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Effects of supplementary light-emitting diodes (LEDs) and UV-A radiation lighting on productivity, photosynthesis and nutritional quality of aeroponically grown red and green leaf lettuce
Author
Koh, Khee Hoon
Supervisor
He, Jie
Abstract
Studies have shown that addition of red (R) and blue (B) light-emitting diodes (LEOs) light plus UV -A radiation can be effective in promoting not only vegetable growth and development but also its nutritional quality. In this project, high-value red and green Lactuca sativa were grown aeroponically in the greenhouse under four different treatments, namely natural sunlight (control), sunlight with red LED (R), sunlight with red and blue LEOs (RB) and sunlight with red and blue LEOs and UV-A radiation (RBU). The goal of this project was to investigate the effects of supplementary LEOs plus UV-A radiation on plant productivity, photosynthesis and the accumulation of photosynthetic pigments, secondary metabolites, soluble protein, carbohydrate, N03_ , total reduced nitrogen (N), and dietary minerals. Treated plants were cultured under 16h photoperiod while the control plants had 12h photoperiod for 26 days. The range of maximal PPFD for R, RB and UV were recorded between 120 to 140 f!mole photon m-2 s-1• All the treated lettuce had higher shoot fresh weight (FW) than that of control though there was no significant difference in shoot I root FW and dry weight (OW) ratio. The data from light-saturated photosynthetic C02 assimilation rate (Asat), light-saturated stomatal conductance (gs sat), internal C02 concentration (Ci), transpiration, chlorophyll (Chl) fluorescence (Fv/Fm) ratio, electron transport rate (ETR), and photochemical quenching (qP) were not significantly difference amongst the treatments. The Fv/Fm ratio was more than 0.8. These data suggested that the plants among the treatments were not under stress and they may share similar PS II efficiency. However, significantly lower non-photochemical quenching (NPQ) was observed in RBU-treated lettuce at PPDF 965. Red lettuce had higher anthocyanin production than green lettuce. Enhanced anthocyanin production was observed in R treated red lettuce only. RB and RBU treated red lettuce looked less red compared to R and control. However, the total Chi, total carotenoid (Car) and Chi a/ b ratio were not significantly different among the lettuce across the treatments. Lettuce grown under RB and RBU had higher Chi/ Car values than the rest of plants. Phenolic compounds were found to be the highest in RB treated red lettuce, followed by RBU treated red lettuce. Green lettuce had similar amounts of phenolic compounds across the treatments. The amount of carbohydrates, total leaf soluble proteins and total reduced N found in green and red lettuce were not significantly different. Accumulation of N03- was significantly lower in RB and RBU treated green lettuce compared to R and control. High accumulation of N03-was found in lettuce under R treatment. Correlation between N03- in root and shoot was observed in RB and RBU treated green lettuce. Treated green lettuce had higher calcium (Ca), potassium (K) and magnesium (Mg) in shoot than that of control. Generally, RB-treated green lettuce had higher dietary minerals than the rest of the green lettuce. Treated red lettuce had significantly similar or lower mineral content than that ofthe control. RB and RBU-treated green lettuce were more productivity, lesser N03- accumulation and higher soluble protein, carbohydrate and minerals. Between RB-and RBU-treated green lettuce, RBU-treated green lettuce may be more effective as it had higher anthocyanin content and lowerN03- content despite slightly smaller compared to RB treated green lettuce. RU-treated red lettuce seemed to be more outstanding than the rest of the red lettuce. Though its FW may not be the highest, it had good shoot/ root ratio, lower N03- content, and the highest soluble protein, carbohydrate and phenolic compounds compared to the rest. One of the key findings of this study is that lettuce plants in the presence of UV -A radiation did not display compromised productivity. The effects of different light treatments differed between the green and red lettuces. The results of this study will provide useful information for the local greenhouse vegetable growers on how to enhance vegetable productivity and nutritional quality.
Date Issued
2016
Call Number
QK757 Koh
Date Submitted
2016