Do thirsty plants produce more cannabinoids?

First, federal news: On Dec. 18, President Donald Trump issued an executive order to amend marijuana’s longstanding classification as a Schedule I federally controlled substance without accepted medical value. The order seeks to finalize a 2023 recommendation by the Department of Health & Human Services calling for cannabis to be rescheduled to a Schedule III controlled substance.

Prior to signing the order, Trump said, “These facts compel the federal government to recognize that marijuana can be legitimate in terms of medical applications.” He called the reclassification “common sense,” adding the policy change would have a “tremendously positive impact.”

With this considered, cannabis and hemp, which have a long history as useful crops in America, continue to be studied and optimized for those growing it. Some plants do well under short periods of stress, and an international team has been looking at how water-deficit stress may help marijuana – specifically, its secondary metabolite levels.

(Secondary metabolites are specialized compounds in plants involved in defense and adaptation. They may increase due to stress and elicitors – but they may also compete with biomass production.)

The research team is made up of Jose Leme, Aldwin Anterola, Jennifer Weber and Shiksha Sharma from Southern Illinois University; Dila Ozev from the University of Bonn; and Fardad Didaran from the University of Tehran. Leme presented their findings at the American Society for Horticultural Science conference.

The important secondary metabolites produced by cannabis are their cannabinoids. The researchers noted that controlled or induced water-deficit stress (DS) can increase secondary metabolite concentration in some essential oil-producing plants. Their study wanted to uncover the optimal stress conditions to maximize cannabinoid production.

There were several objectives in the study:

1. To investigate how different frequencies of induced DS during the flowering stage affects cannabis growth and overall biomass production.

2. To quantify changes in cannabinoid concentration under different frequencies of DS.

3. To identify the optimum frequency of extreme DS that maximizes cannabinoid yield without significantly affecting plant biomass.

4. To assess whether strategic application of DS can act as a water and nutrient conservation method in cannabis cultivation while maintaining consistent yield and quality.

The cannabis cultivar ‘Heidie’ was used for the experiment. There were four kinds of DS during the flowering stage: WS0 (no stress), WS1 (one period of DS), WS2 (two periods of DS) and WS3 (three periods of DS). Measured weekly were plant height, stem diameter, chlorophyll content, photosynthetic efficiency and stomatal conductance. After harvest, yield mass, bucked biomass, trichome density and cannabinoid and terpenes levels were recorded.

WS0 had regular irrigation and fertigation until harvest. WS1 had one 10-day period of DS starting on the first day of the fifth week of the flowering stage. WS2 had two periods of DS totaling 12 days two days before the end of the sixth week of the flowering stage. WS3 had three periods of DS totaling 12 days two days before the end of the eighth week of the flowering stage.

Unsurprisingly, more periods of DS resulted in shorter plants and smaller stems. Chlorophyll decreased after each stress event. The plants recovered from each stress event slowly after watering. The more stress there was, the greater the photosynthetic issues. However, a single period of water stress did not adversely affect biomass. Leme said this was “the ideal amount of stress” in regard to biomass.

As for the secondary metabolites, the highest amounts of CBD were found in the WS0 and WS3 plants. WS1 resulted in the lowest total CBD percentage. The total CBD per plant was highly influenced by the frequencies of water stress.

A higher percentage of THC was found in the WS3 plants – higher than WS0 – and WS1 had the lowest concentration.

“The water-deficit stress appeared to alter the CBDto- THC ratio, where WS3 had the lowest value (though not much lower than the other treatments),” Leme reported.

Ultimately, induced DS significantly affected plant growth, yield and physiological response. Intense and repeated DS led to a reduction in bucked biomass and CBD yield per plant – but a single period of DS didn’t impact the plants noticeably.

The arrangement of the frequencies of DS in this study did not show an increase in secondary metabolite levels in cannabis. But there’s more to be studied. Leme said the team will test different scheduling of stress and different magnitudes of stress as well as different cultivars.

by Courtney Llewellyn