Effects of salinity on growth, photosynthesis, inorganic and organic osmolyte accumulation in Elaeagnus oxycarpa seedlings

To acquire basic information about species' salt tolerance prior to applying Elaeagnus oxycarpa to phytoremediate degraded saline areas, salt-induced changes in growth, photosynthesis, and osmolyte accumulation in E. oxycarpa seedlings were investigated. The responses of 120-day-old seedlings to NaCl application (0, 50, 100, 200, or 300 mM) were assessed for 30 days. Plant growth and biomass were not affected at low salinity (50 mM NaCl) and decreased linearly with an increase in salinity. However, seedlings tolerated up to 300 mM NaCl without any effect on survival and grew normally without toxic symptoms (such as yellow leaves at the base of the seedlings and new leaves burn) at 200 mM NaCl. Gas exchange was unaffected at 50 mM NaCl but was reduced at ≥100 mM NaCl. Maintenance of photosystem II (PSII) function (F _v /F _m) at high salinity (200 mM) could support E. oxycarpa growth. Leaf and root Na⁺ concentrations increased with increasing salinity, although most Na⁺ was retained in the root system at low and moderate salinity (50 and 100 mM NaCl), whereas high concentrations of nutrients (e.g., K⁺ and Ca²⁺) were maintained in the leaves. The seedlings accumulated a set of important osmolytes in leaves under salt stress, showing a marked increase in sucrose, β-alanine betaine, proline, and glycine at 200 and 300 mM NaCl. These compounds indirectly may contribute to osmotic adjustment by maintaining high cation concentrations and osmoprotective functions when stress becomes severe. We conclude that salt tolerance in E. oxycarpa is based on maintenance of PSII function, ionic homeostasis, and accumulation of osmolytes.