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Subarctic shrub expansion may change microbial behaviour in the soil

Simulating shrub expansion in the subarctic, researchers expected to find stimulated microbial degradation of organic material. Instead they found that the microbes changed resource preferences that appeared to lead to an accumulation of the organic material. This could reduce the effect of global warming.
Researcher Johannes Rousk. Photo: Kathrin Rousk
Researcher Johannes Rousk. Photo: Kathrin Rousk

Half of the global soil carbon is held in permafrost soils in high-latitude ecosystems. As the climate is warming, the permafrost is thawing. This causes whole ecosystems to change, inducing a shift in vegetation. Mosses are replaced by shrubs, with leaves and roots that are more easily decomposed.

Researcher Johannes Rousk from Lund University together with colleagues Kathrin Rousk and Anders Michelsen from the University of Copenhagen have studied the decomposition process in simulated environments of shrub expansion in the subarctic soils of Abisko, northern Sweden. They found that decomposer organisms like bacteria and especially fungi shift their resource-use when shrubs grow more dominant. When there is high quality carbon input as the researchers added in form of sugars to simulate root input from shrubs, the microbes targeted the soil organic matter rich in nitrogen.  Alongside this selective use they could observe another feature: the decomposition of other soil organic material, and thus soil carbon, was reduced by half. 

 This is likely to result in accumulating carbon-rich organic material that is poorer in nutrients.

-It is interesting to see how this will affect the carbon turnover in the soil in the longer term, says Johannes Rousk, leading the research of this study, to LU web news.

How these processes will affect the ability of soil to act as a source or sink for carbon dioxide  still require more research. According to Johannes Rousk the changed behavior of microbes is likely to reduce the effect of global warming, as more carbon stays in the ground.  

As the interaction between root input and soil organic matter decomposition is not included in climate models today, the researchers hope that these results could be a component in future models to improve the output predictions.

 

Read the article published in Global Change Biology

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