Effects of Different Light Spectra on Final Biomass Production and Nutritional Quality of Two Microgreens

Abstract

To improve microgreen yield and nutritional quality, suitable light spectra can be used. Two species—amaranth (Amaranthus tricolor L.) and turnip greens (Brassica rapa L. subsp. oleifera (DC.) Metzg)—were studied. The experiment was performed in a controlled LED environment growth chamber (day/night temperatures of 24 ± 2 °C, 16 h photoperiod, and 50/60% relative humidity). Three emission wavelengths of a light-emitting diode (LED) were adopted for microgreen lighting: (1) white LED (W); (2) blue LED (B), and (3) red LED (R); the photosynthetic photon flux densities were 200 ± 5 µmol for all light spectra. The response to light spectra was often species-specific, and the interaction effects were significant. Morphobiometric parameters were influenced by species, light, and their interaction; at harvest, in both species, the fresh weight was significantly greater under B. In amaranth, Chl a was maximized in B, whereas it did not change with light in turnip greens. Sugar content varied with the species but not with the light spectra. Nitrate content of shoots greatly varied with the species; in amaranth, more nitrates were measured in R, while no difference in turnip greens was registered for the light spectrum effect. Polyphenols were maximized under B in both species, while R depressed the polyphenol content in amaranth.

Light and Plant Growth Regulators on In Vitro Proliferation

“…Hence, a minimum threshold of BL is necessary for normal plant growth [ 146 ]. Moreover, regulating the spectral quality particularly by the BL improves the antioxidant defense line and is directly correlated with the enhancement of phytochemicals [ 65 , 90 , 166 ] or with the regulation of gene expression [ 167 ]. All these reasons would explain why the RL:BL illumination resulted effectively in a wide range of species.…”

“…The B-LED illumination also significantly increased the antioxidant enzyme activities in leaves and roots in Amaranthus tricolor and Brassica rapa L. subsp. oleifera [ 166 ]. In the in vitro cultured Pyrus communis plantlets, it was detected that the gene encoding the pathogenesis-related protein PR10 is regulated daily by the body clock of a plant, while PR1 was expressed without clear evidence of circadian regulation [ 167 ].…”

Variation in terpenoids in leaves of Artemisia annua grown under different LED spectra resulting in diverse antimalarial activities against Plasmodium falciparum

“…LED spectra in an environmentally controlled system have been proven to regulate plant productivity. Fresh weight and dry weight of lettuce significantly increased under red LED light [ 25 ], blue spectrum induced biomass of amaranth and turnip greens [ 26 ] and white light promoted leaf, stem, root growth and overall growth rate of spinach [ 27 ].…”

Light Spectrum Differentially Affects the Yield and Phytochemical Content of Microgreen Vegetables in a Plant Factory

“…The chlorophyll index of basil (Ocimum basilicum) "Genovese" was greater when plants were treated with a red/blue ratio of 2 or 3 units compared to 0.5, 1, and 4 units [28]. Toscano et al [47] found that red amaranth grown under monochromatic blue produced greater amounts of chlorophyll a, total chlorophyll, and carotenoids compared to white (21% blue; 38% green; 35% red; 6% far-red) and monochromatic red, while turnip greens did not show a response. In addition, the percentage of blue light did not affect chlorophyll a, b, or the total chlorophyll of four Brassica microgreens, including mustard, while the authors observed a species-dependent effect during the first stage of plant growth [48].…”