Rising atmospheric CO2 may stimulate carbon loss from soil: study

Increased levels of carbon dioxide (CO2) in the atmosphere may cause soil microbes to convert carbon, thereby accelerating global warming, an international team of researchers said Thursday.

CO2 is released to the atmosphere when humans burn oil, coal and gasoline, and is the major cause of global warming. Soils can store carbon, helping counteract rising CO2. Carbon accumulates in soil through many years of plant photosynthesis, and is lost from soil as microscopic organisms, mostly bacteria and fungi, decompose soil carbon, converting it back to CO2 and releasing it to the atmosphere.

Many previous studies have shown that rising atmospheric CO2 stimulates photosynthesis and thus carbon input into ecosystems, potentially leading to carbon sequestration and mitigation of climate warming, but the carbon sequestration in terrestrial ecosystems is not only determined by carbon input but also by carbon loss, study author Yiqi Luo, professor of the University of Oklahoma and Tsinghua University, told Xinhua.

In order to better understand how soil microbes respond to the changing atmosphere, they compared data gathered from tens of elevated CO2 experiments around the world with models of the soil carbon cycle.

"The main finding was surprising: increased plant growth caused by rising atmospheric CO2 was associated with higher rates of CO2 release from soil," Luo said.

"Our findings indicate that rising CO2 may not enhance carbon storage in soil as much as we previously thought or current models project," he said.

These results also indicate that soil carbon may not be as stable as previously thought, and that soil microorganisms exert more direct control on long-term carbon accumulation than currently represented in global models, said the professor.

Luo said that carbon cycle research results still have lots of uncertainty and that more empirical research to further contain model predictions is needed.

The study, also involving researchers from the Northern Arizona University, University of Florida and Trinity College Dublin, was published in the U.S. journal Science.