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Global warming can release carbon from tropical soils

According to a new study published Wednesday in the journal Nature. An experiment that heats the soil below a tropical rainforest to mimic the temperatures expected in the coming decades found that hotter lands emit more carbon dioxide to warm the planet 55 % relative to nearby un-heated areas.

If the result were to be applied across tropical regions, much of the carbon stored underground could be released when the planet heats up.

“The shrinkage rate is huge,” said Andrew Nottingham, an ecologist at the University of Edinburgh and lead the study. “It̵

7;s a bad news story.”

The thin soil that covers most of our planet’s soil stores vast amounts of carbon – more in total than all the plants and the atmosphere combined. That amount of carbon feeds the colonies of bacteria and fungi, which build some of them into more bacteria while inhaling the rest into the atmosphere in the form of carbon dioxide. Many of these bacteria grow more actively at warmer temperatures, speeding up their digestion and respiration.

Eric Davidson, an environmental scientist at the University of Maryland College of Environmental Science in Frostburg, who was not involved in the study, said the finding “is another example of why we need to worry more.” about the rate of global warming.

In an effort to predict the future, in the early 1990s, ecologists began building machines to artificially heat the soil. Such experiments in temperate and montane forests have shown that carbon-rich soils almost always produce carbon dioxide when heated. In 2016, a team of researchers estimated that, by 2050, soil could emit gases that warm the planet to the same level as adding to the carbon footprint of a new country the size of the United States. States.

But that study removed the warm, biodiversity tropical regions forever, where one-third of the total carbon in the soil. Finding the fate of this carbon would require grappling with the many pitfalls of doing research in the tropics: humidity, storms and countless hungry animals can compromise research equipment – no such as chewing wire or protective coating – and about the researchers themselves.

Margaret Torn, an ecologist at Lawrence Berkeley Laboratory in California who was not involved in the study, said that to understand the soil’s contributions to climate change, the tropics “are a really important area. “but” has not really been studied.

In 2014, Dr. Nottingham, then a postdoctoral fellow at the University of Edinburgh, went to Barro Colorado Island, a man-made island in the Panama Canal area where the Institute of Tropical Studies is located. Smithsonian. He buried the wires in five circular plots to a depth of almost four meters. In order to protect against aggressive elements and insects, he shielded the wires inside metal structures shaped like bizarre large spiders. Measurements have been recorded inside the weatherproof box.

Dr. Nottingham said: “Our experiment was basically me making postdoc doing everything from a DIY store.

The team ran into a number of malfunctions, including a poor electrical connection leading to an explosion and costing researchers nearly a year and a lot of budget to repair it. Starting in November 2016, the conductor’s resistance began warming the soil by almost 6 degrees Fahrenheit, in the tropical range that is expected to warm by the end of the century according to current climate models. Other devices measure the amount of carbon dioxide released from both the test plots and neighboring plots that are not artificially warmed and microbial activity in the plots.

A soil warming test in the El Yunque National Forest in Puerto Rico was conducted two months earlier but was hit by a Category 5 hurricane in September 2017; The team had not turned on the power again for a year.

The results from Dr. Nottingham’s team are serious: Over two years, warm soils released 55% more carbon than the control plots. “This is a very big response,” said Dr. Torn, who performed a similar warming experiment in a forest in California, said carbon emissions increased by about 35% after two years. “It’s one of the biggest I’ve ever heard.”

If the entire tropics did the same thing, the researchers estimate that 65 billion tons of carbon would enter the atmosphere by 2100 – more than six times the annual emissions from all human-related sources. .

However, scaling the results to compute the entire tropics is very complicated. Dr. Davidson notes that the soil on Barro Colorado Island is richer in nutrients than many other places, such as the soil of much of the Amazon rainforest. That could make it easier for the Panamanian bacteria to boost their activity. The microbial communities in Africa and Asia are very different from those in the Americas, says Dr. Torn.

And while there is consensus that climate models need to treat the soil more practically, the best way to do that is still unclear. Kathe Todd-Brown, a soil scientist at the University of Florida in Gainesville who is not part of the research team, said the new study dealt a blow to simple theories that predict that tropical soils will reflect Corresponding to warming. But to really get around the problem, she says, modelers will need information about how microbes react to variations in soil moisture and nutrients in addition to temperature.

Tana Wood, an ecologist with the US Forest Service who was leading the experiment in Puerto Rico, said by simply warming the soil, the Barro Colorado experiment failed to capture how the plants function. moving in warmer conditions. For example, if plants photosynthesize more, they can absorb some of the carbon dioxide released by the soil, making the overall impact on the climate less severe. “This is only half the carbon story,” she said. (Her team is warming both the soil and the air with an infrared heater and measuring the response of plants and microorganisms.)

Dr. Torn said she was eager to see more than two years worth of data that could reveal whether the carbon dioxide spike was long-lasting or short-lived. “In the life of a rainforest, it was a very short period of time,” she noted.

Dr. Nottingham has funding to keep the Panama project running for at least another 5 years. But even two years have shown how important it is to find ways to keep ecosystems intact, he says. “It makes you realize how fortunate we have been so far to have a relatively stable climate.”

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