Geochemical control of organic matter turnover in peatlands: Long-term security or short-term vulnerability of a major carbon store?

Peatlands cover vast areas of the world - around 4 million square kilometres - and store about as much carbon as do the living plants in tropical rainforests. For the past 5,000-10,000 years, the plants living on peatlands have been fixing carbon dioxide from the atmosphere and storing it as dead plant matter - 'peat'. In a future warmer, and possibly drier, climate, this stored carbon could be respired back to the atmosphere or leached into rivers. Will increased temperatures and decreased rainfall lead to rapid loss of the peatland carbon store? If so, then the extra carbon released from peatlands could enhance 'greenhouse' warming further, leading to a runaway positive feedback on global climate. Or will rapid climate change trigger a shift to peatland types that accumulate peat (and store carbon) at a faster rate than present-day peatlands? If the latter, then peatlands could buffer further climate change. In this project, we will investigate the three-way interactions between plants, decomposition of peat and environmental factors such as temperature. Although there have been many studies on decomposition of forest and grassland soils, surprisingly little is known about how peat decays. We are particularly interested in how differences in the chemistry of different types of plants (and of the peat they produce) affects how quickly the peat decomposes and how it responds to changes in temperature. Of special concern is the bog-moss, Sphagnum, which has a unique chemical composition that makes it very resistant to decomposition. Our field site is a peatland in central Sweden that shows a great variety of plant types and environmental conditions, ranging from swamp forest to fen to bog. Using the full range of variation, we will analyse in detail the chemistry of a wide variety of living plants and their recently dead remains. We will also examine changes in chemistry and rates of peat accumulation in short cores that provide a historical record of the past 300 years or so. In addition, we will track how the chemistry of new and old peat changes as it decomposes, under higher temperatures and under drier conditions. The results of these studies will help us to predict how the peatland carbon store will fare in the face of future climate change.