SOIL-SALINITY MODIFIES SO2 SENSITIVITY IN SOYBEAN

Soybean (Glycine max L. cv. Buchanan) growing in top-covered chambers was exposed to a factorial combination of three concentrations of SO2 (2, 99 and 189 nl l-1) and three concentrations of soil salinity with electrical conductivities of 0.7, 4.9 and 7.0 dS m-1. Each combination was tested in duplicate chambers. SO2 exposure was for 4 h d-1 for 106 d from planting to final harvest. SO2 increased leaf sulphur concentrations, while high salinity had the opposite effect. Stress interactions were observed late in the season, with leaf sulphur concentrations significantly decreased by simultaneous SO2 and salinity stress when compared with exposure to SO2 alone. SO2 or salinity stress both reduced leaf chlorophyll concentration, leaf area, plant dry weight and seed yields. Although SO2-salinity interactions on the growth variables were not statistically significant, there were stress interactions on seed yield by affecting the number of pods produced. As SO2-induced leaf injury developed it became more severe in the nonsaline plants than in the saline plants, indicating a protective function for salinity against SO2 injury. However, salinity-induced leaf injury occurred earlier and was more severe in the high SO2 and saline-treated plants than in the low SO2 and nonfumigated saline-treated plants.