Nature Geosci. 4, 895–900 (2011)

Credit: © ISTOCKPHOTO.COM/W-INGS

Peatlands lock away the large quantities of carbon that build up in these water-saturated environments owing to the presence of phenolic compounds, which inhibit microbial decomposition. Phenolic concentrations remain high in peatlands because anoxic conditions limit the activity of the enzyme responsible for their breakdown. However, droughts introduce oxygen into these systems, and the frequency of these events is increasing.

Nathalie Fenner and Chris Freeman of the Wolfson Peatland Carbon Capture Laboratory at Bangor University in Wales, UK, used in vitro manipulations, mesocosm experiments and field observations to examine the impact of drought on peatland carbon.

They found that drought stimulates bacterial growth and activity of the enzyme phenol oxidase, reducing the concentration of phenolic compounds in peat. This further stimulates microbial growth, causing the breakdown of organic matter and the release of carbon dioxide. Furthermore, they show that re-wetting the peat accelerates carbon losses to the atmosphere, owing to drought-induced increases in nutrient and labile carbon levels, which raise pH and stimulate anaerobic decomposition. These findings suggest that severe drought, and subsequent re-wetting, could destabilize peatland carbon stocks.