Abstract
A reduction in crop productivity in cultivable land and challenging environmental factors have directed advancement in indoor cultivation systems, such that the yield parameters are higher in outdoor cultivation systems. In wake of this situation, light emitting diode (LED) lighting has proved to be promising in the field of agricultural lighting. Properties such as energy efficiency, long lifetime, photon flux efficacy and flexibility in application make LEDs better suited for future agricultural lighting systems over traditional lighting systems. Different LED spectrums have varied effects on the morphogenesis and photosynthetic responses in plants. LEDs have a profound effect on plant growth and development and also control key physiological processes such as phototropism, the immigration of chloroplasts, day/night period control and the opening/closing of stomata. Moreover, the synthesis of bioactive compounds and antioxidants on exposure to LED spectrum also provides information on the possible regulation of antioxidative defense genes to protect the cells from oxidative damage. Similarly, LEDs are also seen to escalate the nutrient metabolism in plants and flower initiation, thus improving the quality of the crops as well. However, the complete management of the irradiance and wavelength is the key to maximize the economic efficacy of crop production, quality, and the nutrition potential of plants grown in controlled environments. This review aims to summarize the various advancements made in the area of LED technology in agriculture, focusing on key processes such as morphological changes, photosynthetic activity, nutrient metabolism, antioxidant capacity and flowering in plants. Emphasis is also made on the variation in activities of different LED spectra between different plant species. In addition, research gaps and future perspectives are also discussed of this emerging multidisciplinary field of research and its development.
Highlights
Indoor cultivation of crops is best suited for crop breeding projects that are independent of outdoor climatic variations across seasons [1]
It was observed in their study that the number of stomata increased more in plants grown under blue light emitting diode (LED) compared to plants grown under low light intensities and other LEDs, which is in correlation with previous studies [103]
Shimazaki et al [112] reported that values of gs in leaves illuminated with a combination of red and blue light are larger than leaves illuminated under red or blue light alone, which was in agreement with the results reported by other researchers [21,39,121]
Summary
Indoor cultivation of crops is best suited for crop breeding projects that are independent of outdoor climatic variations across seasons [1]. The effect of red, blue, and green light, including other combinations of various spectrums of light, has been found to be effective for plant growth and development, nutrient efficiency, pest control, the production of bioactive compounds, and the induction of flowering, etc. The blue and red wavelengths supply the energy required for the growth and development of plants via photosynthesis and photoreceptors, which regulate morphogenetic events such as plant elongation, leaf expansion, stomatal opening, circadian clock, and flowering [14]. When blue and red light are used in combination, the light appears purplish gray, and for humans, the diagnosis of disease and disorder of plants under this faint light becomes difficult This led to the idea of using a small amount of green light in agricultural lighting [13]. In the second half of this review, we discuss the biochemical effects of LED wavelengths on plants and find out whether an effective light recipe for specific plants is better, or if a single spectrum on specific plants can be supplied to all plant species with varied wavelengths
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