Effect Of Iron,Cobalt And Molybdenum On Growth Of Three Kinds Of Freshwater Algae

The phenomenon of algal bloom is often a combination of many factors.For phytoplankton,the demand of trace elements is not much,but play an important role in the metabolic process of planktonic algae growth.It is mainly used as auxiliary factor of enzyme to participate in a lot of biochemical reaction process,thus affecting the photosynthesis and growth of algae.In this paper,the effects of trace elements iron,cobalt and molybdenum on the growth of three freshwater algae were studied,aims to explore the change rules of the algal cell density and the chlorophyll-a content under different concentration of trace elements and various trace elements and the correlation between the trace elements and the growth indexes of algae,so as to estimate the growth of planktonic algae in fresh water more effectively and lay the foundation for preventing algal bloom.Microcystis aeruginosa,Chlorella vulgaris and Cyclotella sp.were selected as the experimental algae,and cultured in modified Fraquil medium with different concentrations at the certain conditions(temperature of 25?,illumination intensity of 2800 lx,light: dark of 14 h: 10 h)for 20 days,20 days and 14 days respectively.Single factor analysis of variance and Duncan's multiple range test were used to compare the differences of different experimental groups in the independent action experiment.The Logistic growth curve of algae was fitted and the growth difference of algae was analyzed.In the joint action experiment,the regression equation between three kinds of trace elements and algae growth indexes was established by quadratic polynomial stepwise regression.And according to the decision coefficient,the three kinds of trace elements were sort by the comprehensive effect degree.Based on analysis of three trace elements of iron,cobalt,molybdenum independent and joint action,the experimental results are as follows:(1)In the independent action experiment,when the iron concentration was 0.6 mg/L,the growth of M.aeruginosa was the best.When the iron concentration was 1.2 mg/L,the growth of C.vulgaris was the best.And when the iron concentration was 0.3 mg/L,the growth of Cyclotella sp.was the best.When the cobalt concentration was 1.48 ?g/L,the growth of M.aeruginosa and C.vulgaris was the best;and when the cobalt concentration was 4.44 ?g/L,the growth of Cyclotella sp.was the best,and the higher cobalt concentration could stimulate the growth of algae in the early stage of experiment.When the molybdenum concentration was 4.44 ?g/L,the growth of Cyclotella sp.was the best.For M.aeruginosa and C.vulgaris,when the concentration of molybdenum was 1.48?g/L and 5.92 ?g/L respectively,it was more conducive to the cell proliferation,and when the concentration of molybdenum was 4.44 ?g/L,it was good for the synthesis of chlorophyll-a.Three kinds of algae have great adaptability to the concentration of molybdenum.(2)In the joint action experiment of the trace element iron,cobalt and molybdenum: the regression equations between the three trace elements and the growth parameters of M.aeruginosa,C.vulgaris,and Cyclotella sp.were used to estimate the proliferation of three kinds of algae under specific conditions.The effects of three kinds of trace elements on M.aeruginosa,C.vulgaris and Cyclotella sp.were not the same,and effects of iron on growth indexes of C.vulgaris and Cyclotella sp.was the largest.However,iron was second in the effects on the maximum cell density,the average growth rate and the maximum chlorophyll-a content of M.aeruginosa.(3)During the growth of algae,the decrease of chlorophyll fluorescence parameter Fv/Fm value of M.aeruginosa and C.vulgaris was similar to chlorophyll-a content.However,there were no obvious differences in Fv/Fm value between the experimental groups with different concentrations of trace elements.Therefore,the change of Fv/Fm value could't be used to estimate the growth of algae preferably.And when evaluating the nutritional status of trace elements iron,cobalt and molybdenum in different algae species,the value of Fv/Fm could not fully explain the difference of nutrient concentration.Overall,when the concentrations of iron,cobalt and molybdenum are relatively high,the growth of three kinds of freshwater algae can be limited,while the lower ones are favorable for their growth.Iron has a greater impact on three kinds of freshwater algae.Using Fv/Fm value to estimate trace elements of algae,iron,cobalt and molybdenum has a certain restriction.