Microcystis Allelopathy With Differences Between Species And Strains And Its Response To Temperature Changes

Microcystis,a dominant group of cyanobacteria,exist in most of the freshwater eutrophic water bodies from tropical to temperate zones,and have attracted much attention for their possible release of microcystins(MCs)and other harmful secondary metabolites.The inhibition of allelopathy mediated by harmful secondary metabolites of algal sources has been proved to be one of the main mechanisms of Cyanobacteria as the dominant species in the aquatic ecosystem,but the biological factors(such as different species of Microcystis)and environmental factors(such as temperature and illumination)are not clear.In order to investigate the differences of allelopathy between Microcystis in the same species and different strains of Microcystis,and whether the temperature changes would change the allelopathic effects of Microcystis,two species(Microcystis aeruginosa,Microcystis wesenbergii)and Microcystis in four strains were selected as the research object.The dominant species of Chlorophyta Scenedesmus quadricauda was used as the receptor material.The algae secretion method and the blue-green algae cocultivation were used to study the differences between intraspecific and strains allelopathy of Microcystis and the effects of temperature change on this effect.The main results are as follows:(1)The allelopathic inhibitory effect of M.aeruginosa on S.quadricauda was significantly higher than that of M.wesenbergii(P<0.05)at the optimum temperature of 25?,and there were significant interspecific differences.The allelopathic inhibitory effects of the non-toxic M.aeruginosa and M.wesenbergii were significantly higher than those of the corresponding toxic strains.For example,when the concentration of Microcystis secretion was 100%,The inhibition rate of non-toxic M.aeruginosa on S.quadricauda growth was 54%,which was significantly higher than that of Toxicola aeruginosa.The inhibitions rate of non-toxic and toxic M.wesenbergii were 37% and 23%,respectively,there was a significant difference between the strains,it shows that there was no necessary connection between allelopathy and toxic strains.(2)Temperature changes have an important effect on the Microcystis allelopathy.The inhibition effect of M.aeruginosa was significantly increased when the culture temperature was 20? and the concentration of secretions was 100%,but the inhibition effect of non-toxic M.aeruginosa and M.wesenbergii were significantly reduced,and the inhibition effect of toxic M.aeruginosa was significantly stronger than that of non-toxic M.aeruginosa(P<0.05).(3)At the culture temperature of 30?,the allelopathic inhibitory effect of M.aeruginosa and non-toxic M.wesenbergii were significantly reduced,and the temperature increased,resulting in a significantly higher allelopathy of M.wesenbergii than that of M.aeruginosa.(4)At 25?,blue-green algae cocultured for 6 days,the competitive advantage of M.wesenbergii against S.quadricauda was significantly higher than that of M.aeruginosa.And the inhibitory effects of 3 different initial ratios(3:1,1:1,1:3)of M.wesenbergii on S.quadricauda was significantly higher than that of M.aeruginosa.In contrast to the results of the secretions addition,the effects of cyanobacteria were mutual in co-culture,and the two species not only had the competition of resources,but also had allelopathy.(5)Under the condition of co-culture,the inhibitory effect of M.aeruginosa and toxic M.wesenbergii on the growth of S.quadricauda were significantly enhanced at 20?,which may be caused by lower temperature to produce more secondary metabolites of M.aeruginosa to adapt to the environment,and thus have a stronger inhibitory effect on the S.quadricauda.(6)Under co-cultivation conditions,the initial ratio of blue-green algae was 1:3,1:1,so that the inhibitory effect of M.aeruginosa on S.quadricauda was significantly enhanced at 30?,but the inhibition effect of M.wesenbergii was significantly stronger than that of M.aeruginosa,and the results were consistent with the results of the secretion test.The initial ratio of blue-green algae was 3:1.the inhibitory effect of non-toxic M.wesenbergii increased significantly,and the inhibition rate was 100%,which was significantly higher than that of toxic M.wesenbergii(P<0.05).If temperatures continue to increase,M.wesenbergii can be more competitive than other algae.In summary,the allelopathy effect of Microcystis has species/strain differences,and the temperature affects the growth of Microcystis itself or affects the activity of certain substances that have allelopathic inhibitory effects,which leads to the difference in the inhibition of Microcystis at different temperatures on M.wesenbergii.