What is water potential and how do you calculate it? How does it relate to increases and decreases in transpiration?

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jerichorayel eNotes educator| Certified Educator

Water potential is the energy or potential that is a measure of the relative tendency of water molecules to move from one area to another. Water potential, represented by Psi, is caused with certain factors such as osmosis, gravity, pressure, and matrix effects (surface tension/capillary action). This theory is generally useful in understanding the flow of water in living organisms including plants and animals. A practical example is the transpiration happening in the structures of plants which governs the movement of water in the plants. Water potential measures these movements which allow the scientists to study cellular activities. 

Having said that, the over-computation of the water potential is expressed as:

`Psi = Psi_(pi) + Psi_(p)+ Psi_(s)+ Psi_(v)+ Psi_(m) `


`Psi_(pi)` = solute potential

`Psi_(p)` = pressure effects

`Psi_(s)` = gravimetric effects

`Psi_(v)` = potential due to humidity

`Psi_(m)` = matrix potential

Among the Psi values, the most common is the osmotic pressure or the solute potential:

`Psi_(pi) = - MiRT`

M = concentration

i = Van't Hoff factor

R = ideal gas constant

T = temperature (K)

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