The Effect of Light Spectrum on the Morphology and Cannabinoid Content of Cannabis sativa L.

Abstract

Cannabis sativa L. flowers are the main source of Δ-9-tetrahydrocannabinol (THC) used in medicine. One of the most important growth factors in cannabis cultivation is light; light quality, light intensity, and photoperiod play a big role in a successful growth protocol. The aim of the present study was to examine the effect of 3 different light sources on morphology and cannabinoid production. Cannabis clones were grown under 3 different light spectra, namely high-pressure sodium (HPS), AP673L (LED), and NS1 (LED). Light intensity was set to ∼450 µmol/m 2 /s measured from the canopy top. The photoperiod was 18L: 6D/21 days during the vegetative phase and 12L: 12D/46 days during the generative phase, respectively. At the end of the experiment, plant dry weight partition, plant height, and cannabinoid content (THC, cannabidiol [CBD], tetrahydrocannabivarin [THCV], cannabigerol [CBG]) were measured under different light treatments. The experiment was repeated twice. The 3 light treatments (HPS, NS1, AP673L) resulted in differences in cannabis plant morphology and in cannabinoid content, but not in total yield of cannabinoids. Plants under HPS treatment were taller and had more flower dry weight than those under treatments AP673L and NS1. Treatment NS1 had the highest CBG content. Treatments NS1 and AP673L had higher CBD and THC concentrations than the HPS treatment. Results were similar between experiments 1 and 2. Our results show that the plant morphology can be manipulated with the light spectrum. Furthermore, it is possible to affect the accumulation of different cannabinoids to increase the potential of medicinal grade cannabis. In conclusion, an optimized light spectrum improves the value and quality of cannabis. Current LED technology showed significant differences in growth habit and cannabinoid profile compared to the traditional HPS light source. Finally, no difference of flowering time was observed under different R:FR (i.e., the ratio between red and far-red light).

Cannabis Indoor Growing Conditions, Management Practices, and Post-Harvest Treatment: A Review

“…Although the trend of P N increasing with PPFD is similar for different varieties, the magnitude of increase and P Nmax varied considerably with the four varieties studied, with P Nmax higher in three Switzerland varieties than one Mexican variety [34]. However, the relationship between higher photosynthesis rate and higher cannabinoid yields has not been conclusively demonstrated [23]. Potter (2009) compared leaf tissue collected from a rare variegated cultivar, which had leaves coloured green and yellow on opposite sides of the midrib, and found that photosynthetic ability has minimal effect on the cannabinoid synthesis on local glandular trichomes [35].…”

“…More recently, light emitting diode (LED) fixtures with adjustable spectra have been developed. One study compared the effects of three light spectra, including one HPS and two types of LEDs (AP673L and NS1), on the morphology and cannabinoid content of cannabis clones [23]. The spectrum produced by HPS was 96% PAR and was heavily concentrated with green/yellow (68%) and orange/red (21%) and less concentrated in violet/blue (8%).…”

An Update on Plant Photobiology and Implications for Cannabis Production

“…In long day plants, various experiments suggest that flowering is promoted mostly when red light (or light creating a high Pfr/Pr ratio) is delivered during the early part of the photoperiod and when FR light (or light creating a lower Pfr/Pr ratio) is delivered toward the end of the photoperiod (Lane et al., 1965; Evans, 1976; Kadman-Zahavi and Ephrat, 1976; Thomas and Vince-Prue, 1996). However, certain cannabis genotypes such as “G-170” are insensitive to changes in the R:FR ratio, and no effect on flowering has been observed (Magagnini et al., 2018). The authors concluded that a low R:FR ratio during a long photoperiod (18 h light, 6 h dark/vegetative stage) is beneficial to the development of mature cuttings, contradicting popular belief in the cannabis industry.…”

Impact of Different Phytohormones on Morphology, Yield and Cannabinoid Content of Cannabis sativa L.

“…The target for high-quality Cannabis production includes a continuous and uniform inflorescence yield and the production of a specific cannabinoid compound [ 13 ]. Since the pharmaceutical industry requires the highest quality, it is necessary to ensure consistency in the cannabinoid profile of Cannabis plants and the quality of female flowers intended for such use.…”

“…Further, shorter side branches give plants more stability during bud development. Nevertheless, the total yield cannot be rated only by the number and weight of inflorescence, therefore the content of cannabinoids is also of great interest [ 13 ].…”