Negative water vapor feedback in plant evapotranspiration found

Rising CO2 is causing plants to release less water to the atmosphere, researchers say

Stomata are structures that allow plants to exchange gases with the air. Contemporary plants in Florida have fewer stomata than their ancestors did a few decades ago.

BLOOMINGTON, Ind. — As carbon dioxide levels have risen during the last 150 years, the density of pores that allow plants to breathe has dwindled by 34 percent, restricting the amount of water vapor the plants release to the atmosphere, report scientists from Indiana University Bloomington and Utrecht University in the Netherlands in an upcoming issue of the Proceedings of the National Academy of Sciences (now online).

In a separate paper, also to be published by PNAS, many of the same scientists describe a model they devised that predicts doubling today’s carbon dioxide levels will dramatically reduce the amount of water released by plants.

The scientists gathered their data from a diversity of plant species in Florida, including living individuals as well as samples extracted from herbarium collections and peat formations 100 to 150 years old.

“The increase in carbon dioxide by about 100 parts per million has had a profound effect on the number of stomata and, to a lesser extent, the size of the stomata,” said Research Scientist in Biology and Professor Emeritus in Geology David Dilcher, the two papers’ sole American coauthor. “Our analysis of that structural change shows there’s been a huge reduction in the release of water to the atmosphere.”

Most plants use a pore-like structure called stomata (singular: stoma) on the undersides of leaves to absorb carbon dioxide from the air. The carbon dioxide is used to build sugars, which can be used by the plant as energy or for incorporation into the plants’ fibrous cell walls. Stomata also allow plants to “transpire” water, or release water to the atmosphere. Transpiration helps drive the absorption of water at the roots, and also cools the plants in the same way sweating cools mammals.

If there are fewer stomata, or the stomata are closed more of the day, gas exchange will be limited — transpiration included.

“The carbon cycle is important, but so is the water cycle,” Dilcher said. “If transpiration decreases, there may be more moisture in the ground at first, but if there’s less rainfall that may mean there’s less moisture in ground eventually. This is part of the hyrdrogeologic cycle. Land plants are a crucially important part of it.”

Dilcher also said less transpiration may mean the shade of an old oak tree may not be as cool of a respite as it used to be.

IMAGE: Researchers extract stomata-bearing leaves from a peat formation in Florida. At some sites, the peat was estimated to be as much as 150 years old.

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“When plants transpire they cool,” he said. “So the air around the plants that are transpirating less could be a bit warmer than they have been. But the hydrogeologic cycle is complex. It’s hard to predict how changing one thing will affect other aspects. We would have to see how these things play out.”

While it is well known that long-lived plants can adjust their number of stomata each season depending on growing conditions, little is known about the long-term structural changes in stomata number or size over periods of decades or centuries.

“Our first paper shows connection between temperature, transpiration, and stomata density,” Dilcher said. “The second paper really is about applying what we know to the future.”

That model suggests that a doubling of today’s carbon dioxide levels — from 390 parts per million to 800 ppm — will halve the amount of water lost to the air, concluding in the second paper that “plant adaptation to rising CO2 is currently altering the hydrological cycle and climate and will continue to do so throughout this century.”

Dilcher and his Dutch colleagues say that a drier atmosphere could mean less rainfall and therefore less movement of water through Florida’s watersheds.

The Florida Everglades depend heavily on the slow, steady flow of groundwater from upstate. The siphoning of that water to development has raised questions about the future of the Everglades as a national resource.

###

Dilcher’s Dutch coauthors for the two papers were Emmy Lammertsma, Hugo de Boer, Stefan Dekker, Andre Lotter, Friederike Wagner-Cremer, and Martin Wassen, all of Utrecht University in Utrecht, Netherlands. The project received support from Utrecht University’s High Potential research program.

To speak with Dilcher, please contact David Bricker, University Communications, at 812-856-9035 or brickerd@indiana.edu. To speak with any of the Dutch coauthors, please contact Emmy Lammertsma, Utrecht University, at 31 (0) 64 137 6175 or e.i.lammertsma@uu.nl.

“Global CO2 rise leads to reduced maximum stomatal conductance in Florida vegetation” Proceedings of the National Academy of Sciences (online), vol./iss. TBD

“Climate forcing due to optimization of maximal leaf conductance in subtropical vegetation under rising CO2Proceedings of the National Academy of Sciences (online), vol./iss. TBD

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anopheles

And all that water will be lost, forever.

crosspatch

Wouldn’t less water vapor also mean much less greenhouse impact and might this just be a way to link CO2 to colder temperatures now that they realize Earth isn’t warming?
I mean, we have just gone through 20 years of “we are going to cook because of CO2” and now that temperatures are cooling we have this. The logical conclusion, if you buy the study, is “we are going to freeze-dry because of CO2”.
They can’t have it both ways.

