Nitrate accumulation, productivity and photosynthesis of Brassica alboglabra grown under low light with supplemental LED lighting in the tropical greenhouse

Abstract

Vegetables are a large source of nitrate (NO3−) in our diet. As NO2− is toxic to humans, it is undesirable to consume vegetables with high NO3− content. Therefore, this study aimed to investigate the effect of supplementing of red- and blue-LED lighting to B. alboglabra grown in the tropical greenhouse in terms of moderating NO3− accumulation, improving photosynthesis, and enhancing productivity. All plants were grown hydroponically in full nutrients under prevailing greenhouse conditions for 20 days (full sunlight). Thereafter, plants were subjected to three different light treatments for 12 days: full sunlight, shade, and shade supplemented with LEDs. The average midday photosynthetic photon flux density (PPFD) during the light treatment periods were 220 μmol m−2 s−1 (full sunlight), 55 μmol m−2 s−1 (shade), and 220 μmol m−2 s−1 (shade supplemented with LEDs). Shoot nitrate (NO3−) concentration increased significantly in plants grown in the shade. However, shoot NO3− concentration was reduced when plants were supplemented with red- and blue-LED lighting. Photosynthetic CO2 assimilation, stomatal conductance, and productivity also improved in these plants. Our results suggest that supplemental red- and blue-LED lighting in a tropical greenhouse during periods of cloudy and hazy weather could improve productivity and nutrient quality of Chinese broccoli.