Q.6:- Briefly describe water potential. What are the factors affecting it?
The term water potential was first used by Slatyer and Taylor (1960). The free energy per mole of any particular chemical species in a multicomponent system is defined as the chemical potential of that species. The chemical potential of water is referred to as the water potential (ψw). Since the ψ of pure water is zero (0), the presence of solute particles reduces the free energy of water, thus decreases the water potential (negative value). Therefore,ψ of solution is always less than zero or its highest value is zero.
For solutions water potential is determined by three internal factors, i.e.,ψw = ψm + ψs + ψp (where ψm is matric potential which is used for the surface such as soil particles or cell wall to which water molecules are absorbed, ψsis solute potential, also called osmotic potential, the amount by which water potential is reduced and ψp is pressure potential such as TP and WP). Since in plant system ψm is disregarded the equation may be simplified as :
ψw = ψs + ψp