Effect Of Extracellular Allelochemicals Of Microcystis Aeruginosa On Individual Charateristics Of Daphnia Magna And Phytoplankton-zooplankton Interactions

Cyanobacterial bloom is one of the most serious water pollution problems of the world,but the mechanism for its outbreak is far from clear.The allelopathic effect of Cyanobacteria is considered to be one of the important mechanisms of Cyanobacteria bloom,and studies have shown that Cyanobacteria allelopathy can not only inhibit the growth of other phytoplankton in the environment and improve the competitive advantage of Cyanobacteria,but also can directly kill the shepherd at high trophic level,which causes the species to become the only dominant algae in the water,triggers Cyanobacteria bloom.Unfortunately,the current research on Cyanobacteria secretion focused on intracellular secretions,almost no studies of extracellular secretion.Therefore,we studied the extracellular secretions of Cyanobacteria as the object of study to explore the extracellular secretions of cyanobacterium and a kind of synthetic extracellular secretions-the effect of ethyl p-hydroxybenzoate on zooplankton and phytoplankton-zooplankton.The results show:(1)The effects of extracellular secretions and ethyl p-hydroxybenzoate on the mortality of Daphnia magna were studied:the extracellular secretions of copper microcystis and the LC50 of ethyl p-hydroxybenzoate at 24,48 and 72 hours were 7.84 x 106 cells/mL,3.44 x 106cells/mL,0.43 x 106cells/mL and 29.2mg/L,19.2mg/L and 3.51mg/L,respectively,that is,with the increase of concentration and treatment time,(2)The effects of extracellular secretions and ethyl p-hydroxybenzoate on the physiological characteristics of D.magna were studied:the extracellular secretions of copper microcystis and ethyl p-hydroxybenzoate have significant effects on the rate of heartbeat.The rate of heartbeat increased gradually with the increase of secretions.The effect of ethyl p-hydroxybenzoate on the rate of heartbeat was slightly different.In the fourth,the concentration of ethyl benzoate increased,the rate of heartbeat increased and then decreased.After 12hours,the effect of low concentration on heart rate was not significant,and the high heart rate was significantly decreased.(3)The effect of extracellular secretions and ethyl p-hydroxybenzoate on the motor capacity of D.magna davidianus showed that the motor capacity of D.magna davidianus improved as secretions increased and the content of ethyl p-hydroxybenzoate decreased significantly.(4)The effect of extracellular secretions and ethyl p-hydroxybenzoate on the interspecific relationship of phytoplankton-zooplankton:the higher concentrations of extracellular secretions of copper microcystis and the concentration of ethyl p-hydroxybenzoate Which significantly reduced the feeding efficiency of phytoplankton.This study demonstrates that the extracellular secretions of Cyanobacteria have a significant effect on the population of D.magna and Tetranychus cinnabarinus,in particular the high concentration directly affects the survival of the individual,and the low concentration can also significantly reduce the ability to transport,to harm its blood circulation system,thereby reducing its feeding efficiency of phytoplankton,that is,from the food chain point of view,Cyanobacteria extracellular secretions can promote the microcystis aeruginosa in the water which gain growth advantage,leading to the occurrence of blooms The The effect of ethyl p-hydroxybenzoate on the system of D.magna and Tetranychus urticae-D.magna davidianus was consistent with that of Cyanobacteria extracellular secretions,indicating that the substance was highly likely to be a allelopathy of Cyanobacteria extracellular secretions to produce the ecological consequences substance.The results of this study explored the effects of extracellular allelopathic substances on the ecological processes of aquatic ecosystems,provided a potential mechanism for Cyanobacteria bloom,and successfully demonstrated the specific mechanism of extracellular secretions.