Roger Knights

One more feedback the models didn’t take into account.

DJA

“Dilcher and his Dutch colleagues say that a drier atmosphere could mean less rainfall ”
QED

David Schofield

Isn’t this proof of a negative feedback system – so why don’t they say so!? Less water vapour as a GHG balances out more CO2? Surely now all the other bad effects of CO2 like heating and flooding will be negated?
By the way it takes peat 10 years to form 1cm so they could have gone down more than 15cm to get older evidence surely?
And another thing, how do plants grow bigger with more CO2 if they reduce the gas exchange so they can’t use it?

AdderW

Selective information output: I need to read the article I grant you, but:
what was the total leaf area compared to number of stomata ?
is low CO2 a selective agent for decreased stomatal function ?
did the epidermal cells change in size ?
is CO2 a selective agent for decreased stomatal function ?
did the researchers try to estimate/compare plant dry weight ?
Previous papers on the same subject do not agree on this.

Disputin

So? Obviously CO2 has been so short in the atmosphere that plants have had to risk dehydration in order to get enough. As the level rises, the plants need fewer stomata to get enough CO2 for respiration and so can cut down the risk of excessive water loss. Sounds good to me.

A similar finding from Israel shows that less evaporation is of crucial interest for the survival and growth of plants in arid environments:
http://www.jpost.com/GreenIsrael/KKLJNFATUNCLIMATECHANGECONFERENCE/Article.aspx?id=166114
Not directly in the above reference is that the researchers found a reduction of stomata with increased CO2, which helped the trees to reduce their water losses.

JD

It truly sounds as if the involved researchers are trying to find a cesspool instead of a silver lining.

Scarlet Pumpernickel

Nutrients could have changed two. BTW I didn’t know 390×2 = 800? I thought it was 780?

Another Gareth

I guess this will make the Amazon even more resilient to water concerns then it already is.
This could presumably be corroborated with an empirical investigation conducted in glasshouses, raising or lowering CO2 levels and seeing how the plants respond.

BargHumer

This doesn’t make sense to me. The C02 in the atmosphere contributed by man is said to be so small compared to other sources of CO2 in the environment. If the doubling of a gnats whisker amount ofMMCO2 can cause such changes in plants, then it must cause us to rethink the imnpact on the climate generally. It can’t go both ways, either the MMCO2 is significant or it isn’t. I doubt that the MMCO2 can be the cause of the changes noted by the research, but I don’t see why, if it is true, that it is anything negative against AGW.

John Marshall

This is not news as anyone who reads the co2science web site will tell you. Indreased CO2 reduces a plant’s requirement for water. Can only be good for the planet!!!!!!!!!!!!!

John Peter

[snip . . OT]

Alan the Brit

Was it not in the Cambrian Expolosion that most plant/animal/plankton diversity existed, & CO2 was 20 times higher than it is today? Oh, we mustn’t be here then because life all died out because of the CO2, or maybe not?
Anyway, this is only a “puter”model, based on what they think they believe they ought to know they are right about! Still using non-comttal words like “could” & “may”. Just as easily these words can read “could not” & “may not”!
Slightly OT: Recent BBC tv appearance (Tuesday) by maths guru Johnny Ball stated on tv that manmade CO2 content was only 4% of total. My understanding was that this figure was from the IPCC sources & sinks section of their report, can anybody confirm that at all? Namely the 770 Gt or so natrual outgassing as opposed to the 25 Gt or so of manmade outgassing. It is used in the video clip at Climaterealist site presented by a school teacher (very eloquently I must say)!

Jimbo

With climate science there are always new discoveries. These guys and gals are having a field day with their ever changing vegetation discoveries. What next? Yaaaawn!
Plant methane emissions significant
Plant methane emissions insignificant
Amazon greener in dry season
Amazon not greener in dry season
Plants move uphill
Plants move downhill

Sandy

What controls water vapour in the air? The oceans or the plants?

ChrisM

It’s well known that if you increase CO2 levels plants are more able to withstand drought and the probable reason is that they transpire less so this is hardly a surprise.
Also their statement:” That model suggests that a doubling of today’s carbon dioxide levels — from 390 parts per million to 800 ppm” is suspect because most data is showing that the Oceans are cooling so more CO2 will be taken up by the Oceans, and the atmospheric levels will not reach 800ppm.

