Date of Award:

8-2024

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Plants, Soils, and Climate

Committee Chair(s)

Bruce Bugbee

Committee

Bruce Bugbee

Committee

Bill Doucette

Committee

Royal Heins

Committee

Matt Yost

Committee

Brian Corr

Abstract

Cannabis (Cannabis sativa L.) is increasingly being cultivated for industrial and medical uses. Medical cannabis is grown for cannabinoids and terpenes, compounds that continue to show promising therapeutic potential. Cannabidiol (CBD) and delta-9- tetrahydrocannabinol (Δ9-THC) are the two most common cannabinoids, but more than 150 have been identified in cannabis. The 2018 Farm Bill federally legalized cannabis containing less than 0.3% THC and high-THC medical cannabis is legal in 38 states. There is a need to understand environmental effects on yield and quality to ensure safety and quality for medical use.

The cultivation of medical cannabis is centered around the unfertilized female inflorescences, where cannabinoids and terpenes are synthesized and stored. Environmental factors interact to influence yield, quality, and uniformity of these flowers. Here I describe the effects of spectral quality, phosphorus nutrition, temperature, and CO2 on the single-leaf and canopy photosynthesis, morphology, flower yield, and cannabinoid concentration of high-CBD medical cannabis, with an emphasis on efficiency and sustainability.

For electric lighting, fixture efficacy is more important than spectral quality for cost-effective medical cannabis cultivation. Increasing the fraction of blue or UV photons reduced yield per area but did not increase cannabinoid concentration. Elevated root-zone phosphorus above 25 mg L-1 significantly increased leachate P and did not improve yield or quality. High temperature early in the lifecycle increases photon capture but reduces photosynthetic efficiency late in the lifecycle. There was genetic variability in the effect of temperature on cannabinoids, but low temperature late in the lifecycle has the potential to increase cannabinoid concentration in some cultivars. Short-term effects of elevated CO2 on single-leaf and canopy photosynthesis were greater than long-term effects on yield. Elevating CO2 to 1200 ppm increased yield by about 40%.

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Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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