Effect of different mycorrhizal species inoculation on concentration of nutrient elements, yield per plant and antioxidant activity in Peppermint (Mentha piperita) under salt stress

  Salinity is one of obstacles of planting and developing in arid and semiarid regions in the world. Nowadays, one of the major problems in agriculture is the lack of access to fresh water with suitable quality for irrigation. Generally, plants can feel a wide range of environmental stresses which eventually lead to oxidative stress in plant. Mechanism of resistance to some of the stresses is as the internal connection and is the result of a coordinated and complex planning. Contribution of arbuscular mycorrhizal symbiosis can lead to the improvement of growth and resistance to stress. Considering the development of the culture of using medicinal plants, as well as the expansion of salty soils, studying the effects of salinity on peppermint and mechanism of its resistance to salinity is necessary. To explore the effect of symbiosis of different types of mycorrhizal inoculation on yield, physiological characteristics and essential oil of peppermint medicinal plant under salt stress, an experiment was conducted in factorial based on completely randomized design with three replications in greenhouse. The salinity levels were 0, 2, 4, 6 and 8 dS/m and types of mycorrhizal included Glomus mosseae, G. intraradices, G. versiform and non-mycorrhizal. The traits measured were yield per plant, total phenol, antioxidant activity and concentration of nutrient. Results showed that all the characteristics studied were significantly affected by the main and interaction effects of mycorrhizal and salinity stress. Furthermore, the results showed that the highest and lowest amounts of yield per plant, nitrogen, phosphorus and potassium were observed in the treatment of inoculation with R. irregularis under non-stress conditions and the lowest amounts of the characteristics measured were observed in non-mycorrhizal treatment under stress conditions. The highest amount of essential oil was observed in the treatment of inoculation with R. irregularis under 6 and 8 dS/m salinity stress conditions (4.18 and 4.42 percent) and inoculation with G. versiform under 8 dS/m salinity stress condition (4.22 percent), and the lowest amount of essential oil was observed in non-mycorrhizal treatment under non-stress condition (0.29 percent). Treatments of inoculation with F. mosseae and G. versiform were superior to control conditions, but their effects were lower in comparison with the treatment of inoculation with G. intraradices. The concentration of nutrients in mycorrhizal plants was higher, causing an improvement in yield per plant. Mycorrhizal fungus can decrease the effect of salinity stress through an increase in phosphorus uptake in plants. The results also showed that concentrations of potassium in mycorrhizal plants were higher than in non-mycorrhizal plants. Thus, with increase in the ratio of potassium to sodium, mycorrhizal symbiosis can protect plants against negative effects of sodium. Results showed that use of bio-fertilizers can improve quantitative and qualitative yield in peppermint, and it seems that bio-fertilizers are a suitable alternative for chemical fertilizers for sustainability of the production and protection of the environment. Mycorrhizal symbiosis in salty soils caused an increase in plant resistance to salinity and improved growth and yield per plant under stress conditions.