# Why do aquatic plants fold their leaves up at night?



## Zolek (Jul 25, 2007)

Time for a curiosity based question.

Land plants sometimes fold their leaves up to reduce night time water loss. Obviously underwater this shouldn't apply. Since many aquatic plants that show this behavior have different immersed and submersed leaves it can't be explained away as a vestigial immersed growth adaptation.

So my question is: Why do full aquatic plants fold up their leaves at night? How is it adaptive?


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## frogmanjared (Feb 21, 2008)

Which aquatic plants are you talking about? Aquatic plants have more physiological problems to deal with than terrestrial plants... flooding, drought, and nutrients. Maybe its a mechanism to minimize losing salts/minerals, biggest issue for freshwater plants.


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## kingfisherfleshy (Jun 4, 2010)

I have always wondered about this as well. Its most evident with stem plants I feel. My wisteria folds up almost completely at night.


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## mistergreen (Dec 9, 2006)

A lot of the plants we grow underwater will grow on land too.... Maybe it's a mechanism to save water that doesn't go away whether it's growing on land or in the water.


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## deleted_user_7 (Jul 7, 2003)

They fold their leaves out and extend them during the day, and at night there is no sunlight so they fold them back up.


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## IWANNAGOFAST (Jan 14, 2008)

In my plant ecology class, we learned that plants that are in high sun high heat areas will grow their leaves more vertically to reduce the surface area that is hit by the sun and thus reducing the amount of evaporation of water from their leaves. The plants growing in shady areas will have horizontal leaf growth to maximize the light uptake. 

however, this doesn't really explain why the leaves on my stem plants fold up at night vs the day. Maybe at night they fold up to increase the flow around them so that they can have a maximized O2 uptake. 

Guess I should've been paying more attention in class rather then trying to seduce the TA...


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## deleted_user_7 (Jul 7, 2003)

But with the leaves overlapping like that, they wouldn't be maximizing the surface area. It would be maximized by staying expanded.


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## GitMoe (Aug 30, 2010)

I don't have an answer or know anything about this topic but I like this thread. Subscribed to hear an answer. Science rules...


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## IWANNAGOFAST (Jan 14, 2008)

maybe it's just a way of messing with us


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## Sharkfood (May 2, 2010)

Could be a function of growth. Most plants have their growth inhibited during photosynthesis, so the underside of the leaf will grow faster than the top, folding it upwards. I've noticed in most plants the tops are the only part that fold up, which generally is made up of newer leaves which may still be growing. This inhibition is the mechanism by which plants "grow toward the light". At the end of the day, the plants have been under light for a long time and have grown so that they are closed up. I've noticed my plants are "open" in the morning even though my lights don't come on until 5 hours after I leave for work.

This is just a guess. I'm not really sure, but it's my story and I'm sticking to it.


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## Zolek (Jul 25, 2007)

I'll make this about a specific plant since that will rule out a lot of theories.

*Myriophyllum Mattogrossense*

In my tank these plants remain open the entire light period, then close up just after dark, then reopen before the lights come on. Thus we can rule out the growing toward the light theory for this plant as it folds and unfolds in complete darkness.

This plant has a submerged leaf form, therefore we can eliminate the folding as a vestigial property of immersed leaves.

Open:










Closed:










I really feel like there has to be some sort of alternate explanation. Protection from predation maybe?


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## wearsbunnyslippers (Dec 6, 2007)

its called nyctinasty, there have been loads of theories, even from people like darwin.

its not due to growth being faster as sharkfood mentioned as then they wouldnt open and close. at the base of every leaf there are hinge-like structures called pulvini, these contain large, water-filled cells. the water in these cells can be pumped in or out of the pulvini, resulting in changes in turgor pressure. as pressure decreases, the pulvini act like a hinge, allowing the leaf to droop, as pressure is increased, the leaf returns to its daytime position. it seems reversed in aquatic plants, that close up for the night...

no one can seem to come up with a concrete reason, except as zolek mentioned to save water. 

things keep vestigial traits even when the are no longer necessary, like whales still have hind legs under their skin, and we still have a tail - coxyx  so you will probably only find this trait in plants that do have an emersed form, even though they have a completely different immersed leaf structure, it is still the same plant at the end of the day...


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## frogmanjared (Feb 21, 2008)

wearsbunnyslippers said:


> no one can seem to come up with a concrete reason, except as zolek mentioned to save water.


I would argue just the opposite, to stop water retention... remember osmosis? The plants have a higher concentration of solutes in their cells, so water will try to get into the plant, they don't have to be concerned about losing water, rather losing salts/minerals is a major concern.


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## spdskr (Nov 14, 2005)

wearsbunnyslippers said:


> so you will probably only find this trait in plants that do have an emersed form, even though they have a completely different immersed leaf structure, it is still the same plant at the end of the day...


Actually, my Cabomba also does this. Not sure this plant occurs in an immersed form.


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## cah925 (May 18, 2007)

How about night time respiration producing CO2 (a gas) or left over O2 from daily transpiration? The stomates of the leaves are closed at night, thereby trapping most of the gas. The gas is lighter than water and tries to float. The stem/roots hold the plant down, but the leaves still bend upward.


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## wearsbunnyslippers (Dec 6, 2007)

cah925 said:


> How about night time respiration producing CO2 (a gas) or left over O2 from daily transpiration? The stomates of the leaves are closed at night, thereby trapping most of the gas. The gas is lighter than water and tries to float. The stem/roots hold the plant down, but the leaves still bend upward.


that sounds plausible, but, you ever notice bubble streaming from a damaged leaf? the leaves have loads of gas in them already... so dont see why they would only float upward at night.


