Cannabis Inflorescence Yield and Cannabinoid Concentration Are Not Increased With Exposure to Short-Wavelength Ultraviolet-B Radiation

Abstract

Before ultraviolet (UV) radiation can be used as a horticultural management tool in commercial Cannabis sativa (cannabis) production, the effects of UV on cannabis should be vetted scientifically. In this study we investigated the effects of UV exposure level on photosynthesis, growth, inflorescence yield, and secondary metabolite composition of two indoor-grown cannabis cultivars: ‘Low Tide’ (LT) and ‘Breaking Wave’ (BW). After growing vegetatively for 2 weeks under a canopy-level photosynthetic photon flux density (PPFD) of ≈225 μmol⋅m–2⋅s–1 in an 18-h light/6-h dark photoperiod, plants were grown for 9 weeks in a 12-h light/12-h dark “flowering” photoperiod under a canopy-level PPFD of ≈400 μmol⋅m–2⋅s–1. Supplemental UV radiation was provided daily for 3.5 h at UV photon flux densities ranging from 0.01 to 0.8 μmol⋅m–2⋅s–1 provided by light-emitting diodes (LEDs) with a peak wavelength of 287 nm (i.e., biologically-effective UV doses of 0.16 to 13 kJ⋅m–2⋅d–1). The severity of UV-induced morphology (e.g., whole-plant size and leaf size reductions, leaf malformations, and stigma browning) and physiology (e.g., reduced leaf photosynthetic rate and reduced Fv/Fm) symptoms intensified as UV exposure level increased. While the proportion of the total dry inflorescence yield that was derived from apical tissues decreased in both cultivars with increasing UV exposure level, total dry inflorescence yield only decreased in LT. The total equivalent Δ9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD) concentrations also decreased in LT inflorescences with increasing UV exposure level. While the total terpene content in inflorescences decreased with increasing UV exposure level in both cultivars, the relative concentrations of individual terpenes varied by cultivar. The present study suggests that using UV radiation as a production tool did not lead to any commercially relevant benefits to cannabis yield or inflorescence secondary metabolite composition.

Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content

“… Also included are the published maximum values for the known parameters from Lydon et al (1987) and Rodriguez-Morrison et al (2021b) ; the UV dose in Lydon et al (1987) was calculated using an earlier version of the BSWF ( Caldwell, 1971 ) that only integrates UV wavelengths between ≈ 275 and 315 nm). y Radiant flux density.…”

“…The strongest links between UV radiation and cannabinoid content relate to ultraviolet-B (UVB, 280-315 nm), however, radiation from the ultraviolet-A (UVA, 315-400 nm) and 10.3389/fpls.2022.974018 shorter wavelengths in the blue (400-500 nm) wavebands have also been implicated in altering the cannabis inflorescence chemical composition (Magagnini et al, 2018;Bilodeau et al, 2019) and mediating cellular repair provoked by UVB damage in other species (Krizek, 2004), sometimes called photoreactivation (Gill et al, 2015). Rodriguez-Morrison et al (2021b) found only deleterious effects on cannabis morphology, physiology, yield, and quality when two chemotype II cannabis cultivars were exposed to various levels of short wavelength UVB provided by LEDs with a peak wavelength of 287 nm. However, since very little solar UV with wavelengths below 295 nm reaches the earth's surface (Green et al, 1974;Flint and Caldwell, 1996), cannabis plants may have no adaptive or acclimative mechanisms for coping with periodic exposure to such short wavelength radiation.…”

Nitrogen Source Matters: High NH4/NO3 Ratio Reduces Cannabinoids, Terpenoids, and Yield in Medical Cannabis

“…Drug-type medical cannabis plants yield inflorescences rich in hundreds of phytochemicals such as cannabinoids, terpenoids, and flavonoids, which are the source of the plants’ biological activity ( Russo et al, 2003 ; Andre et al, 2016 ; Shapira et al, 2019 ). The biosynthesis of these secondary metabolites is affected by environmental and cultivation conditions ( Magagnini et al, 2018 ; Bernstein et al, 2019a , 2005 ; Danziger and Bernstein, 2021a , b ; Rodriguez-Morrison et al, 2021 ; Westmoreland et al, 2021 ); and the increasing demand by the pharmacological industry for a high-quality chemically standardized plant product requires understanding of the plant physiological and metabolic responses to exogenous factors, which is very limited today.…”

Cannabis sativa L.: Crop Management and Abiotic Factors That Affect Phytocannabinoid Production

“…Recent works have evaluated the influence of UV light supplementation and have presented contradictory results regarding the production of phytocannabinoids. Rodriguez-Morrison and colleagues (2021) [83] evaluated the responses of two cannabis varieties, 'Low Tide' (LT) and 'Breaking Wave' (BW), grown under supplemental UV radiation. The authors observed that the total dry inflorescence yield derived from apical tissues decreased in both cultivars with increasing UV exposure levels, but the total dry inflorescence yield only decreased in LT.…”

“…The UV supplementation decreased the inflorescence yield of 'Larry OG' [85]. Further research with different genotypes is required to determine if there is a combination of UV spectrum, intensity, and time of application that would bring beneficial commercial effects for cannabis production [83,84].…”