Effects of short-term daytime or night-time supplemental LED lighting on mineral elements in greenhouse lettuce

Mineral elements are involved in various biological processes of plants and human beings, acting as cofactors in protein synthesis, activating some enzymes, participating in chlorophyll synthesis, etc. Nowadays, light-emitting diodes (LEDs) have shown the possibility of affecting the content of various phytochemicals in leafy vegetables through light management, including short-term lighting exposure. However, it still lacks information on how short pre-harvest lighting with different monochromatic LEDs can change the content of mineral elements in such plants. Thus, the aim was to determine the short-term daytime or night-time supplemental LEDs light effect on the mineral elements content in lettuce (Lactuca sativa L. ‘Little Gem’). Plants were grown in a greenhouse under high-pressure sodium lamps (HPS) supplemented 4 h by 400-, 455-, 530-, 455+530- or 660 nm LEDs light five days before harvest. Two experiments (EXP) were performed: EXP1 – LED treatment occurred between 22 and 02 at night, and EXP2 – HPS and LED were used between 6 and 10 in the morning. The photosynthetic photon flux density (PPFD) of LEDs was 50 μmol m^‑2 s^‑1. The ICP-OES method was used for the determination of mineral elements. Our results revealed the different effects of supplemental LED light applied at night and day. A more evident effect of 530 nm LEDs on mineral elements was determined at night and 400 nm during the day. However, the response to different lighting depended on the mineral elements. For example, all LEDs lighting at night and day did not affect P, K, Mg, Fe, and increased S and Zn, but B and Na increased only at night. Overall, these results suggest that adequately chosen short-term LED lighting could be suitable for increasing mineral elements in lettuce, but further investigation is needed.