Changes in mineral element content of microgreens cultivated under different lighting conditions in a greenhouse
Many studies have showed that optimizing the light spectrum using light-emitting diodes (LEDs) can increase the content of bioactive compounds in various leafy vegetables, but little is still known about how manipulation of the spectrum can change the content of mineral elements. The objective of our studies was to determine changes in mineral element content in microgreens cultivated under high-pressure sodium (HPS) lamps supplemented by LED lamps. During autumn-winter, kohlrabi and beet microgreens were grown for 10 d in peat substrate under 16 h photoperiod, day/night temperature 19-23/14-16°C and relative air humidity of 50-60%. Two experiments were carried out: I, HPS lighting was supplemented with LED light at 445 and 530 nm during the whole growing period; II, at the pre-harvest stage of 3 d, HPS lamps were supplemented by a solid-state illuminator containing 638 nm LEDs. Reference transplants were grown under HPS illumination. The ICP-OES method was used for determination of macro- (Ca, K, P, Mg, Na, S) and microelements (Cu, Fe, B, Mn, Zn). Nitrate concentration was measured by a potentiometric method. Both microgreens grown under supplemental 445 nm irradiation accumulated higher contents of all macroelements and nitrates in comparison with those grown under solely HPS illumination. Supplemental 530 nm irradiation resulted in increased content of nitrates and almost all mineral elements investigated in beet, but decreased content in kohlrabi. Short-term pre-harvest treatment with 638 nm LEDs to supplement HPS illumination and natural light produced increased content of mineral elements and reduced nitrate concentration in beet, but had almost no effect on kohlrabi. Our results showed that management of the light environment could be a tool for improving uptake of mineral elements in microgreens, but their reaction to changes of light spectrum is species dependent.
Brazaitytė, A., Vaštakaitė, V., Viršilė, A., Jankauskienė, J., Samuolienė, G., Sakalauskienė, S., Novičkovas, A., Miliauskienė, J. and Duchovskis, P. (2018). Changes in mineral element content of microgreens cultivated under different lighting conditions in a greenhouse. Acta Hortic. 1227, 507-516
light-emitting diodes, light spectrum, microgreens, macro- and microelements, nitrates