Optimizing Lighting Conditions for Watercress (Nasturtium officinale) Production in Controlled-Environment Agriculture: Effects on Growth, Physiology, and Nutritional Quality

Light is a critical environmental factor influencing the growth, development, productivity, and nutritional quality of watercress (Nasturtium officinale) in controlled environments. This review examines how light intensity, spectrum, and photoperiod affect watercress physiology, biomass production, morphology, photosynthesis, and accumulation of health-promoting phytochemicals including glucosinolates, phenethyl isothiocyanate (PEITC), chlorophyll a, chlorophyll b, carotenoids (β-carotene, lutein, and zeaxanthin), phenolic compounds, flavonoids (quercetin and kaempferol), and vitamin C (ascorbic acid). Published studies investigating varying light regimes, including irradiance, blue and red wavelengths and photoperiods, were evaluated, considering interactions with temperature, carbon dioxide, water, and nutrient availability. The findings indicate that insufficient light can restrict photosynthesis and biomass accumulation, whereas excessive irradiance may cause photoinhibition and reduced physiological performance, amongst other factors. Light quality also strongly influences plant morphology, photosynthetic activity, and nutritional composition, while photoperiod contributes to growth and developmental regulation. Notably, a red-to-blue LED ratio of 7:3 (7R:3B) produces the highest stem length, shoot fresh and dry weight. Other studies have shown that a 50:50 red-to-white LED combination enhances fresh biomass accumulation and photosynthetic performance, whereas green light promotes vitamin C and phenolic compound accumulation. Supplemental blue light increases carotenoid concentrations but may reduce vitamin C levels. Under an equivalent daily light integral, a 12-h photoperiod maximized instantaneous photosynthetic rates, while a 20-h photoperiod produced the highest mean biomass; however, biomass differences between photoperiod treatments were not statistically significant. Overall, successful watercress production requires lighting strategies that optimize light intensity, spectral composition and photoperiod in conjunction with temperature, nutrient availability and water supply to maximize growth, yield and nutritional quality. Future research should prioritize dynamic, cultivar-specific, and precision lighting approaches integrated with environmental controls to improve resource-use efficiency and consistently produce high-quality watercress.