Field trials in Oregon and Arizona show that poplar trees, which emit trace amounts of the gas isoprene, can be genetically modified not to harm air quality while leaving their growth potential unchanged.

The findings, published today in the journal Proceedings of the National Academy of Sciences, are important because poplar plantations cover 9.4 million hectares (36,294 square miles) globally — more than double the land used 15 years ago. Poplars are fast-growing trees that are a source of biofuel and other products including paper, pallets, plywood and furniture frames.

Poplars and other trees used in plantation agroforestry, including palms and eucalyptus, produce isoprene in their leaves in response to climate stress such as high temperature and drought. The isoprene alleviates those stresses by signaling cellular processes to produce protective molecules; however, isoprene is so volatile that millions of metric tons leak into the atmosphere each year.

The emitted isoprene reacts with gases produced by tailpipe pollution to produce ozone, which is a respiratory irritant. Isoprene also causes higher levels of atmospheric aerosol production, which reduces the amount of direct sunlight reaching the earth (a cooling effect), and it causes the global warming potential of methane in the atmosphere to increase (a warming effect). The warming effect is most likely greater than the cooling effect. The net effect of emitted isoprene is to worsen respiratory health and, most likely, warm the atmosphere.

A research collaboration led by scientists at the University of Arizona, the Helmholtz Research Center in Munich, Portland State University and Oregon State University genetically modified poplars not to produce isoprene, then tested them in three- and four-year trials at plantations in Oregon and Arizona.

The researchers found that trees whose isoprene production was genetically suppressed did not suffer ill effects in terms of photosynthesis or «biomass production.» They were able to make cellulose, used in biofuel production, and grow as well as trees that were producing isoprene. The discovery came as a surprise, given the protective role of isoprene in stressful climates, especially in the case of the Arizona plantation.

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Materials provided by University of Arizona. Original written by Russell Monson. Note: Content may be edited for style and length.