Plant Gas

　　Scientists have been studying natural sources of methane for decades but hadn’t regarded plants as a producer，notes Frank Keppler，a geochem[st at the Max Planck Institute for Nuclear Physics in Heidelberg，Germany1.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 contributeto 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.

　　Beeause there was plenty of oxygen available，it’s unlikely that the types of bacteria that normally make methane were involved. Experiments on plants that weregrown 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.

　　詞匯:

　　methane/5meWein/n.甲烷，沼氣 emission/i5miFEn/n.散發，發射

　　geochemist n.地球化學家 triple/5tripl/v.增加三倍;adj.三倍的

　　Celsius n.&.adj.攝氏(的) bacteria/bAk5tiEriE/n.(bacterium 的復數)細菌

　　microbe/5maIkrEJb/n.微生物 nanogram n.微克

　　biogeochemist n.生物地球化學家 chamber/5tFeimbE(r)/n.室，房間;腔

　　注釋：

　　1. the Max Planck Institute for Nuclear Physics in Heidelberg，Germany：馬克思?普朗克核物理研究所，位于德國海德堡。海德堡系德國西南部城市，在巴登一符騰堡州的內卡河畔。海德堡大學是德國歷史最悠久的大學。

　　2. microbe：細菌，意義同bacterium(bacteria的單數形式)。但microbe不用作專門術語。

　　3. St.Paul：圣保羅，美國明尼蘇達州首府。

　　練習：

　　1. What was scientists understanding of methane?

　　A h 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.

　　2. To test whether plants are a sot，roe 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.

　　3. Which 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 I.iving 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.

　　4. Which 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.

　　5. 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.

　　答案與題解：

　　1. C 短文的第一和第二段都講到，科學家過去曾經認為，沼氣必須在無氧的環境中才能產生。注意，作者用的是過去式：Most scientists assumed that...They had assumed that...。

　　2. B 第三段第一句說，科學家使用密封的房間來做實驗，房間里氧氣的濃度與地球大氣中的氧氣濃度相仿。所以B句符合原文的意思，其他三個選擇則不符合原文內容。

　　3. D 根據第四和第五段的內容，只有D是正確的說法。溫度越高沼氣的釋放量越高，有生命的植物釋放的沼氣遠大于干植物的釋放量，在陽光下，它們的沼氣釋放量是正常情況的三倍。

　　4. D 最后兩段告訴我們，無論在土壤中還是在水中生長的植物都能釋放沼氣，土壤中的微生物消耗沼氣，使沼氣不至于進入空氣。所以A、B、C的內容均符合短文最后兩段中作者的意思。D的內容短文中沒有提到。

　　5. C 最后一段的第二句可以找到本題的答案。

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