Toxic effect of cadmium on rice as affected by nitrogen fertilizer form

A nutrient solution experiment was conducted to determine the influence of N forms on growth, oxidative stress, and Cd and N uptake in rice plants. The treatments were consisted of two Cd levels (0 and 1 μmol ) and three N forms (NH4)2SO4, NH4NO3 and Ca(NO3)2. The results indicated that without Cd addition in the culture solution, the N forms had no significant effect on all measured parameters, including plant growth, photosynthetic traits, malondialdehyde (MDA) concentration, superoxide dismutase (SOD) activity, and Cd and N concentration, while Cd addition in the medium resulted in significant differences in measured parameters among the three forms of N fertilizers. The least inhibition of growth was noted in (NH4)2SO4-fed plants, and the largest in Ca(NO3)2-fed plants, when plants were exposed to Cd stress. The highest photosynthetic rate and chlorophyll content was also recorded in (NH4)2SO4-fed plants. Addition of Cd caused a remarkable increase in SOD activity and MDA content in plants, and the extent of increase varied with N form, with (NH4)2SO4-fed plants being smallest. In comparison with the control plants, the N concentration in roots and shoots was not significantly affected in (NH4)2SO4-fed plants, but significant decrease in root N concentration was found for the NH4NO3 and Ca(NO3)2-fed plants under Cd stress. Moreover, the significant differences were also noted among the three N forms in both root and shoot Cd concentrations, with (NH4)2SO4-fed plants being the lowest. The results indicated that the toxic effect of Cd on rice varied with the form of N fertilizer.