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.
 |
||||
 |
 |
|
 |
|
|
 |
  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.
|
|
|
|
 |
|
 |
|
|
||||
“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
Wait a minute. At the end of the article they say:
“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.”
Isn’t it possible that the plants are reducing stomata in response to the reduction of water due to development and not in response to CO2 levels?
geoff says:
March 4, 2011 at 4:22 am
“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.”
Exactly. Adding insult to injury 71% of the earth’s surface is ocean. Nothing will change there. The entire continent of Antarctica has no terrestrial plant life so add that to the 71% that won’t change. Then during a substantial portion of the year high northern and southern latitudes over land are too cold for any plant growth so that won’t change either.
The notion that CO2 will have any substantial effect on total atmospheric water vapor through changes in plant transpiration is not at all credible. More wasted research funds. It just never ends does it? 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.
****
Article says:
“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.”
****
Bit of a simplification. Stomata aren’t static, they open & close on a daily basis (completely closed at nite). CO2 increases cause relatively less opening during the day. If one assumes that local rainfall is related to transpiration-rate, rainfall may decrease when water is plentiful. But when plants are water-stressed, the stomata additionally close during the day somewhat (independent of CO2 level) to prevent loss of turgidity. If there is more moisture remaining in the soil from lower transpiration, during extended dry periods the stomata may actually be more open than they would be otherwise, and rainfall may increase during the dry periods.
Some guesswork on my part, but their simple statement above is a stretch without some explanation.
Thank you Patrick for pointing that out!
cedarhill says:
March 4, 2011 at 3:31 am:
Just curious; are you from Cedar Hill, Texas? I graduated from CHHS in 1984.
So these grant seekers extrapolated an apparent change in stomata density to global climate change ha?
I got news for them. I know of plants that completely lose their stomata within weeks. They’re called DECIDUOUS plants. You see, plants have adapted in many ways to all sorts of changing conditions. Some actually change hourly, observe flower petals closing or leaves turning down during heavy rain. Heck, remember why the SUNFLOWER is called a SUN flower?
An earlier commentor said these AGW guys are tying themselves in knots. Could it be because their much vaunted climate models are just digital forms of the old TWISTER game? Gunna be hot, gunna be cold, wet, dry, windy, calm, dang their heads are up their ar$e$ now.
Maybe these folks should explore what fields of science already exist before they make their ‘discoveries’. Sounds like finding the existence of a navel would be a novel discovery. It would be interesting if someone extended this related area of study:
From Canada to the Caribbean: Tree leaves control their own temperature June 11th, 2008
The temperature inside a healthy, photosynthesizing tree leaf is affected less by outside environmental temperature than originally believed, according to new research from biologists at the University of Pennsylvania.
Surveying 39 tree species ranging in location from subtropical to boreal climates, researchers found a nearly constant temperature in tree leaves. These findings provide new understanding of how tree branches and leaves maintain a homeostatic temperature considered ideal for photosynthesis and suggests that plant physiology and ecology are important factors to consider as biologists tap trees to investigate climate change.
Tree photosynthesis, according to the study, most likely occurs when leaf temperatures are about 21°C, with latitude or average growing-season temperature playing little, if any, role.
the rest of the abstract is here:
http://www.sciencecentric.com/news/article.php?q=08061131
Doesn’t say much for tree rings as a proxy for temperature.
No. The stomatal index (SI) in these particular plant taxa is unresponsive to water and light conditions. Stomatal density (SD) is responsive to CO2, water and light.
The SI is generally calculated by dividing the SD by the density of epidermal cells (or needle length in conifers).
This research is basically a continuation of Wagner et al., 2004; which thoroughly demonstrated that the CO2 increase from 310-370ppmv (ca. 1940-2000) could be reconstructed from stomatal frequency.
Plant contribution to atmospheric moisture content is different than open water’s contribution. They involve different mechanisms of atmospheric injection.
