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Kevin Hollis, Graduate student, Department of Plant Biology, email@example.com.
Stephen Long, Robert Emerson Professor, Department of Crop Sciences, 217-333-2487, firstname.lastname@example.org
Ozone gas forms a protective barrier from the sun’s ultraviolet rays in the stratosphere about 15 miles above the earth. In recent years, the depletion of this ozone has been making news. This decline increases the ultraviolet radiation that reaches the earth and may increase the incidence of skin cancer and cause other problems. At the same time, the ozone just above the surface of the earth is increasing. This ozone is a secondary pollutant. Nitrogen oxides and volatile hydrocarbons are products of burning fuels. With the aid of sunlight, these compounds combine to produce ozone. Because sunlight is critical, ozone pollution is principally a daytime problem in the summer. Because ozone is a secondary pollutant, concentrations can be high in rural areas far removed from the original sources of pollution. In the northern hemisphere, ozone levels in industrial countries are rising at a rate of 1 to 2 % a year and this trend is predicted to continue. Data collected at the University of North Carolina indicate that soybean is more sensitive to ozone than corn. Soybean yield reductions could be expected when ozone concentrations exceed 40 parts per billion (ppb). In our research plots, the ambient ozone concentration between 10 am and 4 pm averaged 62 ppb in 2002 and 50 ppb in 2003. These levels are almost certainly causing some yield reduction.
At the SoyFACE (Soybean Free Air Concentration Enrichment) facility at the University of Illinois, we can increase the level of ozone gas surrounding field grown soybeans. A ring of pipes 70 feet in diameter releases ozone into the wind as it blows across the plots. A computer continuously measures wind speed and direction, and the ozone concentration within the ring to determine which pipes release ozone and the amount to be released. Approximately a pound of ozone is released into each ring each day to increase the treatment to a level approximately 20% higher than the ambient. Our preliminary data show that this increase can cause significant yield reductions. The most sensitive varieties yielded over 30% less under the elevated ozone concentration compared to ambient conditions. The average yield reduction of the 22 varieties tested was 19%. A few varieties were quite tolerant of the elevated ozone with yield reductions of approximately 5%. We tested varieties that were grown in Illinois more than 50 years ago as well as current varieties. Ozone sensitive and tolerant varieties were found within both groups. There are genetic differences among our current varieties for ozone tolerance but ozone levels are not sufficiently consistent for soybean breeders to select for ozone tolerance under natural conditions. It is very likely that even more tolerant lines exist within the USDA Soybean Germplasm Collection at the University of Illinois. The capacity of SoyFACE permits us to currently evaluate only 22 varieties per year. We are working to develop procedures that will allow us to more extensively evaluate ozone tolerance. This is important to identify those varieties that are most likely yielding at less than full potential under current conditions and to identify more highly tolerant germplasm for developing future varieties.