| MadSci Network: Botany |
Gravitational potential becomes of some significance in tall plants, such as trees. The gravitiational potential increases about 0.1 MegaPascal per 10 meters in height. Usually the soil surface is the reference point or zero height. If the water potential was only due to the gravitational potential, water at the top of a tall tree would spontaneously move downward because the gravitational potential is lower at lower levels in the tree. Water flows spontaneously from high to low (more negative) water potentials. Trees can overcome the higher gravitational potentials at the top of the tree by making their osmotic potential more negative. For more information, search google.com for gravitational potential or check a plant physiology text such as Taiz and Zeiger (1998). There are many websites that discuss plant water potential terminology. It can be confusing. One common error is saying that water potential is increasing when it is becoming more negative, e.g. water potential going from -1 to -2 MPa. When water potential becomes more negative, it is decreasing. References How Water Climbs to the Top of a 112 m-tall Tree Plant water potential terminology Taiz, L. and Zeiger, E. 1998. Plant Physiology. Sunderland, MA: Sinauer Associates.
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