Responses of field-grown soybean (cv. Essex) to elevated SO2 under two atmospheric CO2 concentrations

The objective of this research was to determine the effects of elevated concentrations of carbon dioxide (CO2) and sulfur dioxide (SO2) on field-grown soybean. Soybeans (Glycine max L. Merr. cv. 'Essex') were grown a full-season in open-top field chambers exposed to either ambient (350 mu l L-1) or elevated CO2 (500 mu l L-1) levels under two levels of SO2 (0.00 and 0.12 mu l L-1). Enriched CO2, with or without SO2 treatments, significantly increased net photosynthesis rates, leaf area index (LAI; in R4 growth stage) and leaf dry weight, but did not significantly affect stomatal resistance, transpiration rates, leaf area, plant height, total biomass or grain yield. Elevated SO2 treatments significantly decreased photosynthesis and LAI during pod fill stages, but did not significantly affect stomatal resistance, transpiration, total biomass, plant height or grain yield. Sulfur dioxide inhibited growth and development (i.e., LAI) during canopy coverage before any effects on photosynthesis were detected. The interactive effects of CO2 and SO2 treatments on the gas exchange parameters were significant during pod fill, where high SO2 reduced photosynthesis at ambient CO2 but not under elevated CO2. Leaf area index values were likewise reduced by SO2 exposure under ambient CO2 during late flowering and pod fill stages. Thus, enriched CO2 under high SO2 exposure partially compensated for the negative impact of SO2 stress on PS and LAI during the pod fill stages. (C) 1997 Elsevier Science B.V.