Evaluation of growth and yield of soybean exposed to ozone in the field

Soybeans (Glycine max (L.) Merr. cv Hodgson) were exposed in the field to seasonal 7-h average concentrations of 0·017, 0·035, 0·060, 0·084 and 0·122 μl litre⁻¹ ozone using open-top chambers and ambient plots. Dose-response studies were conducted on growth and yield. Negative linear relationships were found between both growth and yield and ozone exposure. The regression equation: yield= 12·82 − (48·17 × O₃), with yield in grams per plant and O₃ as the seasonal 7-h average, expresses one relationship. Compared with the yield in charcoal filtered air (0·017 μl litre⁻¹), losses ranged from 8% in the 0·035 μl litre⁻¹ treatment to 41% in the 0·122 μl litre⁻¹ treatment.

Aboveground biomass was a good indicator of ozone stress; five weeks after the ozone treatments were initiated, a negative linear relationship was found between ozone exposure and aboveground biomass. In contrast, the percentage of biomass allocated to leaves, stems and pods did not change until after 6 to 7 weeks of exposure to ozone. The change in allocation of biomass was the result of accelerated senescence of older leaves. At final harvest, a lower percentage of aboveground biomass was found in pods and seeds of plants exposed to higher ozone concentrations.