High CO2 spurs wetlands to absorb more carbon

July 16, 2013, Smithsonian
The Smithsonian Environmental Research Center's Bert Drake holds up a cluster of Spartina patens, a marsh grass that absorbed more CO2 than his team expected. Drake's team looks into the future by filling marsh chambers with extra CO2, tracking how plants will grow over the next century.

(Phys.org) —Under elevated carbon dioxide levels, wetland plants can absorb up to 32 percent more carbon than they do at current levels, according to a 19-year study published in Global Change Biology from the Smithsonian Environmental Research Center in Edgewater, Md. With atmospheric CO2 passing the 400 parts-per-million milestone this year, the findings offer hope that wetlands could help soften the blow of climate change.

Plant physiologist Bert Drake created the Smithsonian's Global Change Ecological Research Wetland in 1987 at Edgewater. Back then, most scientists thought plants would gradually stop responding to rising CO2. Whether or not could assimilate additional carbon—and act as powerful carbon sinks—was not known. This study tracked not only how much CO2 wetlands absorb, but also the impact of rising temperature and sea level, changing rainfall and plant type.

To simulate a high-CO2 world, Drake's team surrounded marsh plots with open-top Mylar chambers. For this study they left half of the chambers exposed to today's atmosphere. In the other half they added CO2 and raised the level to 700 ppm, roughly doubling the CO2 concentration as it was in 1987. Other plots of land were left without chambers. They compared the levels of CO2 going in and CO2 going out to determine the carbon exchange between the wetland and the atmosphere.

Two types of plants populate most of the world, and the experiment tested both. C3 plants—which include more than 95 percent of the on earth, including trees—form molecules of three carbon atoms during photosynthesis, and they tend to photosynthesize more as atmospheric CO2 rises. C4 plants form molecules of four . But for C4 plants, photosynthesis is saturated with CO2 at present levels. For that reason the team expected photosynthesis to increase in the C3 plants but not the C4 plants as they raised CO2. In this study, half the plots were dominated by the C3 sedge Scirpus olneyi and half by the C4 grass Spartina patens.

The C3 plants saw the largest increases. Over the 19-year study, they absorbed on average 32 percent more carbon under higher CO2 than under normal CO2. Most of the increase took place during the day, as the plants absorbed extra CO2 through photosynthesis. But the team was surprised to find that elevated CO2 also decreased the amount of carbon the plants lost at night through respiration. That reduction was due in part to a decrease in the amount of nitrogen in both types of plants when they grew in the high-atmospheric CO2. Also contrary to their expectations, the C4 plants saw a 13 percent increase under elevated CO2, also predominantly during the day but partially at night.

"We expected that more carbon would be assimilated during the day due to stimulation of photosynthesis," Drake said. "We did not expect that loss of carbon at night would also be affected by the elevated CO2."

However, climate also affected how much carbon the plants absorbed. For example, droughts crippled the C3 plants' ability to take up carbon. During three dry years (1995, 1999 and 2002), they absorbed a mere 4 percent more CO2 on average under elevated versus normal conditions. Those three years also saw the lowest CO2 absorption overall. Other environmental factors related to , such as sea-level rise and increasing temperature, also affected carbon assimilation.

Ecologists are still working out where all the extra absorbed carbon is going. According to their data, it does not all go into creating plant biomass. However, the plants do not show any sign of slowing their carbon absorption. "The results of this study suggest that wetland ecosystems will assimilate more carbon as atmospheric CO2 levels continue to rise beyond the level of 400 ppm reached in May 2013," said Drake.

The accepted manuscript is available online.

Explore further: Research supports a new approach to counting CO2 emissions

Related Stories

Research supports a new approach to counting CO2 emissions

July 16, 2013

(Phys.org) —Researchers have called for a system of carbon emission assessments that reflect better the true contribution of each emitting nation to the increase in atmospheric CO2 and promote preservation of forests, particularly ...

Elevated carbon dioxide making arid regions greener

May 31, 2013

Scientists have long suspected that a flourishing of green foliage around the globe, observed since the early 1980s in satellite data, springs at least in part from the increasing concentration of carbon dioxide in Earth's ...

Deserts 'greening' from rising CO2

July 3, 2013

Increased levels of carbon dioxide (CO2) have helped boost green foliage across the world's arid regions over the past 30 years through a process called CO2 fertilisation, according to CSIRO research.

Historic carbon peak soon to become global average, WMO says

May 14, 2013

After seeing carbon dioxide levels in the atmosphere surpass a historic threshold last week, the world should brace for the new peak level to soon become the global annual average, the World Meteorological Organization warned ...

