Warmer soils release additional CO2 into atmosphere
In a new study, researchers have found that warmer temperatures due to climate change could cause soils to release additional carbon into the atmosphere, thereby enhancing climate change - but that effect diminishes over the long term.
The study, from University of New Hampshire professor Serita Frey and co-authors from the University of California-Davis and the Marine Biological Laboratory, sheds new light on how soil microorganisms respond to temperature and could improve predictions of how climate warming will affect the carbon dioxide flux from soils.
The activities of soil microorganisms release 10 times the carbon dioxide that human activities do on a yearly basis. Historically, this release of carbon dioxide has been kept in check by plants' uptake of the gas from the atmosphere. However, human activities are potentially upsetting this balance.
Frey and co-authors Johan Six and Juhwan Lee of UC-Davis and Jerry Melillo of the Marine Biological Laboratory were curious how increased temperatures due to climate change might alter the amount of carbon released from soils.
The study examined the efficiency of soil organisms - how completely they utilize food sources to maintain their cellular machinery - depending upon the food source and the temperature under two different scenarios.
In the first short-term scenario, these researchers found that warming temperatures had little effect on soils' ability to use glucose, a simple food source released from the roots of plants. For phenol, a more complex food source common in decomposing wood or leaves, soils showed a 60 percent drop in efficiency at higher temperatures.
"As you increase temperature, you decrease the efficiency - soil microorganisms release more carbon dioxide to the atmosphere - but only for the more complex food sources. You could infer that as the soil warms, more carbon dioxide will be released into the atmosphere, exacerbating the climate problem," Frey explained.
That effect diminishes, however, in the second scenario, in which soils were warmed to 5 degrees Celsius above the ambient temperature for 18 years.
"When the soil was heated to simulate climate warming, we saw a change in the community to be more efficient in the longer term," Frey said lessening the amount of carbon dioxide the soils release into the atmosphere and, in turn, their impact on the climate.
The researchers hypothesize that long-term warming may change the community of soil microorganisms so that it becomes more efficient.
This study was based on work done at the Harvard Forest Long-Term Ecological Research site in Petersham, Mass., where Frey and Melillo have been warming two sites - one 9 meters square, the other 36 meters square -- with underground cables for two versus 18 years.
The research appeared in the journal Nature Climate Change.