Plants Found to Produce Methane

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Scientists in Germany have made a startling discovery: Plants produce methane, one of the greenhouse gases that warm the earth. The finding could change the way scientists view global climate.

RENEE MONTAGNE, host:

Among the things that make living on Earth better than, say, Mars are plants. Plants make the Earth liveable by absorbing carbon dioxide and emitting oxygen. The way plants pump gases back and forth into the atmosphere is a pretty well-studied part of biology. But now scientists are scratching their heads over a new discovery. Plants emit methane, something that could change the way scientists view global climate. NPR's Christopher Joyce has this story.

CHRISTOPHER JOYCE reporting:

Methane's a common gas we mostly associate with underground coal mines or the back end of a cow. It's recently achieved notoriety as one of the greenhouse gases that warms the planet. Conventional wisdom is that plants only make methane when they're submerged, without oxygen, in places like swamps. It bubbles up out of the mud. But scientists in Europe have made what they say is an astonishing discovery. Leafy plants above ground make methane. The lead scientist on this is Frank Keppler at the Max Planck Institute of Physics in Germany. He says he was certainly astonished.

Mr. FRANK KEPPLER (Max Planck Institute of Physics): I think the really fascinating thing with our study, that this has been overlooked for such a long time, that plants produce a greenhouse gas methane and liberate it to the atmosphere.

JOYCE: Keppler says he read a scientific paper that reported large clouds of methane hanging in the air above some tropical forests. Many scientists thought it must be coming from hidden swamps. But Keppler went to his laboratory in Heidelberg and put plants and leaves in special growth chambers. They produced methane; in fact, a lot of it. When you add up all the plants on the planet, it's a startling amount.

Mr. KEPPLER: We have made the first--our first guess is that about one-third of the methane which goes in the atmosphere comes from--could come from living vegetation. I think that's one--that's--the second thing that's just so unbelievable.

JOYCE: Keppler tried to see if something else, like bacteria in plants, was the source of the methane. It wasn't. He published a paper in the journal Nature, which first sent it out to experts to review.

Mr. DAVID LOWE (National Institute of Water and Atmospheric Research): When I first read that paper, I just--I was in disbelief. I thought, you know, this is ridiculous.

JOYCE: David Lowe is an atmospheric chemist at the National Institute of Water and Atmospheric Research in New Zealand.

Mr. LOWE: It's really difficult to figure out what the mechanism could be that would produce that gas in what is essentially an aerobic or oxygen-containing environment. That's what's surprising about this. This is really a huge, huge new discovery. The numbers that they quote are very, very big. It's a very substantial source.

JOYCE: Lowe says Keppler's research techniques look thorough, and he expects the results will cause a stir, not least because efforts to control global warming depend a lot on knowing how much greenhouse gas is floating up into the atmosphere and where it's coming from. For example, countries that are part of the Kyoto Treaty on global warming keep a careful account of their greenhouse gases, especially the main one, carbon dioxide. If a country's factories and cars emit too much CO2, they can make up for it by planting a certain number of trees, which absorb CO2. Lowe says maybe that calculation needs rethinking.

Mr. LOWE: Now this paper shows that, in fact, if you plant trees, you're actually going to be releasing methane into the atmosphere, which is also a greenhouse gas. So suddenly this carbon accounting is not so simple.

JOYCE: Scientists who've seen the research say it will provoke a round of new experiments to explain what's going on here. Keppler says so far, he thinks it might have to do with pectin, a substance that holds plant cells together. Pectin's actually well known, especially among grandmothers. It's what makes fruit thicken into jam. Christopher Joyce, NPR News.

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