Climate chief warns of 'urgency' as CO2 levels rise

April 29, 2013

The UN's climate chief called for urgency Monday as she opened a new round of global talks amid warnings that Earth-warming carbon dioxide levels were approaching a symbolic threshold never seen in human history.

Recommended for you

Researchers name new ocean zone: The rariphotic

March 20, 2018

Based on the unique fish fauna observed from a manned submersible on a southern Caribbean reef system in Curaçao, Smithsonian explorers defined a new ocean-life zone, the rariphotic, between 130 and 309 meters (about 400 ...

Geoengineering polar glaciers to slow sea-level rise

March 19, 2018

Targeted geoengineering to preserve continental ice sheets deserves serious research and investment, argues an international team of researchers in a Comment published March 14 in the journal Nature. Without intervention, ...

Palm trees are spreading northward. How far will they go?

March 19, 2018

What does it take for palm trees, the unofficial trademark of tropical landscapes, to expand into northern parts of the world that have long been too cold for palm trees to survive? A new study, led by Lamont-Doherty Earth ...


Adjust slider to filter visible comments by rank

Display comments: newest first

1.5 / 5 (24) Jul 16, 2013
One more negative feedback.
2.3 / 5 (25) Jul 16, 2013
Because they'll find this article sooner or later....

Climate change deniers using dirty tricks from 'tobacco wars'

Science under fire from 'merchants of doubt': US historian

Leaks show group's climate efforts

Learn more about logical fallacies and real critical thinking here:
or here http://rationalwi...y_theory
1.2 / 5 (19) Jul 16, 2013
yeah but what about the methane that is being expelled from fracking that is 85 times more polluting than co2?
1.2 / 5 (23) Jul 16, 2013
1.3 / 5 (23) Jul 17, 2013
Oops. IPCC did ofcourse know about this in retrospect because they know all about the carbon cycle.
1.4 / 5 (27) Jul 17, 2013
Hate speech flinging Astroturf deniers of natural climate change...

...are doomsday religious followers of divinity student and family tobacco farm owner Al Gore whose recent half billion dollar sale of his greenie cable TV channel for a half a *billion* dollars will help him add new palaces to his collection, here being an example of one of his mafia movie worthy ocean view estates:


Science is indeed under fire from propagandists, as I cathartically exposed in a single postcard Cliff Note:


Main alarmist blogs were established by huge PR firms such as those with solar energy interests or just plain scams like the autism vaccine scare whereas skeptical blogs are singularly owned by volunteers. Google isn't their friend: Fenton Communications Autism.

The main logical fallacy of all time (left out of Neinsense's links) is the consensus-claimed Call To Authority.
1.3 / 5 (26) Jul 17, 2013
P.S. The jet ski on Gore's yacht can be seen in volunteer video footage, here:


His Astroturf organizing site is very amusingly here:


That's where these link bombing activists come from after they read one of many conspiracy theory books that claim skeptics are getting their information from Glenn Beck instead of the other way around.
1.4 / 5 (29) Jul 17, 2013
Open letter to Greenpeace: I will stop posting about climate for a mere $1000 a month over the next five years. This is a hobby that I now enjoy as a work-at-home break, especially when I'm procrastinating during product design mental blocks, but I can think of a lot more rewarding and less masochistic breaks at sidewalk cafes or at 3AM in Little Korea where I can delve into the translation of Aristotle's fallacies I put on my iPhone last month. I like to eventually delve down into the original work, to the agitated chagrin of climate "scientists" and their Astroturf enablers, but the delving is its own reward and the Internet is a cesspool that rubs off on me too much and that's bad for my health, I imagine. Anybody out there could fund this offer using Kickstarter.com, or at least try. That skeptics already won over the anti-science instincts of Republicans means the boringly meandering climate itself can now argue for us, minus severe energy rationing during a recession.
4.6 / 5 (10) Jul 17, 2013
Even so, this doesn't mean we should push the environment to the point that it does so.
2.3 / 5 (21) Jul 17, 2013
Nice video full of beautiful naked ladies.

3.8 / 5 (13) Jul 17, 2013
Nik: "P.S. The jet ski on Gore's yacht can be seen in volunteer video footage, here"

Ahhh - I get it - Al Gore has a jet ski - that one for sure disproves everything the scientists have learned about the climate, and certainly adds a great deal of insight into an article about the absorption of C02 in the wetlands. Thanks for that great contribution to the body of knowledge Nik!!!!!!!!!
2.2 / 5 (19) Jul 20, 2013
NYC Nicky lacks the humour to be entertaining, the knowledge to be informative, and has all the charm and attraction of a deceased rat which suffered from leprosy and incontinence. He is like an insane woodpecker looking for a grub in a block of concrete.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.