Rising CO2 is causing plants to release less water to the atmosphere, researchers say
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.
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  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 CO2” Proceedings of the National Academy of Sciences (online), vol./iss. TBD
We’ve touched on this topic before on WUWT:
http://wattsupwiththat.com/2009/02/09/high-co2-boosts-plant-respiration-potentially-affecting-climate-and-crops/
I agree with others, these biological phenomenon haven’t been even discussed by the climate modelers! I doubt if there’s a single biology B.S. between all of ’em.
David Middleton says:
March 4, 2011 at 10:59 am
The funny thing about Beck’s 1942 CO2 peak, Finsinger & Wagner-Cremer (2008) found a similar peak in a reconstruction from Betula (birch) leaf samples from northern Europe.
But if you take the stomata data from Van Hoof in The Netherlands (oak leaves at St. Odiliënberg), far closer to the main dataseries which caused the 1942 peak in Beck’s graph (Giessen, Germany), there is no peak at all:
http://www.ferdinand-engelbeen.be/klimaat/klim_img/van_Hoof.jpg
Even if a sharp rise of CO2 of 80 ppmv (160 GtC) is theoretically possible, it is physically impossible that the same amount disappears in less than 7 years. The current removal rate of CO2, while some 100 ppmv above (temperature dictated) equilibrium is 4 GtC/year…
Your CO2 averaging model is quite different of what the firn densification models calculate, neither what is found in measurements: at closing depth, the average gas age is measured only 10 years younger at 75 m depth than at the surface and the averaging is more a Gaussean peak around that age than an average. See:
http://courses.washington.edu/proxies/GHG.pdf page 4
That means that a one-year peak of 80 ppmv, still would give a 4 ppmv peak in the ice core, but as the high level remained several years, according to Beck, it may reach over 10 ppmv in the Law Dome ice core, but it isn’t seen at all (accuracy of the ice core measurements: 1.3 ppmv – 1 sigma).
Neither in coralline sponges: any huge, short peak is either from the oceans or from decaying vegetation. The former would give a moderate, but measurable increase in d13C, the later an enormous decrease of d13C. Which isn’t seen at all.
In your web page you say:
The air trapped in the 1939 layer should be a blend of air from 1909 to 1969.
In fact, as the average gas age is only 10 years younger in average composition than the (1993) surface air at closing depth, where the ice is 40 years older than at the surface, halve of it is from the period 1983-1993, the other halve from 1953-1983 and near nothing from 1913-1953. After all, near the surface and even (much) deeper, the gases have plenty of time to migrate (up to 80 years)…
This also demonstrates that plants prefer higher temperatures. Less evapo-transpiration results in higher local (for the plant) temperatures. The plants have voluntarily reduced their rate of evapo-transpiration through restricting their production of stomata to produce better growing conditions.
It’s agonizing reading such stupidity.
Uh, not really. See, using the same amount of water, THE PLANTS WILL GROW TWICE AS MUCH!
Biologists and arithmetic are a mismatched pair, clearly.
I find it interesting that plants have evolved a mechanism to deal with the allegedly unprecedented.
Hmmm…
Mainly desert areas, which are limited by water, would be affected by this. Vegetation would prosper with increased CO2. The extra vegetation would emit exactly the same H20 as the original cover emitted.
Unfortunately the desert would now be less reflective, decreasing the albedo, absorbing more solar energy, increasing temperatures.
I don’t care much though.
“David Middleton says:
Even if a sharp rise of CO2 of 80 ppmv (160 GtC) is theoretically possible, it is physically impossible that the same amount disappears in less than 7 years. The current removal rate of CO2, while some 100 ppmv above (temperature dictated) equilibrium is 4 GtC/year…”
Only if we believe that removal of CO2 from the atmosphere is driven by chemical processes, rather than biotic ones. If biotic ones were the major cause of overall atmospheric CO2 efflux than the steady state level would be dependent on the affinity of RuBisCO for CO2 and the steady state level would hover around about 280 pp.
Wait a minute……………..
cedarhill says:
March 4, 2011 at 3:31 am
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.
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If you accept that plants are in the business of surviving and thriving, it’s not difficult to imagine that they try to maximize resources.
There wouldn’t be much point in deliberately depriving themselves of water when water is abundant, especially since exposure to increased CO2 concentration is far from harmful. Either plants are really dumb or there’s method in their madness.
Stomata opening and closing is done by the plant so as to achieve a compromise between importing as much CO2 as possible while permitting the least possible waste of water.
If there is an abundance of water available to the roots, a plant can be as extravagant as it likes with it as it tries to capture the maximum CO2 possible. That is, it can open wide the stomata.
In a drought, the plant is obliged to constrict water loss at the expense of CO2 capture and nutrient transport up the shoot. The plant is frugal in order to stay alive.
Of course, drought is not a permanent, nor a chronic state of affairs for most of the world’s vegetation, so plants allow more transpiration than is actually required because they’re keen to get a hold of more CO2.
Plants are clever but they’re not geniuses and so the balance is not perfectly achieved, however they have long-term strategies such as making fewer stomata and they can adjust in the short term by opening and closing them quickly.
