Scientists who study Arctic ecosystems have forewarned a “sleeping giant” hidden within permafrost soils–trillions of tons of planet-warming greenhouse gases that will be released when rapid thaw awakens microbes, activating soil decomposition. Improving what is known about microbial community makeup and behavior in these fragile ecosystems could help determine how consequential rapid permafrost thaw will be to the release of carbon dioxide and the less prevalent but 30 times more potent gas methane.
New genome analysis of soil microbial community composition and metabolism from one climate-sensitive Arctic island ecosystem suggests substantial, sustained release of carbon dioxide, not methane, when soils decompose. A paper published in the journal FEMS Microbiology Ecology describes a collaborative study involving Berkeley Lab researchers who developed advanced computing methods to help define microbial function within a 2m permafrost core sample collected by University of Bergen researchers from the remote archipelago, Svalbard, Norway.
“Places like Svalbard, which lies at the border of the Atlantic and Arctic Oceans, are isolated and very difficult to reach. There is no opportunity to collect hundreds to thousands of permafrost core samples from these extremely fragile places,” said Neslihan Taş, study author and research scientist in Berkeley Lab’s Climate and Ecosystem Sciences Division.
“This collaboration is meaningful because our Norwegian colleagues had access to the data from one rather large core sample that we could analyze at Berkeley Lab in depth. This enabled us to examine the permafrost microbiome in one location in as much detail as possible.”
A sobering warning: Permafrost can be a sustained source of CO2
Although they could release 1.5 trillion tons of carbon dioxide into the atmosphere with permafrost thaw, the Arctic’s cold-adapted microbial communities are poorly understood. The permafrost soil type is obscure in general, but even less information exists about the permafrost microbiome. Taş explains that insights into microbial composition and behavior could tell us more than soil physicality does about what abrupt thaw would mean for soil decomposition. Microbial composition and soil chemistry is after all constantly changing, making their mark on soil’s physical properties and altering any conclusions that might have been drawn from them.
“Microbes live for thousands of years. By examining them, there’s more potential to represent what’s happening in any environment, especially in the Arctic,” Taş said.
The researchers set out to define and compare microbial communities present in the core sample and determine how they change by soil depth; their shared genome characteristics and metabolic traits; and whether and how those factors might influence the release of carbon into the atmosphere.
Using a combination of bioinformatics, biostatistics, and metagenomics at Berkeley Lab, they discovered microbial community composition in Svalbard soils shifted markedly by depth. One metabolic trait, however, stood out regardless of soil layer: that is, the prevalence of aerobic respiration known to produce sugars that would later be broken down as carbon dioxide, rather than the methane-producing anaerobic respiration.
“In both top soils and deep permafrost soils, we didn’t uncover any substantial methane-producing archaea,” said Taş. “As earth scientists, we usually assume that methane is the most important greenhouse gas because it is so potentially damaging to the atmosphere.
“But the evidence of carbon-dioxide producing metabolics, persisting from shallow top soils all the way down into the deepest layers of permafrost, is still of concern. This amounts to a sobering warning to us all: That even in very wet Arctic environments where the presence of methane may be insignificant, there exists the possibility that decomposing soils will release such an abundance of carbon dioxide that could be equally devastating to the atmosphere.”
This research study complements ongoing research by Taş, through the DOE Early Career Research program, examining how microbial processes, biogeochemical transformations, and hydrology interact during permafrost thaw in Alaska to determine how these factors drive biogeochemical cycles in Arctic soils.