Effects of Drought on Inflorescence Yield, and Secondary Metabolites in Cannabis sativa L.

The use of medical products derived from Cannabis sativa L. has increased significantly in recent years. While drought is known to negatively affect the yields of many crops, growers often recommend controlled periods of drought for cannabis cultivation to increase concentrations of secondary metabolites. This is especially pertinent when considering the relationship between medicinal effects and the secondary-metabolite profile.

We examined the effects of tightly controlled drought treatments on biochemical (111 phytocannabinoids and 132 terpenoids), physiological, and anatomical responses of three Type-I chemotype cultivars, specifically the THCA-dominant cultivars ‘Odem’, ‘MVA’, and ‘187’.

Our results revealed strong correlations between inflorescence and phytocannabinoid yields, on the one hand, and cumulative transpiration on the other (0.96 < r ² < 0.99). Drought treatment reduced canopy conductance, with inflorescence weight decreasing by 40% and total fresh weight decreasing by 48%. The concentrations of the major phytocannabinoids, THCA and CBGA, decreased over increasing levels of drought stress (by 26% and 61%, respectively). Interestingly, terpene concentrations showed greater stress-induced variation, and that variation was genotype-dependent.

Our findings suggest that the decreases in inflorescence weight and concentrations of major phytocannabinoids under drought conditions are mainly due to a lack of biochemical-production processes, as opposed to metabolic degradation.