Tuesday, Nov. 23, 2010
SOIL RESEARCH PROVIDES NEW INSIGHT INTO FUTURE GLOBAL WARMING PREDICTIONS
MANHATTAN -- Soil that was once thought to be the least vulnerable to decomposition is actually the most sensitive to increasing temperatures, making it more likely to release carbon into the atmosphere as the climate warms, according to researchers at Kansas State University and a colleague in Colorado.
Joseph Craine, K-State research assistant professor of biology; Kendra McLauchlan, K-State assistant professor of geography; and Noah Fierer, assistant professor of ecology at the University of Colorado at Boulder, are the authors of "Widespread Coupling between the Rate and Temperature Sensitivity of Organic Matter Decay," published recently in the journal Nature Geoscience. Their data will be used to develop a model for more accurately predicting future global warming.
With more than $450,000 in grants from the National Science Foundation, the three researchers analyzed microbial decomposition of soil organic matter from 28 different sets of soils collected from sites across North America -- stretching from Alaska to Puerto Rico. The samples were incubated for a year, periodically altering the temperatures to measure changes in the rate of soil microbe respiration.
"We found that as we warmed different soils, those soils that were the hardest for microbes to degrade showed the greatest response to the increase in temperature," Craine said. "We were the first to demonstrate that chemical laws discovered more than 120 years ago predict how warming affects microbial decomposition of soil carbon."
Based on their research and the results from other studies that incubated a range of organic materials like simple sugars, leaves, roots and other soils, the group discovered a general relationship that clearly shows that carbon molecules in the soil with the most chemical resistance to microbial enzymes are most sensitive to temperature increases.
"The future of the Earth's temperature depends on the ability of soils to retain carbon as the world warms," Craine said. "Globally, soils contain about twice as much carbon as found in the atmosphere and three times as much found in vegetation. That means even a small percent increase in carbon released from the soil could have a major impact on the atmosphere and future warming."
The process of removing carbon from the atmosphere and storing it in the soil is a natural part of the carbon cycle, although soil carbon varies greatly in quality, Craine said. A small portion of the carbon stored in the soil can be returned to the atmosphere through decomposition, when soil microbes digest organic matter and release carbon dioxide as a byproduct.
"Soil carbon quality is best explained by how easy it is for organic matter in the soil to decompose," McLauchlan said. "Chemically speaking, things with a lower carbon quality are harder for microbes to eat, and they're just more complicated structurally."
Evidence from the study contradicted the group's original hypothesis by finding that complicated carbon molecules are more sensitive to increasing temperatures in varied soil samples.
"The results were surprising, in a sense, because we think that the more complicated a carbon molecule is, the more difficult it should be to break down," McLauchlan said. "It should be protected; basically it should be inaccessible and be very stable in the soil; however, what's protecting it is thermodynamics. When you add heat, that makes those reactions go, and the soil becomes vulnerable."
The group will be developing an equation that can be used in models to simulate data about future emissions of carbon dioxide from the soil in response to warming, Craine said. The data could ultimately become the basis for politicians to enact legislation to prepare for and to mitigate future warming.
"The work does not, in and of itself, tell us how much more carbon dioxide will enter the atmosphere as the Earth warms, but it does provide a key equation that can be incorporated into computer models," Craine said. "It's possible that we have been vastly underestimating how much additional carbon dioxide will enter the atmosphere."