عنوان مقاله [English]
The effectiveness of LED lamps was evaluated as an alternative to other supplementary lights in different conditions in terms of the growth stage of each plant and the purpose of the cultivation. A factorial experiment was carried out based on completely randomized design. The first factor was the terminal cuttings of three different cultivars of chrysanthemum, given codes of (C1:440), (C2:542) and (C3:567) and the second factor was the light levels of L1, L2, L3 and L4 which represent red-blue, red, blue and white, respectively. Cuttings were planted in the pots filled with small sized perlite, then transferred to the growth chamber. Characteristics such as leaf surface and number, root and stem characteristics, chlorophyll a and b and total, photosynthetic quantum performance index (Fv/Fm), PIabs, malondialdehyde, proline, leaf anthocyanins and soluble carbohydrates were measured. Based on the results, the highest amount of total chlorophyll content was observed in the red-blue combined spectrum, the highest amount of photosynthetic quantum performance index (Fv/Fm) in C1 cultivar under the blue spectra, the maximum amount of leaf anthocyanins in C1 under red light and the lowest amount of malondialdehyde in C2 under the white light. Meanwhile, the maximum value of leaf area was related to C3 under red-blue light treatment and the maximum number of leaves to C1 under red-blue light. The best characteristics of the root were belonged to the C1 cultivar under combined red-blue light. As a result, in terms of physiological and morphological indicators, among the used LED lights, red-blue lights and monochromatic blue light were the best treatments in the growth chamber conditions.
Light is the most important environmental factor that controls various aspects of plant growth and development. Plants dynamically respond to the light of their surrounding environment. The response of the plant to light is different depending on the light properties, climate, season, genotype, cultivar, cultivation methods and some other factors. Light provides the necessary energy to steer photosynthesis and also acts as a source of spatial and seasonal signals for plants. This factor is not only an energy source for photosynthesis, but also a stimulating factor for a number of developmental processes from seed germination to the flowering. The rapid development of lighting technologies using LED lamps has increased the use of this technology for lighting in closed and vertical systems. In fact, this technology has made it possible to optimize plant growth by using monochromatic wavelengths or their combinations. The physiological response of different chrysanthemum cultivars to different light spectrums can be different and is not clear, particularly for the earliest stages of growth. Therefore, the effect of different LEDs light spectrums on some key traits of different cultivars of chrysanthemum in the growth chamber compared to the greenhouse environment from the rooting to flowering stages of cuttings was investigated. The stimulating effects of different light spectrums and their impact on photosynthetic systems were also considered.
Materials and Methods
This research was conducted in a growth chamber equipped with a floor system with LED lighting. The LED chamber had four shelves and in each shelf there were three floors (the location of the pots) with a width, length and height of 60, 90 and 50 cm, respectively and each shelf was related to one of the light treatments. The light intensity was set to 70 μmol.m-2s-1 (UT383). To create the combination of red-blue light, the ratio of 3:7 red to blue LED lamps was used. This research was carried out as a factorial based on completely randomized design with three replications and 25 observations in each replicate. The first factor was the terminal cuttings of three different cultivars of chrysanthemum with codes of (C1:440), (C2:542) and (C3:567), and the second factor was the light levels of L1, L2, L3 and L4 which represent red-blue, red, blue and white light, respectively. The terminal cuttings were prepared in 12 cm length, planted in the pots filled with sugar perlite and finally transferred to a growth chamber with a floor system equipped with LEDs. The plants were kept for about 50 days until the roots spread.
Based on the results, the highest amount of chlorophyll content was observed in the red-blue combined spectrum. The maximum amount of chlorophyll a was corresponded to C1 under red-blue light treatment, and the maximum amount of chlorophyll b to C1 and C3 under the white light spectrum. The highest amount of photosynthetic quantum performance index (Fv/Fm) were observed in the blue spectrum, the maximum amount of leaf anthocyanins in C1 under the red light and the lowest amount of malondialdehyde in C2 under the white light spectrum. The maximum leaf area of C3 was recorded under red-blue light treatment and the maximum number of leaves was recorded in C1 under red-blue light spectrum. The best characteristics of the root were obtained in C1 under the combined red-blue light. The maximum length of the stem was measured in red light and the highest wet and dry weight of the branch was obtained in C1 under blue light spectrum.
Discussion: The function of photosystem II plays an important role in carbohydrate production. It was also shown that an increase in carbohydrate production decreases the slope of ROS production. Fv/Fm is the maximum quantum efficiency in photosystem II. In normal conditions and without any stress, this ratio is usually constant. Insufficient blue light causes dysfunction in photosystem II by reducing the Fv/Fm ratio. In fact, it has been proven that supplementing blue light with red light improves stomatal characteristics and prevents damage to the photosynthetic apparatus, especially photosystem II.
The overall results of this research showed that photosynthetic pigments had a better response to the white and combined red-blue light spectra. Also, among the LED lights, red-blue lights and monochromatic blue light were recognized as the best treatments in terms of photosynthetic characteristics and had better photosynthesis efficiency. Blue light increased proline and malondialdehyde and red light increased anthocyanins and soluble carbohydrates. Also, in most of the examined traits, the combined red-blue treatment resulted better than other spectrums.