Surface Microbes Make Thawing Permafrost Release More Greenhouse Gas, Lab Test Finds

In a laboratory study published Sept. 25 in Nature Communications, microbes from the soil that thaws above permafrost each summer sharply raised the greenhouse gas output of formerly frozen ground below. Sylvain Monteux and Eveline Krab of the Swedish University of Agricultural Sciences and colleagues report that the microbial communities sealed inside permafrost are missing biological functions their neighbors above can supply.

The paper frames the finding as a forecasting problem: emission estimates built by scaling up earlier permafrost experiments do not account for surface microbes moving in.

The team ran a 389-day experiment with oxygen present, adding a deliberately function-rich microbial community from a temperate grassland to four common permafrost types. Total carbon dioxide production rose in all four, by 20% to 60%, and nitrous oxide production started in two of them. Microbes taken from each soil's own surface layer produced less; the authors attribute that either to those communities missing the same functions or to their failing to take hold.

A second experiment sealed peat-bog permafrost from sub-Arctic Sweden without oxygen. Adding its own surface microbes multiplied methane production fivefold over six months, in all eight replicates, while carbon dioxide production fell. Taken together, the warming potential of what the soil released rose 35%. Both experiments ran in jars, not in the field.

Arctic permafrost holds large stores of soil carbon that microbes turn into greenhouse gases once the ground thaws. Earlier work had found missing functions of this kind only in Yedoma, ice-rich deposits frozen since the Pleistocene; the new results extend them to soils frozen for far less time. The authors call for field tests across different thaw scenarios, and recommend that laboratory studies of thawing permafrost routinely include surface soil for comparison.