, is misleading. The term τ, which is supposed to show the influence of a solid phase on Ψ, is zero if a consistent definition of pressure is used in the standard thermodynamic derivation. However, it can be usefully defined by τ = Ψ + π<inf>D</inf>, where π<inf>D</inf> is the osmotic pressure of the equilibrium dialysate of the system. The practical and theoretical significance of this definition is discussed.