Effects of different light intensities on anti-oxidative enzyme activity, quality and biomass in lettuce

Recently, the worldwide demand for romaine lettuce (Lactuca sativa L.) has been increasing. Thus, regulation measures of supplementary or shading light are often used in the production of lettuce in some regions. However, inconsistent results on the light saturation point of lettuce from previous studies do not facilitate the regulation of light intensity. In the present study, the effects of different light intensities on anti-oxidative enzyme activity, yield and quality of lettuce were investigated. The results reveal the following: (1) judged by the dynamics of anti-oxidative enzyme activity, there was no light stress to occurr in the 100, 200 and 400 mu mol/m(2)s treatments, a mild light stress occurred in the 600 mu mol/m(2)s treatment, and a serious light stress occurred in the 800 mu mol/m(2)s treatment; (2) increased light intensity gradually reduced the contents of soluble protein and nitrate in lettuce, whereas the content of soluble sugar remarkably increased. The biomass of a single plant of lettuce in the 600 mu mol/m(2)s treatment was the highest and second highest in the 400 mu mol/m(2)s treatment but was the lowest in the 100 mu mol/m(2)s treatment. No significant difference in the biomass of single plant was observed between the 400 and 600 mu mol/m(2)s treatments. Based on these results, the range of 400 mu mol/m(2)s to 600 mu mol/m(2)s is a recommendable light intensity for lettuce production.