Effects of different amino acids and different ratios of lysine and nitrate on the growth and quality of Chinese cabbage (Brassica pekinensis L.)

Objectives The effects of seven amino acids on the growth and quality of Chinese cabbage were studied for the selection of efficient amino acids, and the suitable ratios of the selected amino acids and nitrate were further tested for the practical application.

Methods Partial sterile hydroponic culture method was used for the hydroponic experiment, which was carried out in the artificial climate laboratory of Zijingang Campus of Zhejiang University in 2017, with the Chinese cabbage cultivar Brassica pekinensis L. as tested materials. In experiment I, seven amino acids were used to treat Chinese cabbage, and the index related to fresh weight and quality of Chinese cabbage were determined. In experiment Ⅱ, according to the results of Experiment 1, the lysine with more significant effects on the growth and quality of Chinese cabbage was selected, lysine concentrations were 0.2, 0.5 and 1 mmol/L (namely B1, B2, B3, respectively), and nitrate concentrations were 0.5, 1 and 3 mmol/L (namely A1, A2, A3, respectively). Lysine mixed with nitrate treated Chinese cabbage, and the index related to fresh weight and quality of Chinese cabbage were determined.

Results The biomass, soluble protein content and nitrate content of lysine treated Chinese cabbage were the highest, and were significantly higher than some other treatments. The root activity and SPAD value of the Chinese cabbage treated with serine were the maximum, and the differences were significant with some other treatments. Different treatments had no significant effect on root fresh biomass, root to shoot ratio, V_C and soluble sugar contents. When nitrate concentration was fixed, the increased lysine concentration decreased shoots and root fresh biomass (except A2 treatment). The differences between some treatments were significant. The fresh biomass of Chinese cabbage treated with A1B1, A3B1 and A3B2 was obviously higher than other treatments. Different ratios of lysine and nitrate had no significant effect on soluble protein, V_C and nitrate contents in leaves of Chinese cabbage.

Conclusions Among the seven necessary amino acids, lysine shows the best effect on the growth and quality of Chinese cabbage. However, amino acids do not show satisfactory effect on the quality of Chinese cabbage. Under normal N supply, high concentration of lysine will inhibit the growth of Chinese cabbage. Only when N nutrition is deficient, lysine might be a supplement nitrogen source for Chinese cabbage.