06 Plant Water Relation - part 05 - Water Potential

06 Plant Water Relation - part 05 - Water Potential


Water Potential :[ ψ] 
  • According to the principle of thermodynamics, every component of a system is having a definite amount of free energy which is used to do work. 
  • Osmotic movement of water is on the basis of free energy. 
  • Free energy per molecule in a chemical system, is called its chemical potential. 
  • Chemical potential of water is called water potential. It is represented by Greek letter psi (ψ). 
  • Water potential of protoplasm is equal but opposite in sign to DPD It has negative value. 
  • The unit of measurement is in bars/ pascals/ atmospheres. 
  • Water potential of pure water is always zero. 
  • Addition of any solute in it, decreases its psi (ψ) value. Therefore, it has negative value. 
  • D. P. D. is now termed as water potential. 
  • O. P. is now termed as osmotic potential. 
  • T. P. is now termed as pressure potential. It has always positive value. 
  • Water always flows from less negative potential to more negative water potential (i.e. from high water potential area to low water potential area).
  • Difference between water potential of the adjacent cells decides movement of water through plasmodesmata across the cells.
 Factors affecting water absorption: 
  1. Presence of capillary water is essential. 
  2. Rate of water absorption is maximum at soil temperature between 200 to 300C. 
  3. High concentration of solutes in soil waterreduced the rate of absorption of water.
  4. Poorly aerated soil shows poor absorption rate.
  5. Increased transpiration accelarates the rate of absorption of water in the irrigated soil.

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