Guttation

Guttation

Guttation is the "oozing out" or exuding of drops of water on the tips or edges of leaves of some vascular plants. An example of guttation is visible in the figure below.

Guttation in plant leaves

Below is an explanation of how guttation occurs:

• At night, when it is dark, less transpiration occurs since the stomata are closed.
• When soil moisture is very high, water will enter the plant roots because the water potential of the roots is lower than that of the surrounding soil.
• Thus, water accumulates in the plant, resulting in root pressure.
• The root pressure forces some water to exit the leaf tip or edge structures called hydathodes or water glands, forming drops.
• Root pressure is what drives the flow of water out of the plant leaves, rather than transpirational pull.

For guttation to occur there must be a high water content in the soil to create the root pressure. The transpiration rate must be slow in order for the root pressure to be higher than the transpirational pull. Guttation must not be confused with transpiration. The table below highlights the differences between guttation and transpiration.

Table comparing guttation and transpiration