High CO2 levels cause plants to thicken their leaves, could worsen climate change effects

October 1, 2018 by James Urton, University of Washington
Tropical forest canopy in Caxiuanã, Brazil. Credit: Jake Bryant

Plant scientists have observed that when levels of carbon dioxide in the atmosphere rise, most plants do something unusual: They thicken their leaves.

And since human activity is raising atmospheric dioxide levels, thick-leafed appear to be in our future.

But the consequences of this physiological response go far beyond heftier leaves on many plants. Two University of Washington scientists have discovered that plants with thicker leaves may exacerbate the effects of because they would be less efficient in sequestering atmospheric carbon, a fact that change models to date have not taken into account.

In a paper published Oct. 1 in the journal Global Biogeochemical Cycles, the researchers report that, when they incorporated this information into under the high atmospheric carbon dioxide levels expected later this century, the global "carbon sink" contributed by plants was less productive—leaving about 5.8 extra petagrams, or 6.39 million tons, of carbon in the atmosphere per year. Those levels are similar to the amount of carbon released into the atmosphere each year due to human-generated fossil fuel emissions—8 petagrams, or 8.8 million tons.

"Plants are flexible and respond to different environmental conditions," said senior author Abigail Swann, a UW assistant professor of atmospheric sciences and biology. "But until now, no one had tried to quantify how this type of response to climate change will alter the impact that plants have on our planet."

This map shows the global distribution of additional warming due to thickened leaves -- beyond the effect of elevating atmospheric carbon dioxide to 710 ppm -- that was projected in simulations by Kovenock and Swann. Credit: Kovenock and Swann, 2018, Global Biogeochemical Cycles

In addition to a weakening plant carbon sink, the simulations run by Swann and Marlies Kovenock, a UW doctoral student in biology, indicated that global temperatures could rise an extra 0.3 to 1.4 degrees Celsius beyond what has already been projected to occur by scientists studying climate change.

"If this single trait—leaf thickness—in high carbon dioxide levels has such a significant impact on the course of future climate change, we believe that global climate models should take other aspects of plant physiology and plant behavior into account when trying to forecast what the climate will look like later this century," said Kovenock, who is lead author on the paper.

Scientists don't know why plants thicken their leaves when carbon dioxide levels rise in the atmosphere. But the response has been documented across many different types of plant species, such as woody trees; staple crops like wheat, rice and potatoes; and other plants that undergo C3 carbon fixation, the form of photosynthesis that accounts for about 95 percent of photosynthetic activity on Earth.

Leaves can thicken by as much as a third, which changes the ratio of surface area to mass in the leaf and alters plant activities like photosynthesis, gas exchange, evaporative cooling and sugar storage. Plants are crucial modulators of their environment—without them, Earth's atmosphere wouldn't contain the oxygen that we breathe—and Kovenock and Swann believed that this critical and predictable leaf-thickening response was an ideal starting point to try to understand how widespread changes to plant physiology will affect Earth's climate.

"Plant biologists have gathered large amounts of data about the leaf-thickening response to high carbon dioxide levels, including levels that we will see later this century," said Kovenock. "We decided to incorporate the known physiological effects of leaf thickening into climate models to find out what effect, if any, this would have on a global scale."

Scene near the Wayqecha Cloud Forest Biological Station in Peru's Manú National Park. Credit: Abigail Swann

A 2009 paper by researchers in Europe and Australia collected and catalogued data from years of experiments on how plant leaves change in to different environmental conditions. Kovenock and Swann incorporated the collated data on carbon dioxide responses into Earth-system models that are widely used in modeling the effect of diverse factors on global climate patterns.

The concentration of carbon dioxide in the atmosphere today hovers around 410 parts per million. Within a century, it may rise as high as 900 ppm. The that Kovenock and Swann simulated with thickened leaves was just 710 ppm. They also discovered the effects were worse in specific global regions. Parts of Eurasia and the Amazon basin, for example, showed a higher minimum increase in temperature. In these regions, thicker leaves may hamper evaporative cooling by plants or cloud formation, said Kovenock.

Swann and Kovenock hope that this study shows that it is necessary to consider plant responses to climate change in projections of future climate. There are many other changes in plant physiology and behavior under climate change that researchers could model next.

"We now know that even seemingly small alterations in plants such as this can have a global impact on climate, but we need more data on plant responses to simulate how plants will change with high accuracy," said Swann. "People are not the only organisms that can influence climate."

