Arctic greenery likes warmer world and arctic bacteria eat more carbon for breakfast

Don’t look now. Might be another negative feedback the modelers forgot. When the cold arctic warms up, there are more plants and less tough old moss. The real, err, surprise — was what happened to the bacteria and fungi. The micro-critters that normally decompose organic matter are pretty happy about the switch from tough moss to tasty tundra shrubs (or in this case, to cake, I’ll explain in a minute). They adapt in a jiffy to chewing through the freshly dead bits of gourmet plants with more nitrogen. So instead of decomposing more in warmer weather, the soils got richer with carbon and decomposed less.

After reading the press release, I watched the video and was a bit surprised to find them seeding the ground with sugar, rather than gourmet arctic plants. I’m a bit underwhelmed by the study design. Though the end result sounds believable because life on Earth spent 500 million years figuring out ways to suck that CO2 out of the sky.

The researchers even suggest this might slow global warming. If it does, it will be a symbolic, unmeasureable semi-hundredth of a degree. But perhaps the nicest thing about this is that at Lund University there are still researchers allowed to put out press releases suggesting “good news” for the climate.

Climate change creates more shrub vegetation in barren, arctic ecosystems. A study at Lund University in Sweden shows that organisms, such as bacteria and fungi, are triggered to break down particularly nutritious dead parts of shrubbery. Meanwhile, the total amount of decomposition is reducing. This could have an inhibiting effect on global warming.

A large amount of the Earth’s carbon and nitrogen is stored in arctic ecosystems where the ground is permanently frozen, known as permafrost. Climate change causes such soil to heat up. Johannes Rousk at Lund University, together with colleagues Kathrin Rousk och Anders Michelsen from the University of Copenhagen and the Center for Permafrost (CENPERM), have conducted field studies outside Abisko in the very north of Sweden, studying what happens to the decomposition of organic material as the climate gets warmer.

“As the Arctic region becomes warmer, more shrubs start to grow, rather than moss which is difficult to break down. The shrubs have leaves and roots that are easy to break down and secrete sugar. What we have shown is that decomposition organisms, such as bacteria and fungi, are triggered to look for nutrient-rich organic materials that contain more nitrogen, while decomposition as a whole is reduced,” says Johannes Rousk.

When the nutrient-rich material is decomposed, the nutrient-poor part of the organic material is enriched, probably causing the amount of carbon to increase. Current climate models do not consider the connection between increased shrub vegetation as a result of ongoing climate change, and soil becoming less nutritious.

“It will be exciting to see how this will affect the soil carbon turnover in the long term. Perhaps our results will help complement future climate models,” says Johannes Rousk.

Today no one knows what less nutritious soil in the Arctic ecosystem and an overall decreased decomposition of organic material will lead to. However, Johannes Rousk dares to venture a guess:

“I suspect it will have an inhibiting effect on global warming,” he says.

Video: https://www.youtube.com/watch?v=mo1oCVOLCsQ

Press release REFERENCE Kathrin Rousk, Anders Michelsen, Johannes Rousk. Microbial control of soil organic matter mineralisation responses to labile carbon in subarctic climate change treatments. Global Change Biology, 2016; DOI: 10.1111/gcb.13296

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