Heat Hinders Ground's Ability to Absorb CO2

Sept. 17, 2008 -- Plant and soil can take up to two years to recover from an exceptionally hot year, a finding that has implications for the combat against global warming, according to research published on Wednesday.

The recovery lag could cause a rethink about the ability of grasslands and soil to act as a sponge, also known as a "sink," that removes carbon dioxide (CO2) from the air, its authors said.

In an unusual experiment, scientists in Nevada carved out plots of grassland in central Oklahoma, each measuring more than 2.4 meters (7.8 feet) long, 1.2 meters (3.9 feet) wide and 1.8 meters (5.85 feet) deep, with their plant communities and soil left intact.

These miniature ecosystems were then installed in four container-sized labs in which light, darkness, temperature and rainfall could be carefully replicated and levels of CO2 monitored.

Over the next four years, two of the four chambers were programmed to reproduce the weather conditions of the original site, previously determined by a seven-year monitoring of that location.

The other two chambers, though, were exposed to a sudden rise in temperature during the second year of the experiment -- a hike of four degrees Celsius (7.2 degrees Fahrenheit).

"We wanted to create an extreme year and look at how the ecosystem recovered from it," said Jay Arnone, a professor at the Desert Research Institute (DRI) in Reno, Nev.

"Basically, we dosed it with heat one year, then we removed the heat and asked, 'how long do the effects that occurred in that year persist, and which processes are affected?'"

Arnone's team found that during this anomalously warm year and the year that followed, the two plots sucked up two-thirds less carbon than the plots that had been exposed to normal temperatures.

Carbon capture comes from plant growth, through synthesis, and from micro-organisms that break down carbon in the soil.

The hike of 4 C (7.2 F) is at the far end of core estimates made last year by the UN expert group, the Intergovernmental Panel on Climate Change (IPCC), for the average worldwide warming this century.