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Thanks to microbes, methane bubbles out of rice paddies and escapes from the back ends of termites and the front end of cows. Ov

admin2015-03-25  2
问题     Thanks to microbes, methane bubbles out of rice paddies and escapes from the back ends of termites and the front end of cows. Over the years, researchers have gained a good handle on these and other sources of this potent greenhouse gas. But a report in the 12 January issue of Nature suggests that one source has been overlooked: plants. Although the surprising finding doesn’t change the total amount of methane emitted to the atmosphere, it could force a reappraisal of how much various sources contribute, how to mitigate some of them, and how they might change. "This paper will shake the methane community," predicts Christian Franken-berg of the University of Heidelberg, Germany.
    Methane is largely made by microbes. Living in oxygen-poor environments, they ferment organic matter or reduce carbon dioxide. Methane is also produced in massive quantities from wild and controlled fires and is released from natural gas leaks. But among biological processes, researchers had no idea that anything other than microbial anaerobic reduction was responsible.
    The clue for the new research came from chloromethane, a halogenated organic gas that avidly destroys ozone and was thought to come mainly from burning biomass. But a few years ago, Frank Keppler, a geochemist now at the Max Planck Institute for Nuclear Physics in Heidelberg, and colleagues discovered that living plants make chloromethane. Because methane is also released from burning biomass, Keppler and his colleagues wondered whether plants might make it, too.
    The group first tested dead plants, placing leaves from about 30 species in a chamber with typical atmospheric oxygen concentrations. They released between 0. 2 and 3 nanograms of methane per gram of dry plant matter, a relatively paltry amount. When they then conducted similar experiments with living plants, however, the rates per gram of plant matter " increased dramatically," Keppler says, jumping to 10 to 100 times those of the dead leaves. As a control, they grew some plants hydroponically to exclude microbes and saw comparable results. Moreover, the methane was slightly enriched in carbon-13 compared to bacterially produced methane, further suggesting that the plants were making it. "It must be a new mechanism," says Keppler, although what that could be, no one knows. Some experts remain skeptical. "I’m kind of incredulous," says methane chemist Ronald Sass of Rice University in Houston, Texas. How much could plants contribute to the methane budget? The authors estimate—very roughly, they admit—that it could be between 10% and 30% of the 500 million to 600 million metric tons that enter the atmosphere annually. Other experts caution that their assumptions are quite uncertain and that further lab and field experiments are necessary to determine whether these emissions account for much in the wild.
We can learn from the second paragraph that
选项 A、microbes like to live in oxygen-poor environments.
B、people know less about plant methane production.
C、methane can be made into natural gas.
D、methane is always produced in quantities.
答案B
解析 推理判断题。根据题干提示定位至第二段。四个选项的内容文章似乎都有所提及。但在谈到oxygen-poor environments时文章指的是微生物在厌氧环境下才会产生沼气，而非[A]所论及的微生物喜居厌氧环境；文章谈到natural gas但没提及沼气可以生产天然气，[C]属偷换概念；而[D]是对句子“沼气大量产生于野火或控制的火”的断章取义。而第二段末则谈到“除以上所谈之外研究者们没有其他方式”，也就是[B]“人们对植物形成沼气知之甚少”。
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