2
$\begingroup$

Knowing that guttation occurs through a plant's hydathodes due to root pressure forcing liquid water out of the leaves, I am curious as to why so many small drops of water are observable on plants in the morning. Could this potentially have to do with the moisture in the air at night vs day? Since humidity tends to increase at night?

Thanks in advance!

$\endgroup$
  • $\begingroup$ Perhaps you are thinking of the atmospheric phenomenon called dew, which is not caused by plants, or limited to them: en.wikipedia.org/wiki/Dew $\endgroup$ – jamesqf Apr 12 '18 at 5:55
  • $\begingroup$ I don't think so, these are two different phenomena as guttation is water coming out of the plant while dew is condensation of air on the plant! But perhaps their cause is related. $\endgroup$ – ro_the_electron Apr 12 '18 at 14:45
  • $\begingroup$ I understand the difference. What I'm saying is that dew is a far more likely explanation for those small drops of water you observe, especially if they are on things other than plants. $\endgroup$ – jamesqf Apr 12 '18 at 18:41
  • $\begingroup$ You should add an image if you're trying to convince us that you're talking about guttation vs just dew formation. $\endgroup$ – Graham Chiu Apr 12 '18 at 20:01
  • 1
    $\begingroup$ @jamesqf I know it's just anecdotal evidence, but I have a Monstera deliciosa in my room and I see it guttate way more in the morning, sometimes by night, never by day. In this case, it just cannot be dew. $\endgroup$ – LinuxBlanket Jun 22 '18 at 0:29
1
$\begingroup$

Guttation is commonly seen at night and early morning. Plants release excess of water via the guttation. During day time as the transpiration rate increases, excess of water is released via transpiration and hence guttation decreases. Also due to high temperature these small droplets are quickly evaporated during day time.

$\endgroup$
1
$\begingroup$

A stable mass of air holds, more or less, a fixed amount of water vapor. As the air is cooled it reaches the point where water will begin to condense (form a cloud) - this is the dew point. If this amount of moisture is fixed, the relative humidity (rH) decreases with increasing temperature, meaning the air could hold more water vapor if there were a source for additional water vapor - like from a plant leaf, say.

The relative humidity is generally maximum at night (just before the dawn, to borrow a phrase). Hence little if any moisture evaporates from the leaf.

Plant roots actively load mineral salts into their cells which creates an osmotic potential that draws in water. This can create a 'root pressure' that forces water out vein ends on the edges of a leaf. During day time, the relative humidity is generally low and any water presented as guttation evaporates before it is easily noticeable. At night and early morning, the relative humidity tends to be close to the dew point, so the guttation doesn't readily evaporate.

There is a bit more to this in terms of movement of water thru the xylem and how this reduces the 'root pressure' seen at the leaf edges when the stomata are open. Stomata tend to be closed at night (when it is dark), so there is very little or no transpiration occuring at night (independent of rH) - hence root pressure is 'fully' expressed at the leaf margins --> guttation possible.

$\endgroup$
-1
$\begingroup$

The stomata are mostly closed at night and early morning. Early morning rising temperatures cause efflux of H2O from the hydathodes while stomata are still closed, and by the time the stomata are opened, the efflux switches to the shorter route through the stomata.

$\endgroup$
  • $\begingroup$ Hello! I fear that your answer isn't really different from the Jim Young one, and, as such, it may attract downvotes. If you like it (as it seems) go upvote it :) and elaborate on something that has not already covered by existing answers (for instance none of the answers provide references). $\endgroup$ – LinuxBlanket Jun 22 '18 at 8:19

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.