Interactive Effects of Salinity Stress and Irrigation Intervals on Plant Growth, Nutritional Value, and Phytochemical Content in Mesembryanthemum crystallinum L.

Halophytes such as ice plants are concurrently subjected to salt and drought stresses in their natural habitats, but our knowledge about the effects of combined stress on plants is limited. In this study, the individual and combined effects of salinity and irrigation intervals on the plant growth, mineral content, and proximate and phytochemical composition of M. crystallinum were evaluated. Treatments consisted of four irrigation treatments ((1) 100 mL once a day: (2) 100 mL once every 2 days: (3) 100 mL once every 4 days: (4) 100 mL once every 8 days) with four salt concentrations (0, 200, 400, and 800 ppm) applied in each treatment. Salt concentrations were set up by adding increasing concentrations of NaCl to the nutrient solution, while the control treatment was irrigated daily without NaCl. The results revealed a significant increase in the leaf number and fresh and dry weights of plants irrigated with 800 ppm salinity every four days. However, the highest chlorophyll content was consistently recorded in the control treatment (0 ppm, 4-day irrigation interval), although no significant variability in chlorophyll content was observed at week 6. The highest yields of N, Mg, and Cu were consistently recorded in plants without saline treatment, while P, K, Ca, Na, Zn, and Fe were consistently recorded in plants subjected to a combination of salinity and irrigation intervals. The combination of salinity and irrigation intervals was significant for Fe and Ca, whereas, for other elements, no significant differences occurred. The salt concentration did not influence the high yields of acid detergent fibre (ADF), crude fat, protein, or neutral detergent fibre (NDF), as they were recorded in high amounts in plants subjected to irrigation intervals only, whereas a combination of salinity and irrigation intervals resulted in the highest ash and moisture contents. Invariably, the 8-day irrigation interval without salinity optimized the yields of assayed polyphenols, flavonols, Ferric Reducing/Antioxidant Power (FRAP), and 2,2-diphenyl-1-picrylhydrazyl (DPPH), suggesting that salt stress does not influence the quantities of phytochemicals and antioxidants of M. crystallinum. These findings suggest that M. crystallinum can minimize the impact of salt stress on the accumulated minerals, phytochemicals, and proximate and antioxidant substances. Therefore, it is a suitable vegetable for regions affected by both salinity and water stress, as it can provide additional minerals, phytochemicals, antioxidants, and proximate nutrients when cultivated in saline soils.