Nitrogen deficiency stimulates cannabinoid biosynthesis in medical cannabis plants by inducing a metabolic shift towards production of low-N metabolites

The primary and secondary metabolism of plants is closely connected to the resources supplied and obtained by the plant, including their mineral nutrition. We recently reported that nitrogen (N) deficiency enhances the production of terpenoids and cannabinoids, the unique biologically-active secondary metabolites in medical cannabis plants. Knowledge-gaps concerning effects of N supply on primary metabolism in cannabis hinder understanding of the interrelations between N inputs and biosynthesis of the therapeutic secondary metabolites. The present study therefore evaluated the hypothesis that a decrease in the plant's C (carbon): N ratio by N-limitation, induces a shift in the plant metabolism towards lower production of N-containing metabolites and higher production of metabolites that do not contain N. Effects of N input levels (30, 80, 160, 240, and 320 mg L⁻¹) on total C and N concentrations and C: N ratio in leaves and inflorescences of medical cannabis plants were studied; and gas chromatography-mass spectrometry (GC-MS) analysis of primary metabolites added to the analyses of secondary metabolites. Elevation of N supply resulted in an increase in total N and N-containing compounds (chlorophylls and most amino acids), and decreased total C and compounds that do not contain N, such as sugars (fructose, glucose, and xylose), and phosphates (phosphate and glucose-6-phosphate) in both inflorescences and leaves. In the inflorescences, the elevation of N input also decreased total cannabinoids, phenols, and flavonoids, that do not contain N. Integrating the metabolic datasets revealed positive correlations between C sources (fructose and glucose) and most of the cannabinoids and terpenoids; the latter were negatively correlated with N-compounds (most amino acids). Taken together, these results suggest that elevated N supply induce a metabolic shift in the inflorescences towards increased production of N-compounds via deflecting the C sources from the biologically active compounds. In addition, the cannabis leaf was found to be more sensitive than the inflorescence to N supply, presenting greater changes in primary metabolism and more coordinated metabolic associations. These findings highlight the importance of adequate and precise N nutrition for standardization of the therapeutic-metabolite profile and for preventing undesirable metabolic repartitioning in medical cannabis plants.