Halotolerant Mycorrhizal Symbiosis Enhances Tolerance in Limonium Species Under Long-Term Salinity

To survive in saline environments, plants establish complex symbiotic relationships with soil microorganisms, including halotolerant arbuscular mycorrhizal fungi (AMF). The main objective of this study was to uncover how inoculation with a consortium of halotolerant AMF influences recretohalophyte <i>Limonium</i> species tolerance to long-term salinity, at physiological and molecular levels. In this study, the physiological performance, ultrastructure of leaf epidermal cells, and expression of seven genes involved in salinity response were studied in <i>Limonium daveaui</i> and <i>Limonium algarvense</i> plants exposed to 200 mM NaCl and inoculated with an AMF consortium, dominated by <i>Rhizoglomus invernaius</i>. An isohydric response was observed for both species after one year in salinity. Inoculation with AMF led to higher stomatal conductance for plants in non-saline conditions and improved photosystem II efficiency under salinity. In <i>L. algarvense</i>, inoculation enhanced stomata and salt gland epidermal area under tap water. While salinity significantly increased salt gland, stomata and pavement cells areas but not cell size. In <i>L. daveaui</i>, AMF led to an increased salt gland density as well as salt gland size under saline conditions. In both species, salinity increased the expression of Na⁺/H⁺ antiporter <i>AtSOS1</i>, aquaporin <i>TIP5</i>, and salt gland development related genes <i>LbTRY</i>, <i>Lb7G34824</i> and <i>Lb4G22721GIS2</i>. The expression of such genes was significantly reduced in AMF-inoculated plants under salinity. Besides, higher levels of gene expression were observed in <i>L. algarvense</i> than in <i>L. daveaui</i>. Overall, our findings highlight the protective role of halotolerant AMF and emphasize their potential as sustainable effective bio-inoculants for enhancing plant salinity tolerance.