Explore further: As climate changes, plants might not suck carbon from the air fast enough

More information: Marlies Kovenock et al, Leaf Trait Acclimation Amplifies Simulated Climate Warming in Response to Elevated Carbon Dioxide, Global Biogeochemical Cycles (2018). DOI: 10.1029/2018GB005883

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19 comments

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Shootist
2.3 / 5 (9) Oct 01, 2018
co2 has been 6x-8x higher.

was global warming©® 6x-8x worse?

The facts are, Vikings raised wheat barley and cattle, on Greenland, for ~400 years between 850-1250. TOO COLD today. not conjecture.

fact: vineyards in Scotland in CE80 and CE1250, taxed by Romans during the Roman Climate Optimum and taxed by England during the Medieval Climate Optimum. You know? When it was warmer than it is now?
Old_C_Code
2.3 / 5 (9) Oct 01, 2018
Huh? But during most of Earth's life history CO2 was at thousands of ppm with heavy vegetation, we are at 400 ppm.

This is such alarmist BS, it's just incredible they write this crap. Bigger leaves are bad. Ugh...
barakn
3.7 / 5 (9) Oct 01, 2018
No evidence for wheat growing in Greenland at all. Zip, zilch, nada. The evidence for barley consists of a few scorched grains in a single layer at the bottom of one trash heap. "The find also substantiates a well-known text from about 1250, 'King's mirror (Konungs skuggsjá)', which mentions in passing that the Vikings attempted to grow grain on Greenland. It is the only report about cultivating barley that we have from that time and says: "As to whether any sort of grain can grow there, my belief is that the country draws but little profit from that source. And yet there are men among those who are counted the wealthiest and most prominent who have tried to sow grain as an experiment; but the great majority in that country do not know what bread is, having never seen it."" https://ancientfo...eenland/
Old_C_Code
2.3 / 5 (9) Oct 01, 2018
Put plants in varying levels of CO2, plants with more CO2 are bigger, grow healthier, better.
This is very very basic science a 4th grader can do.
Alarmists are either crooked or stupid, or ignorant politic nitwits.
antigoracle
2.5 / 5 (8) Oct 01, 2018
CO2 is thickening the skulls of the ignoramuses in the AGW Cult.
barakn
3.7 / 5 (10) Oct 01, 2018
Put plants in varying levels of CO2, plants with more CO2 are bigger, grow healthier, better.
This is very very basic science a 4th grader can do.

Yes, 4th graders do that. So do grownup scientists. And what they consistently find is that the plants have fewer nutrients and more toxins.
Parsec
3.9 / 5 (7) Oct 01, 2018
Put plants in varying levels of CO2, plants with more CO2 are bigger, grow healthier, better.
This is very very basic science a 4th grader can do.
Alarmists are either crooked or stupid, or ignorant politic nitwits.


One could argue that increased thickness is in fact evidence of bigger leaves and thus larger plants with more mass. The question asked however is quite different. That is, "Are these plants more efficient at taking up CO2"?

The problem is that if the plants become less efficient at taking up CO2, which should probably be expected when this nutrient is more available, the effect of these bigger thicker leaved plants is that the overall amount of CO2 per pound of plant is lower.

This result has a strong effect on models which take into account the increased growth expecting the same amount of absorption per pound, which is most of them.

It is hubris in the extreme when the uneducated automatically believe they are brighter than than anyone else.
leetennant
3.9 / 5 (7) Oct 01, 2018
Huh? But during most of Earth's life history CO2 was at thousands of ppm with heavy vegetation, we are at 400 ppm.

This is such alarmist BS, it's just incredible they write this crap. Bigger leaves are bad. Ugh...


Yeah, the Earth was covered in green, lush vegetation that was completely the same as the food crops we need to feed ourselves today... oh wait, no it wasn't. Can we just stop with this nonsense already? We're tired of having to repeat ourselves debunking this garbage.

As we've said a million times - plant toxicity is a thing, the shrinking of arable conditions for food crops is a thing, and plants exposed to CO2 become less efficient, exhaling more CO2 overnight and - we now know - thickening their leaves to protect themselves. This not only affects our food source, it means trees become part of the CO2 problem, not the solution.
mtnphot
3.7 / 5 (6) Oct 01, 2018
"Huh? But during most of Earth's life history CO2 was at thousands of ppm with heavy vegetation, we are at 400 ppm."

