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
I’ve read that the amount of water vapor in the (upper?) atmosphere has mysteriously decreased in recent decades. Any relation to the reported decreased water transpiration? (Apologies in advance if this has been covered above. I don’t have time to read all entries before sending this due to having to go out for several hours.)
IanM
Perhaps I am understanding this incorrectly but would not the need of less transpiration also mean a more drought tolerant plant? Ergo a plant more likely to survive through harsher conditions. In point of fact it almost makes it seem like plants thrive on a higher CO2 concentration and become much more hardy. This sound like a situation where the conclusion drawn is meant to inspire fear without examining the possible benefits ( why does that seem to be the only science nowadays? ) As I was reading the pess release I was actually getting excited as it meant that the amount of irrigation that has been used historically and you know meant that we had to tap into all that ground water stored underneath the earth and spew it into the atmosphere would not be needed as much anymore, that rainfall alone may be enough to water crops and the periods of dry spells would not be as ‘hard’ to weather. Of course I am probably just crazy in thinking in those terms as it is obvious plant respiration and its unknown direct effect on climate is obviously much more important.
Question, If there is an increase in temperature would that not in turn lead to a longer growing cycle and therefore lead to a greater amount of CO2 absorption?
Ferdinand Engelbeen, round and round we go, you think that the planet is a wet rock, where as I believe that from 40 meters down to 70 miles up the whole thing is a product of life.
You adore dead, static, equilibrium descriptions of of living, dynamic steady states.
To prove that the system is dead and chemical, you quote the IPCC, which shows the validity of your approach.
Dave Springer says:
” We need a lot fewer unaccountable scientists wasting time and money in academia and a lot more engineers getting practical things done and being held accountable when they fail.”
Dave (and many others!) I have been astounded by the depth of knowledge in this post and admit, as an engineer that biology was something I only touched on. Your posts have enlightened me!
Dave, as an engineer, I have to say that we use proven science to do our work, using formula and laws proven by academia. Sadly the real brains these days are grabbed up by the financial sectors as they pay the best! Why else would we be chasing windmills!
Worldwide, academia is a real mess…Can you or anyone else show me one Climatologist that has a degree in Climatology? If there is one, does part of the degree course include Math?
So in 2000, AGW will cause less snowfall, but in 2011, it increases the moisture in the air, thus more snowfall.
NOW we see: “Dilcher and his Dutch colleagues say that a drier atmosphere could mean less rainfall and therefore less movement of water through Florida’s watersheds.”
So, I’m guessing that they’ll say, the increased evaporation due to warmer temperatures will stop, but only when we have less rain, or at least that what’s we’ll be hearing next; correct?
IF we have less snow, it’s due to AGW.
IF we have more snow, it’s due to AGW.
IF we have more rain, it’s due to AGW.
IF we have less rain, it’s due to AGW.
IF they cancel future seasons of the TV show Wheel Of Fortune, it’s due to AGW too!!! 😉
DocMartyn says:
March 5, 2011 at 9:02 am
Ferdinand Engelbeen, round and round we go, you think that the planet is a wet rock, where as I believe that from 40 meters down to 70 miles up the whole thing is a product of life.
You adore dead, static, equilibrium descriptions of of living, dynamic steady states.
To prove that the system is dead and chemical, you quote the IPCC, which shows the validity of your approach.
In this case, the IPCC figures are based on rather solid observations: fossil fuels sales, CO2, O2 and d13C measurements in the atmosphere and the oceans,…
Of course a lot of details are not known to the kg of CO2 exchanged, but we have a pretty good idea where the exchanges are and the overall results, including year by year variability. We are less sure how much is exchanged for individual flows. But that doesn’t influence the total balance, which is more natural sink than source at least over the past 50+ years.
Thus, while there are lots of errors and exaggerations in the IPCC reports, this is not one of them…
And not one of my last hairs thinks that the planet is static. Of course it is dynamic, but the past has shown that temperature dictates the CO2 equilibrium setpoint of the atmosphere, incredibly linear, including all natural feedbacks from oceans and biosphere and more, of which many may be far from linear.
If there are fewer stomata, or the stomata are closed more of the day, gas exchange will be limited — transpiration included.
What a bunch of B.S.
Here’s a different intrepretation. Plants absorb CO2 through stomata. Increasing CO2 may have caused the evolution of less stomata. Water loss is a problematic side-effect of required open stomata for CO2 absorption. If they want to support this thesis, show me data on the number of chlorophyll/unit area in these same plant specimens. Then I will predict water use efficiency. Until then, it’s just data without a cause and effect.
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.”
Agreed. Plants strive to find the optimum balance between all growth factors and have evolved mechanisms to balance changes in availability to always provide optimum growth. As CO2 levels goes up and more sunlight is available they can get better growth with better use of that unreliable but vital resource, water.
Evidence for this is the current greening of the planet due to multiple factors being beneficial to growth.
