Potential effects of arbuscular mycorrhizal fungi in mitigating the salinity of treated wastewater in young olive plants (Olea europaea L. cv. Chetoui)

Abstract The reuse of treated wastewater for olive irrigation is becoming a common practice in areas with limited water resources. However, this water may contain high level of salts (Na+ and Cl−) that could affect plant performances when used for a long period. In order to enhance the tolerance of plants to salt stress induced by treated wastewater, the application of arbuscular mycorrhizal fungi (AMF) may be a suitable solution. In this study, the ability of different AMF inoculums to improve young olive plants (Olea europaea L. cv. Chetoui) performances under long term irrigation with treated wastewater was studied. One-year-old olive trees inoculated with Glomus deserticola and/or Gigaspora margarita were irrigated with treated wastewater for one year. As compared to plants irrigated with tap water, treated wastewater irrigation caused a significant decrease in relative water content (RWC), total fresh and dry weights, gas exchange parameters, and chlorophyll and starch contents. Nevertheless, a significant increase in Na+ and Cl−, proline, soluble sugars, total polyphenols as well as flavonoids contents was observed under treated wastewater irrigation. Interestingly, colonization with different AMF inoculums, particularly the 1:1 mixture of G. deserticola and G. margarita, alleviated the negative effect of saline treated wastewater on young olive plants and significantly improved the above parameters. In fact, mycorrhizal symbiosis decreased the Na+ and Cl− contents and improved the RWC, the total fresh and dry weights and the photosynthetic activity. Furthermore, mycorrhizal plants showed higher concentrations of proline and soluble sugars as well as higher antioxidant defense systems as compared to the non-inoculated plants.