Enhancing Growth and Glucosinolate Accumulation in Watercress ( Nasturtium officinale L.) by Regulating Light Intensity and Photoperiod in Plant Factories

Recent advancements in light-emitting diode technology provide an opportunity to evaluate the correlation between different light sources and plant growth as well as their secondary metabolites. The aim of this study was to determine the optimal light intensity and photoperiod for increasing plant growth and glucosinolate concentration and content in watercress. Two-week-old seedlings were transplanted in a semi-deep flow technique system of a plant factory for 28 days under four photoperiod–light intensity treatments (12 h—266 µmol·m −2 ·s −1 , 16 h—200 µmol·m −2 ·s −1 , 20 h—160 µmol·m −2 ·s −1 , and 24 h—133 µmol·m −2 ·s −1 ) with the same daily light integral. The mean values of shoot fresh and dry weights were the highest under the 20 h—160 µmol·m −2 ·s −1 treatment, although there was no significant difference. Net photosynthesis and stomatal conductance gradually decreased with decreasing light intensity and increasing photoperiod. However, total glucosinolate concentration was significantly higher under 20 h—160 µmol·m −2 ·s −1 and 24 h—133 µmol·m −2 ·s −1 compared with 12 h—266 µmol·m −2 ·s −1 and 16 h—200 µmol·m −2 ·s −1 . The total glucosinolate content was the greatest under 20 h—160 µmol·m −2 ·s −1 treatment. These data suggest that the 20 h—160 µmol·m −2 ·s −1 treatment promoted the maximum shoot biomass and glucosinolate content in watercress. This study supplies the optimal light strategies for the future industrial large-watercress cultivation.