The Inclusion of Green Light in a Red and Blue Light Background Impact the Growth and Functional Quality of Vegetable and Flower Microgreen Species

Abstract

Microgreens are edible seedlings of vegetables and flowers species which are currently considered among the five most profitable crops globally. Light-emitting diodes (LEDs) have shown great potential for plant growth, development, and synthesis of health-promoting phytochemicals with a more flexible and feasible spectral manipulation for microgreen production in indoor farms. However, research on LED lighting spectral manipulation specific to microgreen production, has shown high variability in how these edible seedlings behave regarding their light environmental conditions. Hence, developing species-specific LED light recipes for enhancement of growth and valuable functional compounds is fundamental to improve their production system. In this study, various irradiance levels and wavelengths of light spectrum produced by LEDs were investigated for their effect on growth, yield, and nutritional quality in four vegetables (chicory, green mizuna, china rose radish, and alfalfa) and two flowers (french marigold and celosia) of microgreens species. Microgreens were grown in a controlled environment using sole-source light with different photosynthetic photon flux density (110, 220, 340 µmol m−2 s−1) and two different spectra (RB: 65% red, 35% blue; RGB: 47% red, 19% green, 34% blue). At harvest, the lowest level of photosynthetically active photon flux (110 µmol m−2 s−1) reduced growth and decreased the phenolic contents in almost all species. The inclusion of green wavelengths under the highest intensity showed positive effects on phenolic accumulation. Total carotenoid content and antioxidant capacity were in general enhanced by the middle intensity, regardless of spectral combination. Thus, this study indicates that the inclusion of green light at an irradiance level of 340 µmol m−2 s−1 in the RB light environment promotes the growth (dry weight biomass) and the accumulation of bioactive phytochemicals in the majority of the microgreen species tested.

Morpho-Metric and Specialized Metabolites Modulation of Parsley Microgreens through Selective LED Wavebands

“…Indeed, parsley microgreens treated with red light showed the highest yield, indirectly demonstrating that this plant had the highest photosynthetic light use efficiency and consequently the highest soluble sugars content potentially available for plant growth. RGB light determined the highest leaf length, width, and DM percentage, accordingly with Kim et al [40] and Orlando et al [20] who reported that the inclusion of green light in the red/blue light environment promoted dry weight biomass. Green light has the advantage of penetrating into the plant canopy better than red or blue light [41], where the transmitted green light could be used to boost photosynthesis [42] and enhance plant growth [43].…”

“…Therefore, most of the responses normally present with red or blue monochromatic lights appear reversed in our study. Probably the presence of a 10% green-yellow component in red and blue LEDs is capable of reversing the mechanisms controlled by these light wavelengths, determining phenotypes different from those normally expected, as also reported by Orlando et al [20]. Indeed, parsley microgreens treated with red light showed the highest yield, indirectly demonstrating that this plant had the highest photosynthetic light use efficiency and consequently the highest soluble sugars content potentially available for plant growth.…”

“…Nowadays, in growth chambers, high-tech greenhouses and plant factories, light quantity (intensity and photoperiod) and quality (spectral composition) may be modulated in order to manipulate plant development and yield [18]. In particular, by using light-emitting diodes (LEDs), the spectral composition of artificial lighting can be adapted in order to promote the synthesis of health-promoting phytochemicals and increase the functional quality of microgreens [19,20]. Recently, the effects of selected spectral narrow-band LEDs lighting (red, blue, blue-red) on the phytochemical profile and antioxidant properties of several microgreens species have been investigated [21][22][23][24][25][26][27].…”

Trial Protocol for Evaluating Platforms for Growing Microgreens in Hydroponic Conditions

“…The light spectrum shall be determined by using a spectrometer. These measurements shall be made above each tray [58] and at differences of 10, 20, 30 and 40 cm above their canopy.…”

Investigating the response of green and red spinach microgreen yield and chlorophyll content in varied light-emitting diode and plant nutrient

“…LEDs have promoted rapid plant growth and increased phytochemical accumulation, enhancing environmental control's quality and productivity. LEDs have the potential to regulate the photoperiodism of irradiation and the wavelength of the produced light spectrum to boost plant yield in indoor farming [6], [7]. In a previous study, various LED colors led to distinct growth and development, including the chlorophyll content of the leaves [4].…”