There are cold specialists as well as warm specialists.

The study was undertaken at the Niwot Ridge Long Term Ecological Research site west of Boulder. The site is home to one of several dozen so-called AmeriFlux installations on the continent that measure CO2 activity. The Niwot Ridge AmeriFlux site features five towers studded with climate instruments that are funded by the U.S. Department of Energy, the National Science Foundation and the National Center for Atmospheric Research.

The researchers used the 100-foot-high towers -- which were erected at 10,000 feet in a forest of lodgepole pine, sub-alpine fir and Englemann spruce adjacent to CU-Boulder's Mountain Research Station -- to measure CO2, water and energy exchanges between the biosphere and atmosphere, said Monson. They used the instruments to zero in on the subtle, swirling winds drifting over the rugged terrain and took millions of individual CO2 data readings from 1998 to 2004.

"The deeper the snowpack, the more CO2 we observed leaving the forest," he said. "This forced us to look at the wintertime period more closely than before."

The researchers discovered a unique collection of microbes under the snow soils with life spans of only hours to days thriving at temperatures hovering around zero, Monson said. They used DNA fingerprinting techniques to show the winter microbe community was very different genetically from the summer microbe community.