Soils may not always act as carbon sinks, a new study suggests
Credit: Derek Jensen
CAIRO: Rising levels of carbon dioxide in the air may turn soil from a potential carbon sink into an emission source by stimulating microbes to release carbon dioxide, according to a new study.
The research, published in the latest issue of the U.S. journal, Proceedings of the National Academy of Sciences, suggests that tampering with microbial activity in soil to counteract this effect could help stabilise atmospheric carbon dioxide levels and help slow global warming.
Previous studies have shown that higher carbon dioxide levels increase plant growth ― and therefore the sequestration of carbon dioxide by plants ― with soil serving as a sink for excess carbon.
But the new study indicates that, despite the increased plant growth, doubling carbon dioxide levels in an ecosystem actually causes a reduction in carbon storage in the soil.
"We thought that higher plant growth at elevated carbon dioxide levels would add more carbon to soils or at least leave it the same," said lead researcher Patrick Megonigal from the U.S.-based Smithsonian Environmental Research Centre in Maryland.
"We now need to consider a third possibility — that the carbon already in soils will end up back in the atmosphere as a greenhouse gas," he added.
The researchers say elevated carbon dioxide levels increased microbial activity in the soil, leading to decomposition of organic matter and the release of carbon dioxide.
Soils exposed to the elevated carbon dioxide were found to contain more fungi and higher levels of activity of a carbon-degrading enzyme.
The study compared samples in a Florida scrub oak ecosystem over a six-year period. The researchers found that the carbon dioxide loss from soils negated about 52 per cent of the additional carbon that had been sequestered by the trees.
"Because the loss of soil carbon was due to the actions of soil microorganisms, our work highlights the importance of understanding these tiny creatures and their responses to rising carbon dioxide and global climate change," Megonigal said.
He plans to further investigate the changes in microbial activity and the extent to which this happens in other forests.
