The effects of different spectral compositions of light-emitting diode (LED) sources and fertilizer containing biologically active silicon (Si) in the nutrient solution on morphological and physiological plant response were studied. Qualitative indicators and the productivity of plants of a red-leaved and a green-leaved lettuce were estimated. Lettuce was grown applying low-volume hydroponics in closed artificial agroecosystems. The positive effect of Si fertilizer used as a microadditive in the nutrient solution on the freshly harvested biomass was established on the thirtieth day of vegetation under LEDs. Increase in productivity of the red-leaved lettuce for freshly harvested biomass was 26.6%, while for the green-leaved lettuce no loss of dry matter was observed. However, being grown under sodium lamps, a negative impact of Si fertilizer on productivity of both types of plants was observed: the amount of harvested biomass decreased by 22.6% and 30.3% for the green- and red-leaved lettuces, respectively. The effect of using Si fertilizer dramatically changed during the total growing period: up to the fifteenth day of cultivation, a sharp inhibition of the growth of both types of lettuce was observed; then, by the thirtieth day of LED lighting, Si fertilizer showed a stress-protective effect and had a positive influence on the plants. However, by the period of ripening there was no effect of using the fertilizer. Therefore, we can conclude that the use of Si fertilizers is preferable only when LED irradiation is applied throughout the active plant growth period.

In city farming, when growing green crops, a significant part of the production cost is the cost of electricity for lighting. The physiology, biochemistry, morphology and productivity of plants can be affected by changing irradiation modes and these changes reduce electricity costs. However, the results of studies in the literature are contradictory. In this work, we investigated the effect of impulse (frequency 1000 Hz and duty cycle 67%), scanning (the principle of running lights) and constant 16 h and 24 h modes of operation of white light LED irradiators on the physiological, biochemical and morphometric parameters of lettuce with red and green leaves. The daytime integral of light in all variants remained unchanged ~15.6 mol m−2 day−1. Daily electricity consumption also did not differ significantly. Plants were grown on racks in a climatic chamber up to 35 days of age. For lettuce with red leaves, the most optimal for biomass accumulation and synthesis of anthocyanins was the impulse illumination mode, while for lettuce with green leaves, no statistically significant differences in biomass were observed under different irradiation modes. For red-leaved lettuce, it was found that the highest concentration of carotenoids in the leaf was observed under constant (24 h) and scanning irradiation, which is associated with a more active reaction of the photosynthetic system to prolonged irradiation and increased intensity during scanning irradiation. Also, increased photosynthetic activity was found in both varieties of lettuce at 16 h of operation of LED irradiators, which, however, did not affect their final productivity. The results may be useful for the development of LED illuminators for use in rack growing.

Investigation is devoted to the optimization of light spectrum and intensity used for red mustard growing. Notably, most of the studies devoted to red mustard growing were conducted on micro-greens, which is not enough for the development of methods and recommendations for making the right choices about the irradiation parameters for full-cycle cultivation. In this study, we tested four models of LED with different ratios of blue, green red and far red radiation intensity: 12:20:63:5; 15:30:49:6; 30:1:68:1, in two values of photon flux density (PFD)—120 and 180 µmol m−2 s−1—to determine the most effective combination for red mustard growing. The study was conducted in a container-type climate chamber, where the red leaf mustard was cultivated in hydroponics. On the 30th day of cultivation, the plant’s morphological, biochemical and chlorophyll fluorescence parameters, and reflection coefficients were recorded. The results indicated that the PFD 120 µmol m−2 s−1 had a worse effect on both mustard leaf biomass accumulation and nitrate concentration (13–30% higher) in the plants. The best lighting option for growing red mustard was the blue–red spectrum, as the most efficient in terms of converting electricity into biomass (77 Wth/g). This light spectrum contributes to plant development with a larger leaf area (60%) and a fresh mass (54%) compared with the control, which has a maximum similarity in spectrum percentage to the sunlight spectrum. The presence of green and far red radiation with the blue–red light spectrum in various proportions at the same level of PFD had a negative effect on plant fresh mass, leaf surface area and photosynthetic activity. The obtained results could be useful for lighting parameters’ optimization when growing red mustard in urban farms.

In this study, we investigated the effects of additional ultraviolet radiation (UV) on the main growth fluorescent lamp light on pigment content and essential oil accumulation in sweet basil (Ocimum basilicum L.). Three different UV light sources from light-emitting diodes and discharge lamps, which emit UV in the UV-A (315–400 nm), UV-B (280–315 nm) and UV-C (100–280 nm) ranges, were tested for basil plant growing. The plants, growing under additional UV-A and UV-B from mercury lamps, on the 60th growing day were higher than control plants by 90% and 53%, respectively. The fresh leaf mass of the UV-A irradiated basil plants was 2.4-fold higher than the control plant mass. The dry mass/fresh mass ratio of the UV-A and UV-B irradiated plants was higher by 45% and 35% in comparison to the control plants. Leaf area was increased by 40% and 20%, respectively. UV-C affected the anthocyanin content most strongly, they increased by 50%, whereas only by 27% and 0% under UV-A and UV-B. Any UV addition did not affect the essential oil total contents but altered the essential oil compositions. UV-A and UV-B increased the linalool proportion from 10% to 20%, and to 25%, respectively, in contrast to UV-C, which reduced it to 3%. UV-C induced the eugenol methyl ether accumulation (17%) and inhibited plant growth. Moreover, UV increased the proportion of α-guaiene, β-cubebene and α-bulnesene and decreased the proportion of sabinene and fenchone. Thus, we concluded that UV (except UV-C) used jointly with main light with PPFD 120 ± 10 μmol photons·m−2·s−1 for sweet basil cultivation may be justified to stimulate basil growth and optimize the essential oil accumulation.

The intensively developing area of modern phytophysiology is the ecological plants physiology, which important section is the ecology of photosynthesis, by which we understand the intensity and photosynthesis productivity dependence on environmental factors, primarily on optical radiation. The urgent problem of growing plants under artificial conditions is to increase energy efficiency, reduce energy intensity and degree of environmental impact. Using LED irradiators with the function of controlling the spectral composition and optical radiation power, it is possible to increase photosynthesis efficiency and vegetable crop productivity in greenhouses. The comparative study of the effect of sodium lamp radiation and LED irradiators with different spectral composition on the growth and productivity lettuce varieties with red leaves (Anthony, Lolo-Rossa) and with green leaves (Levistro, Lifli), was conducted. The research results showed the different susceptibility of lettuce varieties to the spectral composition of radiation. For the Anthony, Levistro and Lolo-Rossa lettuce varieties, LED radiation application provided the positive effect on plant productivity (8-20%) compared to sodium lamps, and simultaneous reduced in energy consumption of the irradiation system by 40 - 50%. Diodes emission increase in the blue region of the spectrum had a significant positive effect on the synthesis of anthocyanins in the culture of lettuce varieties with red-leaves, compared to sodium lamps. For these varieties, a variable irradiation regime is necessary with a change in the spectrum and increase in the proportion of blue radiation towards the end of growth.