Study ups plant CO2 intake estimates

May 21, 2012 By Tom Marshall
Study ups plant CO2 intake estimates

Plants may be able to limit the impact of our CO2 emissions even more than we previously thought, an innovative new experiment suggests.

The study is the first to try to create a simplified self-contained replica of the Earth's land-based , using and in airtight containers. As researchers increased temperature and CO2 levels, the plants kept absorbing the extra gas for longer than computer models and earlier experiments had predicted.

In fact, they took in 62 per cent of the extra CO2 and prevented the temperature from increasing by more than 2.3°C. At that point the gas's concentration was still beneath 500 parts per million (ppm). Without the plants' increased activity, it would have been 760ppm, implying warming of around 4.4°C.

It's hardly a solution to ; plants couldn't keep this up for ever, and the experiments did not include the changes in the availability of water and nutrients that will be another consequence of climate change and that will almost certainly limit plant growth in many areas. But the study does suggest that plants may be more capable of adapting to changing conditions than we thought, and it will give us a more accurate idea of the consequences of climate change.

"The scenarios we used were very optimistic in terms of future CO2 anthropogenic emissions, so there are still very serious concerns about climate change," says Dr. Alex Milcu of Imperial College, London, the paper's lead author. "But it does look like plants may be able to take in more CO2 than previous experiments and models predicted."

At the moment, scientists estimate that terrestrial plants mop up around a quarter of the CO2 we emit. Increasing CO2 levels means they can grow faster and absorb even more of the gas. But the higher temperatures predicted from climate change will also make the microbes in the soil more active, increasing their respiration and hence their .

Study ups plant CO2 intake estimates
Closed experiment to show how plants will respond to climate change

So we don't know what the overall effect will be - will more land ecosystems absorb more CO2 on balance, or less? Understanding this would let us make better predictions of the effect releasing different amounts of carbon into the air would have.

Previous studies have tried to answer the question either using computer models or by putting plants in an experimental setup and changing just one variable at a time - for instance, raising CO2 and seeing how they react.

But this approach doesn't do justice to the complexity of the carbon cycle, which is full of hidden tipping points and feedback loops. When the environment changes and affects how plants grow, their response changes the environment again, in turn affecting their growth, and so on. The researchers behind this study decided to try to model this complexity by building a closed, airtight system that worked as a simplified version of the whole terrestrial carbon cycle.

"Computer climate models have become increasingly complex and I wanted to go back to basics. We achieved this by somewhat radically building a 'physical' model of the terrestrial carbon cycle. This is equivalent to using a wind tunnel, as opposed to a computer simulation, to test the aerodynamics of a new structure," says co-author Professor Phil Ineson, from the University of York. "Our experimental findings made total sense but suggested that the capacity of the Earth to buffer against rising carbon dioxide may be greater than the computer models imply - we still have the same major concerns about climate change, but the system may have some tricks up her sleeve!"

They put plants growing in microbe-rich soil into sealed plastic cabinets and varied the conditions they grew under, monitoring what happened under different scenarios for three months. Some were kept in unchanged conditions; others got more CO2 but unchanged temperatures. A third group got more CO2 and temperatures that changed according to a climate model's predictions of the effects of its CO2 levels - so the higher CO2 levels climbed, the hotter it got.

They found that the plants in the final category didn't just absorb the extra carbon released by the soil microbes; they also took in much of the extra CO2 that had been added to their cabinets' atmosphere, limiting temperature increase. But the plants didn't bring or temperatures back down again; conditions never returned to how they'd started throughout the life of the experiment.

Milcu says the team would have liked to have carried on for longer, but that the experiment was so difficult to set up that by the time they sealed every leak and got a truly closed system working, they had just three months left.

They have done limited trials of a more sophisticated follow-up experiment whose cabinets also included an aquatic component, as the oceans are at least as important as plants on land in absorbing CO2 from the atmosphere. But these weren't conclusive, and Milcu would like to carry out much more extensive and longer-lasting trials using this improved setup. He'd also like to use much more diverse plant communities, rather than just one kind of plant as here, to give a better idea of the overall response of whole ecosystems.

The NERC-funded study, published in Nature Climate Change, was authored by scientists at Imperial College London and the Universities of Newcastle, Reading, Stirling and York. It took place at NERC's Ecotron controlled-environment facility at Imperial.

Explore further: US plans widespread seismic testing of sea floor

More information: Biotic carbon feedbacks in a materially closed soil-vegetation-atmosphere system. Alexandru Milcu, et al. Nature Climate Change 2, 281-284 (2012) doi:10.1038/nclimate1448
www.nature.com/nclimate/journa… ll/nclimate1448.html

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jonnyboy
1 / 5 (3) May 21, 2012
hmmmmmmmmmmmmmmm
Sigh
4.2 / 5 (5) May 21, 2012
According to the incentive theory, that scientists only publish alarmist results because that pays best, this study (and quite a few others reported here on physorg) should never have been published. Could there be a problem with the incentive theory?
Howhot
2.3 / 5 (3) May 21, 2012
Actually, the experiment is kind of alarming in its results. It's too bad the story wasn't buried. It might give the fossil fuel industry an excuse to put more CO2 into the air. As it is now, we have already dumped an ADDITIONAL 780 GIGATONS of CO2 into a 5 mile high atmsosphere since the the 50s and have managed to tweak out about a 1.7C increase in global average temperature (of course the polar regions are getting the worst of it, with polar ice melts and HUGE methane releases from the tundra and frozen bogs).

Of course plants don't use the methane in the Carbon cycle.

Its good to know the plants will save us and we can happily pollute as much as we would like and not see the consequences of that bad-old-AGW-global-warming alarmists have warned about. (sarcasm included for free).

jnjnjnjn
3.4 / 5 (5) May 22, 2012
@Howhot,
Not so, its only 1C average temperature increase and not 1.7C (http://news.softp....shtml). And the cause of the increase could even be a natural 'long term' climate variation.
Also, pollution and CO2 isn't the same. Pollution is for example fine dust emitted by diesel engines that causes cancer in animals (and humans) or leaded fuel that causes major health problems in animals (and humans) or DDT that is disastrous in the long run for animal live.
Habitat loss of animals and the plundering and exploitation of nature caused by the rapid increasing of the Human population is the main thing to worry about, not a few ppm CO2.

J.
StarGazer2011
2.3 / 5 (3) May 22, 2012
I wonder how they managed the 'more CO2 but unchanged temperatures' scenario. They must have had some cooling to offset the heat which, without CO2, would have escaped the system as IR but was 'trapped' by the greenhouse effect of the higher CO2 level?
Does anyone know what cooling was required?
Howhot
3 / 5 (2) May 23, 2012
@njnjnjn; It is 1.74C over the Northern hemisphere. My bad. But your idea the CO2 is not a pollutant is mistaken. It's a pollutant in the sense that it is being released from sources that would not normally be part of the Carbon Cycle. I wouldn't trivialize a few ppm. Each ppm(v) represents 7.8 Billion tons of additional CO2 added to the carbon cycle that has stayed and is wafting in the atmosphere. It doesn't include all the gigatons added to the oceans above normal 50s levels.

The incredible scale of the human population growth is certainly of concern because it is unsustainable. And it's an issue of concern for the near future too, 50 years or less.