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Uncovering LED light effects on plant growth: new angles and perspectives - LED light for improving plant growth, nutrition and energy-use efficiency

Z. Bian, N. Jiang, S. Grundy, C. Lu
Acta horticulturae 2018 v. no.1227 pp. 491-498
Brassica rapa subsp. chinensis, Lactuca sativa, blue light, crop yield, energy costs, fluorescent lamps, greenhouses, horticulture, leaf area, lettuce, light emitting diodes, light intensity, nitrates, nutrition, photons, photosynthesis, plant growth, radiation use efficiency, sodium, stomatal conductance, tomatoes
Light supplementation can increase crop yield in greenhouses by promoting photosynthesis and plant growth. However, the high energy costs associated with light supplementation are a predominant factor that limits development and profit improvement of controlled environment agriculture. Light-emitting diodes (LEDs) are a promising technology that has tremendous potential to improve irradiance efficiency and to replace traditionally used horticultural lighting. Compared with traditional light sources (e.g., high-pressure sodium lamps and metal halide lamps) used in crop production, LEDs have distinct advantages, such as their small size, long lifetime and high photoelectric conversion efficiency. Most importantly, as a monochromatic light source, the spectrum of LEDs can be adjusted based on plant growth requirements. This project aimed to investigate energy-use efficiency, vegetable nutrition and photosynthesis improvement of light supplementation in a protected horticulture system. In the initial phase, the effects of LED light on plant growth and light-use efficiency for pak choi and photosynthetic performance were investigated. The results showed that the highest fresh and dry weight and leaf area were observed under red and blue LED light, with the blue light percentage at 23%. Compared with fluorescent lamps (FL) with photosynthetic photon flux density (PPFD) at 220 μmol m(-2) s(-1), the light-use efficiency increased by 55, 114 and 115% for mixed red and blue LEDs with PPFD at 100, 150 and 220 μmol m(-2) s(-1), respectively. Monochromatic red- and blue-light LEDs resulted in significant decreases in P(n) of tomato plants, but the stomatal conductance (G(s)) for monochromatic blue LEDs was higher than that for FL. The effect of light spectrum composition on lettuce nutrition quality was also studied. Continuous light with combined red, green and blue LEDs exhibited a remarkable decrease in nitrate. Moreover, continuous LED light for 24 h significantly increased phenolic compound content and free-radical scavenging capacity in lettuce leaf.