Inoculation effects of Rhizobium on the tolerance increase of Persian clover (Trifolium resupinatum) under SO2 pollution

Plant growth-promoting rhizobacteria are beneficial bacteria that increase the growth of plants and induce resistance to various stresses. SO 2 air pollution is one of these stresses that is known as strong damaging air pollutants. Persian clover is one of legume family plants that consider as a forage crop and can form a symbiosis with Rhizobium bacteria. In this study, the effects of Rhizobium (native and standard strains) on amounts of photosynthetic pigments and phosphorus and potassium elements of Persian clover under different concentrations of SO 2 (0, 0.5, 1, 1.5 and 2ppm) were evaluated. The results showed that inoculation has beneficial effects on the amounts of photosynthetic pigments and phosphorus and potassium content compared with non-inoculated plants. High concentrations of SO 2 (1, 1.5, or 2ppm) caused a significant decline in the amounts of photosynthetic pigments and phosphorus and potassium elements of the clover plant in comparison to the control plants, however low concentration of SO 2 (0.5 ppm) had positive effects on measured parameters. Inoculation of Persian clover with two strains of Rhizobium decreased the negative effects of high concentrations of SO 2 on the amounts of photosynthetic pigments and phosphorus and potassium elements. The highest values of these parameters were measured in a combination with the local strain plus 0.5 ppm of SO 2. It was suggested that Rhizobium could increase plant resistance and tolerance against abiotic stresses such as air pollution.