Macronutrient deprivation eustress elicits differential secondary metabolites in red and green‐pigmented butterhead lettuce grown in a closed soilless system

Abstract BACKGROUND Through precise control of the nutrient solution (NS), closed soilless systems enable targeted manipulation of plant secondary metabolites, which constitute health‐promoting components of the human daily diet. A nutrient film technique (NFT) system was employed to assess the effect of NS macronutrient‐based concentration (full, half‐, and quarter‐strength corresponding to electrical conductivity (EC) of 1.5, 0.75, and 0.5 dS m −1 ) on the bioactive profile of red and green‐pigmented Salanova® butterhead lettuce. RESULTS Half‐strength NS reduced fresh biomass of both cultivars by 14%, whereas quarter‐strength NS reduced the fresh biomass of green and red Salanova by 24% and 38%, respectively. However, moderate nutrient stress (half‐strength NS) boosted red Salanova total ascorbic acid, chlorogenic, chicoric, caffeoyl‐meso‐tartaric, total phenolic acids, and anthocyanins concentrations by 266%, 199%, 124%, 251%, 162%, and 380%, respectively compared with the control, full‐strength NS. CONCLUSIONS Nutritional eustress and appropriate cultivar selection are effective means to increase phytochemical content and optimize year‐round production of lettuce in closed soilless systems. © 2019 Society of Chemical Industry