Vegetative and reproductive stage lighting interactions on flower yield, water use efficiency, terpenes, and cannabinoids of Cannabis sativa

Cannabis is among the most water-demanding crops, facing ongoing expansion and water use regulations. This study evaluated the effects of greenhouse sunlight plus increased LED supplemental lighting on flower yield, water use (WU), and efficiency (WUE), as well as flower partitioning, cannabinoids, terpenes, and leaf gas exchange in Cannabis sativa 'Suver Haze'. The supplemental lighting programs applied during the vegetative and flowering stages were: (1) Static LED levels (PPFD: 150, 300, 500, or 700 µmol m^-2 s^-1 for 72 days) and (2) Dynamic LED levels (PPFD: 150, 300, or 500 for 28 days, followed by 700 µmol m^-2 s^-1 for 44 days). Flower yield and crop WUE increased linearly with the increase of Dynamic and Static lighting. For instance, a 4.7-fold Static lighting increase caused a 4.1-fold increase in flower yield and reduced the evapotranspiration per gram of flower by 37%. Furthermore, plants in Dynamic lighting produced up to 10.4% more flowers and 24.8% higher WUE than plants in Static lighting at the same cumulative lighting. Higher leaf photosynthetic rate, WUE, and lower stomatal conductance due to higher light intensity supported the crop results. Cannabinoid and terpene changes were small and complex, with terpene concentration affected by the light program and light level. In conclusion, supplemental lighting substantially enhanced production and WUE, particularly when higher light was provided during flowering.