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The influence of spectral quality of light on plant secondary metabolism and photosynthetic acclimation to light quality

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Title: The influence of spectral quality of light on plant secondary metabolism and photosynthetic acclimation to light quality
Author: Hawley, Dave
Department: School of Environmental Sciences
Program: Environmental Sciences
Advisor: Dixon, Mike
Abstract: Light quality can have a profound effect on many aspects of plant development. In this thesis, the influence of light quality on yield, morphology, and secondary metabolite profiles was evaluated in basil, strawberry, and cannabis, and the acclimation to light quality was quantified in lettuce and strawberry. These experiments were conducted using four fixed light spectra described as the “Red-blue (RB) Blade”, “Red-green-blue (RGB) Blade”, “Far-red (FR) Blade”, and “Red-blue + red-green-blue (RB+RGB) Blade” (the term blade refers to the industry nomenclature for this lamp configuration), as well as an array of nine variable-spectra LED arrays. Growing basil plants under the RB and RGB Blades showed the two spectra to produce statistically comparable profiles of volatiles in basil leaf extracts. Growing strawberry plants under RB, RGB, RB+RGB, and FR Blades, the FR spectrum produced plants with significantly longer petioles than the RGB spectrum. Berry flavour was unaffected by any of the light spectra, with berry juice being comparable in sugar content, pH, and total acid content. Analysis of volatiles in berry juice was inconclusive, with irregular profiles between replications. Deploying the RB and RGB Blades below cannabis canopies as supplemental light sources resulted in a significant impact on yield and secondary metabolite profiles with both Blades compared to canopies with no sub-canopy lighting. The RGB Blades made the greatest impact on modifying terpene content, and the RB Blades produced the most homogenous bud cannabinoid and terpene profile throughout the canopy. Exploring the potential photosynthetic acclimation of lettuce and strawberry plants to light qualities over time, both species were grown to vegetative maturity under various fixed spectra to acclimatize the plants to given light environments. After acclimation, plants were rapidly subjected to many different light qualities (30 – 60 minutes each), with whole-plant photosynthesis measured under each light quality. Plants preconditioned to certain basal light spectra were able to achieve significantly different photosynethic rates in various post-conditioning light qualities. This thesis concludes that spectral quality does significantly modify plant morphology and secondary metabolism, and spectral acclimation can have significant effects on whole-plant photosynthesis. The observations regarding plant acclimation are novel and have meaningful consequences in both research and commercial production, warranting further exploration.
Date: 2018-09
Rights: Attribution-NonCommercial-NoDerivs 2.5 Canada

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Attribution-NonCommercial-NoDerivs 2.5 Canada Except where otherwise noted, this item's license is described as Attribution-NonCommercial-NoDerivs 2.5 Canada