Assessment of various salt water stresses with mineralization on plant growth and antioxidants activity to regulate oxidative stress and ROS scavenging of halophyte ice plant

Halophyte such as ice plant is subjected to salinity and drought stress in their natural habitats, but our understanding of the effects of combined stress on plants is limited. This study aimed to investigate the mechanisms by which ice plant responds to combined salinity and alkalinity stress, which are currently unknown. This study evaluated the combined effects of salinity and alkalinity stress levels on the growth, mineral content, and phytochemical composition of <i>Mesembryanthemum crystallinum</i>. Therefore, experiment consisted of seven different salt treatments CK: distilled water control; T1: saline-alkali solution of 5 g/L; T2: saline-alkali solution of 10 g/L; T3: saline-alkali solution of 15 g/L; T4: saline-alkali solution of 20 g/L; T5: saline-alkali solution of 25 g/L; T6: saline-alkali solution of 30 g/L. The specific configuration method of the composite saline-alkali solution is to mix Na₂SO₄, NaCl, NaHCO₃, CaCl₂, MgCl₂ in the proportion of 8:8:1:1:1 on the basis of distilled water. The results indicated that the T6 treatment (saline-alkali solution of 30 g/L) strongly decreased the plant height, stem thickness, leaf area and SPAD value of ice plants, and obviously suppressed the shoot and root biomass with the increase in salinity. While T2 treatment (saline-alkali solution of 10 g/L) application significantly increased the root activity, soluble sugar, soluble protein, vitamin C and flavonoid content, POD (Peroxidase), AsA (reduced ascorbate), MDA (Malondialdehyde), and reduced the proline content; H₂O₂, O₂, K⁺ content, Na⁺ content, Cl⁺ content, and ratio of Na⁺/K⁺, respectively. Furthermore, plants grown with saline-alkali solution of 30 g/L presented the highest values of proline content, hydrogen peroxide, superoxide radicals and Na⁺ content, Cl⁺ content, ratio of Na⁺/K⁺ with the severity of the saline-alkali solution. The aboveground biomass of ice plant under saline-alkali stress was closely related to the Na⁺, K⁺, Na⁺/K⁺ ratio, proline, SOD, and CAT, indicating that the T2 treatment may alleviate the inhibition of ice plant growth by reducing the Na⁺/K⁺ ratio and improving antioxidant capacity. Therefore, planting ice plant in saline-alkali stress soil can provide additional minerals, phytochemicals, antioxidants, and related nutrients, and it is a vegetable suitable for saline-alkali stress areas.