Carbon in soil poses climate change risk
4 September 2014

Carbon stored in the world’s soils is more vulnerable to climate change than expected, a study suggests.

Scientists say the response by soil microbial communities to changes in temperature increases the potential for more carbon dioxide to be released from the world’s soils as global temperatures rise.

The potential for global warming to stimulate decomposition rates in soils – releasing large quantities of carbon dioxide to the atmosphere – has long been considered to be one of the potentially most important positive feedbacks to climate change.

However, physiological and biochemical theory suggest that responses within microbial communities to rising temperatures could greatly reduce, or even eliminate, the potential for soil carbon losses.

The idea was tested using soils collected from a natural thermal gradient spanning from the Arctic to the Amazon rainforest.

The results show that microbial community responses resulted in an overall increase in the effects of temperature on the rates of carbon dioxide release from soils.

Lead author, Dr Kristiina Karhu, University of Helsinki said: “Because soils store more than twice as much carbon as is in the atmosphere, changes in rates of decomposition and carbon dioxide release could be very important. Our findings suggest that warming will on average increase the activity of soil microbes to a greater extent than was previously expected, which could affect climate change by increasing carbon dioxide emissions.”

Responses were not found to be equal in all soils, with differences observed among geographical regions and ecosystem types.

Managed agricultural soils were the only soils in which the response by microbes to a temperature change was to reduce the effect on rates of carbon dioxide release.

The greatest stimulating effects were seen in soils with the largest carbon contents and from regions which are warming most rapidly – boreal and arctic ecosystems.

This indicates that the observed responses could increase the vulnerability of some of the world's most important soil carbon stocks to climate warming.

Professor Patrick Meir, of The Australian National University and The University of Edinburgh UK said: “We are only beginning to understand how the microbial community in different ecosystems influences soil carbon dioxide emissions during warming. This knowledge gap is especially large for tropical forests, which show distinct patterns of biodiversity, and which cycle more carbon annually than any other terrestrial ecosystem. Our finding marks an opportunity to really advance understanding of the global carbon cycle.”

The study is published in the journal Nature. It was led by Exeter University (Dr Iain Hartley) and funded by the Natural Environment Research Council (NERC, UK), with support for Professor Meir from the Australian Research Council and NERC.

The study also involved teams from the University of Aberdeen, Heriot-Watt University, University of Stirling, Rothamsted Research, the Pontifical Catholic University of Peru, and collaborators in continental Europe.

Image: Montane Andean to lowland Amazonian forest in Peru. This is the location of the tropical component of the Karhu study, with the work led by Patrick Meir’s team  

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