Effect of Saline Irrigation Water on Antioxidants in Three Hydroponically Grown Leafy Vegetables: Diplotaxis tenuifolia, Eruca sativa, and Lepidium sativum

Abstract

Our study evaluated changes in nutritional content of leafy vegetables at harvest and during postharvest in response to nutrient solutions of increasing salinity using a recirculating ebb and flow irrigation system within a controlled environment (CE). Two antioxidants, ascorbic acid (AsA) and total phenolics (TP), were used as proxies for nutrition as determined by the 2,6-dichloroindolphenol titrimetric and the Folin-Ciocalteu methods, respectively. Two arugulas, Diplotaxis tenuifolia (L.) DC cv. Sylvetta and Eruca sativa (P. Mill.) Thell. cv. Astro, and a garden cress, Lepidium sativum L. cv. Presto, were grown with five salinity levels ranging from 1.5 to 9.5 dS·m−1 electrical conductivity (EC) during two trials. We observed no difference in TP at harvest in response to salinity treatments in Trial 1 for all species collectively evaluated; however, during Trial 2, the TP at harvest responded to salinity treatments. In contrast, we observed a response in AsA at harvest to salinity treatments during both trials. The response of both TP and AsA to treatments was characterized by variability, both increases and decreases, when contrasting species and trials. We concluded that the variability in the nutritional content of the specific crucifers evaluated might reflect both individual species responses and the modest CE microclimate changes we recorded between trials. In addition, our research suggests that salinity levels greater that an EC of 9.5 dS·m−1 may be required to define the salinity tolerance of these specific crucifers within a CE.