Abstract
Light is one of the most important limiting factors for photosynthesis and the production of plants, especially in the regions where natural environmental conditions do not provide sufficient sunlight, and there is a great dependence on artificial lighting to grow plants and produce food. The influence of light intensity, quality, and photoperiod on photosynthetic pigments content and some biochemical and growth traits of cucumber seedlings grown under controlled conditions was investigated. An orthogonal design based on a combination of different light irradiances, ratio of LEDs and photoperiods was used. Treaments consisted of three light irradiance regimes (80, 100, and 150 µmol m−2 s−1) provided by light-emitting diodes (LEDs) of different ratios of red and blue (R:B) (30:70, 50:50, and 70:30) and three different photoperiods (10/14, 12/12, and 14/10 h). The white light was used as a control/reference. Plant height, hypocotyl length, stem diameter, leaf area, and soluble sugar content were highest when exposed to LM9 (150 µmol m−2 s−1; R70:B30; 12/12 h) light mode, while the lowest values for the above parameters were obtained under LM1 (80 µmol m−2 s−1; R30:B70; 10/14 h). Higher pigments contents (chlorophyll a, chlorophyll b, and carotenoid) were obtained when light regime LM9 (150 µmol m−2 s−1; R70:B30; 12/12 h) was applied. In general, cucumber seedlings grown under the LM9 regime showed a significant increase in growth as well as photosynthetic capacity. It seems that the content of photosynthetic pigments is the key factor responsible for the performance of cucumber seedlings grown under different lighting modes, compared to other traits studied. We recommend monitoring the content of chlorophyll a, b, and their ratio value when studying the light requirement of cucumber plants.
Highlights
The cucumber is an economically important vegetable grown in over 80 countries w orldwide[1], and its annual production is estimated to be about 80 million tons, including about 3 million tons grown in the European Union (EU 28)[2]
Stem diameter, total leaf area, hypocotyl length, shoot fresh weight, root fresh weight, shoot dry weight and root dry weight were increased by 85.07, 52.73, 57.37, 172.81, 77.94, 98.88, 133.33 and 62.5% when LM9 was applied on cucumber seedlings (Fig. 1A–H) as compared to control (WL) while application of LM8 increased these attributes by 79.1, 47.27, 40.16, 149.19, 67.64, 90, 111 and 46.59% respectively as compared to control (WL)
Our results showed that the combination of red and blue Light-emitting diodes (LEDs) light with high red light (LM9) was observed to be favorable for chlorophyll a, chlorophyll b, and carotenoids content (Fig. 2)
Summary
The cucumber is an economically important vegetable grown in over 80 countries w orldwide[1], and its annual production is estimated to be about 80 million tons, including about 3 million tons grown in the European Union (EU 28)[2]. Humidity, light irradiance, and nutrient availability are ideal conditions for this typical subtropical plant, which is highly sensitive to adverse environmental c onditions[3]. Characterized by their tenderness, these plants thrive in a temperature range between 18.3 to 23.9 °C, with a minimum temperature of 15.6 °C and a maximum of 32.2 °C. Green when harvested but quickly becomes yellow when stored The sensitivity of these young vegetables to low light irradiance is greater than that of the older vegetables from the same p lant[3]. During the shift from conventional to LED light sources, many inventions have been made, such as the combination of fluorescent lamps and L ED15, the replacement of fluorescent tubes with L EDs16, and the retrofitting of LEDs for fluorescent tubes without b allasts[17]
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