| Cyanobacteria bloom is one of the most serious water environmental problems in the world.As the cyanobacteria blooming dominant species,Microcystis aeruginosa has critical effects on aquatic ecosystems.It is necessary to study the effect of M.aeruginosa on freshwater zooplankton.Rotifers serve as the bait of a lot of fishes and the grazers of plankton-algae,and it plays an important role in the water food web.In this paper,the influence of M.aeruginosa on the life history and maternal effect of Brachionus calyciflorus,the population growth of B.calyciflorus and competition between the species of rotifers and cladocerans were studied.It has a good guiding significance for understanding the ecological harm caused by M.aeruginosa bloom and provides a lot of basic data for the research on interaction between M.aeruginosa and plankton.In the second chapter,the effects of two strains of M.aeruginosa?microcystin-producing and microcystin-free?at different concentrations on the life history parameters of B.calyciflorus were investigated by conducting a life history study at25°C.The results showed that both M.aeruginosa strains and concentration had significant effects on the net reproduction rate?R0??F=31.83,P<0.01;F=30.36,P<0.01?and intrinsic growth rate?rm??F=34.67,P<0.01;F=18.73,P<0.01?of B.calyciflorus and they also showed a significant interactive effect.Microcystin-free M.aeruginosa promote the rotifer population and could be used as a food source for rotifers at low concentration?1×104 cells/mL?has been found.However,due to the lack of fatty acids and other nutrients,the food quality was lower than that of Chlorella pyrenoidosa.At high concentration?1×105,5×105 cells/mL?,rotifers were more likely to ingestion microcystin-free M.aeruginosa,and the overall food quality was decreased,which had an inhibitory effect on rotifers.The inhibition effect of microcystin-producing M.aeruginosa on rotifer population was obvious,and the net reproductive rate and intrinsic growth rate of B.calyciflorus increased significantly with increasing concentration of microcystin-producing M.aeruginosa.In the third chapter,I investigated the responses of life cycle parameters of B.calyciflorus to microcystin-producing M.aeruginosa concentrations at five temperature gradients.The results showed that temperature and microcystin-producing M.aeruginosa concentration had significant independent and interactive effects on the net reproduction rate?R0??F=30.46,P<0.01;F=148.29,P<0.01;F=28.00,P<0.01?and intrinsic growth rate?rm??F=29.71,P<0.01;F=143.87,P<0.01;F=33.94,P<0.01?of B.calyciflorus.The results showed that the growth and reproduction of rotifers became faster at 30 and 35°C,and the generation time was shortened.However,high temperature?30°C,35°C?promoted inhibitory effect of microcystin-free M.aeruginosa on rotifers.In the fourth chapter,I investigated effects of M.aeruginosa on matermal effect of B.calyciflorus.The first,second and third generations of B.calyciflorus by M.aeruginosa were fed to microcystin-producing and microcystin-free M.aeruginosa to investigate the changes of fitness,average life span and total number of neonates of the three generations of rotifers.The fitness of rotifers was determined by life table experiments.The results showed that the first generation of M.aeruginosa of microcystin-producing was more suitable than that of microcystin-free M.aeruginosa?P<0.01?.The fitness of the second and third generation of rotifers showed that the generations adaptability of M.aeruginosa of microcystin-producing did not improve.However,in the second generation and the third generation of B.calyciflorus exposed to microcystin-producing M.aeruginosa,the survival time of rotifers increased and the total number of neonates decreased,indicating that the tolerance of offspring to microcystis was improved at the cost of reducing the number of neonates to improve the survival of offspring.In the fifth chapter,I investigated effects of M.aeruginosa on interspecific competition between B.calyciflorus and Daphnia magna.So I design three concentration M.aeruginosa,by population growth of the rotifers,cladocerans,and rotifers+cladocerans.The results showed that the different concentrations of M.aeruginosa affected differently on the population of rotifers,cladocerans and inerspecific competition.At low concentration?5×104 cells/mL?,the population of B.calyciflorus?P<0.01?and D.magna?P<0.01?were promoted,and the results of interspecific competition showed that the population of B.calyciflorus declined,and the dominant species was D.magna.At the medium concentration?105 cells/mL?,the B.calyciflorus population?P<0.01?increased slowly,and the cladocerans population?P<0.01?showed an increasing trend.The results of interspecific competition showed that the population of B.calyciflorus declined,and the dominant species was D.magna.The population of B.calyciflorus with high concentration?5×105 cells/mL?decreased in fifith day,and the number of cladocerans population?P<0.01?showed a downward trend.The results of interspecific competition showed that the population of B.calyciflorus declined and D.magna was dominant.The strains and concentrations of M.aeruginosa and their interactions have significant effects on the life history parameters of B.calyciflorus.The increase of temperature will aggravate the inhibitory effect of M.aeruginosa of microcystin-producing on B.calyciflorus.The maternal effect of M.aeruginosa on B.calyciflorus and the results of the fitness of the offspring showed that the adaptability of the offspring did not improve.Changes in the concentration of M.aeruginosa could not“reverse”the dominant position of D.magna.It is important to study the population changes of freshwater zooplankton under different concentrations of M.aeruginosa in order to understand the mechanism. |
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