Jimbo

“The carbon cycle is important, but so is the water cycle,” Dilcher said. “If transpiration decreases, there may be more moisture in the ground at first, but if there’s less rainfall that may mean there’s less moisture in ground eventually.

Let’s continue shall we. Less water vapour in the air means less of the most powerfull greenhouse gas called water vapour. I recall that plants also become more drought resistant. These people are tying themselves in knots. Gaia at work?

George Turner

That’s very interesting, as it would be yet another negative feedback, and considering how much more important water vapor is than CO2, it could even mean the effect of CO2 is cooling.
The paper’s argument about air temperatures is probably not significant, and even if the temperatures are slightly warmer, the air will be drier, and since we are also evaporatively cooled, we’ll probably feel more comfortable.
However, mammals will also be losing water faster, since we don’t have stomata that adapt to CO2 levels. To verify how this will effect animal life I’ve input horse DNA into a multi-billion dollar computer simulation that extrapolates horse behavior from chemical interactions, protein transport, electrical charges, Van der Waals forces, and Brownian motion. My model horse quickly dehydrated, because even though there is increased surface water because of the reduced plant draw from the soil, he simply refuses to drink. I’ve had my underpaid lab assistant double check the code, and he says there’s no way it’s a glitch in a subroutine.
So, taking the average of 350 model runs, I predict a 35% species loss by 2050 and the devastation of agricultural production, causing widespread famine on top of the human deaths due directly to dehydration/drowning caused by lower humidity and increased surface water. I’m sure Science or Nature will publish my results with all possible haste.

[ah yes the old sayings are often the best]

Arizona CJ

Interesting… I wonder if anyone will try correlating past desertification cycles with CO2 levels? Lowering CO2, if the stomata theory is correct, could increase water needs, and in a borderline environment that could cause desertification.
I know there are other factors at play, but ice ages tend to have low CO2 levels, and desertification on a global scale. If the climate was getting drier while plants were needing more and more water due to CO2 declines, that would contribute to desertification.

Don Keiller

As a plant physiologist I find this “new” discovery all profoundly depressing.
The effect of incresed CO2 on stomatal density and evapotranspiration has been known for more than 50 years.
In fact stomatal density has been used as a proxy for past atmospheric CO2 concentrations
(Stomatal density and stomatal index as indicators of paleoatmospheric CO2 concentration)
See http://droyer.web.wesleyan.edu/RPP.pdf
Why do I not find it surprising that if vegetation covers some 50% of the Earth’s dry land a reduction in evapotranspiration is likely to have a global effect?
I bet this is not factored in GCMs
Why is so much of Climate “Science” reinvention of the wheel?

Jimbo

More negatives:
Biological productivity of the tundra has increased since 1981.
http://www.esajournals.org/doi/abs/10.1890/09-0102.1
1982 – 1999
http://www.sciencemag.org/cgi/content/abstract/300/5625/1560
Fungal Co2 uptake forecast to increase.
http://www.pnas.org/content/early/2010/05/21/0912421107.abstract

Metryq

Do we know that CO2 is the cause of fewer stomata, or could it be something else? People long acclimated to high altitude environments have a different lung morphology than those who live at sea level. Does that mean that either group of people breathe less?

Chris H

Nicely confirming, yet again, that today’s CO2 levels are sub-optimal for plant life. Yikes, I’ve just realised what that means for my gardening chores!

Glory satellite (aerosols, climate etc. ) launch appears to have failed .

Glory satellite (aerosols, climate etc. )
http://en.wikipedia.org/wiki/Glory_(satellite)
launch appears to have failed .

Stephen Richards

How the hell did they separate out the CO² signal from everything else? I can’t see it in the article. Someone help me please.

Kev-in-Uk

heck, I am struggling to recall my Biology from 30+ years ago but a check reveals the following:
In most plants, transpiration is a passive process largely controlled by the humidity of the atmosphere and the moisture content of the soil. Of the transpired water passing through a plant only 1% is used in the growth process. Transpiration also transports nutrients from the soil into the roots and carries them to the various cells of the plant and is used to keep tissues from becoming overheated. Some dry environment plants do have the ability to open and close their stomata. This adaptation is necessary to limit the loss of water from plant tissues. Without this adaptation these plants would not be able to survive under conditions of severe drought.
I would guess that the purpose of reduced stomata is an environmental response by the plants because they have either increased CO2 and therefore need less water to photosynthesize (?), or increased ambient moisture, or reduced soil moisture (i.e. unavailable/reduced precipitation) and possibly increased temperature which means increased evaporative rates – and, of course, a possible random mixture of these and many other reasons?
All in all, it seems like a difficult thing to explain?

interglacial

My old botany text-book (printed in the 1950s) has a whole chapter on plant transpiration and describes how stomata density and water loss decrease with increased CO2 concentration. It’s written for children and lay-people but even has a graphs showing the realtionships.
Makes me wonder about the value of interdisciplinary science when I now find out Professor Emeritus in Geology David Dilcher has just rediscovered what botanists have known since at least the turn of the last centruty.

