Soil to release more carbon than expected as temperatures rise

New research has found that carbon stored in the planet’s soil is more vulnerable to climate change than previously predicted.

 

Soil may not look too impressive, but it stores around 2,000 billion tonnes of carbon, four times more than plants, and plays a huge role in mitigating climate change. But new research has revealed that soil may be a less stable carbon sink than previously predicted as temperatures increase.

The study, involving scientists from the Hawkesbury Institute for the Environment at the University of Western Sydney in Australia, has found that soil microbes - tiny organisms such as bacteria that live in soil - will release more CO2 than previously expected as temperatures rise.

The researchers studied soil from 22 ecosystems ranging from the Arctic to the Amazon, and discovered that current climate models have underestimated how much CO2 soil microbes will release into the atmosphere as temperatures increase. The results have been published inNature, and could change medium and long-term climate predictions.

“Our climate is regulated by soils (as well as) the ocean systems. That’s how important they are", Brajesh Singh, a microbial ecologist from the Hawkesbury Institute for the Environment and co-author of the paper, told John Ross from The Australian.

The Intergovernmental Panel on Climate Change, which aims to predict future temperature increases, had already factored into their climate models the fact that soil microbes will release more carbon as temperatures increase. But the study found that these models have greatly underestimated this increase in soils with high carbon-to-nitrogen ratios, and those in cold temperatures.

Microbes in the soil in Arctic regions, for example, will release 40 percent more CO2 than predicted, The Australian reports.

"It will have a significant impact on our carbon budget because that's where most of our carbon soil is locked in," Singh told Peter Hannam for the Sydney Morning Herald.

Experts also previously expected that microbes would eventually get used to the new, increased temperatures, and gradually stabilise their carbon emissions. But the new research shows no evidence that this will happen.

To test how soil would respond to changed temperatures, the scientists kept soil collected from regions with average temperatures ranging from -6 to 24 degrees Celsius, and stored them at 3 degrees Celsius above their natural temperature for 90 days. Previously studies had only looked at the soil for a few days after increasing its temperature.

They found that the majority of soil samples released more CO2 than current models predict. However, the scientists still aren’t sure why this is the case. Kristiina Karhu from the University of Helsinki in Finland, and the lead author of the paper, told Matt McGrath from the BBC that it could be a result of varying nitrogen and carbon contents in the soil.

"The soils that had this enhancing response were also soils that had a high carbon to nitrogen ratio," Karhu told BBC.

"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."

Singh explained to The Australian that their discovery would affect medium and long-term estimates of climate change. Further research is now needed to ensure scientists are making accurate climate predictions.

The Hawkesbury Institute for the Environment is interested in hearing from the world'sfuture scientists. Scholarship opportunities are available until late October - make contact with a researcher today.