Introductory Crop Physiology

WATER POTENTIAL

• Every component of a system possesses free energy capable of doing work under constant temperature conditions. For non-electrolytes, free energy / mole is known as chemical potential. With reference to water, the chemical potential of water is called as water potential. The chemical potential is denoted by a Greek letter Psi, ?.
• The water molecules possess free energy and the free energy of pure water is greater than the free energy of other solutions prepared in water. The difference between the free energy of water molecules in pure water and the free energy of water molecules in any other system is termed as water potential.
• For pure water, the water potential is zero (the maximum value). The presence of solute particles will reduce the free energy of water or decrease the water potential. Therefore it is expressed in negative value. The water potential of any solution is always less than zero and hence expressed in negative value. For cell, water potential is determined by three internal factors i.e.
?w:?m + ?s + ?p
• Where, ?m : is the matric potential.
• ?S : solute potential or osmotic potential
• ?p : pressure potential or turgor potential