Chris Freeman, a biologist at the University of Wales, Bangor, UK, discovered the crucial role of the enzyme, phenol oxidase, The New Scientist reported in its 10 January issue. Freeman found that inside a wet, oxygen-poor bog, the enzyme’s activity is low and cannot promote huge volumes of organic carbon from decomposing and escaping into the air as CO2. But as the bog dries out, the influx of oxygen molecule boosts the enzyme’s activity seven-fold, triggering decomposition. Freeman calls the enzyme “a fragile latch mechanism holding in place a vast carbon store”.

Peat bogs in northern latitudes contain an estimated 455 billion tonnes of carbon in the form of buried plant matter, equivalent to 70 years of industrial emissions, and as many climate models predict that global warming will cause peat bogs to dry out, there could be a catastrophic release of CO2. This theory is backed up by Melvin Cammell, Director of the Centre for Ecology and Hydrology in Edinburgh who found that found that after Scottish Highland peat bogs are drained, they release up to 3.5 tonnes of carbon per hectare each year. “The releases carry on for hundreds of years,” he said.

Until now, scientists have been unclear why buried plants inside wet bogs do not decompose. The absence of oxygen is clearly important, says Freeman. “But that is not enough. You can get fast decomposition in anaerobic conditions – such as inside the guts of ruminants.” Now he and his colleagues have revealed that phenol oxidase is the key. In a wet bog, the enzyme is largely inert and the phenolic compounds it would otherwise destroy can build up. These compounds prevent bacteria from decomposing the organic material. But if the bog dries out, the enzyme activates and destroys the phenolic compounds, triggering decomposition.

“I discovered the enzyme by chance while investigating wetland processes,” says Freeman. “But it took me a while to realise its importance as a feedback to climate change.”

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