Effect of supplemental UV-A radiation on mineral elements content and nitrate variation in Brassica microgreens

Limited studies showed the positive effect of UV-A radiation on increasing contents of health-beneficial compounds in various leafy vegetables. We hypothesised that UV-A could promote the uptake of mineral nutrients and affect nitrate assimilation as well. Therefore, the study aimed to evaluate how the UV-A radiation changes the contents of these substances in Brassica microgreens. Broccoli, kohlrabi, mizuna, red pak choi and tatsoi were grown under the main lighting of blue 447-, red 638- and 665-, and far-red 731 nm light-emitting diodes (LEDs), and the UV-A wavelengths of 366-, 390- or 402 nm were added for experiments. The contents of Ca, K, Mg, P, S, Fe and Zn were evaluated by spectrometric (ICP-OES) and of nitrates by potentiometric methods. The overall results showed that UV-A negatively affected the accumulation of mineral elements in all plants, except mizuna, when the 366 nm had the impact of increased contents of nutrients. The supplemental UV-A radiation significantly decreased the assimilation of nitrates in kohlrabi, mizuna, red pak choi, but increased in broccoli and tatsoi microgreens. Whereas the data revealed that the impact of UV-A radiation on investigated substances is species-depended, the necessity of further detailed investigations to explain the role of UV-A radiation in conventional lighting systems for various plants is definite.