Thousands of ppm C02. Really. CO2 is anasthetic at high concentrations. I don't think you would like to be in a room with more than 1000ppm. So if you volunteer, we can put you in a space with the concentration of CO2 that you think is optimal and you can find out for yourself.
mtnphot
3.4 / 5 (5) Oct 01, 2018
Put plants in varying levels of CO2, plants with more CO2 are bigger, grow healthier, better.
This is very very basic science a 4th grader can do.

Yes, 4th graders do that. So do grownup scientists. And what they consistently find is that the plants have fewer nutrients and more toxins.

Plants only use CO2 during the day when they are photosynthesizing. In a dense crop you will find that C02 levels decrease because it is depleted near the leaf. So increasing the level of C02 at the crop does help, however high concentrations of CO2 have a negative feedback loop during respiration. Simple plant physiology that anyone can test. Read Salisbury Ross Plant Physiology.
howhot3
3.9 / 5 (7) Oct 02, 2018
Here is a nice simple graph showing CO2 levels over the past 400,000 years. It's pretty self-explanatory. Simple to axis graph plotting time vs CO2 levels in ppm.
https://climate.n...dioxide/

This should be a graph that would make anybody nervous about the future when you see the dramatic increase in CO2 levels over the past 50 years. The curve plotted out in this graph is definitely an exponential and as much as the deniers of climate change would like to say that it doesn't mean anything it most certainly does. There's a well-established fact of a relationship between CO2 densities and temperature levels. Ie global warming. The warming will affect plant life as much as the added CO2, if not more so.

It's sad that the denier goon-squad can't take a few minutes to read a little science to improve their deductive reasoning skills and quit being such goofy twits.
Old_C_Code
2.1 / 5 (7) Oct 02, 2018
" And what they consistently find is that the plants have fewer nutrients and more toxins."

With increased CO2? Oh you lying sack of chit they do not.
Show the links, dope.
antigoracle
2.6 / 5 (5) Oct 02, 2018
Yeah, the Earth HAWW...HEE...HAWW..HEE... We're tired of having to repeat ourselves debunking this garbage.

As we've said a million times - plant toxicity is a thing, the shrinking of arable conditions for food crops is a thing, and plants exposed to CO2 become less efficient, exhaling more CO2 overnight and - we now know - thickening their leaves to protect themselves. This not only affects our food source, it means trees become part of the CO2 problem, not the solution.

The leetennant jackass brays again.
This is the jackass, who cares so much, that he boasts about his CO2 spewing pleasure cruise to the Antarctic and his plans to do the same to the Arctic.
This jackass just likes the sound of his braying and not the substance, because it's all hypocritical shite. Keep braying jackass....you'll save the world.
barakn
3.7 / 5 (6) Oct 02, 2018
Cassava leaves have higher levels of cyanogenic glycosides in increased CO2 (cyanogenic means "produces cyanide"). Oddly the tubers are also smaller. https://www.ncbi....19778371
Lower iron and zinc in rice https://www.tandf...11863730 and in a variety of C3 grains and legumes https://www.natur...ure13179

Old_C_Code
2.3 / 5 (3) Oct 02, 2018
"have higher levels of" ... everything, they are bigger.
Lower iron and zinc, but more carbon for sugars.
CO2 is plant food, barakn, you are literally insane.
barakn
4.2 / 5 (5) Oct 02, 2018
Who said it wasn't plant food? The question is whether those plants will provide adequate food for you.
leetennant
5 / 5 (3) Oct 02, 2018
This is like someone throwing you into the ocean and then when you ask them to save you, yelling "But humans need water to live!"
howhot3
5 / 5 (1) Oct 02, 2018
It's pretty obvious that @old_c_code and the @antigoracle both don't care about what they leave behind when they're bodies eventually become plant food. I still don't get the motivation of people that refuse to accept science when it's presented to them in a such a simplistic manner and truthful manner. Well, the carbon cycle is not as simple as one plus one equals two but the principle upon which the Science is based is pretty obvious to the trained person. So when climate scientists make predictions about global warming impact on the planet it's best to follow and examine the claims being made.

My advice to the climate change deniers and the Denier Goon Squad is to give up the fight and start listening to what is being said.

leetennant
5 / 5 (1) Oct 02, 2018
Howhot3 - pretty sure that OldC at least is a Russian bot or at least a paid troll. Not sure about AntiG - he could just be batshit crazy.

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