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Exploration on Using Light-Emitting Diode Spectra to Improve the Quality and Yield of Microgreens in Controlled Environments

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Title: Exploration on Using Light-Emitting Diode Spectra to Improve the Quality and Yield of Microgreens in Controlled Environments
Author: Ying, Qinglu
Department: School of Environmental Sciences
Program: Environmental Sciences
Advisor: Zheng, Youbin
Abstract: Light is essential for plant production, and adjusting light quality has potential in enhancing their desired growth characteristics and secondary metabolite profiles. This study explored the effects of light spectral quality from light-emitting diodes (LEDs) on the growth, yield, appearance quality and phytochemical content in four species of Brassicaceae microgreens (arugula, cabbage, kale and mustard) in controlled environments. Microgreens were cultivated under a combination of blue (B) and red (R) LEDs with different photon flux ratios from B5R95 to B30R70 at photosynthetic photon flux density of 300 µmol·m-2·s-1 with 16-hour photoperiod. The fresh weight (FW) and dry weight of microgreens were generally not affected, except for cabbage. However, the hypocotyl length and cotyledon area of kale and mustard decreased proportionally as B light percentage increased. Moreover, the hue angle of cotyledon color decreased when B light percentages increased in four microgreen species. Under the same lighting treatments, varying B and R ratio did not affect the extractable levels of total chlorophyll, carotenoid, or nitrate content in any of the four microgreen species. Conversely, increasing B light percentage elevated ascorbate, total phenolic and total anthocyanin levels, although the magnitude of the elevation varied across species and phytochemicals. To increase the height of microgreens for facilitating machine harvest, low intensity supplemental lighting strategies supplied at night were evaluated in both growth chamber and greenhouse. In the growth chamber, 20 µmol·m-2·s-1 supplemental B light with or without 20 µmol·m-2·s-1 far-red light for 8-hour during the night effectively promoted stem elongation without compromising microgreen visual quality or yield. The plants were grown under 300 µmol·m-2·s-1 B20R80 LED lighting for 16 hours during the day. Similarly, supplementing 14 µmol·m-2·s-1 B light at night promoted stem elongation by 10% and 16% in arugula and mustard microgreens, respectively, in the greenhouse during winter months; this coincided with respective 32% and 29% increase in FW. Total chlorophyll, carotenoid, and phenolic levels were unaffected by supplemental B light. This thesis concludes that light quality significantly affects plant morphology and secondary metabolism, and provides useful information for commercial growers to improve their production using cost-efficient lighting strategies.
URI: https://hdl.handle.net/10214/21200
Date: 2020-09
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Related Publications: Ying, Q., Y. Kong, and Y. Zheng. 2020. Applying blue light alone, or in combination with far-red light, during nighttime increases elongation without compromising yield and quality of indoor-grown microgreens. HortScience 55:876-881. doi.org/10.21273/HORTSCI14899-20


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