Guttation: Definition & Mechanism

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  • 0:04 A Brief Overview of Guttation
  • 1:09 Guttation Versus Transpiration
  • 1:49 Hydathodes and Stomata
  • 2:35 The Guttation Process
  • 3:25 Lesson Summary
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Instructor: Bryan Cowing

Bryan is a freelance writer who specializes in literature. He has worked as an English instructor, editor and writer for the past 10 years.

What exactly is guttation? How does it happen and how is it different from transpiration? If you are curious about these questions and want to get to the root of this process, read on.

A Brief Overview of Guttation

It may be easy to look at a plant and assume that it works simply. The plant takes in water and uses photosynthesis to grow. While this is true, plants also have a secret life where their survival depends on the balance of water and nutrients. One way that plants can balance the amount of water they take in is by a process called guttation.

Guttation is when water is secreted from the tips of the leaves of plants. Guttation happens in certain plants that have vascular systems, such as grass, wheat, barley, tomatoes, strawberries, and other small plants. Since guttation relies on pressure, it can't occur in large plants, such as trees, because the pressure required to force the water out is too large.

Guttation happens at night when the soil is very moist and the roots absorb water. If there is too much water, root pressure causes the water to squeeze out of the plant and onto the tips of the leaves or the blades of the plant. As water from soil passes through the guttation process, it picks up minerals, enzymes and other chemicals and is called xylem sap.

Guttation on a strawberry leaf
Guttation

Guttation Versus Transpiration

Since water is vital for plants, many of the fancy words relating to plants have to do with water. Guttation and transpiration are two such words. Fortunately, there are some major differences that can help you differentiate between the two.

  • Guttation happens when the stomata are closed, and transpiration happens when they are open.
  • Therefore, guttation happens at night or in the early morning when it is cold and humid. Transpiration, on the other hand, happens during the day and usually when there's dry heat.
  • In transpiration_, water is pushed out in the form of vapor, while in guttation, it's secreted as water or xylem sap.

Hydathodes and Stomata

The reason that guttation happens at night (unlike transpiration) is that transpiration relies on the stomata. Stomata are pores found on the surface of leaves. Plants also use stomata for photosynthesis, and since photosynthesis doesn't happen at night (it can't happen without the sun, after all), the stomata close shop. Once these go night-night, the plant may still need to get rid of excess water. In order to do this, the plant pushes the water out through a different exit called hydathodes.

Hydathodes are a lot like stomata except they can't actually open and close like stomata can. Hydathodes are sometimes called water stomata, but they're more like a pore. They simply allow water to slowly secrete from the plant.

Diagram showing hydathodes, labeled WP (water pores)
guttation diagram

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