The Highs and Lows of P Supply in Medical Cannabis: Effects on Cannabinoids, the Ionome, and Morpho-Physiology

Abstract

Environmental conditions, including the availability of mineral nutrients, affect secondary metabolism in plants. Therefore, growing conditions have significant pharmaceutical and economic importance for Cannabis sativa. Phosphorous is an essential macronutrient that affects central biosynthesis pathways. In this study, we evaluated the hypothesis that P uptake, distribution and availability in the plant affect the biosynthesis of cannabinoids. Two genotypes of medical “drug-type” cannabis plants were grown under five P concentrations of 5, 15, 30, 60, and 90 mg L–1 (ppm) in controlled environmental conditions. The results reveal several dose-dependent effects of P nutrition on the cannabinoid profile of both genotypes, as well as on the ionome and plant functional physiology, thus supporting the hypothesis: (i) P concentrations ≤15 mg L–1 were insufficient to support optimal plant function and reduced photosynthesis, transpiration, stomatal conductance and growth; (ii) 30–90 mg L–1 P was within the optimal range for plant development and function, and 30 mg L–1 P was sufficient for producing 80% of the maximum yield; (iii) Ionome: about 80% of the plant P accumulated in the unfertilized inflorescences; (iv) Cannabinoids: P supply higher than 5 mg L–1 reduced Δ9-tetrahydrocannabinolic acid (THCA) and cannabidiolic acid (CBDA) concentrations in the inflorescences by up to 25%. Cannabinoid concentrations decreased linearly with increasing yield, consistent with a yield dilution effect, but the total cannabinoid content per plant increased with increasing P supply. These results reveal contrasting trends for effects of P supply on cannabinoid concentrations that were highest under <30 mg L–1 P, vs. inflorescence biomass that was highest under 30–90 mg L–1 P. Thus, the P regime should be adjusted to reflect production goals. The results demonstrate the potential of mineral nutrition to regulate cannabinoid metabolism and optimize pharmacological quality.

Impact of Harvest Time and Pruning Technique on Total CBD Concentration and Yield of Medicinal Cannabis

“…In the study from Yang et al [ 17 ], similar trends for a plateau of total CBD concentrations in the studied range of harvest times were reported for five CBD-rich cannabis genotypes grown in open-field. All five genotypes presented an increasing trend of total CBD concentration until a peak by six to seven weeks of flowering.…”

“…The importance of optimizing indoor systems has increased due to the demand for yield maximization and improved efficiency of growing systems [ 13 ]. Final yield quantity and quality of inflorescences are highly variable and depends on numerous factors such as genotype [ 14 , 15 , 16 ]; the agronomic practices, such as irrigation and fertilizer regimes [ 17 , 18 , 19 , 20 ], light spectra [ 14 , 21 ], intensity [ 22 , 23 ] and photoperiod [ 24 ]; plant density [ 25 ]; environmental conditions (humidity and temperature) [ 12 ] and the influence of biotic and abiotic stresses [ 26 , 27 ]—including pruning and defoliation techniques [ 28 , 29 ]—and finally, the duration of the vegetative and generative period. Thus, so many differences can be found for reported yield of medicinal cannabis currently in literature.…”

“…The typical duration of the generative period of conventional medical cannabis genotypes for indoor systems ranges from 7 to 14 weeks of flowering [ 31 , 32 , 33 , 34 , 35 ]. The composition of cannabinoids in inflorescences changes over time as cannabigerolic acid (CBGA) is synthesized in growing inflorescences, and both CBDA and THCA are converted from CBGA [ 14 , 15 , 16 , 17 ]. These conversions are determined by genomic expression of CBDA- and THCA-synthases, responsible for the content and ratios among cannabinoids in different chemotypes [ 36 ].…”

Shape Matters: Plant Architecture Affects Chemical Uniformity in Large-Size Medical Cannabis Plants

“…While the potential for production of a specific secondary metabolite profile in cannabis is determined by the genetic background of the plant [4], the actual levels of the produced metabolites are affected to a large extent by environmental conditions during cultivation, such as mineral nutrition [4][5][6][7], light intensity and light spectrum [8,9], and elicitation of stress conditions [10]. Variability in the chemical profile between inflorescences was observed also along the plant [4,6,7,11]. Furthermore, as plant organs sense their environments locally, differences between micro-climates within the shoot further induce changes in physiology [12] and secondary metabolism [13].…”

Manipulation of Cannabinoid Biosynthesis via Transient RNAi Expression

“…Using gene silencing tools, designer strains with high levels of CBD producing zero THC are possible, as are strains with elevated levels of CBG, which contains anti-cancer properties ( Borrelli et al, 2014 ), through the knockdown of the downstream enzymatic processes of THCAS, CBDAS , and CBCAS . The use of environmental pressures applied through varying nutrient concentrations ( Saloner and Bernstein, 2021 ; Shiponi and Bernstein, 2021 ) or light spectrum and lighting source ( Magagnini et al, 2018 ; Namdar et al, 2019 ) has previously demonstrated significant modulation of secondary metabolites, up to 300% in some instances ( Shiponi and Bernstein, 2021 ). While this ability to variably control cannabinoid content in cannabis using environmental conditions is significant, the synergistic effects of all cannabinoids either increasing or decreasing make this approach incapable of producing a complete knockdown/significant downregulation of specific cannabinoids to create novel chemotypes.…”