“The scientists gathered their data from a diversity of plant species in Florida, including living individuals”,
The leaves of different plants and the sections of leaves will have different number of stomata, just pointing out the obvious here, but they really only have to study the stomata of one plant species over a longer period of time to get an estimate of what the ecology is like for that plant and it’s surrounding area,
Was it mentioned anywhere that when one variety of plant species loses water vapor through Transpiration, another variety of plant species takes advantage of this or compensates and vice versa?.
I know… lets use this speculative research on a variety of plant species in Florida to speculate on the future of the entire earths climate./sarc

Schrodinger's Cat

If extra CO2 is used by the plant then extra water is required as well. The photosynthesis combines CO2 and water to make sugars.

jason

So this is a new negative feedack. Why can’t these people just be honest. Every paper is dressed in global doom.

cedarhill

David Schofield March 4, 2011 at 12:45 am: how do plants grow bigger with more CO2 if they reduce the gas exchange so they can’t use it?
If you double the amount of CO2 and if all other factors are the same, then you can halve the number of pores (think of them as “open ports”) and still get the same amount. If only a 40% decrease you’d still get a large percent uptake of CO2. Obviously, with water vapor the reverse would be true.
Regardless, what is really interesting is the way plants regulate themselves. If the only control they have is the number of stomata they make. Which, in turn implies the plant has little control or no control over the volume of gasses going in or going out. But they can control their water uptake from the soils. If Darwin were a plant, he’d be able to describe why plants evolved this way. Shame Darwin isn’t a warming believer.

Chris Edwards

Good news, surely more CO2 means arid places can support plant life? has to be good news , with the cooling perhaps parts of the Sahara will become arable?

StuartMcL

“As carbon dioxide levels have risen during the last 150 years, the density of pores that allow plants to breathe has dwindled by 34 percent, restricting the amount of water vapor the plants release to the atmosphere,”
What they didn’t mention:
“At the same time, because of the increased plant food available, total leaf surface area has risen by X percent, (partially/completely/more than) offsetting the reduction of water vapour released per unit area.”

Ed MacAulay

So what percent of global evaporation occurs from our 70% ocean surface?
The plants of the NH above 40 degrees N are not transpiring much water this winter so we should expect less snowfall.

Maybe the next climate-related Nobel Prize can go to Wagner-Cremer, Dilcher, Kurscher, Kouwenberg, van Hoof and the rest of the Utrecht stomata people.

Scarface

What I find intriguing is that the number of stomata decreases at higher CO2-levels. That means imho that CO2 is not the bottleneck for plantgrowth, but cold and waterloss. So this research is another proof that moist and warm are the best conditions for plantlife and therefore for animals and humans too. That’s of course why you want to use a greenhouse to grow crops (moist and warm) and that’s why in the tropics plants can get huge quickly (moist and warm).
Based on this, together with the knowledge that rising CO2-levels have little or no effect on global temperatures, one can conclude that:
– warm is good, warmer is better;
– CO2 is good, more CO2 is better.
CAGW has now definitely been falsified, period.

Hang on a minute. Finding 34% less stomata density in living samples than in samples taken from 150-year-old peat certainly does not show that “The increase in carbon dioxide by about 100 parts per million has had a profound effect on the number of stomata and, to a lesser extent, the size of the stomata.” That’s correlation, not causation.
And then they have the chutzpah to create a climate model predicting that the amount of water released too the air by plants will be halved, resulting in a drier atmosphere and lower rainfall.
Climate models produced by climatologists themselves are woefully inadequate and plain wrong. A climate model produced by a biologist has no chance of accuracy. Sadly, it has every chance of being cited as yet more “scientific evidence” of climate change forced by anthropogenic CO2.

geoff

I wonder if the study took into consideration the fact that plants grow more quickly with higher levels of atmospheric CO2. If levels double, there will be more plants and larger ones, so while each leaf might release less water, since there will be more leaves, the total water released might be the same or higher.

AdderW

Metryq says:
March 4, 2011 at 2:35 am
Do we know that CO2 is the cause of fewer stomata, or could it be something else?

