Morphological and Photosynthetic Parameters of Green and Red Kale Microgreens Cultivated under Different Light Spectra

Abstract

Microgreens are plants eaten at a very early stage of development, having a very high nutritional value. Among a large group of species, those from the Brassicaceae family, including kale, are very popularly grown as microgreens. Typically, microgreens are grown under controlled conditions under light-emitting diodes (LEDs). However, the effect of light on the quality of grown microgreens varies. The present study aimed to determine the effect of artificial white light with varying proportions of red (R) and blue (B) light on the morphological and photosynthetic parameters of kale microgreens with green and red leaves. The R:B ratios were for white light (W) 0.63, for red-enhanced white light (W + R) 0.75, and for white and blue light (W + B) 0.38 at 230 µmol m−2 s−1 PPFD. The addition of both blue and red light had a positive effect on the content of active compounds in the plants, including flavonoids and carotenoids. Red light had a stronger effect on the seedling area and the dry mass and relative chlorophyll content of red-leaved kale microgreens. Blue light, in turn, had a stronger effect on green kale, including dry mass. The W + B light combination negatively affected the chlorophyll content of both cultivars although the leaves were significantly thicker compared to cultivation under W + R light. In general, the cultivar with red leaves had less sensitivity to the photosynthetic apparatus to the spectrum used. The changes in PSII were much smaller in red kale compared to green kale. Too much red light caused a deterioration in the PSII vitality index in green kale. Red and green kale require an individual spectrum with different proportions of blue and red light at different growth stages to achieve plants with a large leaf area and high nutritional value.

Effects of Extended Light/Dark Cycles on Solanaceae Plants

“…Among various environmental factors, light has been found to be one of the most important variables affecting phytochemical concentrations in plants [ 29 , 30 ]. While it is widely understood that light intensity [ 31 , 32 ], photoperiod [ 32 , 33 , 34 , 35 , 36 , 37 ], and spectral composition of light [ 32 , 38 , 39 , 40 ] have significant effects on the nutritional value of plants, this research and few previous studies [ 9 , 12 , 13 , 14 , 15 , 16 , 17 , 41 ] have shown that unconventional light distribution in time as an independent variable may also significantly affect plant nutritional value. Accumulation of substances with antioxidant properties improves plant nutritional value and makes the product beneficial to health and more competitive.…”

Evaluating the Impact of Controlled Ultraviolet Light Intensities on the Growth of Kale Using IoT-Based Systems

“…Plant developmental stage [62,65] UV light sensitivity is dependent on the plant's developmental stage. Younger plants may be more susceptible to UV damage; therefore, variable light management strategies that adjust as the plants develop may be required.…”