Study On The Competition Mechanism Of Three Species Of Cyanobacteria

Eutrophication of water is a global problem of water pollution.Eutrophication will cause blooms,seriously threaten the health of aquatic ecosystems and humans,how to use economic and safe methods,to effectively control blooms for a long time has become one of the hotspots of scientists research today.There is a competition between microalgae species.The environmental conditions such as nutrient,light and temperature,all of which would effect the competition.In our study the common water bloom cyanobacteria,Microcystis aeruginosa,Phyllostachys pubescens and Pseudomonas aeruginosa were used as subjects,the common water bloom cyanobacteria,Microcystis aeruginosa,Phyllostachys pubescens and Pseudomonas aeruginosa were used as subjects,Inorder to study the competition between these three microalgae and explore its competition mechanism,the single-factor experiment was used to study these three algae growth condition and competitive behavior which were cultured in pure and mixed culture under different cell density,nutrient levels(super eutrophication,eutrophication,mesotrophy,olitrophy),light,temperature.The results were as follows:The effects of different environmental factors on the three algae under pure culture conditions are as follows.Under the oligotrophic,nutrient and eutrophic conditions,the biomass was positively correlated with the nutrient richness,while under the super-eutrophic conditions,the biomass decreased with the increase of nutrient concentration;In the range of 15 to 30℃,the biomass of the Phyllostachys pubescens was positively correlated with the temperature,but at 25℃ the OD value of the algae was not significantly different from that at 30℃.The biomass of the Phyllostachys pubescens was positive to light intensity.It grew well under 20~25℃,and it can still grow at a low rate under the low temperature of less than 20℃.At the same time,it can be inhibited at a high temperature,Pseudomonas aeruginosa could grow well under medium-intensity illumination between 90~120μmol/(m~2·s).The strong light has a certain inhibitory effect on its growth.Under the olitrophic,and sotrophic and eutrophic conditions,its biomass was positively correlated with the nitrogen concentration,while the maximum OD value was decreased under super-trophic conditions.The biomass of Microcystis aeruginosa was positively correlated with temperature,light intensity and nitrogen concentration.It means that Microcystis aeruginosa is more suitable to grow under high temperature and light intensity,and the upper limit of the environmental capacity of the algae is relatively large,which may also explain the existence of a large number of microcystis in summer and the sudden outbreak of Microcystis in some areas.The Phyllostachys pubescens is also suitable for growing under high temperature,light intensity and nitrogen concentration,while the Pseudomonas aeruginosa is suitable for growing under low temperature,low light and low nitrogen concentration.(2)Under the mixed culture of Microcystis aeruginosa was dominant in the condition that the temperature was higher than 25℃,the light intensity was higher than 120μmol/(m~2·s),and the nitrogen concentration was higher than 2.25.When the initial cell density of Microcystis aeruginosa was high,it had a more obvious,inhibitory effect on the Pseudomonas aeruginosa and the Pseudomonas aeruginosa almost does not grow.The Pseudomonas aeruginosa has a competitive advantage at the conditions that the temperature below 25℃,light intensity below120μmol/(m~2·s)and nitrogen concentration lower than 2.25.When the initial cell density is high.The inhibition of Microcystis aeruginosa was significantly reduced,and the growth of Pseudostellaria was better than in other cell density conditions.(3)The D.serrata had a competitive advantage under the condition that mixed culture of D.serrata and P.angustifolia,temperature higher than 20℃,light intensity is higher than 90μmol/(m~2·s),and the nitrogen concentration higher than 1.5-3.0 g/L.when the initial cell density of the Phyllostachys pubescens is high,its inhibitory effect on Pseudomonas aeruginosa is more significant than the other initial cell density conditions,and the competitive advantage is more obvious.However,the Pseudomonas sinensis has a competitive advantage under the conditions of low temperature below 25℃,low light intensity below 120μmol/(m~2·s)and low nitrogen concentration below 2.25.When the initial cell density of the algae is high,the inhibitory effect of the Phyllostachys pubescens is weakened,and the growth condition of the genus Pseudomonas is better than other cell density conditions.(4)Under the mixed culture condition of Microcystis aeruginosa and Microcystis aeruginosa,Microcystis aeruginosa has a competition when the initial density ratio of the two algae is 1:1 and 1:10,at a temperature higher than 27℃,light intensity above120μmol/(m~2·s)and nitrogen concentration higher than 2.25,the growth of Microcystis aeruginosa was better and the maximum cell density was greater.However,under the condition that the initial density ratio of the two algae is 10:1,the temperature is not higher than 30℃,the light intensity is not higher than 120μmol/(m~2·s),and the nitrogen concentration is not higher than 2.25.The algae accounted for a competitive advantage,and the growth of Microcystis aeruginosa was inhibited.The experimental results show that nitrogen concentration,illumination and temperature are still important factors in determining the competition of three algae.In addition,the initial density of each species has a great influence on competition.