Bruce Hungate

Research shows that global warming
alters soil as well as air

Soil researchers hoping for some good news for the fight against global warming recently got some bad news when it comes to carbon release from soil.

They discovered that carbon once thought to store in soil might actually release into a warming atmosphere.

In March, Bruce Hungate, an NAU biology professor and researcher from NAU's Merriam Powell Center for Environmental Research, co-published a paper in the Proceedings of National Academy of Sciences, "Altered soil microbial community at elevated carbon dioxide leads to loss of soil carbon."

Hungate, along with co-authors Karen C. Carney, Bert G. Drake and J. Patrick Megonigal, from the Smithsonian Environmental Research Center, attempted to simulate the changing environment by doubling the level of atmospheric carbon dioxide for six years and measuring the carbon storage in an oak ecosystem in Florida. They discovered that as atmospheric carbon dioxide levels rose, rather than the ground soaking up greenhouse gases, as previously believed, fungi living in the soil caused a carbon loss into the atmosphere.

"It's bad news because soil stores tons of carbon," Hungate said. "Releasing even a small part of that stored carbon to the atmosphere as carbon dioxide will amplify global warming."

Hungate said increasing carbon dioxide also increased the amount of fungi, which boosts the decomposition of organic matter in the soil, releasing the stored carbon into the atmosphere through respiration.

"This means a 'sink' scientists were counting on for storing carbon won't be there in the future," he said. "Our experiment simulated a future atmosphere with high concentrations of carbon dioxide, about what we expect to see sometime between 2050 and 2100, depending on how rapidly we continue to burn fossil fuels. Our experimental result revealed that a loss of soil carbon was caused by elevated carbon dioxide concentrations."

Since plants grow faster as carbon dioxide levels rise and take more carbon from the air, the scientists hoped that this might cause soil to soak up excess carbon and accumulate more root mater.

"I've been measuring soil carbon at this site since 1998. I was really surprised to see that elevated carbon dioxide reduces soil carbon," Hungate said. "This is exactly opposite of what we expected to find and challenges the general expectation that soil carbon will increase with rising carbon dioxide."