By decomposing, because of the increase in temperature, the tundra will produce carbon dioxide and thus accelerate further the warming.
So far, most studies have predicted that global warming would make tundra a greener area. Under this scenario, the plants that occupy it would grow rapidly by storing more carbon dioxide. Paul Grogan, a Northern Ecosystem Specialist at Queen's University, and his colleagues come to the opposite conclusion: they believe that warming will also promote the decomposition of peat, moss and other vegetation. And that will increase by about 25% the concentration of carbon dioxide in the atmosphere. Michelle Mack, who conducted the study, studied artificially fertilized plots in Alaska. By adding nitrogen and phosphorus to their soil, it has reproduced the nutritional quality that would be produced by a pronounced warming of the Arctic zone. Between 1981, the beginning of the experiment, and 2000, the soils she studied suffered a net loss of 2 kilograms of carbon per square meter. The largest loss occurred more than 5 centimeters below the ground surface. It had gone unnoticed until now because the measurements only covered the superficial layer.
As the soil warms up, microbial activity increases. Microorganisms digest organic matter and release carbon dioxide, nitrogen and phosphorus, which stimulates plant growth. This growth has doubled with global warming: shrubs of about fifty centimeters now replace sedges [a compact grass] growing close to the ground. But the amount of carbon emitted by the acceleration of decomposition exceeds that absorbed by this new vegetation cover.
Paul Grogan and Michelle Mack point out that their experiments focused on one aspect of the complex carbon cycle between the atmosphere and the earth: the effect of increasing nutrients in the soil. These results do not necessarily apply to other northern regions, such as huge boreal peatlands or the polar desert. And there are other environmental factors to consider, such as permafrost melting and soil warming, researchers say. However, "these results challenge some of our assumptions. It used to be thought that if you had more plants and trees, you would automatically store carbon, if only temporarily, "says Tim Moore, a geography professor at McGill University who studies the carbon cycle. in a peat bog near Ottawa.
Peter Calamai The Toronto Star
Source: Courier Internationnal