Plant roots increase carbon emission from permafrost soils

An international team led by VU alumnus Frida Keuper of the French research institute INRAE, shows that around the year 2100 an extra emission of 40 gigatons of carbon can be released from permafrost soils. VU ecologist James Weedon was part of the research team.

07/21/2020 | 10:20 AM

A key uncertainty in climate projections is the amount of carbon emitted by thawing permafrost in the Arctic. Plant roots in soil stimulate microbial decomposition, a mechanism called the priming effect. An international research team shows that the priming effect alone can cause emission of 40 billion tons carbon from permafrost by 2100. The study was published this week in Nature Geoscience.

Permafrost is permanently frozen ground which stores as much carbon as there is in all plants on Earth and in the atmosphere together. The surface of the permafrost thaws in summer, allowing plant and soil life to thrive. 

Increasing microbial activity
When microorganisms breathe, they emit greenhouse gases. Scientists have previously anticipated that rapidly rising temperatures will drive the emission of 50-100 billion tons permafrost carbon by 2100. On top of that, plant roots feed sugar to the microorganisms in the soil, which the microbes can use to break down more soil organic matter – the priming effect – resulting in even higher greenhouse gas emissions.

 “We have known about the priming effect since the 1950’s, but we did not know whether or not this small-scale ecological interaction had a significant impact on the global carbon cycle”, says Frida Keuper, affiliated with the French National Research Institute for Agriculture, Food and Environment, INRAE.

Extra 40 gigatons of carbon
The team of researchers combined maps of plant activity and data on soil carbon content from the Northern Circumpolar Soil Carbon Database with an extensive literature survey on priming and plant root properties, to estimate the priming effect in permafrost ecosystems and its influence on greenhouse gas emissions.

They show that the priming effect increases soil microbial respiration by 12 percent, which causes the additional loss of 40 billion tons carbon by 2100 compared to current predictions for permafrost. This equals almost a quarter of the remaining ‘carbon budget’ for human activities to limit global warming to max 1.5°C. “It has long been known how important and sensitive the arctic region, with its carbon-rich soils, is in relation to climate change. Our study emphasizes the importance of further research into the dynamic interaction between plants, soils and micro-organisms in order to better understand the functioning of the earth”, says James Weedon (department of Ecological Sciences VU).

Photo: lush vegetation in the northern permafrost area. Photo: Ive van Krunkelsven

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