❄️ Thawing arctic soils awaken half of their dormant microbes

In Svalbard, an isolated Arctic archipelago located between mainland Norway and the North Pole, soils remain frozen for most of the year. These cold environments, poor in nutrients and largely devoid of vegetation, nevertheless contain significant amounts of carbon trapped in the permafrost.

With the rapid warming of the Arctic, these soils now thaw for longer periods each summer. A new study shows that this thaw does not lead to a complete activation of microbial life. In fact, about half of the microorganisms present in these soils remain dormant, even after several months of thawing.

Tracking the resumption of microbial activity

Despite their austere appearance, Arctic soils host diverse microbial communities that play a key role in regulating carbon emissions to the atmosphere. When the soil thaws, liquid water becomes available, allowing microorganisms to resume their activity.

To better understand this process, an international team including scientists from the CNRS at the Mediterranean Institute of Oceanography (MIO) incubated soils from Svalbard and directly tracked microbial growth using a DNA isotopic labeling technique. This approach made it possible to precisely identify which microorganisms developed after thawing.

The results show that some microorganisms activate quickly, while others only begin to grow after several weeks. A large part of the community, however, remains inactive.

This work was carried out as part of the ERC SIESTA project, which aims to better understand the role of microbial dormancy in extreme environments.

Beyond decomposition: key biological interactions

Unexpectedly, the active microorganisms are not limited to decomposers of organic matter. The study also highlights the growth of predatory bacteria, capable of consuming other microorganisms. This result underscores that interactions within microbial food webs play an important role in the functioning of Arctic soils after thawing.

A major issue for climate

Arctic soils store about one-third of the world's soil carbon. With accelerating warming, the fate of this carbon depends closely on microbial activity.

This study shows that carbon emissions are not only controlled by temperature, but also by the identity of the microorganisms that become active, and the timing of their activation. These results suggest that current climate models may oversimplify the response of Arctic soils to warming.