• salt stress
• oxalic acid
• hydroponics
• halophytes
• antioxidant

In the present study, crop yield and quality were analyzed in red orache (Atriplex hortensis L.; a halophyte) and Swiss chard (Beta vulgaris subsp. cicla L., a salt-tolerant glycophyte) grown hydroponically for baby-leaves production in nutrient solutions with different NaCl (0 and 428 mM) and N-NO3 (1 and 10 mM) concentration, in a factorial design. The experiment aimed to mimic the major defects of wastewater for saltwater aquaculture systems, that is high salinity and low N-NO3 concentration.
Using NaCl-enriched nutrient solutions markedly reduced crop yield of both orache and Swiss chard, albeit to a minor extent in the first species. This suggests that these effluents should be diluted with freshwater or a standard nutrient solution before use. High salinity impacted plant growth and leaf quality much more than reduced nitrate level. Leaf concentration of pigments, flavonoids, nitrate, and total antioxidant capacity decreased in both plant species grown with a saline nutrient solution in comparison with the control solution. On the contrary, leaf concentration of Na and oxalate markedly increased in salt-treated plants as compared to non-salinized plants. The pattern of oxalate accumulation supports the hypothesis that an increase in oxalate is linked to reduced catabolic activity of the enzyme oxalate oxidase. The Oxalate profile was not affected by nitrate levels in the nutrient solution. Oxalate levels were quite high in both species, especially in orache. However, seeing the moderate intake of baby-leaves (often found as a ready-to-eat salad mix), their consumption should not pose serious risks to human health.