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When soil in the tundra thaws: Arctic microorganisms heat up climate change

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Plants in the arctic tundra have only a few weeks a year when they can grow. Soil microorganisms also spend many months in a kind of cold sleep and are only active for a short time when the top layer of the soil thaws. They then break down organic material – but less than what the plants grow during the same time. This is how thick peat soils have been formed over thousands of years. They store about twice as much carbon worldwide as the entire atmosphere. But climate change is turning tundra soils from carbon sinks into carbon sources: as temperatures rise, the soil remains frozen less long and thaws into deeper layers in the summer. This is particularly advantageous for micro­organisms, which can as a
result break down more organic material than the plants form. The carbon dioxide released further intensifies the greenhouse effect and thus climate change. And it could get even worse, as the microbiologist Beat Frey explains: “The climate models predict that the Arctic will become more humid. In a water-saturated soil, different microorganisms from those found in dry soil could become active and release more potent greenhouse gases.”


Nitrous oxide and methane instead of carbon dioxide

Beat’s colleague Aline Frossard, who is also a microbiologist, is therefore taking a close look at microorganisms in both dry and wet tundra soil. Her measurements on Svalbard show that, as suspected, the microorganisms active in wet soil differ from those in dry soil. As a result, much more methane and nitrous oxide are released from the wet soil. These  gases amplify the greenhouse effect from roughly twenty-five to three hundred times more than carbon
dioxide. Aline: “Global climate models should take this into account so that forecasts can be made more reliable.”

Aline and Beat study micro­organisms in tundra and permafrost soils in all seasons – in winter with its perpetual night and icy cold, in spring during the snow melt and
in summer with the midnight sun. Genetic investigations of their soil samples are providing insights into a largely unknown treasure trove of species. As hostile as the tundra may seem to life, it is the natural habitat for many microorganisms.
(Birgit Ottmer, Diagonal 2/19)