Open water uses evaporation, as its mechanism, which means its injection rate is entirely dependent on temperature, relative humidity, air circulation speed, body surface area.
Plants however, push water molecules, one at a time, directly into the atmosphere. It has its own internal drivers governing this atmos injection processes. This pumping action cannot be compared to the normal evaporation process. When environmental evaporation is low, plant water vapor injection could be conversely high.
Plants do modify their own micro-climate. Collectively, uncountable numbers of them, affect and modify our global climate.
If we could poll plants they would respond to increased temperatures, available moisture, and enhanced CO2, with a deafening “YES PLEASE!”
When our food source flourishes… So do WE! GK
So when you point out to them that this leads to a lower greenhouse effect due to water vapour, how will they respond? Maybe they’ll say ‘ah, but most water vapour comes from the oceans.’
When you point out that if most of the water vapour comes from the oceans, then how can reduced transpiration from vegetation in Florida lead to drying up of its swamps (Florida is a peninsula, after all), how will they respond this time?
Good gawd, what spin!
Could they be more negative about how they report neutral facts?
“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, …”
‘That allow plants to breath’ – makes it sound like its a bad thing that plants develop fewer stomata in response to higher CO2. Nothing is further from the truth.
The reality is that stomata cause plants to waste water. They dont ‘allow the plants to breath’, they allow the plants to eat. Their food is CO2. When there is more CO2 in the air, it makes it easier for plants to get the food they need. They can get the same amount of food using fewer stomata. Since having more stomata than necessary causes plants to waste water, and thus be less resistant to drought, they grow fewer when they can get away with it. This is a good thing.
The whole article is written with the doom and gloom filter turned to “high”.
@JJ…
The negative spin is in the text of the press release from Indiana University… Not from the authors of the papers.
If you read any of the papers by David Dilcher, Lennie Kouwenberg, Tom van Hoof, Wolfram Kürschner, Friederike Wagner-Cremer and the other stomata experts, you’ll find their approach amazingly non-alarmist. They also don’t strike me as fellow skeptics/deniers. They are doing very solid, basic science. They call it as they see it – And this often ruffles the feathers of the so-called scientific consensus – particularly the ice core people.
Over the last 10-15 years, they have clearly demonstrated that pre-industrial Holocene atmospheric CO2 levels were higher and much more variable than indicated by Antarctic ice cores… For this, they have been vilified by the Warmistas.
I have used CO2 enhancement to promote plant growth. I did not see any reduction in the water requirements. I did, on the other hand note a greater need for nutrients.
David Middleton,
Never had botany, so I need a little help here. You differentiate stomatal index and stomatal density. Then in your last paragraph you refer to stomatal frequency. Is this a third parameter, or one (which one?) of the first two?
Dave Springer and Geoff,
I agree with your assumptions that the release of vapour from plants may very well remain nearly the same, given that CO2 will lead to an increase in biomass. But, would not an increase in biomass bind more atmospheric CO2, thus serve to reduce or stabilize the amount of atmospheric CO2?
Thanks David M.
I found an intersting website that has some basic info about plant biology. Interesting stuff.
http://plantcellbiology.masters.grkraj.org/html/Plant_Cellular_Physiology8-Loss_Of_Water_II-Transpiration.htm
David Middleton says:
March 4, 2011 at 8:37 am
Over the last 10-15 years, they have clearly demonstrated that pre-industrial Holocene atmospheric CO2 levels were higher and much more variable than indicated by Antarctic ice cores… For this, they have been vilified by the Warmistas.
Although I agree that stomata (index) data do have some value, one need to be a little cautious with claims of absolute height and variability of the CO2 levels found. Stomata data suffer from the same problems as many of the historical data had: they reflect CO2 levels over land, which are by definition more variable and show a positive bias.
