The arbuscular mycorrhizal symbiosis alleviating long-term salt stress through the modulation of nutrient elements, osmolytes, and antioxidant capacity in rosemary

Salinity is considered as one of the most destructive abiotic stresses for plants, and its prevalence is growing globally. This study assayed the impacts of single inoculation with the arbuscular mycorrhizal fungi (AMF) Rhizophagus irregularis (Ri) or Funneliformis mosseae (Fm), and co-inoculation of Ri and Fm, on rosemary plants exposed to long-term salinity stress [0, 50, 100, 150 mM NaCl] with three replications under controlled conditions of greenhouse. The results exhibited that Ri and Ri + Fm differentially colonized the roots of rosemary plants under moderate NaCl stress (50 and 100 mM) compared to Fm. Under non-saline conditions, AMF symbiosis increased plant growth, promoted biomass and chlorophyll contents, and improved the nutrient uptake and antioxidant capacity of the host plant. However, long-term salinity stress, even at a low level (50 mM), adversely affected the growth parameters of rosemary plants. Furthermore, AMF inoculation improved plant growth and alleviated ion toxicity under NaCl stress. Plants inoculated with single and consortia AMF species had high values of photosynthetic pigments, Fv/Fm index (0.80 for Fm + Ri), proline content (4.69 mu M.g(-1) FW for Fm), total phenolic content (58.38 mg GA.g(-1) DW for Ri), K (9.46 mg.g(-1) DW for Ri), P, and K: Na ratio (0.88 for Ri), but had low values of electrolyte leakage (42.34% for Ri), Na+ concentration in the shoot (11.56 mg.g(-1) DW for Ri), and malondialehyde content (3.62 mu M.g(-1) FW for Fm) under high salinity levels, as compared to non-inoculated plants. Further, shoot fresh weight, root length, and Zn content in Fm inoculated plants under NaCl stress were higher compared to non-inoculated plants. Specifically, the results of this study suggest that the utilization of consortia AMF species does not necessarily lead to better capacity to compensate for hazardous effects of salinity compared to single species. Finally, this study indicated that arbuscular mycorrhizal symbiosis could improve the growth, ion homeostasis, osmoregulation, and reactive oxygen species scavenging capabilities of rosemary plants under salinity stress.