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He, Jie
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Vegetables are an important part of the daily diet. In the recent years, food security has become a concern in the world and the need to increase crop yields has become imperative. Due to limited availability of land, countries like Singapore greatly depend on food imports for daily consumption. Hence, a smart, high-yield, agricultural approach which is less affected by environmental changes is essential.

In this study, effects of different combinations of LED lightings on productivity, photosynthesis and nitrogen (N) metabolism of leafy vegetables such as Kai Lan, Nai Bai and Mizuna were investigated. Using a vertical aeroponics systems plants were grown with four different combinations of red, blue and white LED treatments at two photosynthetic photon flux densities (PPFDs) of 300 and 500 μmol m-2 s-1 with 18 h photoperiod for 3 weeks. Plants in the aeroponics troughs were provided with a full-strength Hoagland’s nutrient medium set at 25ºC. The shoots of plants were exposed to hot ambient temperatures while their roots were sprayed with 25 °C cool nutrient solution. Three weeks after transplanting, plants were harvested and productivity, photosynthetic light use efficiency, Chl fluorescence, photosynthetic pigments, total reduced nitrogen (TRN), soluble proteins and Rubisco were analyzed.

Shoot FW of Kai Lan and Nai Bai plants grown at a PPFD of 500 μmol m-2 s-1 increased significantly by 5-fold, compared to plants grown at a PPFD of 300 μmol m-2 s-1. However, enhanced productivity was not observed in mizuna plants, where great variations were noticed. This could be due to its large number of leaves and fast growth of certain leaves leading to overlapping and self-shading during the growth. Parameters of light saturated photosynthetic CO2 assimilation rate (Asat), light saturated stomatal conductance (gs sat), internal CO2 concentration (Ci) and transpiration did not vary much among the different treatments in all three plant species. Similarly, photosynthetic pigments Chl and Car did not show significant differences among the different treatments. In addition, there were no significant differences in Electron transport rate (ETR), photochemical quenching (qP) and non-photochemical quenching (NPQ) among various combinations of LEDs at both PPFDs. Chl fluorescence and Fv/Fm ratios above 0.8 indicated that plants were healthy and growth conditions were favourable, implying that they were not exposed to any stresses. No substantial differences in Fv/Fm ratio were observed among the different treatments. Furthermore, in all three plant species TRN, total soluble protein and Rubisco protein content did not vary much among the different treatments.

Kai Lan and Nai Bai shoot productivity improved with the use of high light intensity. Shoot productivity of Kai Lan plants indicated that optimal combinations of LED depend on vegetable species and the intensity of LED. Significant increases in productivity of Kai Lan and Nai Bai were not complemented by other parameters studied. Productivity of Kai Lan had no clear correlation with photosynthetic gas exchange, photosynthetic pigments or photosynthetic light use efficiency of these plants. Neither, it was related to N metabolism as TRN, total soluble protein and Rubisco protein showed no clear relationship to the enhanced productivity of Kai Lan and Nai Bai. Kai Lan and Nai Bai plants grown under PPFD of 500 μmol m-2 s-1 had greater leaf thickness and expanded leaf area compared to plants grown under PPFD of 300 μmol m-2 s-1. Increased leaf area provides a much larger photosynthetic area. Thus, the total amount of carbon fixed by these plants under a high PPFD could be much higher compared to the plants grown at a low PPFD. This could contribute to higher biomass accumulation reflected in the shoot productivity of Kai Lan and Nai Bai plants.
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QH307.2 Pit
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Appears in Collections:Master of Science (Life Sciences)

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