Pre-harvest LED lighting strategies for reduced nitrate contents in leafy vegetables

Abstract

Short-term pre-harvest red light treatment was evaluated as a tool to reduce nitrate (NO3 ) contents in leafy vegetables, cultivated under low-light conditions in a greenhouse. Corn salad (Valerianella locusta L., ‘Vit’), amaranth (Amaranthus chlorostachys Willd., ‘Red Army’) and tatsoi (Brassica rapa var. rosularis L., ‘Rozetto F1’) were cultivated under low-light conditions and 1–7 days before harvest were treated with 638 nm red light emitting diode light. The effects of light treatment on NO3 and nitrite (NO2 ) contents, reducing enzyme activities and plant photosynthetic performance of different leafy vegetable species were explored seeking for comprehensive approach for the control of NO3 metabolism. Nitrate, nitrite, total protein contents and reducing enzyme activity depend on plant species, lighting treatment duration and their interaction. A remarkable decrease in nitrates and an increase in NO3 reductase activity were observed 3 days after red light treatment. It followed by a significant increase in NO2 and protein contents in corn salad and amaranth. A medium correlation between photosynthetic rate and NO3 contents was determined for tatsoi and corn salad. A negative statistically insignificant correlation between these indicators was established for amaranth. Short-term pre-harvest red light treatment can be applied as a technological tool to reduce NO3 contents in green vegetables, cultivated under low-light conditions. The obtained results confirm the significant relationship between plant photosynthetic rate and nitrate metabolism, as well as indicate the sensitive, but differential physiological response of different vegetable species to the applied lighting.