Soils store carbon – or do they? The effect of climate change on soil carbon

Dr Sabine Reinsch gives an overview of a new paper in Biogeochemistry detailing a soil carbon study at a long-term experimental site in Denmark...

The global soil carbon stock is estimated to be 2000 gigatonnes of carbon. Every year, ~95 gigatonnes of carbon is released to the atmosphere. The amount of carbon that is stored in the soil is the difference between the carbon that goes into the soil and the carbon that is released from the soil. In a world of climate change the behaviour of soils to store or lose carbon might change.

In a world of climate change the behaviour of soils to store or lose carbon might change.

In a recent study, we investigated if the soil carbon concentration will increase or decrease in the future. We used a climate change manipulation experiment in a Danish heathland to test this. In this experiment, vegetation plots were exposed to increased night-time temperature, summer drought and increased atmospheric carbon dioxide concentration.

Climate change experimental site in Denmark

We sampled soils after eight years of climate manipulations and examined if the soil carbon concentration and stocks in the climate manipulated plots was different compared to an untreated control. We observed a decrease in labile carbon stocks in climate change plots. We also found that labile carbon in the soil will turnover faster in the future than it does today, leading to a net carbon loss from the soil.

We found that labile carbon in the soil will turnover faster in the future than it does today, leading to a net carbon loss from the soil.

We separated soil organic material into three fractions. We measured the carbon concentration from each fraction which led to the main finding.

The atmospheric concentration of carbon dioxide was increased with the free-arid carbon dioxide enrichment (FACE). FACE blows carbon dioxide over the vegetation. The carbon dioxide has a lower isotopic signature (δ13C = -29‰) than atmospheric carbon dioxide (δ13C = -8‰). The carbon dioxide is taken up by plants and mixes with carbon that is stored in plants and their roots and the soil. Using the isotopic signature of carbon in the soil allowed us to distinguish between old soil carbon and new carbon that came from the FACE manipulation..

Sabine Reinsch

Additional information

Full paper reference: Thaysen, E M, Reinsch, S, Larsen, K S, Ambus, P. Biogeochemistry (2017). "Decrease in heathland soil labile organic carbon under future atmospheric and climate conditions", doi: 10.1007/s10533-017-0303-3

Details of the Brandbjerg (CLIMAITE) experimental site in Denmark

Staff page of Dr Sabine Reinsch, Centre for Ecology & Hydrology

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