Dynamic Of Interspecific Competition Between Microcystis Aeruginosa And Scenedesmus Quadricauda Affected By Three Kinds Of Pollutants

Water body eutrophication becomes the environmental problem of freshwater lakes and reservoirs demanding prompt solution all over the world in recent years.Eutrophication leads to harmful algae blooms which are harmful to aquatic ecosystem.There are a lot of algae species distributing in water body around the world,Microcystis is the commonest when cyanobacterial blooms occur during summer and autumn in a majority of eutrophicate water body.But as a kind of prokaryote,cyanobacteria is more sensitive to pollutants comparing with eukaryotic algaes.Under the background of world water pollution sustainable increasing,cyanobacteria may lose their competitiveness due to resistance weakened which may lead different types of algae blooms,or Microcystis may synthesize more harmful substance for other aquatic organisms to maintain their competitive advantage.In order to investigate what effects of increasingly environmental pollution will influence the dynamic changes among phytoplankton community,my research employed Microcystis aeruginosa and Scenedesmus quadricauda,which are common species in water blooms,to analysis the effect of microcystis and Scenedesmus suffering from three kinds of pollutants(norfoxacin,cadmium and eythlparaben)then discuss tendency of competitive dynamics between two algaes.The results show:(1)When conduct short-term single culturing,after 4 days,chl.a contents of M.aeruginosa were inhibited by 30?g/L norfloxacin about 39%.But chl.a contents of S.quadricauda were inhibited by 40mg/L norfloxacin just about 17%.When conduct co-culturing exposed to 5?g/L norfloxacin,despite M.aeruginosa was more inhibited by norfloxacin and S.quadricauda was not sensitive to norfloxacin,in the condition that M.aeruginosa was dominant in intial ratio(M.aeruginosa to S.quadricauda is 3:1),stress from norfloxacin enhanced inhibition of M.aeruginosa to S.quadricauda.The performance was that S.quadricauda chl.a content of treatment group could not be detect at 12 day but S.quadricauda chl.a content of control group still kept in a certain level.(2)When conduct short-term single culture,after 4 days,chl.a contents of M.aeruginosa were inhibited by 3mg/L cadmium over 90%but chl.a contents of S.quadricauda were inhibited by 3mg/L cadmium just about 31%.When conduct co-culture exposed to 0.5mg/L cadmium,competitiveness of M.aeruginosa to S.quadricauda was alleviated in any intial ratio between 2 algaes.The proportion of S.quadricauda among co-culture system showed proportion of treatment group was higher than control group all the time.(3)When conduct short-term single culture,after 5 days,chl.a contents of M.aeruginosa were inhibited by 16mg/L ethylparaben about 28%but chl.a contents of S.quadricauda were enhanced by 16mg/L ethylparaben about 19%.But when conduct co-culture and the initial ratio of M.aeruginosa to S.quadricauda was 1:1,ethylparaben was beneficial to competitive advantage of M.aeruginosa to S.quadricauda and this phenomenon would sustain for a long time.(4)The one of the major reason why competitiveness of M.aeruginosa is enhanced by ethylparaben may be that synthetic amount of microcystins is enhanced because of ethylparaben stress.In my reaserch I found that:When exposed to 16mg/L ethylparaben after 5 days,compareing with control group,MC-LR contents of unit M.aeruginosa cells in treatment group increased from 1.67ng/10~6cells to 2.55ng/10~6cells.According to the above research results,M.aeruginosa was more sensitive to three kinds of pollutants than S.quadricauda in single culturing condition,but there were diffirent competition results in co-culturing condition:cadmium was helpful S.quadricauda to resist competitive inhibition effect from M.aeruginosa;norfloxacin was helpful M.aeruginosa to maintain blooming in high initial ratio;ethylparaben was helpful M.aeruginosa to maintain blooming in equal initial ratio.At present,in eutrophic water body dominated by microcystis,increasingly serious norfloxacin and ethylparaben pollution may lead to allelopathic effect of M.aeruginosa enhanced,which will cause severe hazard to other aquatic organisms,occupy more niches in a shorter period of time,replace other phytoplanktons among phytoplankton communities and decrease biodiversity in water body.In order to alleviate even evade those potential ecological risks,people need to reduce pollutants emission especially antibiotics and preservatives.