Nitrate content in Valerianella locusta L. plants is affected by supplemental LED lighting

- Supplemental LED lighting with red:blue in ratio 9:1 decreased nitrate content in V. locusta.
- In winter, nitrate content in V. locusta was lower in evening than at noon in two LED treatments.
- Nitrate level was higher in younger plants compared to older.

Nitrate concentration in edible parts of plants is still at the center of interest. Nitrate metabolism in plants is regulated among others by light. Therefore, the effect of LED and HPS lamps, as supplemental to solar radiation, on nitrate concentration and metabolism in Valerianella locusta 'Nordhollandse' was tested (in 30th and 60th day of lighting, at noon and evening hours). In two years of study, in autumn and winter, nitrate content decreased significantly in lamb's lettuce grown under 90% red + 10% blue LED light in comparison to HPS treated plants. The highest decrease (by about 1600 mg NO3− kg−1 fresh weight) was observed in 60th day of lighting, in winter, during irradiation (in the evening). We recommend just this combination of LED light for lamb's lettuce in the greenhouse cultivation. Nitrate reductase activity (NRA) was affected to a greater extent by the length of vegetation than by the light treatment. On average, after 30 days of lighting in V. locusta leaves, levels of NRA activity and nitrates were higher (about 25% and 40%, respectively) in comparison to 60 days of treatment. Our results indicate the need for extension of similar research on other species that can potentially accumulate high amounts of nitrate in greenhouse crop production.