They are off the hook after all. Last year a paper appeared that suggested, to widespread amazement, that plants are major emitters of methane, a powerful greenhouse gas (快猫短视频, 14 January 2006, p 13). Now a trial in a gas-tight greenhouse has negated this. Plants do not, it turns out, contribute to climate change by emitting methane.
Tom Dueck at Plant Research International in Wageningen, the Netherlands, and colleagues grew six species of plants 鈥� maize, tomato, wheat, sage, evening primrose and basil 鈥� in air in which the carbon in the CO2 was the heavy isotope carbon-13. The only gases in the greenhouse were pumped in from cylinders, ensuring that if the plants produced any methane it would contain carbon-13. Despite using a sensitive laser measuring technique called photo-acoustic spectroscopy, Dueck鈥檚 team failed to detect methane containing the heavy isotope (New Phytologist, DOI: 10.1111/j.1469-8137.2007.02103.x).
This was the first test of last year鈥檚 claim, which was made by Frank Keppler, now at the Max Planck Institute for Chemistry in Mainz, Germany. 鈥淚f it was true, it would be revolutionary,鈥� Dueck says. 鈥淏ut no one can think of a logical explanation.鈥� Bacteria in soil may produce methane when breaking down organic matter in oxygen-starved conditions, but Keppler鈥檚 experiment was conducted in air. Dueck, who grew his plants hydroponically, speculates that Keppler鈥檚 study might not have allowed enough time for residual methane in the soil, and in the intercellular spaces in plants, to be flushed out of the system, making it look as though it had been emitted by the plants.
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鈥淭he original study might not have allowed enough time for methane in plants鈥� intercellular spaces to be flushed out鈥�
鈥淲e still have absolute confidence in our results and cannot support the conclusion that vegetation does not produce methane,鈥� insists Keppler, though he says he has no explanation for Dueck鈥檚 results. Using carbon-13-grown plants is an artificial approach that cannot be used to derive natural rates of methane emission, he claims.
Dueck and Keppler both say they look forward to seeing the results of other groups who are repeating the experiments.
