If you’ve walked through a meadow just after sunrise, you might have noticed tiny droplets of water arranged in neat lines along the edges of plant leaves. Although they look a bit like dew, these water droplets in fact came out of the plant.
To photosynthesise, plants need water, which they absorb from the soil with their roots, and carbon dioxide, which they take up from the air through tiny leaf pores, called stomata.
Moisture evaporates from the stomata, so plants can close these pores to conserve water at night or during drought. When the stomata are open, water constantly moves through the plant from root to leaf, and this also helps to pull more water into the roots. If the soil is very wet, then water continues to enter the roots by osmosis, even if the stomata are closed. This causes water to build up inside the roots with nowhere to go.
To relieve the pressure, plants perform guttation – they ooze sap through special pores on the edges of the leaf, called hydathodes. Guttation is most common at night or very early in the morning, when the air is cool and moist, and the soil is warm, but it can even happen during the day if the humidity is very high.
The droplets are mostly water, but they may also contain dissolved nutrients, such as salts and sugars. Often, the water droplets will drip from the leaf, but sometimes they evaporate, leaving nutrients behind as a thin white crust.
If the plant has been treated with insecticides, guttation droplets may contain high concentrations of these chemicals, which can kill bees that drink the water. Guttation is generally harmless to the plant, but sometimes, the moisture can create ideal conditions for bacteria and mould to develop.
Read more:
- Why (and how) does dew form?
- Which came first, the plant or the seed?
- Do plants grow better you sing to them?
- Plants let out secret high-pitch screams when stressed
Asked by: Heather Kennedy, via email
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