Effects of Sulphur Dioxide Pollution on Biochemical Parameters of Alfalfa (Medicago Sativa) Inoculated with Rhizobium

Sulphur dioxide (SO2) is one of the major atmospheric contaminant that induces negatively effects in the cellular biochemistry and physiology of the plants. However, Rhizobium inoculation can cause increas in plant resistance to abiotic and biotic stresses. In this study, effects of different concentrations of Sulphur dioxide gas (0, 0.5, 1, 1.5 and 2 ppm) on photosynthetic pigments, proline, protein, sulphur, potassium and phosphorus of inoculated alfalfa with Rhizobium (native and standard strains) were evaluated in Arak city. The Results showed that high concentrations of Sulphur dioxide (1, 1.5 and 2 ppm) caused a decline in photosynthetic pigments, protein, potassium and phosphorus and an increase in sulphur and proline content of alfalfa plant in compared to the controls. In low concentration of SO2 (0.5 ppm), the increase in photosynthetic pigments, protein, potassium and phosphorus were observed. Rhizobium inoculation itself caused an increase in photosynthetic pigments, protein, potassium and phosphorus contents but did not effect on the proline content and sulfur uptake. Inoculation of alfalfa with two strains of Rhizobium decreased induced effects of high concentrations of SO2 on these biochemical parameters significantly (at 0.01 level) in comparison with the control plants. Therefore, rhizobial inoculant be able to increase host plants resistance to SO2 pollution stress and have been applied as a biofertilizer.