Guttation
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Guttation on a strawberry leaf |
Guttation is the appearance of drops of
xylem sap on the tips or edges of leaves of some
vascular plants, such as
grasses.
At night,
transpiration usually does not occur because most plants have their stomata closed at night. When there is a high soil
moisture level, water will enter plant roots at night because the
water potential of the roots is lower than in the soil solution. The water will accumulate in the plant creating a slight
root pressure. The root pressure forces some water to exude through special
leaf tip or edge structures,
hydathodes, forming drops. Root pressure provides the impetus for this flow, rather than
transpirational pull.
Guttation fluid may contain a variety of organic compounds, mainly sugars, and mineral nutrients, mainly potassium.
[Goatley, J.L. and Lewis, R.W. 1966. Composition of guttation fluid from rye, wheat, and barley Seedlings. Plant Physiology 41: 373-375. [1]] On drying, a white crust remains on the leaf surface.
Guttation is not to be confused with
dew, which condenses from the atmosphere onto the plant surface.
