30 April 2007

Plant-Methane Brouhaha Put To Bed

by Kate Melville

The suggestion that plants may be a prodigious source of the greenhouse gas methane has finally been put to the sword by Dutch scientists. Reporting in New Phytologist, Tom Dueck and co-researchers concluded that methane emissions from plants are negligible and do not contribute to global climate change.

The researchers executed a novel experiment that used plants grown in a facility containing atmospheric carbon dioxide with a heavy form of carbon (13C). The heavy carbon makes any carbon released from the plants relatively easy to detect.

Thus, if plants are able to emit methane, it will contain the heavy carbon isotope and can be detected against the background of lighter carbon molecules in the air.

Saturating the plants with heavy carbon. 13C-Methane emission was measured under controlled, but natural conditions with a photo-acoustic laser technique. This technique is so sensitive that the scientists are able to measure the carbon dioxide in the breath of small insects like ants.

The researchers found that the measured emission rates were so close to the detection limit that they did not statistically differ from zero. Conscious of the fact that a small amount of plant material might only result in small amounts of methane, the researchers sampled the "heavy" methane in the air in which a large amount of plants were growing. Again, the measured methane emissions were negligible.

While Dueck concluded that there is no reason to reassess the mitigation potential of plants, he did stress that questions still remain about the gap in the global methane equation.

Related articles:
Researchers Slam Media Over Wrong-Headed Plant-Methane Hype
Laughing Gas Levels From Biodiesel Crops Not Funny

Source: New Phytologist