New Berkeley Lab research published in the journal Nature Communications Thursday explores the impact of a changing climate on Arctic ecosystems with permanently frozen soils. As the Arctic continues to warm at about twice the rate of the rest of the world, scientists expect these frozen soils known as permafrost to thaw, activating microbes capable of decomposing soil and releasing carbons and other nutrients to the atmosphere and water.   

Neslihan Taş, a microbial ecologist in Berkeley Lab’s Ecology Department, set out to learn more about how soil microbes can contribute to greenhouse gas emissions under a warming climate. Her research team collaborated with Berkeley Lab’s Joint Genome Institute to conduct their study funded by the Department of Energy’s Office of Biological and Environmental Research. BER is supporting a Next-Generation Ecosystem Experiments in the Arctic (NGEE Arctic) project.  

Above: Birds-eye view of the Barrow Environmental Observatory (BEO) containing many thaw lakes, river drainages and polygonal grounds with thawing Arctic Ocean in the horizon.

The remote location and harsh weather conditions of Arctic landscapes make them difficult to access for research. Yet, the team led by Taş managed to gain new insights into microbial processes that result in  greenhouse gas emissions by studying differences in microbial communities and ecosystem functions across polygonal tundra soils of Barrow, Alaska. They focused their studies on the terrain of the Barrow Environmental Observatory (BEO), which contains different polygonal shapes from which they collected samples.

Above: Chamber for soil greenhouse gas flux measurements (left); ice in polygon soils frozen in cracks (middle); close up to polygon vegetation: moss and grasses (right)

“The first challenge we faced was dealing with the overwhelming microbial diversity soils have,” says Taş. “Current advances in DNA sequencing technologies help us to access genes and genomes of soil microorganisms despite the fact that there are billions of microorganism in soils.”

The researchers sequenced soil and permafrost samples and examined which microbial genes were found in each sample and what functions the soil microbes perform. They compared this information to measurements of greenhouse gas emissions and geophysical and geochemical soil characteristics obtained from the polygons.

Microbial functions such as fermentation and methanogenesis were dominant in wetter polygons. Taş says that this is not unexpected because wet soils are the preferred environment for anaerobic conditions that facilitate the breakdown of soil organic matter to fuel methane and carbon dioxide production.  

Drier polygons had drastically different microbial composition. In dry parts of the landscape, soil carbon mineralization and methane oxidation were important. The balance between methane generation and oxidation was a key differentiator across the polygons.

Low nitrous oxide flux measurements obtained by the study team indicate that in both wet and dry polygon types, microbes were assimilating nitrogen rather than releasing nitrous oxide.

Microbes were retaining the nitrogen, according to Taş, who explains that it would be wasteful for them to emit nitrous oxygen because most Arctic soils are deprived of their nitrogen. “The nitrogen cycling process which would normally result in nitrous oxide or nitrogen gas was not favored by these arctic soil microbes  — instead nitrogen was recycled  to be used  for cell growth,” she says.

According to Taş, the team’s findings that microbiological processes are taking place are significant in and of themselves. “Microbes are critical to soil decomposition. Our results corroborate that microbial response will ultimately depend on how soil moisture is distributed across the landscape,” she says.

Evidence of microbial potential in permafrost soils can be used later on in larger simulations designed to predict what will happen under a warming climate over future decades, or even the next century.