Abstract:We investigated the growth and physiological effects of Ni2+ at 3 concentrations (0 mg·L-1, 0.1 mg·L-1, 1 mg·L-1) with 22.4 mg·L-1 N on nitrogen uptake in the seedling stage of Lactuca sativa L. using hydroponic. The results showed: (1) the root and shoot biomass of the lettuce increased with the increase of treatment time. Compared with the control T1 (0 mg·L-1 Ni2+ and 112 mg·L-1 N), T2 treatment (0 mg·L-1 Ni2+ and 22.4 mg·L-1 N) had certain inhibitory effects on the root growth and leaf growth of the lettuce; the fresh weight of the plant, dry weight, root to shoot ratio, root length, mean diameter, surface area, volume, number of root tips, number of roots, leaf surface area and volume were significantly higher under T3 (0.1 mg·L-1 Ni2+ and 22.4 mg·L-1 N) treatment for comparison, T4 treatment (1 mg·L-1 Ni2+ and 22.4 mg·L-1 N) promoted the growth of roots and leaves of the lettuce, but showed some inhibition on the number of root tips and roots. (2) With the increase of Ni2+ concentration, the contents of chlorophyll a, chlorophyll b and total chlorophyll in the leaves of the lettuce showed a first increase and then decrease, and both of them significantly increased under T3 (0.1 mg·L-1 Ni2+ and 22.4 mg·L-1 N) treatment. (3) With the increase of treatment time, the net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) of the leaf lettuce gradually increased, and the intercellular CO2 concentration (Ci) gradually decreased. The stomatal conductance (Gs) of leaves with T3 (0.1 mg·L-1 Ni2+ and 22.4 mg·L-1 N) treatment was significantly higher than that of the control, the intercellular CO2 concentration (Ci) was the lowest, and the net photosynthetic rate (Pn) was the largest. (4) Applying Ni2+ to pointed leaf lettuce, organic acid, soluble protein, soluble sugar content, POD and SOD activities had significant effect. With T3 (0.1 mg·L-1 Ni2+ and 22.4 mg·L-1 N) treatment, organic acid content decreased, while soluble sugar and soluble protein contents increased significantly,SOD and POD activities were significantly improved. (5) With T3 treatment, the contents of B and Ca in roots and N in leaves were higher; the Ni content in roots was higher than that in leaves, the Ni content in leaves was lower, and the Mg content was higher; Cu content in plants decreased with the increase of Ni2+ concentration. Research shows that exogenous Ni2+ treatment can affect the growth and physiological status of rapeseed lettuce seedlings under low nitrogen conditions (22.4 mg·L-1 N). The appropriate concentration (0.1 mg·L-1) Ni2+ can effectively improve the nitrogen absorption and utilization efficiency of the root system of rapeseed lettuce, reduce the amount of nitrogen application, promote the growth of the root system and aboveground leaf of rapeseed lettuce, increase the photosynthetic pigment content, and improve the net photosynthetic rate, thus improve the yield and nutritional quality of the plant.