~~~~ Ozone, the simple combination of three oxygen atoms, is both a naturally occurring and human-created gas in the Earth’s atmosphere. Atmospheric ozone is created naturally from gaseous substances emitted by lightning, soil, and vegetation, but it is also formed from pollutants emitted by human activities. Ozone is a mixed bag whose downside is a growing concern worldwide because of its negative impact on human and crop health.
On the good side, it has long been known that stratospheric ozone shields us from harmful ultraviolet light. Concerns over the seasonal thinning of this protective layer over polar regions, a phenomenon often referred to as the “ozone hole,” led to the phase-out of certain industrial chemicals that destroy stratospheric ozone.
Less is known, however, about the effects of ground-level ozone, where we have the opposite problem—too much of it. Human health concerns have received the most research. A 2013 study from the Massachusetts Institute of Technology, for example, estimates that ozone pollution causes between 4,700 and 19,000 deaths annually in the U.S.
Ozone’s effects on agriculture are less understood although legumes, such as soybeans and peanuts, are especially sensitive. Studies have shown that the yield of soybeans is reduced by 8-14% percent in areas exposed to high levels of ozone.
Ground-level ozone pollution originates from chemical reactions in the atmosphere, driven by warm temperatures and sunlight. Ozone formation tends to accelerate in the hottest periods of the year. The ingredients for ozone production come from multiple sources including particularly when fuel is not burned completely in cars, trucks, airplanes and other engines, emitting exhaust containing carbon monoxide, nitrogen oxides, and hydrocarbons.
Over the last few decades, background levels of ground-level ozone have steadily increased. Considering the serious implications of ground-level ozone pollution for human health and crop production, there is an urgent need to better understand how ozone is produced and lost from the atmosphere, and how this balance may change with increasing human activity and a warming climate.
One little understood aspect of ground-level ozone is that plants themselves contribute to the ozone problem by producing nitric oxide (NO), one of the ingredients for ozone formation. With that in mind, researchers at Michigan State University’s Kellogg Biological Station Long-term Ecological Research (KBS LTER) program are trying to determine how much crops themselves contribute to ground level ozone.
Ying Zhang, a resident scholar on sabbatical at KBS from China’s Beijing Forestry University, spent the summer working in LTER investigator Phil Robertson’s lab measuring the impact of rainfall and temperature variation on NO emissions from corn and switchgrass at the Great Lakes Bioenergy Research Center field site at KBS.
“As the climate changes,” Zhang said, “there will be changing patterns of rainfall during the growing season, with more dry periods between heavier rainfalls. We are looking at how the changing patterns of rainfall and temperature affect NO emissions by plants.”
While NO has a number of functions in the life of plants, there are technical difficulties in measuring and determining the amount of NO production.
Zhang and colleagues placed measuring equipment on small plots with covers so rainfall could be manipulated. Under each cover were crops growing in containers fitted with devices to measure the NO emissions and temperature.
“It is a real-time analysis of NO emissions under varying water and temperature conditions,” Zhang said. “The results are preliminary, but varying rainfall and temperatures as we expect to see with climate change definitely have an effect on NO emissions.”
Zhang, who has a Ph.D. from China Agricultural University, said that this kind of research contributes to understanding the overall changes that are occurring as the climate changes.
She said the preliminary findings are important enough to justify further research both in the US and in other agricultural regions around the world including China.