Microbe diet key to carbon dioxide release

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Washington, August 1 : Scientists have determined that as microbes in the soil break down fallen plant matter, a diet "balanced" in nutrients appears to help control soil fertility and the normal release of the greenhouse gas carbon dioxide into the atmosphere.

When plants drop their leaves, stems and twigs, this organic matter slowly becomes part of the soil as a result of decomposition, which is facilitated by bacteria and other microbes.

This process adds plant nutrients to the soil and releases carbon dioxide into the atmosphere.

Duke University scientists found that the proportion of nitrogen to carbon in this organic matter determines how much nitrogen becomes available to plants in the soil and how much CO2 is released into the atmosphere.

Their study also yielded a universal mathematical formula that can predict the decomposition process anywhere in the world.

"For the first time, we have been able to demonstrate that the pattern of carbon dioxide release into the atmosphere through decomposition is governed by the same properties everywhere, from the Arctic Circle to tropical rain forests," said Stefano Manzoni, who works in the laboratory of senior scientist Amilcare Porporato, associate professor of civil engineering in Duke's Pratt School of Engineering.

"This provides a mathematical way of describing a critical natural process," he added.

During decomposition, microbes digest fallen organic matter from plants and slowly break it down. Two of the important byproducts of this process are mineral nitrogen and carbon dioxide.

Nitrogen is an essential nutrient for both plants and microbes, and once it becomes mineralized, it becomes available for plants to use.

Carbon - the most abundant element in plants and organic matter - is released into the atmosphere in the form of carbon dioxide, one of many of the so-called greenhouse gases implicated in global warning.

This carbon dioxide release is known as respiration.

"One of the key findings of this study is that microbes can adapt and do fairly well in a nutrient-poor environment," said Porporato.

"When their diet is lacking in nitrogen, microbes tend to react by releasing more carbon dioxide into the air and taking in less mineral nitrogen from the soil. So plants can get the much-needed mineralized nitrogen earlier in the decomposition process from the fallen organic matter," he added.

According to Manzoni, a diet rich in carbon causes microbes to release more carbon into the atmosphere in the form of carbon dioxide as they strive to maintain the healthy balance between nitrogen and carbon in their diet.

"For this reason, if more carbon is added to the soil in the form of plant residues, the microbes would then just pump out more carbon in response," he added.

ANI

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