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 nl1^-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 is 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 non-fumigated saline-treated plants.