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He, Jie
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Light-emitting diodes (LED) lighting is currently receiving a great deal of international attention and is deemed a potential technology for indoor vegetable production. However, a major challenge of growing vegetable plants indoors is controlling and supplying sufficient amount of light and the light quality that the vegetable plants are subjected to. Both the red and blue parts of the light spectrum are effective in ensuring various aspects of photosynthesis. In this project, Chinese Broccoli (Brassica alboglabra) grown under four different red- and blue-LED light treatments were studied, under 0B (100% red-LED and 0% blue-LED), 8B (92% red-LED and 8% blue-LED), 16B (84% red-LED and 16% blue-LED) and 24B (76% red-LED and 24% blue-LED) lighting conditions. This project showed that the yield of the Chinese Broccoli (B.alboglabra) was enhanced under the appropriate combination of 84% red-LED and 16% blue-LED (i.e. 16B) lights. The yield of Chinese Broccoli for 8% and 24% blue light supplement were all shown to be better than the 0% blue light condition but were not significantly different with the 16% blue light supplemented plants. Preliminary observations made on the growth of Chinese Broccoli indicated that plants grown under solely red light had thinner stems, thinner and smaller leaves and less developed roots. Plants grown under a combination of red- and blue-LED lights, for all combinations, generally had thicker stems, thicker and larger leaves and a more extensive network of roots. Robust growth under red- and blue-LED lights caused plants to show signs of epinasty. Blue light is known to be important for plant physiological processes like photomorphogenesis and stomatal opening. In this project, the presence of 16% blue light resulted in a significant difference in stomatal density, stomatal conductance (gs), total leaf number, total leaf area, specific leaf area (SLA), fresh weight (FW) and dry weight (DW) of stem, leaf and roots compared to plants that were grown under red light alone. Carbon assimilation (A) values showed an increasing trend, while internal CO2 concentration (Ci) values showed a decreasing trend with increasing blue light supplementation. Under the optimal 16% blue light combination with red light, plants grown under 14h photoperiod had significantly higher total leaf number and higher stem DW and FW. However, other aspects of plant productivity were similar to those grown under 12h photoperiod while plants grown under 14h photoperiod were significantly different with plants grown under 10h photoperiod. The gs for plants grown under 12h photoperiod were significantly higher than those under 10h and 14h photoperiods. Exposure to different durations of night breaks affected Chl content, development of the roots, transpiration rate, gs, leaf temperature and total reduced nitrogen (TRN) concentration in the roots of the Chinese Broccoli. A continuous period of darkness (10h night break) was found to be beneficial to the Chinese Broccoli, increasing the Chl a, Chl b and, thus, the total Chl content. However, from the results obtained, the combination of red- and blue-LED light ratios, the length of photoperiods and the duration of night breaks did not have significant impact on the total nitrate concentration in all parts of plants (stem, petioles, leaves and roots) studied. There was also no significant difference observed in the non-photochemical quenching (NPQ), photochemical quenching (qP), electron transport rate (ETR), A and Ci values in all the plants. As blue light is important during the growth of the plants, it is crucial to manage the interaction of blue light with other wavelengths like red and far-red lights to obtain the desired yield. In this project, it was identified that the optimal LED combination for B. alboglabra plants was a 16B combination, 14h photoperiod with a 10/5/4/5 h (day/night/day/night) cycle to ensure high productivity in stem and leaves and a well developed root system.
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QK495.C9 Liu
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Appears in Collections:Master of Science (Life Sciences)

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