The bias in the past century can be compensated for by calibrating the SI data to direct measurements and… ice cores. Which BTW reject the 1942 peak found by the late Ernst Beck. But we have little idea how the CO2 levels in the neighbourhood of the SI samples changed over time in the previous centuries. In The Netherlands there was a tremendous change in landscape (sea and marshes – forests – agriculture – industry, traffic) over the past few thousands of years in the main wind direction of one of the main SI finding places. Even the main wind direction may have changed over the centuries (MWP – LIA), all with a hardly correctable impact on local CO2 levels…
Stomatal index (SI) and stomatal density (SD) are measures of stomatal frequency. Both express inverse relationships to atmospheric CO2. SI is far less likely to be affected by other environmental stresses than SD.
G. Karst says: “If we could poll plants they would respond to increased temperatures, available moisture, and enhanced CO2, with a deafening “YES PLEASE!”
Or a deafening “Feed me! Feed me!”
Agree with jorgekafkazar. This is just rubbish. These people have no idea what human activities relating to our water management are doing. Notice how much water evaporates from my pool.
http://www.letterdash.com/HenryP/more-carbon-dioxide-is-ok-ok
@ferdinand meeus Engelbeen
I agree that one has to be careful in relying on the absolute values in the stomata reconstructions. The data are “noisy” and many reconstructions are based on Quercus (oak) leaves; which are unresponsive above ~350ppmv. Most stomata reconstructions employ a 3-pt running average to smooth the data out a bit. But the relative change and variability is solid.
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. The really funny thing is that, like Beck, the stomata reconstruction exhibits a sharp drop in CO2 in the late 1950’s, bringing it into fairly good agreement with MLO.
Beck’s early-1940’s CO2 peak could quite easily have occurred and not been resolved in the ice cores. Law Dome’s firn densification offset in the 20th century is 30 years. Each layer’s gas bubbles represent a 60-yr average of atmospheric CO2. A 60-yr running average across a simulated CO2 peak of 345ppmv in the early 1940’s looks a lot like the Law Dome CO2 curve… http://debunkhouse.wordpress.com/2011/01/05/antarctic-ice-cores-diffusion-confusion/
Y’know, for once, this is something testable. They could raise identical plants, even possibly cloned plants, in different C02 environments, and observe the results. Even if it is generational, it could be tested in a relatively short period of time.
So why are they essentially modeling a change against a possibly corrupt temperature record, instead of testing? Is testing no longer considered necessary at all to scientists?
So…plants are releasing less water into the atmosphere because man is causing CO2 levels to rise? Hmm, I wish we had a scientific way of testing how much water is in the air (Humidity) and we had access to data over a long period of time – then we could support or disprove the supposed relationship.
Oh wait, we do! Has humidity been decreasing in stable forest areas in correlation to the supposed relationship to stomata denisity? I bet we can’t find a relationship.
Of course, if we do, then we have to show one causes the other (not just a correlation). But its a start.
Also, I wonder if the stomata denisty is decreasing at the same rate across latitude? If not, it shouldn’t be related to CO2 but instead to temperature or some over variable since CO2 mixes so well in the atmosphere.
The plants don’t respond any differently to anthropogenic CO2 than they do to natural CO2.
The negative plant feedback wouldn’t necessarily cause specific humidity to decline… It would just retard any increase that might result from warming.
Or the CO2 is not actually well-mixed.
Different plant taxa respond differently. Not all taxa are sufficiently responsive to CO2 to be suitable for CO2 reconstructions. In each of these studies, they build training sets to test the stomatal response of living plants to CO2 and other variables. They establish a mathematical relationship and then apply it to herbrarium and fossil samples of the same taxon to reconstruct past CO2 levels.
The methodology has been extensively tested and the effects of other variables can be largely reduced by using a stomatal index (SI) rather than just stomatal density (SD).
Plants are an example of a specie which has nearly destroyed its environment. Overuse of Co2 by plants has produced desert where nearly no plant can grow. Humans have the potential to destroy their environment, but the production of Co2 is not a problem.