Research On Effects Of Neodymium And Yttrium Of Rare Elements On The Growth And Physiological Characteristics Of Microcystic Aeruginosa

Rare earth elements(REEs) are widely used in agriculture,forestry,animal husbandry and aquaculture as fertilizers or animal food in China.A large quantity of soluble rare earth elements enter the water body through runoff from farmland and food of organisms which would bring some effects to algae as the primary producer of aquatic ecosystem and even become the secondary factor of water bloom occurring and developing.In this study, effects of different concentrations of neodymium(Nd) and yttrium(Y) on the growth curve, the contents of chlorophyll a,soluble protein,soluble sugar and malondialdehyde(MDA), the activities of superoxide dismutase(SOD),peroxidase(POD) and catalase(CAT) and the ultrastructure of Microcystic aeruginosa were studied and BG11 culture medium was served as the control by simulated test in the laboratory.The main results were shown as follows:1.Effects of different concentrations of neodymium on the growth and physiological characteristics of Microcystic aeruginosa:(1)The growth of Microcystic aeruginosa was stimulated at lower concentrations of Nd³⁺(0.1～2mg/L).The optimum dose of Nd³⁺ for Microcystic aeruginosa was 1mg/L. Lower concentrations of Nd³⁺ existed in water may be a chemical inducement for the brake-out of water bloom.Nd³⁺ had the inhibitory effect on the growth of Microcystic aeruginosa at higher concentrations(5～20mg/L).When the concentration of Nd³⁺ approached 40mg/L,Microcystic aeruginosa stopped growing and tended to die.(2)The contents of chlorophyll a and soluble protein were increased at lower concentrations of Nd³⁺,while the contents of chlorophyll a and soluble protein were inhibited at higher concentrations of Nd³⁺.(3)The contents of soluble sugar increased gradually with the enhancing of concentrations of Nd³⁺ and treatment time from the fouth to twelfth day.The contents of soluble sugar decreased within the concentration range(0.1～20mg/L)on the sixteenth day,but the contents of soluble sugar at higher concentrations of Nd³⁺ were higher than that of control.(4)The contents of malondialdehyde(MDA) decreased firstly and increased afterwards with the enhancing of concentrations of Nd³⁺ from the fouth day to the twelfth day.The contents of malondialdehyde(MDA) at lower concentrations of Nd³⁺ were higher than that of control,but they were no significant difference(p＞0.05) on the sixteenth day.The activities of superoxide dismutase(SOD),peroxidase(POD) and catalase(CAT) increased first and decreased afterwards with the enhancing of concentrations of Nd³⁺ during the course.Under lower concentrations of Nd³⁺ stress,the protective systems reacted on mosses, and the activities of superoxide dismutase(SOD),catalase(CAT) and peroxidase(POD) were induced in high level to eliminate and resolve reactive oxygen species(ROS) in order to maintain stability of membrane systems.With more serious damage,the defensive system could not protect cells,the contents of MDA increased evidently.(5)The thylakoid structure of Microcystic aeruginosa was more clear than that of control at 1mg/L concentration of Nd³⁺.The thylakoid structures of Microcystic aeruginosa were damaged by higher concentration of Nd³⁺.2.Effects of different concentrations of yttrium on the growth and physiological characteristics of Microcystic aeruginosa:(1)0.05mg/L concentration of Y³⁺ had no significant effect on the growth of Microcystic aeruginosa.The growth of Microcystic aeruginosa was stimulated distinctly at 0.1～0.2mg/L concentrations of Y³⁺.The growth of Microcystic aeruginosa was stimulated partly or completely under higher concentrations of Y³⁺(0.5～10mg/L) stress.(2)The contents of chlorophyll a,soluble protein and soluble sugar and the activities of superoxide dismutase(SOD),catalase(CAT) and peroxidase(POD) increased first and decreased afterwards with the enhancing of concentrations of Y³⁺.(3)Lower concentrations of Y³⁺(0.05～0.2mg/L) had no significant effect on the contents of MDA of Microcystic aeruginosa.The contents of MDA of algae cells had continued to increase with the enhancing of concentrations of Y³⁺(0.5～5mg/L) and time.(4)The ultrastructure of Microcystic aeruginosa had no difference from that of control at 0.1mg/L concentration of Y³⁺.The thylakoid structures of Microcystic aeruginosa were damaged by higher concentration of Y³⁺.