The Study On Interspecific Competition Among Cyclotella Sp., Chlorella Vugaris And Microcystis Aeruginosa And The Inhibitory Effect On Their Growth By Daphnia Magna And Ceratophyllum Demersum

Water eutrophication has been a global problem of water pollution,resulting in the outbreak of water bloom which is a serious threat to the ecological environment and human health.How to use economic and safe methods to control blooms effectively for a long time has become one of hot topics in the scientists' studies today.There is a competition among different species of microalgae and some environmental conditions,such as nutrients,light,temperature,can affect the result of competition among planktonic algae.The bio-manipulation technology and restoration and reconstruction of large aquatic plants are common and effective ecological restoration methods for the treatment of water bloom.However,the phosphorus concentration in water have significant effect on the bio-manipulation and restoration and reconstruction of large aquatic plants,Therefore,this study selected three representative algae species in different phylum,namely,Cyclotella sp.,Chlorella vugaris and Microcystis aeruginosa.The experiment was carried out to research interspecies competition among the three species of microalgae to determine their competitive mechanism,then adding Daphnia magna and Ceratophyllum demersum to study the inhibitory effects of zooplankton and submerged plant on the growth of the three species of microalgae.Based on the characteristics of water eutrophication in china,Set culture solution with different phosphorus concentration to discuss the effects of D.magna and C.demersum to control the growth of algae,to reveal ecological mechanism of phosphorus concentration on biological control and submerged plant inhibiting the three species of algae.(?)The experiment conditionsThe B+D(50% BG11 and 50% D1 mixture)were the suitable culture solution for the co-culture of three species of algae.The culture conditions were set to temperature 25?,light intensity 2600~3000 lx,light dark ratio 14 h:10 h and cultivation period 16 days.The inhibition of D.magna and C.demersum on three species of algae in the experiment of different phosphorus concentration,the nitrogen concentration was 11 mg/L and the phosphorus concentration was 0.05,0.1,0.5 and 2 mg/L,respectively.(?)The co-culture of Cyclotella sp.,Chlorella vugaris and Microcystis aeruginosa(1)When co-culture with the two species of algae,the competitive inhibition parameters of Cyclotella sp.was the biggest,but the growth rate was slowest and cell density was the lowest.At the end of the experiment,Cyclotella sp or M.aeruginosa became the dominant species.When co-cultured with Cyclotella sp.and M.aeruginosa,the growth of Cyclotella sp.was in a dominant position 8 days before.Finally,M.aeruginosa became the dominant species,because of the stronger competition in the space,nutrient,light and so on.(2)When co-culture of the three species of algae,the competitive inhibition parameters of the three algae descending: Cyclotella sp.,C.vugaris,M.aeruginosa,but M.aeruginosa growth rate was faster,resulting in the absolute advantage of cell density.Then due to some factors such as space,nutrients,shading effect,the cell density of Cyclotella sp.and C.vugaris began to decrease on the 12 th day,the 16 th day Cyclotella sp.completely died,resulting in M.aeruginosa showed rapid growth and became the dominant species.(?)The effect of Daphnia magna and Ceratophyllum demersum to the three algae growth(1)When co-culture of Daphnia magna and three species of algae,D.magna had obviously inhibiting effect on the three algae,especially on the growth of M.aeruginosa.Finally,C.vulgaris became the dominant species.The maximum cell density of total algal had reached 6.5×10~6 cells/mL.The growth of algae had obviously inhibitory effect on the reproduction of D.magna.Put 5 D.magna in the culture medium in the initial experiment,after the experiment,the number of Daphnia magna was less than 50,less than the density at appropriate conditions 1/20.(2)When co-culture of C.demersum and three species of algae,C.demersum had some control effect on three species of algae,especially the most obvious inhibition on the growth of M.aeruginosa,C.vugaris became the dominant species.The maximum cell density of total algal was 9.2×10~6 cells/mL.Effect on inhibiting algae growth of D.magna was the better than that of C.demersum.The algae blooms can inhibit the growth of C.demersum.The 12 th day C.demersum began to disintegrate,the final weight was 0.098 g,less than the initial weight(0.1 g).(3)Put the three species of algae into culture solution that had cultivated C.demersum,the growth of them was obviously inhibited the cell density decreased with the culture time.In the end the cell density of total algal was only 7% of initial algal cell density,so water was clear.(4)When co-culture of D.magna,C.demersum and the three species of algae,the number of average survival of D.magna was 283,the average weight of C.demersum was 0.142 g,and they all grew better than one of them with three species of algae cultured together.The maximum cell density of total algal was 5.8×10~6 cells/mL which was relatively small.So adding D.magna and C.demersum at the same time would have the best inhibitory effect on the growth of algae.(?)Influence of phosphorus concentration on effect that D.magna and C.demersum control growth of algae.(1)When co-culture of D.magna and the three species of algae in the culture medium with different phosphorus concentration,the growth rate of D.magna increased with the increase of concentration phosphorus,number of D.magna even reached more than 1000.The growth rate of the three algae decreased with the increase of phosphorus concentration.When the phosphorus concentration was 2 mg/L,the inhibitory effect was the best,and when the phosphorus concentration was 0.05 mg/L,cell density of total algal reached the maximum,which was only 4×10~5 cells/L.Thus it can be seen that phosphorus concentration in the range of 0.05~2 mg/L,D.magna had obvious inhibitory effect on the three species of algae.(2)When co-culture of C.demersum and the three species of algae in the culture medium with different phosphorus concentration,and the phosphorus concentration was 0.05~0.5 mg/L,the growth rate of C.demersum increased with the increase of phosphorus concentration.When the phosphorus concentration was 2 mg/L,the high phosphorus concentration and the rapid growth of three species of algae would also limit algae growth.The cell density of total algal increased with the increase of phosphorus concentration.When the phosphorus concentration was 2 mg/L,the cell density of total algal was 4.33 ×10~6 cells/mL,and when the phosphorus concentration was 0.05 mg/L,the cell density of total algal was minimum(1.9 ×10~6 cells/mL).C.demersum had significant inhibitory effect on the growth of three species of algae,especially on the growth of M.aeruginosa,but the effect was not ideal,the water still showed green(C.vugaris as the dominant species).(3)When co-culture of D.magna,C.demersum and the three species of algae in the culture medium with different phosphorus concentration,the number of D.magna and the weight of C.demersum increased with the increase of concentration of phosphorus.On the contrary,the growth rate of the three species of algae decreased with the increase of the concentration of phosphorus.The inhibitory effect on algae growth was significantly better than that of the other two groups.When the phosphorus concentration was 0.05 mg/L,the total growth rate of algae was the largest,but the cell density was only 3.78×10~5 cells/mL.When the phosphorus concentration was 2 mg/L,the inhibitory effect was the best.Therefore,when the phosphorus concentration was 0.05~2 mg/L,it can achieve good inhibitory effect.(4)When phosphorus concentration was 0.05~0.1 mg/L,the phosphorus removal rate was above 90%,so phosphorus concentration became the limiting factor.Phosphorus concentration was 0.5~2 mg/L,the removal rate of phosphorus concentration was 20%~70%.When C.demersum co-cultured with three species of microalgae,the cell density of C.vugaris was higher,so the nitrogen and phosphorus removal rate was higher than the other two groups.The initial phosphorus concentration was higher,nitrogen removal rate would be higher.The phosphorus removal rate decreased with the increase of phosphorus concentration,but the total amount of phosphorus increased with the increase of phosphorus concentration.