There is no doubt that climate change has taken its toll on Arctic environments. In addition to increasing ocean temperatures and melting sea ice, warmer and wetter climates facilitate the loss of carbon stored in the tundra and permafrost soils. This, in turn, boosts global temperatures and accelerates climate change.
This discovery comes from a study led by researchers at Dartmouth College in New Hampshire. Grasses, shrubs and plants in the Arctic have been sequestering carbon from the atmosphere for thousands of years and storing it deep in the tundra soil. Here, microbes feed on decomposing organic matter, keeping climate change at bay.
While shrubs appear to be expanding across the tundra landscape, little is known about the impact they have on the carbon storage in high-latitude soils. It is believed that Arctic soils contain half of all global soil carbon and more than twice the amount of carbon as the entire atmosphere.
However, the rate of soil carbon decomposition is temperature sensitive and, therefore, an important source of greenhouse gases. In other words, decomposing organic matter releases greenhouse gases into the atmosphere, thereby transforming the Arctic tundra from a carbon sink to a carbon source.
Dartmouth researchers collected soil samples from shrub and grass vegetation in western Greenland. They then measured carbon dioxide emissions from mineral soils of the two vegetation types incubated at varying temperatures and moisture levels.
Their analyses revealed that soils collected from grassy areas had greater carbon storage, greater carbon losses from decomposition and a higher temperature sensitivity of decomposition than shrub soils. This suggests that soil respiration and organic carbon decomposition in the tundra, especially in grassy areas, will increase with increasing temperatures and soil moisture.
"Our results highlight the importance of the interactive effects of vegetation type, temperature and moisture in determining of the response of soil decomposition to climate change," said lead author Julia Bradley-Cook, who conducted the study as part of her doctorate in Ecology and Evolutionary Biology at Dartmouth and who is now a Congressional Science Fellow. "Any soil moisture increases consistent with climate model projections are expected to increase soil respiration in both vegetation types."
Under these circumstances, greater amounts of carbon dioxide will be released into the atmosphere.
"Also, higher soil moisture should increase the temperature sensitivity of grassy soils, but may have little to no effect on shrub soils," Bradley-Cook added. "Shrub expansion into grassy areas could reduce soil carbon accumulation and the temperature sensitivity of carbon mineralization, such that these soils would more closely resemble the carbon storage and temperature sensitivity of shrub soil."
The findings were recently published in the journal Climate Change Responses
