The power of zinc: excess and deficiency of Zn decrease cannabinoids in cannabis without Zn toxicity concerns to consumers

Some of the mineral nutrients essential for plants are heavy metals, which their consumption may involve health concerns to the consumers. Hence, for safe consumption, optimized fertilization protocol for cannabis plants needs to focus also on minimizing the accumulation of potentially toxic minerals in the inflorescences. Zinc is an essential microelement for plants that has a toxic effect on the human body when consume in high concentration. The present study aimed to understand the drug-type (medical) cannabis plant response to Zn supply, for identifying the optimal Zn supply that balance high quality production with safe product. cannabis plants were grown under five Zn levels (0.05, 0.1, 0.35, 1.0, 4.0 mg L− 1) in controlled environment; and morpho-physiology analyses, cannabinoid profile, and ionome-profiling in the plant-organs were conducted. Increased level of Zn supply reduced the relative accumulation of Zn in the inflorescences, and excess Zn was stored in the plant root, and therefore does not impose additional health risk to consumers. Cannabinoid concentrations were highest under 0.35 mgL− 1 Zn supply, and decreased with further increase in Zn supply. The acidic cannabinoids THCA, CBDA, CBCA, CBDVA, THCVA increased with the increase in Zn supply up to 0.1–0.35 mgL− 1 and declined with further increase in Zn. Zn deficiency (under 0.05 mgL− 1 Zn supply) reduced physiological performance, plant growth and inflorescence yield, and stimulated uptake of Zn, P, S, Ca, Fe, and Mn. Symptoms of excess Zn were death of leaf tips; however plant performance was overall not affected by Zn excess. Excess Zn is retained in the root and excluded from the inflorescence, thereby not imposing health risk to the consumers. The recommended Zn concentration in the fertigation solution that was found to attain highest specialized-metabolite concentrations, and optimal yield and plant performance is 0.35 mgL− 1.