Ferdinand Engelbeen, you (none rotating) planet is far different from mine, yours in always on the knife edge leading to one of two catastrophic endings:-
1) a slight increase in CO2, say from a volcano, increases CO2. This CO2 causes warming of the oceans and so increases the rate at which CO2 is released. This release causes warming and so increases ocean temperature. The Earths temperature increases, droughts and changing weather patterns causes desertification. The melting polar caps decrease land area due to flooding and increases the albedo. Run away heating, caused by CO2 heating the oceans and releasing CO2 in a positive feed back. The Earth boils.
2) a slight drop in CO2 causes cooling. The cooling of the oceans increases the uptake of CO2. The atmosphere loses CO2 and cools. Cooling causes the ice caps to expand. The increasing ice causes a decrease in albedo. More and more land is covered in ice, causing cooler air and cooler oceans. More CO2 is removed from the atmosphere and the world becomes a snow ball, due to the positive feedback of CO2/ocean cooling.
These outcomes are not probable, but certain, as your planet has no elasticity.
You are incapable of understanding that additional inputs of 23,100 MtCO2/year are trivial when the typical influx is 770,000 MtCO2/year and the efflux is on the same order; 781,400 MtCO2/year.
You inability to even analyze steady state kinetics is both alarming and sad.
DocMartyn,
I think you might be misunderstanding Ferdinand Engelbeen. His argument has always been that the recent increase in CO2 is due to human emissions. He’s convinced me with data and facts that the cause of most if not all of the the rise is anthropogenic. [And it took some convincing.]
Ferdinand has mentioned a number of times that the rise in CO2 doesn’t seem to have caused any real problems. And that is the crux of the matter, isn’t it? If the rise in CO2 has only brought about some trivial warming – not a bad thing – and has the added advantage of promoting agricultural growth, then the scare stories about “carbon” have turned out to be not only baseless, but completely wrong. More CO2 appears to be on balance a good thing.
Smokey says:
March 5, 2011 at 2:00 pm
Thanks Smokey, at last someone I have convinced!
DocMartyn says:
March 5, 2011 at 1:16 pm
If you know something about dynamic processes, you should know that what you describe, a runaway process (and I have seen the results of a few in my working life!), can only be true if the fortifying factor of the two-way influences is larger than 2.
In this case, there is a small influence from temperature on CO2 levels (8 ppmv/°C), as seen over the past 800,000 years. And there is a small influence of more CO2 on temperature (1°C/2xCO2 or 1°C for a 280 ppmv increase, based on radiation absorption). That is by far not enough to make it a runaway reaction. Not even to have much influence on the real temperature with the current (or future) increase(s) of CO2. And as already said by Smokey, mostly beneficial: longer growth seasons in the mid to high latitudes, more CO2 which increases growth…
There are a lot of dynamic processes at work here, where, at a certain temperature, as much Gt CO2 is coming in as is going out the atmosphere, even massive quantities. Thus for a certain temperature there was a dynamic equilibrium (“steady state”) CO2 level over the past 800,000 years, but a different equilibrium for a different temperature. What do you think that will happen if someone adds a relative tiny amount of CO2 per year, but does that continuously for 160 years?
And for those who haven’t heard of Le Châtelier’s principle, have a look at Wiki:
http://en.wikipedia.org/wiki/Le_Chatelier's_principle
Alan the Brit says:
March 4, 2011 at 1:59 am
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?
Plants do indeed have considerable form in terms of a history of dynamic interaction with atmospheric CO2, even to the point of having a dominant effect on the same.
The paper linked below points to an evolutionary explosion of megaflora leading to trees as we now know them, during the Devonian and early Carboniferous, which sucked much of the CO2 out of the air – leading to responsive changes in plant anatomy, such as the density of stomata discussed in the paper from Bloomington.
https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0B9p_cojT-pflYzZjNDc3YTYtNDFhOS00YmNlLWJiNjctOTU5ODBiYjM4NTM4&hl=en_GB
The earth’s plant biota cannot be excluded from any discussion of atmospheric CO2 – it is as much biology as it is physics.
Stomata density reduces but surface area increases. What is the net effect? In the quoted part I see no definite answer. As I understand it, plants with lower-density stomata and which transpire at a lower rate (per unit volume) retain water better and so are much more drought-resistant. They therefore require less irrigation, which is good news for dry agricultural regions. Sounds like win-win to me.
****
Smokey says:
March 5, 2011 at 2:00 pm
DocMartyn,
I think you might be misunderstanding Ferdinand Engelbeen. His argument has always been that the recent increase in CO2 is due to human emissions. He’s convinced me with data and facts that the cause of most if not all of the the rise is anthropogenic. [And it took some convincing.]
*****
Smokey, he convinced me, too. Not easy. So did Leif S, so far.
Thanks, Ferdinand, for your detailed & unbiased work on this subject. This is how science should be done.