The activity of a single enzyme in peat bogs from Scotland to Siberia is the only thing preventing a massive release of the greenhouse gas carbon dioxide, says a British scientist.
But global warming could transform it from a planet-saver to a planet-wrecker, warns Chris Freeman, a biologist at the University of Wales, Bangor and discoverer of the crucial role of the enzyme, phenol oxidase.
Inside a wet, oxygen-poor bog, the enzyme鈥檚 activity is low and cannot promote huge volumes of organic carbon from decomposing and escaping into the air as CO2.
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But as the bog dries out, the influx of oxygen molecule boosts the enzyme鈥檚 activity seven-fold, triggering decomposition. Freeman calls the enzyme 鈥渁 fragile latch mechanism holding in place a vast carbon store鈥�.
Peat bogs in northern latitudes contain an estimated 455 billion tonnes of carbon in the form of buried plant matter 鈥� equivalent to 70 years of industrial emissions.
Many climate models predict that global warming will cause peat bogs to dry out. If so, says Freeman, there would be a catastrophic release of CO2, sending temperatures soaring yet further.
Melvin Cammell, director of the Centre for Ecology and Hydrology in Edinburgh underlined the importance of the finding. His research in Scotland found that after highland peat bogs are drained, they release up to 3.5 tonnes of carbon per hectare each year. 鈥淭he releases carry on for hundreds of years,鈥� 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. 鈥淏ut that is not enough. You can get fast decomposition in anaerobic conditions 鈥� such as inside the guts of ruminants.鈥�
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.
鈥淚 discovered the enzyme by chance while investigating wetland processes,鈥� says Freeman. 鈥淏ut it took me a while to realise its importance as a feedback to climate change.鈥�
More at: Nature (vol 409, p 149)
