Plant Gas

Scientists have beenstudying natural sources of methane（甲烷，沼气）for decades but hadn't regarded plants as a producer, notes Frank Keppler,a geochemist（地球化

学家）at the Max PlanckInstitute for Nuclear Physics in Heldelberg,Germany. Now Keppler and his colleaguesfind that plants,from grasses to trees,may also be sources of

the greenhouse gas.Thisis really surprising, because most scientists assumed that methane production requiresan oxygen-free environment.

Previously,researchershad thought that it was impossible for plants to make significant amounts of thegas. They had assumed that microbes（微生物）need to be in

environments withoutoxygen to produce methane.Methane is a greenhouse gas, like carbon dioxide.Gasessuch as methane and carbon dioxide trap heat in Earth's

atmosphere and contributeto global warming.

In its experiments, Keppler'steam used sealed chambers（室，房间；腔）that contained the same concentration of oxygen that Earth's atmospherehas.They measured the

amounts of methane thatwere released by both living plants and dried plant material,such as fallen leaves.

With the dried plants,theresearchers took measurement at temperatures ranging from 30 degrees Celsius to70 degrees C.At 30 degrees C.,they found,a gram of dried plant

material released upto 3 nanograms（微克）of methaneper hour(One nanogram is a millionth of a gram). With every 10-degree rise in temperature,theamount of methane

released each hour roughlydoubled.

Living plants growingat their normal temperatures released as much as 370 nanograms of methane per gramof plant tissue per hour. Methane emissions tripled when living

and dead plant was exposedto sunlight.

Because there was plentyof oxygen available,it's unlikely that the types of bacteria(bacterium的复数，细菌）that normally make methane were involved.Experiments on

plants that were grownin water rather than soil also resulted in methane emissions.That's another strongsign that the gas came from the plants and not soil microbes.

The new finding is an"interestingobservation,"says Jennifer Y. King,a biogeochemist（生物地球化学家）at the Universityof Minnesota in St. Paul. Because some types of

soil microbes consumemethane,they may prevent plant-produced methane from reaching the atmosphere.Fieldtests will be needed to assess the plant's influence,she notes.What was scientists'understanding of methane?

A.It was produced fromplants.

B.It was not a greenhousegas.

C.It was produced inoxygen-free environments.

D.It traps more heatthan any other greenhouse gas.