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Porcini mushroom in a grassy landscape

Photo: IMAGO/M. Wuchenauer / IMAGO/blickwinkel

Chanterelles, porcini mushrooms, truffles or poisonous fly and tuberous mushrooms: some mushrooms live in symbiosis with countless plants, such as trees. The subterranean network of these mycorrhizal fungi provides nutrients to the roots of their hosts – and in return, they receive some of the carbon that the plants remove from the atmosphere during photosynthesis. In this way, mycorrhiza contribute to reducing the CO2 concentrations in the atmosphere – and to a significant extent, as a study now shows.

In the journal Current Biology, an international team of researchers calculates the amounts of carbon that end up in these fungi each year. According to the study, mycorrhizal fungi store up to 13.12 gigatons of carbon annually – more than a third (36 percent) of the amount emitted worldwide each year when burning fossil fuels. With this previously unnoticed ability, fungi are of great importance in mitigating global climate change, writes the group led by Heidi-Jayne Hawkins from the University of Cape Town.

Mycorrhizal fungi have played a key role in ecosystems for more than 400 million years, the scientists write. It is said that up to 90 percent of the world's plants benefit from symbiotic relationships.

So far, climate research has focused primarily on the protection and restoration of forests. This is because plants and trees are known to store huge amounts of carbon. But: "We always had the suspicion that we might have overlooked a large carbon sink," Hawkins is quoted as saying in a statement by the magazine.

Carbon storage hotspots

In order to track down this subterranean carbon sink, the researchers evaluated 194 biological data sets in a large-scale analysis and thus came up with the amount of up to 13 gigatons – billion tons – of carbon per year. However, it remains unclear how long the carbon remains stored in the mycorrhiza.

"We know that this is a river where something remains in the mycorrhizal structures while the fungus is alive and even after it dies," explains Hawkins. "Some of it is broken down into small carbon molecules and either bound to particles in the soil or even reused by plants. And certainly some of the carbon is lost as carbon dioxide gas during respiration by other microbes or the fungus itself."

The scientists point out that the result of their study is based on estimates and is not complete. The flow of carbon and nutrients between plants and mycorrhizal fungi needs to be studied more intensively. Among other things, field experiments could provide information on this, also by simulating future climate conditions. In addition, organizations such as the Fungi Foundation and GlobalFungi want to collect soil samples to create a worldwide map of fungal networks. This would make it possible to map carbon storage hotspots and document those fungal species that could defy drought and heat in particular.

Protecting eco-engineers

The study shows how important it is to protect fungi as ecosystem engineers, the team says, pointing to the threat to soils from agriculture, for example. The Food and Agriculture Organization of the United Nations (FAO) recently estimated that about 2050 percent of the world's soils could be affected by 90. This endangers not only ecosystems, but also the supply of people with food and the climate, the FAO warned.