Effects of Supplemental Night Lighting and NO3- Exclusion on the Growth and NO3- Concentration in the Leaf Sap of Greenhouse-grown Spinach under NFT

The effects of supplemental night lighting and nitrate exclusion in the nutrient solution on the growth, nitrate concentration, and nitrate reductase activity (NRA) in the leaf of spinach plants grown under NFT and natural light in the greenhouse were studied. When the plants became of marketable size, they were grown in a nutrient solution without nitrate and exposed to artificial lighting of different light intensities and qualities from 23 : 00 to 6 : 00 1. Two days after treatments, top fresh weight was not affected by nitrate exclusion, whereas 7 days after treatments, plant growth was markedly reduced by nitrate exclusion. However, supplemental night lighting after nitrate exclusion on the subsequent growth of spinach were ineffective. 2. After nitrate exclusion, sap nitrate concentrations of leaf blades and petioles under supplemental night lighting decreased more rapidly than that without the treatment. The decrease of sap nitrate concentrations was unaffected with light quality. However, light intensities affected markedly, and the sap nitrate concentrations of leaf blade at two days after treatment were 1, 059, 799, 612 and 531 ppm under 0 (without lighting), 50, 150 and 250 m mol m-2s-1 (PPFD), respectively. 3. NRA of the plants with supplemental night lighting was higher than that without lighting.