Carbon in Soil Vulnerable to Climate Change

The huge stores of carbon locked in the Earth's soil are more vulnerable to climate change than previously thought, according to new research.

Researchers found that microbes in the soil were more likely to enhance the release of carbon dioxide (CO2) in a warming world, especially for soils in colder regions.

"Our findings suggest that warming will increase the activity of soil microbes to a greater extent than was previously expected, which could have implications for future rates of climate change," Dr. Kristiina Karhu of the University of Helsinki, lead author of the study, said in a press release.

The world's soils hold about twice the amount of carbon as the atmosphere, and the microbes release around 60 billion tons of this carbon dioxide into the air every year.

But previous studies have shown that these microbes can swing both ways, effectively reducing CO2 as well as releasing it into the atmosphere.

So scientists set out to test 22 different soil samples from the Arctic to the Amazon, testing their response to increased temperatures over a course of 90 days.

"There were some suggestions that microbes could get accustomed to higher temperatures with climate warming and then the temperature sensitivity of soil respiration would decline," Karhu told BBC News.

What they found was that arable or managed lands were the only ones where microbes reduced the effects of a temperature change on the amount of carbon dioxide released. For all other soils tested, the microbes in fact enhanced the release of CO2 into the atmosphere.

The research team speculates that nitrogen in the soils may be causing this response.

"So it could be something in this interaction between carbon and nitrogen cycles, and there are some studies that suggest that maybe the enzymes related to nitrogen may be more temperature sensitive than the carbon related enzymes," Karhu explained to BBC.

Whatever the root of the problem, scientists are nonetheless concerned that current soil carbon and Earth system models may be underestimating the impact of warming on the huge reserves that sit in the ground.

The findings were published in the journal Nature.