The role of Arctic microbes in climate change
Due to the vast carbon reserves sequestered within Arctic soils, the carbon cycles of these areas must be understood if the risks of global warming are to be accurately assessed. Permafrost stores carbon within the ground, creating scattered deposits that collectively form vast ‘reservoirs’. Although they cover only nine percent of the Earth’s total landmass, permafrost soils may in fact contain between 25 to 50 percent of the globe’s soil organic carbon. Following thawing and soil movements, this carbon is eventually exhumed and released back to the surface. It is then either absorbed by vegetation, or enters the atmosphere and water before it is reclaimed by the soil. Since it is atmospherically discharged in the form of methane or carbon dioxide, Arctic carbon has been identified as both a potential symptom and driver of global warming. Several processes are involved in stimulating the carbon’s release, including seasonal thaws, forest fires, soil erosion and vegetation growth. A recent research project coordinated by the University of Bergen has sought to examine the role of microorganisms in the earth. 'For many years, I’ve been examining arctic soil, particularly the "active layer" of permafrost, which is subject to thawing and refreezing,' explains Professor Lise Øvreås, the project leader. 'During this period I’ve witnessed a lot of surprising activity and diversity there. As soon as it thaws, the whole structure of the permafrost changes. Methane and greenhouse gases are emitted, but this catalyst also stimulates dormant microbes frozen in the permafrost. They wake up and contribute to some of the processes that are driving the whole carbon cycle. In our project, we focused on how to better understand these microbes by examining their physiology and the mechanisms which control them as communities.' Conducted between 2013 and 2015, the project examined a frozen core of excavated permafrost removed from two metres beneath the Arctic soil. Half of the sample consisted of the active layer, with the other segment comprising permafrost. 'During our analysis we sliced the core into thin sections,' explains Øvreås. 'This was so that we could not only examine the genes of microbial organisms located there, but also scrutinise transition zones between the active layer and permafrost. DNA and genomic analysis was carried out, to measure attributes of the microbial community, which exhibited distinct changes in the cores. Our samples were also subjected to additional thermographic computer analysis so that we could discern physical and chemical changes within the segments. We will also imminently be trying to stimulate microbes from the permafrost, to test if they are partly responsible for the release of methane and carbon dioxide.' Microbes have revealed themselves to be remarkably resilient, says Øvreås. 'Organisms have been studied which can actually function in extreme cold; at around minus 17 degrees,' she says. 'They have adapted to surviving under harsh conditions, although they need water to function. As soon as this becomes available, along with certain nutrients, their processes resume. A Californian group conducted experiments on incubating permafrost microbes, which had been frozen for more than 10,000 years. After a couple of hours of stimulation, they could see that the whole system was revitalised, and gases were exchanged through microbial respiration.' This is one important source of carbon release – as is the death of the microbes, which liberates carbon through decomposition. 'Once we know more about the organisms, we can begin to project the consequences of temperature changes in the Arctic upon them, and what kind of processes they might stimulate,' anticipates Øvreås. 'It’s vital for us learn more about the processes which involve them, and how they interact with each other, to predict the possible impacts of climate change.'
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