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Elevated CO2 Completely Ameliorates SO2 Damage in Soybean
Deepak, S.S. and Agrawal, M.  2001.  Influence of elevated CO2 on the sensitivity of two soybean cultivars to sulphur dioxide.  Environmental and Experimental Botany 46: 81-91.

What was done
The authors grew two cultivars of soybean (Glycine max L. Merr. Cv. PK472 and Bragg) in open-top chambers receiving atmospheric CO2 concentrations of 350 and 600 ppm alone and in combination with 60 ppb SO2 to study the interactive effects of elevated CO2 and this detrimental air pollutant on growth and yield of this important agricultural species.

What was learned
Exposure to elevated SO2 significantly reduced every growth parameter studied in the two soybean cultivars.  Total plant biomass and grain yield, for example, were both reduced by SO2 by approximately 18%, regardless of cultivar.  In contrast, elevated CO2 significantly increased every growth parameter in both soybean cultivars.  Elevated CO2, for example, increased total plant biomass and grain yield in both cultivars by averages of 30 and 34%, respectively.  Moreover, when the plants were exposed simultaneously to elevated CO2 and SO2, the negative effects of SO2 on these growth parameters were completely ameliorated.  In fact, their observed values were not significantly different from those obtained under CO2-enriched conditions alone.

What it means
As the air's CO2 concentration increases, it will likely allow soybean plants to experience less stress and growth reductions from SO2 pollution.  In this particular study, for example, SO2-induced growth and yield reductions were completely offset by atmospheric CO2 enrichment.  Thus, agricultural fields near industrial areas that have historically produced low soybean yields due to SO2 pollution will likely exhibit increases in yield in response to the ever-increasing CO2 content of the air.