They investigated the responses of seven different soybean genotypes to eight ozone concentrations. The plants were exposed to ozone concentrations ranging from ambient levels of 38 parts per billion up to 200 parts per billion.

“This is quite high, but unfortunately, those kinds of concentrations are what very polluted areas of China and India are looking at today,” Ainsworth said.

The researchers found that any increase above the ambient concentration was enough to reduce seed yield: roughly half a bushel per acre for each additional part per billion.

“This is significant,” Ainsworth said. “Especially considering that background concentrations of ozone today vary year to year, anywhere from about 38 to 39 parts per billion to about 62. That can be 15 bushels per acre from one year to the next that farmers are losing to ozone.”

The researchers compared the results of this study, which used modern genotypes, with results from experiments conducted in controlled environments in the 1980s.

They found the responses of the modern genotypes were similar to those of the older genotypes.

“Breeders haven’t inadvertently bred for ozone tolerance in more modern lines,” Ainsworth said. “They’re still sensitive to ozone, which means that farmers are still subject to these yearly variations in ozone and are losing yield accordingly.”

Potential increases in background ozone are predicted to increase soybean yield losses by 9 to 19 percent by 2030.

Levels were particularly high during this year’s growing season because most days were sunny and warm, and thus they were favorable for ozone formation. Peaks on many days exceeded 80 parts per billion, twice the known sensitivity threshold.

The research was recently published online in Plant Physiology and can be accessed at http://www.plantphysiol.org/content/early/2012/10/04/pp.112.205591.abstract. Amy Betzelberger, Craig Yendrek, Jindong Sun, Courtney Leisner, Randall Nelson and Donald Ort are co-authors.
This research and the SoyFACE experimental facility were supported by the USDA ARS and the Agriculture and Food Research Initiative competitive grant no. 2010-65114-20355 from the USDA National Institute of Food and Agriculture to E.A.A.