<i>Cannabis sativa</i> L. Response to Narrow Bandwidth UV and the Combination of Blue and Red Light during the Final Stages of Flowering on Leaf Level Gas-Exchange Parameters, Secondary Metabolite Production, and Yield

Abstract

Many modifications to growing environments and specific stress induction techniques exist which are supported by preliminary research to increase yield and/or concentration of secondary metabolites in Cannabis sativa L. One such technique is the modification of the spectral composition of light late in flowering-stage development. In this study, we evaluated the hypothesis that the addition of narrow bandwidth UV-A light and the combination of narrow bandwidth blue and red light, during the final two weeks of the flowering cycle affect the concentration of cannabinoids and terpenes, with no difference in harvest dry weight. Three treatments were used in this experimental design, 1) control-full spectrum illumination, 2) UV-A (~390 nm) at ~66 PPFD in addition to control lighting, and 3) blue (~450 nm) and red (~660 nm) at ~158 PPFD in addition to control lighting. Light treatments were initiated during the final two weeks of flowering to assess secondary metabolite concentration (cannabinoids and terpenes) and yield of three cannabis cultivars (Type I (Larry OG), Type II (Pootie Tang), and Type III (Super White)). With two of the three cultivars used in this study responding with enhanced production of THC our results support the potential beneficial effects of attributed light-mediated treatments on cannabinoid production. On the other hand, our results show contrasting trends for terpene production and yield of dry weight flower.