Background
The authors write that "globally, soybean is the most widely planted dicot crop and has economic significance due to its wide variety of uses, ranging from food and health products to printing inks and biodiesal [fuels]," but they say that "little to no work has evaluated the influence of future atmospheric conditions on soybean diseases," which seems a bit strange, seeing they add that "worldwide yield losses to all soybean diseases combined are about 11% (Wrather et al., 1997), which is equivalent to more than 24 million metric tons based on current production."

What was done
In an initial attempt to begin to fill this knowledge void, Eastburn et al. evaluated the individual and combined effects of elevated carbon dioxide (CO2, 550 ppm) and ozone (O3, 1.2 times ambient) on three economically important soybean diseases -- downy mildew, Septoria brown spot and sudden death syndrome (SDS) -- over the three-year period 2005-2007 under natural field conditions at the soybean free-air CO2-enrichment (SoyFACE) facility on the campus of the University of Illinois (USA).

What was learned
The five researchers report that "elevated CO2 alone or in combination with O3 significantly reduced downy mildew disease severity by 39-66% across the three years of the study." On the other hand, they say that "elevated CO2 alone or in combination with O3 significantly increased brown spot severity in all three years," but they add that "the increase was small in magnitude." Last of all, they say that "the atmospheric treatments had no effect on the incidence of SDS."

What it means
Taken in their entirety, these several findings suggest that, on balance, elevated CO2 -- either by itself or in conjunction with elevated O3 -- should provide a net benefit to soybean productivity throughout the world, as the concentrations of these two atmospheric trace gases continue to rise in the years and decades to come.

Reference
Wrather, J.A., Anderson, T.R., Arsyad, D.M., Gai, J., Ploper, L.D., Porta-Puglia, A., Ram, H.H. and Yourinori, J.T. 1997. Soybean disease loss estimates for the top 10 soybean producing countries in 1994. Plant Disease 81: 107-110.