Interaction effects of light intensity and nitrogen concentration on growth, photosynthetic characteristics and quality of lettuce (Lactuca sativa L. Var. youmaicai)

- A significant interaction of light intensity and nitrogen concentration on regulating lettuce production and nutritional quality was proved.
- The combination of higher light and lower nitrogen enhanced the photosynthesis and increased the yield of lettuce.
- Moreover, the combination of higher light and lower nitrogen was beneficial to increase vitamin C and decrease nitrate in lettuce.

Light intensity and nitrogen concentration of nutrient solution are considered crucial for the contents of vitamin C and nitrate in cultivated leaf vegetables. We here investigated the effects of various combinations of light intensity (60, 140 and 220 μmol m−2 s−1) and nitrogen concentration (7, 15 and 23 mmol L−1) of the solution on the growth, photosynthetic characteristics, vitamin C and nitrate content of lettuce. Our results demonstrate that the lettuce had the largest dry biomass at the high illumination of 220 μmol m−2 s−1 and low nitrogen of 7 mmol L−1. The higher light and low nitrogen also contributed to the accumulation of vitamin C and decrease of nitrate in lettuce leaves. The effect of nitrogen supply on chlorophyll concentrations was more efficient under low light than high illumination. Our results reveal that there was an obvious interaction between light intensity and nitrogen available for the photosynthesis, yield and quality of lettuce. This study provides valuable insights into the combinational regulation of light intensity and nitrogen supply for improving growth and nutritional quality of vegetables grown in greenhouse and plant factory.