Abstract
Today, the use of light emitting diodes (LEDs) are rapidly increasing in horticulture industry as a result of technological advancements. Lighting systems play an important role in the commercial greenhouse productions. As an artificial source of light, LED lamps can contribute to the better and faster growth of horticulture products such as vegetables grown in greenhouses. In this study, the effects of red and blue light spectrums were implemented and performed as a pot experiment under the cultivation-without-soil condition in greenhouse based on a completely random plan with 3 lighting treatments including natural light (control), 60% red light +40% blue light (60R:40B), and 90% red light +10% blue light (90R:10B), repeated 3 times. The results showed that the application of blue and red lights affected the fresh and dry weights of cress as well as its biomass, demonstrating a considerable increase compared to the plants grown under natural sunlight condition. In this regard, the fresh weight of the plant under the 60R:40B treatment had 57.11% increase compared to the natural light treatment. Compared to the control sample, the dry weight had 26.06% increase under 90R:10B treatment. The highest extent of biomass was observed under the 60R:40B lighting treatment with a value of 1.51 (g per kg dry weight of the plant), which was a 68.87% increase compared to the natural light treatment. Under the 60R:40B treatment, cress had its highest length at 19.76 cm. Under the similar treatment, the cress leaf had a total area of 56.78 cm2 which was the largest. The stem diameter and the number of leaves under the 60R:40B treatment had their highest values at 3.28 mm and 8.16, respectively. Accordingly, a growing trend was observed with 56.7 and 61.27% increase compared to the control treatment. Furthermore, the biochemical traits of cress, the amount of a, b and total chlorophyll, the amount of anthocyanin and phenolic contents under the application of red and blue light were at their highest values compared to the control treatment. The highest amount of chlorophyll was observed under 60R:40B treatment as 15.09 mg g−1 FW leaf. Moreover, the phenolic contents and the amount of anthocyanin were of significant difference at 1% level of likelihood compared to the control treatment. Therefore, the vegetative growth of cress was substantially affected by red and blue lights, resulting in the enhancement of the plant's biochemical features compared to control condition via adjusting the lighting quality and impacts of each red and blue light spectrum on their specific receptors. As a result, the presence of both lighting spectrums is essential for expanding and increasing the quality of the plant. At the large scale, this technology is capable of improving the commercial greenhouse production performance while helping farmers achieve maximum products. This particular combination of lights is one of the beneficial features of LED lighting systems intended for different types of commercial greenhouse productions, especially the valuable greenhouse products.
Highlights
Light is a necessary source of energy for plants, and an important signal which plays a major role in plant growth, morphological characteristics, cell molecule biosynthesis, and gene expression during the entire growth period of plants
Given the effects of blue and red light spectrum on plants, their positive impacts on leaf vegetables, the main purpose of this study is to examine and compare different combinations of blue and red lights on morphological and biochemical feature of cress plant as an important leaf vegetable and medicinal plant relative to the control treatment; this is done in order to introduce the most ideal growing condition of cress in terms of lighting ratios of blue and red spectrum combinations and compare the use of this technology with the control treatment in which natural sunlight is used
When light emitting diodes (LEDs) lamps with different light percentages including 60% red light þ40% blue light (60R):40B and 90% red light þ10% blue light (90R):10B were used, considerable increase (p 0.01) was observed in the amount of anthocyanin in cress during growth period with respect to the control treatment (Fig. 13)
Summary
Light is a necessary source of energy for plants, and an important signal which plays a major role in plant growth, morphological characteristics, cell molecule biosynthesis, and gene expression during the entire growth period of plants. Each different light spectrum has an exclusive effect on particular gene expressions in plants resulting in a number of different impacts (Huche-Thelier et al, 2016) Several processes such as photosynthesis, germination, flowering, and biomass accumulation can be controlled and optimized via adjusting light wavelengths (Pinho, 2008; Yeh and Chung, 2009; V€anninen et al, 2010). Greenhouses in which LED sources of lights are used are of high potential power to adjust the environment's lighting Small plants such as leaf vegetables, small roots, and a number of medicinal plants are the most ideal types of plants to culture at greenhouses where LEDs are used.
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