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## mistergreen (Dec 9, 2006)

frogmanjared said:


> I would argue just the opposite, to stop water retention... remember osmosis? The plants have a higher concentration of solutes in their cells, so water will try to get into the plant, they don't have to be concerned about losing water, rather losing salts/minerals is a major concern.


terrestrial plants lose water through evaporation... 

I'll check tonight to see if my emersed aquatics close up.


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## frogmanjared (Feb 21, 2008)

mistergreen said:


> terrestrial plants lose water through evaporation...
> 
> I'll check tonight to see if my emersed aquatics close up.


Right, I wasn't mentioning terrestrial plants though.


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## Axelrodi202 (Jul 29, 2008)

I don't think my emersed plants close up. Their leaves look the same when I turn on the light in the morning as they do when I turn it off at night.


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## plantbrain (Dec 15, 2003)

wearsbunnyslippers said:


> that sounds plausible, but, you ever notice bubble streaming from a damaged leaf? the leaves have loads of gas in them already... so dont see why they would only float upward at night.


Most true aquatics lack stomata, little need.
Some retain them, but they are non functional.

Milfoils are only 2-3 cells thick with the leaves, no cuticle.

Mechanical stress to the plants can be strong in some cases, lots of critters come out at night that may harm fully extended leaves, also, it might aid in better light within canopies so the plants can detect their canopy architecture.

Wind often increases in the afternoon in many locations, so the higher current energy might play a role.

No need to try and catch more light also, but also, it does allow the water to flow better and refill the surrounding region with fresh nutrients, CO2 vs fully extended plants..........which severely reduces flow and exchange. It may also reduce O2 and nutrient loss as well.

This occurs mostly in fast growing weedy stem plants, few others show this trait. 

I think the reasons are similar to land plants overall.
Aquatics do have some water transport, highly reduced, but they still have some.

See Ole Petereson's papers on that topic.



Regards, 
Tom Barr


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## spdskr (Nov 14, 2005)

Thanks for the valuable information Tom.


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## plantbrain (Dec 15, 2003)

I do not know, it's nothing more than speculation.
Why do we sleep at night?


Regards, 
Tom Barr


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## spdskr (Nov 14, 2005)

All those assertations certainly seem plausable. I was also thinking it could be a means of protecting the growth point of the plant when leaves didn't need to be extended for photosynthesis.


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## Sharkfood (May 2, 2010)

Just out of curiosity, has anyone ever heard of the "sensitive plant"? Supposedly it folds up its leaves if you touch it.


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## thrak76 (Aug 3, 2009)

I had this discussion a couple months ago, too.

http://www.plantedtank.net/forums/g...sion/112088-about-tips-plants-closing-up.html


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## chad320 (Mar 7, 2010)

Thats a good link as well as the Barr report one in there.


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## frogmanjared (Feb 21, 2008)

Sharkfood said:


> Just out of curiosity, has anyone ever heard of the "sensitive plant"? Supposedly it folds up its leaves if you touch it.


 Sensitive ferns are awesome! Not as fast of a reaction as you'd think though, and it takes a while to reset.


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## JMN16150 (Jul 21, 2012)

Commencing thread revival!
MY nymphaea, limnophila, and rotalas do this too.


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## Ras (Nov 7, 2013)

i wondered this too
I always assumed that since a leaf is pretty comparable to solar panels, then why leave your very expensive and important equipment out in the open where it could get stolen(eaten)? Especially if it isnt being used? Might as well pack it up right?

there is a plant I have been growing for a few years called mimosa pudica "sensitive plant" and it folds its leaves up anytime something comes in contact with it, its assumed it does this to protect it from being eaten, rain damage, etc. basically a tactic to reduce physical damage, maybe it is something similar with aquatic plants 
and like 2 other people said in this thread
1 its most evident in stem plants
2 most aquatic plants can grow terrestrially 

and if im not mistaken aren't most stem plants more often found growing emerged rather than submerged 
thats always been the case when I go hunting for native aquatic ludwigia, mainly L. palustrus, its always chillin on the side of the river or rain pond
it could be them carrying this terrestrial trait over into the aquatic life


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## Italionstallion888 (Jun 29, 2013)

My stargrass, red rubin, and corymbosa do this. My light goes off at 9pm, by 8:45 they are starting to close up. Not just the top of the stems but the entire stem closes up. Pretty neat.


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## lochaber (Jan 23, 2012)

Sharkfood said:


> Just out of curiosity, has anyone ever heard of the "sensitive plant"? Supposedly it folds up its leaves if you touch it.


I can't remember where, but I used to see this stuff growing wild on roadsides and such. Small, creeping/viney type groundcover, used to sweep my foot across an area and watch the whole ground change color as the leaves folded up. Might of been in Okinawa, not certain though.


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## plantbrain (Dec 15, 2003)

In aquatic macrophytes:

1.
Reduces mechanical stress. Most aquatic plants are very flimsy. They minimize the structural biomass and are honeycombed. This way they can grow straight towards the light rapidly and get to the surface(lots of light and CO2/O2).
They do not need support like terrestrial plants, due to water buoyancy.
Many fine needle plants that do this live in the wave zones or in moving waters. 

2. Prevent snails and other herbivores from eating the tender high value nutrient part of the plant at night when many are active. 

3. Increases flow around the plants when the sun is gone helping growth and O2. 

4. Likely makes it harder for epiphytes to grow on the leaves.


So there's 4 off the top of my head.


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## AirstoND (Jun 17, 2011)

lochaber said:


> I can't remember where, but I used to see this stuff growing wild on roadsides and such. Small, creeping/viney type groundcover, used to sweep my foot across an area and watch the whole ground change color as the leaves folded up. Might of been in Okinawa, not certain though.


http://en.wikipedia.org/wiki/File:Mimosa_Pudica.gif


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