Trees Eat Pollution Better Than Expected

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Deciduous plants take up about a third more oxygenated VOCs than previously thought.
Thomas Karl / Science/AAAS

THE GIST

- Genes have been found that help plants absorb volatile organic compounds (VOCs).

- Field work shows that deciduous plants use the genes to suck up a third more VOCs than suspected.

- The discovery will change our understanding of how compounds move around and affect climate.

Some common and dangerous air pollutants found in cities can be absorbed by plants at far greater rates than ever suspected.

The discovery has big implications for modeling how vegetation affects pollutants, as well as how particles in the atmosphere affect human health and global warming.

The finding comes from a fruitful and unusual collaboration of plant geneticists and atmospheric scientists. The plant scientists found the genes used by plants and the conditions under which they are activated to allow more volatile organic compounds (VOCs) to be absorbed, while the atmospheric scientists lugged equipment around the globe to verify that the plants were indeed sucking up pollutants in the real world.

"It's been hard to measure this in the real world," said Thomas Karl of the National Center for Atmospheric Research. "That's why we hauled this instrument all around the world."

Karl led the field work which involved gathering and immediately analyzing air samples in remote forests using a 200-pound, washing machine-sized mass spectrometer. He is also the lead author on a paper reporting the discovery in the Oct. 21 issue of Science Express.

"Our goal was to really be in places that were undisturbed to mimic the most natural case," said Karl. That took them to seven locations in more than six years.

Among the specific discoveries is that deciduous plants take up about a third more oxygenated VOCs -- a form of pollutant that has reacted with oxygen -- than previously thought. These oxygenated VOCs come from burning gasoline, forest and other biomass fires and are e even released by some kinds of trees.

"The trees actually clean up more than we thought," said Karl.

That's extremely useful information when trying to figure out what's happening globally. The work will be used by modelers, Karl said, working on Earth systems models which attempt to try to take into account and simulate as many processes as possible.

"This paper is very interesting to me because we want to understand the sources and the sinks" of VOC pollutants, said researcher Qi Zhang of the University of California at Davis.

Of particular interest are particles, called secondary organic aerosols (SOAs), that are created by oxygenated VOCs. These SOAs are extremely important, Zhang said, because they can serve as seeds for cloud droplets, affect the way the atmosphere holds heat and they are major cause of disease and death in urban areas.

"(SOAs) are more deadly than car accidents," Zhang told Discovery News.

Now that the plant genes for grabbing VOCs are understood, there could be a future application for them in helping to clean cities, said Chhandak Basu of the University of Northern Colorado, a co-author on the paper. He envisions a day when plants with these VOC-sucking genes line highways, or other sources of pollution, sucking the harmful compounds out of the air.

As for the unusual cross pollination that produced the discovery, it was not easy, said Brenda Thornton, of the University of Northern Colorado, who identified the plant genes at work.

"It's really difficult to get different fields working together," said Thornton. They often seemed to be speaking separate languages, she said, but they managed to bridge the gaps.

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