Effects of SO 2 and salinity on nitrogenase activity, nitrogen concentration and growth of young soybean plants

Abstract

Young soybean plants ( Glycine max L.) were exposed to three SO 2 concentrations (2, 110 and 250 ppb) and two levels of soil salinity (no added NaCl and 27 mM NaCl) in a factorial experiment for 16 days. SO 2 exposure was for 5 hr day −1. Exposure to 250 pbb (high) SO 2 decreased the number and weight of root nodules, suppressed nitrogenase activity, and reduced shoot and root nitrogen concentrations, whereas 110 ppb (low) SO 2 usually had no effect on these parameters. High and low SO 2 concentrations increased the shoot-to-root ratios by reducing root growth and stimulating shoot growth, respectively. Soil salinity decreased root nodulation and N-fixation, but it ameliorated SO 2-induced injury. Twelve days after exposure to SO 2, foliar injury was apparent in the treatment of high SO 2 alone but was negligible in the high SO 2 and salinity treatment. The reduced SO 2 injury under saline conditions was probably achieved by decreasing SO 2 uptake through stomatal closure.