Na+ and K+ compartmentalization in Spinacea oleracea and their effects on growth, water relations, endogenous melatonin, and non-structural carbohydrates

•Spinacea oleracea growth and nutrition are impacted by the changes in its hydraulic traits due to soil salinity caused by the fluxes of Na+ and K+.•The application of NaCl significantly reduced K+ concentrations, growth, stomatal conductance, photosynthesis, relative water content and also impacted the veins and stomata.•The maximum amount of Na+ was compartmentalized in leaf-blade while the minimum was in roots. Meanwhile, maximum K+ was compartmentalized in the mid-rib and minimum in the stem.•Endogenous melatonin exhibits an elevated concentration in response to the application of stress. Furthermore, the concentration of melatonin was found to be further increased with the administration of treatment. Spinacea oleracea is an economically important vegetable crop. Its growth and nutrition are impacted by the changes in its hydraulic traits due to soil salinity caused by the fluxes of Na+ and K+ which need further investigations to promote its cultivation in degraded agriculture lands. The objective of this study was to assess the impact of different concentrations of NaCl on water relations and non-structural carbohydrates of S. oleracea. For which the hydraulic traits such as rate of photosynthesis, transpiration, stomatal conductance, relative water content, stomatal and vein anatomy, non-structural carbohydrates, and growth were assessed. The compartmentalization of Na+ and K+ was analyzed in both the above and below ground parts. We found that the application of NaCl significantly reduced K+ concentrations, growth, stomatal conductance, photosynthesis, relative water content and also impacted the veins and stomata. The maximum amount of Na+ was compartmentalized in leaf-blade while the minimum was in roots. Meanwhile, maximum K+ was compartmentalized in the mid-rib and minimum in the stem. The K+ and K+: Na+ decreased significantly with the increasing salinity in the treatments. Non-structural carbohydrates also decreased with an increase in sodium concentration. Further, some significant linear relationships were also found between Na+, K+ and the studied hydraulic traits. Endogenous melatonin exhibits an elevated concentration in response to the application of stress. Furthermore, the concentration of melatonin was found to be further increased with the administration of treatment T1 to T4. We conclude that S. oleracea can tolerate NaCl stress up to 80 mML−1. The findings can be helpful to cultivate S. oleracea in excessive sodic soil and can als