THE surprising discovery that plants may be responsible for up to 30 per cent of the world's methane, a powerful greenhouse gas, is no reason to stop planting forests, a scientist has warned.According to the research, living plants may produce between 60 million tonnes and 240 million tonnes of methane a year. It was already known that methane is released by decaying plant matter, as well as by the roots of plants in oxygen-starved environments, such as wetlands.
It was also known that methane is given off by cows and sheep, and by the burning of forests and fossil fuels.
But a team led by Frank Keppler, of Max Planck Institute for Nuclear Physics in Germany, found that living plants emit 10 to 1000 times more of the gas than decaying matter.
And plants increase their methane emissions when warmed by the sun, it was found.
"Until now all the textbooks have said that biogenic methane can only be produced in the absence of oxygen," Dr Keppler said. "For that simple reason nobody looked closely at this."
Plants have long been seen as weapons against global warming because they absorb another greenhouse gas, carbon dioxide.
"It's a surprise," said David Etheridge of the CSIRO's Marine and Atmospheric Research division. "You think you know everything."
But Dr Etheridge said it was no reason to stop planting forests."We do need plants. It's simplistic to say we can't grow forests. You need to look at the net effect of plants. Forests take carbon out of the atmosphere, which is good."
Dr Etheridge said the research's findings that living plants contribute up to 30 per cent of the atmosphere's methane, and that they produce more methane as they get warmer, could help explain the sharp rise in the world's methane levels in recent centuries.