New Research Unravels the Mysteries of Deep Soil Carbon

Energy-starved microbes may be the force that causes huge amounts of carbon to be stored in deep soils, according to a Dartmouth College study.  The research finds that less food energy at depth makes it more difficult to decompose deposits of organic carbon, creating an underground storehouse for the climate-destabilizing chemical element.

The study, published in Soil Biology and Biochemistry, outlines the conditions that underlie whether deep soil acts as a source or a sink for carbon.

The fate of deep soil carbon is of major consequence to researchers studying climate change.  It is estimated that 2400 gigatons of carbon is stored in soil, with two-thirds of that lying below the 20 cm depth.  The amount of deep soil carbon alone is about double the amount of carbon in the form of carbon dioxide that exists in the Earth's atmosphere.

If decomposition rates increase as a result of climate change, then carbon stored in deep soils will be released into the atmosphere as the greenhouse gas carbon dioxide.  The research tested how decomposition changes with soil depth to help predict whether deep soil carbon would be vulnerable to such climate-induced changes.

"Deep soil carbon is a really big deal for understanding the future of climate change," said Caitlin Hicks Pries, an assistant professor of biology at Dartmouth.  "Understanding the forces that cause that much carbon and all of its greenhouse gas potential to be stored underground helps us predict what our future climate will look like."

Soil organic carbon comes from the decomposition of dead plants and can remain in soil for thousands of years.  The research team set out to see how root litter decomposes at different depths to understand why some deep soil carbon can be stored for such a long period of time and why other carbon is released into the atmosphere.

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