I should have said ‘restrict’, not ‘constrict’
We are learning a lot more about he climate (although I note that this latest bit is in fact very, very old stale news).
We are now learning so much that I do believe that we are almost, I say Almost, at the point where we realise that we know almost nothing about what makes the climate to change and change, always change.
Strange.
This could provide another mechanism for Miskolczi’s theory.
“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.”
Well, duh, that means more water available for the rest of us! If plants aren’t sucking as much water from the ground, then logically more water will stay in the ground to flow to the southern part of Florida, the Everglades. Honestly, I thought going to college was supposed to teach you critical thinking skills. And why would you stick in a blurb about land use development to imply linkage to CO2 and water flow to the Everglades? What has land development got to do with plant transpiration? Ignorance or Deceit?
btw- for those of us who live(d) in Florida if plants transpire less then that means lower humidity during the summertime. I would say that’s a good thing not to sweat as much.
Oh no, not again! More from the field of Climastrology: weasel words, model, if, could, may, possible and so on. Not Science!
I thought that during the age of the dinosaurs, the world was much warmer and C02 levels were much higher than today. But the plant life was abundant, so there was more than enough for the herbivores to eat an grow large, so there was more than enough food for the carnivores.
Everything grew bigger. Surely there was plenty of water to support all this massive growth?
Am I misunderstanding something?
For each additional CO2 assimilated by a plant, there is a corresponding additional H2O incorporated into a carbohydrate:
6 CO2 +6 H2O -> C6H12O6 + 6 O2
Thus plants will transpire less if photosynthesizing more. Stomata respond to minute changes in pH, raise the pH of the air, and stomata will close and vice versa. Increasing CO2 raises the pH of the air.
This all begs the question:
Are stomata there to let CO2 in or to let H2O out?
This comes as no surprise to me. There have been studies of the effect on plants grown in artificially high CO2 atmospheres. In addition to spurring growth, there is usually an increase in drought resistance.
These scientists are plain silly. Almost anywhere on the face of Earth except in rain forests where water availability is not a limiting factor, much sunlight reaches ground level. It means if individual plants use less water to produce the same biomass, plant density increases accordingly. Therefore gross volume of evapotranspiration remains about the same, just as stomata, which may be distributed among more individual plants or more leaves on branches, but their overall number does not change.
My impression that the world around me is getting greener is not entirely out of track perhaps. And it is not “greener” in a political sense, but most places I remember from my childhood actually have more vegetation now than in the good ol’ days.
In any event a higher level of CO2 makes plants healthier.
As everybody knows, the CO2 level is enhanced to ca. 1000 ppm in Real Greenhouses.
Now that plants transpire less water due to increased CO2 atmospheric content, they are now MORE drought resistant.
Isn’t that good news?
Funding Recipe:
Take whatever you study (doesn’t matter what it is) and show how it will be affected by a doubling of CO2. (Matters not whether you are right or wrong.)
–
Our research funding systems have degenerated into a reliable source of balanced anger & humor.
Imagine a drug that cures cancer. The authors of the articles being discussed would probably argue as follows: If this cancer cure drug is approved, millions more octogenarians will die each year.
They would be right. Millions would die in their 80s or beyond, instead of in their 60s or 70s.
Alan the Brit says: March 4, 2011 at 1:59 am
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?
http://i52.tinypic.com/vlud.jpg
“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.”
This is true, but the comment below indicates why there is no contradiction. Kevin’s book was 30 years old. Perhaps 1.3% is now used for growth.
“Kev-in-Uk says:
March 4, 2011 at 2:55 am
Of the transpired water passing through a plant only 1% is used in the growth process.”
DocMartyn says:
March 4, 2011 at 3:08 pm
Only if we believe that removal of CO2 from the atmosphere is driven by chemical processes, rather than biotic ones. If biotic ones were the major cause of overall atmospheric CO2 efflux than the steady state level would be dependent on the affinity of RuBisCO for CO2 and the steady state level would hover around about 280 pp.
Wait a minute……………..
You react on what I said, not a quote from David Middleton…
A doubling of pCO2 in the atmosphere gives an average increase of about 50% in plant growth, but much of that returns in fall/winter as vegetation decay. The current real longer term deposit of carbon in vegetation is somewhat over 1 GtC/year, based on oxygen production:
http://www.bowdoin.edu/~mbattle/papers_posters_and_talks/BenderGBC2005.pdf
The rest of the current ~4 GtC sink capacity is going into the oceans.
Thus while the ocean-vegetation-temperature equilibrium would be around 280 ppmv for the current temperature, the yearly addition of fossil CO2 is larger than the current removal rate even with an increased pCO2 some 100 ppmv higher than equilibrium for both oceans and vegetation.
Alan the Brit says:
March 4, 2011 at 1:59 am
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)!
Eloquently but completely irrelevant. As Mike McMillan referenced from the IPCC:
Natural releases: 770,000 MtCO2/year
Human releases: 23,100 MtCO2/year
Natural absorption: 781,400 MtCO2/year
Increase in the atmosphere: 11,700 MtCO2/year
Thus the natural balance is a net 11,400 MtCO2 absorption per year and thus nature doesn’t contribute to the CO2 increase in the atmosphere…