Adding UVA and Far-Red Light to White LED Affects Growth, Morphology, and Phytochemicals of Indoor-Grown Microgreens

Abstract

White light emitting diodes (LED) have commonly been used as a sole light source for the indoor production of microgreens. However, the response of microgreens to the inclusion of ultraviolet A (UVA) and/or far-red (FR) light to white LED light remains unknown. To investigate the effects of adding UVA and FR light to white LEDs on plant biomass, height, and the concentrations of phytochemicals, four species of microgreens including basil, cabbage, kale, and kohlrabi were grown under six light treatments. The first three treatments were white LED (control) and two UVA treatments (adding UVA to white LED for the whole growth period or for the last 5 days). Another three treatments consisted of adding FR to the first three treatments. The total photon flux density (TPFD) for all six light treatments was the same. The percentages of UVA and FR photons in the TPFD were 23% and 32%, respectively. Compared to white LEDs, adding UVA throughout the growth period did not affect plant height in all the species except for basil, where 9% reduction was observed regardless of the FR light. On the contrary, the addition of FR light increased plant heights by 9–18% for basil, cabbage, and kohlrabi, regardless of the UVA treatment, compared to white LED. Furthermore, regardless of UVA, adding FR to white LEDs reduced the plant biomass, total phenolic contents, and antioxidant concentrations for at least one species. There was no interaction between FR and UVA on all the above growth and quality traits for all the species. In summary, microgreens were more sensitive to the addition of FR light compared to UVA; however, the addition of FR to white LEDs may reduce yields and phytochemicals in some species.

The Effects of Light Spectrum and Intensity, Seeding Density, and Fertilization on Biomass, Morphology, and Resource Use Efficiency in Three Species of Brassicaceae Microgreens

“…This occurs via the Red:Far-Red ratio, which converts the biologically inactive red absorbing form (Pr) of phytochrome to the biologically active far-red absorbing form (Pfr), which then can cause downstream shifts in gene expression for specific responses to the environment, such as a shade-avoidance [ 69 ]. This has also specifically been shown for microgreens; for instance, studies have shown that adding Far-Red light directly led to improvements in height, leaf area, FW, and DW [ 14 , 70 , 71 ]. Furthermore, a study on microgreens found that adding small amounts of Far-Red to a pure-Blue recipe improved height and stem extension rate (SER) compared to UV + Blue, pure Red, and pure Blue Light Recipes [ 72 ].…”

Non-destructive real-time analysis of plant metabolite accumulation in radish microgreens under different LED light recipes

“…It is well known that far-red and UV-A lights stimulate anthocyanin production, as shown in some research studies ( Carvalho and Folta, 2016 ; Li and Kubota, 2009 ; Brazaitytė et al., 2016 ; Brazaitytė et al., 2019 ; He et al., 2021 ), while the combined effect of both lights has to be studied on radish microgreens. Hooks et al. (2022) studied the effect of far-red and/or UV radiation on basil, kale, cabbage, and kohlrabi microgreens, and a variation in anthocyanin concentration was not observed even though experimental conditions were different from the data here presented: the control light was a white LED with 100 μmol m -2 s -1 of PPFD, and UV and far-red light were added having a total flux still equal to 100 μmol m -2 s -1 , therefore reducing white intensity.…”

“…For example, in radish, fresh and dry weight was increased by 25% after the addition of far-red to the RB recipe ( Demir et al., 2023 ). In general, far-red radiation induced stronger effects on microgreens than UV-A when added to a white full-spectrum light ( Hooks et al., 2022 ). The effects of UV induction of secondary metabolism accumulation are highly dependent on the wavelength selected (UV A-B-C) and the genetic background.…”

Factors Affecting Production, Nutrient Translocation Mechanisms, and LED Emitted Light in Growth of Microgreen Plants in Soilless Culture

“…Low density polyethylene (LDPE) coated calcium carbonate mitigates peroxidase, phenylalanine, ammonia lyase, polyphenol oxidase, bacterial count, browning index, and total phenol and malondialdehyde content and maintains titrated acid and ascorbic acid in microgreen plants. Silicon oxide nanoparticle–chitosan complexes (NSSCs) enhance shelf life, retard weight loss, and maintain softness and acids, promotes high antimicrobial activity, and ensures long term preservation of microgreen plants …”

“…Silicon oxide nanoparticle− chitosan complexes (NSSCs) enhance shelf life, retard weight loss, and maintain softness and acids, promotes high antimicrobial activity, and ensures long term preservation of microgreen plants. 190 4.7. Plant Size.…”