Plant Gas
Scientists have been studying natural sources of methane for decades but hadn't regarded plants as a producer, notes Frank Keppler, a geochemist at the Max Planck Institute for Nuclear Physics in Heldelberg, Germany. Now Keppler and his colleagues find that plants, from grasses to trees, may also be sources of the greenhouse gas. This is really surprising, because most scientists assumed that methane production requires an oxygen-free environment.
Previously, researchers had thought that it was impossible for plants to make significant amounts of the gas. They had assumed that microbes2 need to be in environments without oxygen to produce methane. Methane is a greenhouse gas, like carbon dioxide. Gases such as methane and carbon dioxide trap heat in Earth's atmosphere and contribute to global warming.
In its experiments, Keppler's team used sealed chambers that contained the same concentration of oxygen that Earth's atmosphere has. They measured the amounts of methane that were released by both living plants and dried plant material, such as fallen leaves.
With the dried plants, the researchers took measurement at temperatures ranging from 30 degrees Celsius to 70 degrees C. At 30 degrees C, they found, a gram of dried plant material released up to 3 nanograms of methane per hour. (One nanogram is a billionth of a gram.) With every 10-degree rise in temperature, the amount of methane released each hour roughly doubled.
Living plants growing at their normal temperatures released as much as 370 nanograms of methane per gram of plant tissue per hour. Methane emissions tripled when living and dead plant was exposed to sunlight.
Because there was plenty of oxygen available, it's unlikely that the types of bacteria that normally make methane were involved. Experiments on plants that were grown in water rather than soil also resulted in methane emissions. That's another strong sign that the gas came from the plants and not soil microbes.
The new finding is an "interesting observation," says Jennifer Y. King, a biogeochemist at the University of Minnesota in St. Paul3. Because some types of soil microbes consume methane, they may prevent plant-produced methane from reaching the atmosphere. Field tests will be needed to assess the plant's influence, she notes. (367 words)
41 that was scientists' understanding of methane?
A) It was produced from plants.
B) It was not a greenhouse gas.
C) It was produced in oxygen-free environments.
D) It traps more heat than any other greenhouse gas.
42 To test whether plants are a source of methane, the scientists created
A) a oxygen-free environment.
B) an environment with the same concentration of oxygen as the Earth has.
C) a carbon dioxide-free environment.
D) an environment filled with the greenhouse gas
43 hich statement is true of the methane emissions of plants in the experiment?
A) The lower the temperature, the higher the amount of methane emissions.
B) Living plants release less methane than dried plants at the same temperature.
C) When exposed to sunlight, plants stop releasing methane.
D) The higher the temperature, the greater the amount of methane emissions.
44 What of the following about methane is Not mentioned in the passage ?
A) Plants growing in soil release methane.
B) Plants growing in water release methane.
C) Soil microbes consume methane.
D) Microbes in plants produce methane.
45 What is the beneficial point of some microbes consuming plant-produced methane?
A) Methane becomes less poisonous.
B) methane is turned into a fertilizer.
C) Less methane reaches the atmosphere.
D) Air becomes cleaner……
参考答案：41 C 42 B 43 D 44 D 45 C
译文：
植物，沼气的又一来源
德国马克思·普朗克核物理研究所地球化学家Frank Keppler提到，科学家已经研究沼气几十年，但一直没认为植物能产生沼气。现在Keppler和同事们发现从草到树的植物也可能是温室气体的来源。这的确是令人惊讶的，阅为大多数科学家认为沼气是在缺氧环境中产生的。
以前，研究人员认为植物不可能产㈩大量的气体。他们认为微生物需要在无氧环境下生产沼气。沼气和二氧化碳一样都是温室气体，它们在地球大气中吸收热量导致全球变暖。
在实验中，Keppler一组使用内含与地球大气中同等密度氧的密闭室来测量从活植物和干植物如落叶中释放的沼气量。
研究人员测量干植物时温度在30摄氏度到70摄氏度。3()摄氏度时，他们发现一克干植物每小时释放3微克沼气(1微克是1克的十亿分之一)。温度每上升10度，每小时释放的沼气量约会增加一倍。
对于正常温度下生长的活植物，每一克植物组织每小时释放出370微克的沼气。当活的或者死的植物暴露在阳光下时，沼气释放量会增加两倍。
由于有大量的氧气，正常生产沼气的细菌不可能加入。在对生长在水中而不是土壤中的植物进行实验时也发现有沼气释放。这也表明气体产生于植物而不是土壤微生物。
圣保罗明尼苏达州大学：生物地球化学家Jennifer Y.King说，这些新发现是一项“有趣的观察记录”。因为一些土壤微生物消耗沼气，它们会阻止植物产生的沼气到达大气中。Jennifer Y.King指出，需要对土地进行测试以判定植物的影响。