Plants create less stomata as an adaptation to conserve energy.
No need for an excessive amount of stomata when less can do the same work.
The research fails to show if the plants’ dry weight changes with lower number of stomata.
Keep your eyes on the pea.
What the researchers in this paper is trying to prove/show is that CO2 concentrations in the atmosphere is rising, hence the low stomata count.
So, nothing new there…

ScuzzaMan

Here’s the money shot:
“But the hydrogeologic cycle is complex. It’s hard to predict how changing one thing will affect other aspects. We would have to see how these things play out.”
THAT’s the plain truth: The climate is complex. It IS very hard to predict how changing one thing, i.e. CO2 concentration, will affect other aspects.
Thank you, and good night!
(You gotta love unintended honesty)

Kev-in-Uk

Schrodinger’s Cat says:
March 4, 2011 at 3:23 am
…If extra CO2 is used by the plant then extra water is required as well. The photosynthesis combines CO2 and water to make sugars….
I would have said it might be a yes and no answer. More CO2 may make the process more efficient? and then of course, it depends on whether the plant is in its growing season? do plants show stomata cell changes through a season? we know growth rates increase with CO2 and temperature (up to a point, obviously) – but how much of the water demand is required for cooling and photosynthesis, I don’t know.

Dave Springer

It’s quite well known (for a long time) that:
1) increasing CO2 up to as much as 2000ppm substantially increases plant growth rate so long as there are no other limiting factors (sunlight, water, nutrients, temperature)
2) optimum growth temperature rises with increasing CO2
3) water use per unit of growth decreases with increasing CO2
This makes sense in light of evolutionary adaptation and history of the earth’s climate. The earth is usually NOT in an ice age as it is today. Ice ages are characterized by low temperatures and low levels of CO2. The vast majority of the earth’s history is characterized by no polar ice caps, global average temperature 6-8C higher than today, and CO2 concentration as much as 20 times higher. These latter conditions persisted for tens and hundreds of millions of years at a stretch. Green plants evolved under these conditions and these conditions are hence what they are best adapted for. There is absolutely nothing mysterious going on in why plants prefer higher atmospheric CO2 and warmer temperatures for optimum growth.
Stomata can open and close as required to accomplish and regulate gas exchange. The anatomical structure that opens and closes the stomata is called “the closest thing to a muscle that plants have”. So plants have no great need to change the number or density of stomata in response to gas concentration. It would appear to be a metabolic adaptation so that energy isn’t wasted by building more stomata than are needed. The density and number of stomata vary on the same plant during the same growing season. If I recall correctly the regulatory mechanism has been recently identified. A signalling protein is produced by mature leaves that informs newly forming leaves what stomata density is optimal for the current environmental conditions.
The water savings under higher CO2 conditions is straightforward. The stomata regulate gas exchange i.e. excreting oxygen and taking in CO2 when photosynthesis is happening. When there is a higher concentration of CO2 in the air the stomata remain open for a shorter period of time because the exchange goes faster. Water is lost through evaporation when the stomata are open so less time spend open means less water loss during gas exchange. No mystery there either.
This is one reason why climatologists are the last people you should ask about the consequences of so-called anthropogenic global warming. Evidently few if any of them know jack diddly squat about botany and if they do know something they dishonestly disregard (called a lie of omission) the benefits of anthropogenic CO2 and global warming. It’s disgusting. And the talking dimwitsoobs on the Weather Channel wonder why CAGW boffins get no respect. There’s a simple answer for that too – CAGW boffins deserve no respect.

Water-use efficiency of plants goes up with increased atmospheric CO2. The plants become more drought resistant. My neighbor, an old farmer, now dead, told me in 2002 during a severe drought, “It’s just a miracle. This is worse than ’36 and in ’36 we had nothing. All the crops died, all the weeds died, and were left with dust.” In 2002 we harvested 25-30 bushels an acre of soybeans and 50+ bushels of corn, dryland. My neighbor’s “miracle” has a complex, not a simple explanation; new crop genetics are part of the answer. But I thought back in 2002, and I still think, increased atmospheric CO2 is responsible for big gains in water-use efficiency in plants.

philincalifornia

Nothing particularly new here, although it is interesting to note that the Miskolczi effect can be catalyzed by vegetation (rather than being a passive equilibration).
Anyone know if this effect is linear based on CO2 levels ?? A logarithmic CO2 effect meets an opposing linear water vapor feedback effect ?? Just wondering.

rukidding

Don’t think the NH and the SH are singing from the same hymn sheet.We in Australia are being told that due to la nino we can expect more rain from global warming but then again 6 months ago we were being told we would never see heavy rain again.It is hard to keep up.

TimH

As others have pointed out here… they are assuming total biomass stays the same. I’m not a scientist, but my bet is that nature balances the water cycle just fine all by itself.