Juglone's Allelopathic Inhibitory Effect On Microcystis And Scenedesmus And The Influence Of Interspecies Competition

Cyanobacterial bloom is becoming a severe environmental problem globally due to aquatic eutrophication and climate warming.Bloom-forming cyanobacteria can produce odor and smelly metabolites which decrease water quality.Some cyanobacterial species release cyanotoxins along with the cell lysis,which threatens aquatic food webs and human health.Thus,how to control or eliminate cyanobacterial blooms has been becoming an urgent environmental issue.A novel biological technology using allelopathic effect of macrophytes to control the harmful algal bloom has been focused in water environmental field.Allelochemicals are easy getting and being environmentally-friendly.Juglone,5-hydroxy-1,4-naphthoquinone,is one of the most recognized allelochemicals produced by trees of the genus Juglans.In this paper,we explored the allelopathic inhibition of juglone on the growth and physiological performance in Microcystis aeruginosa and Microcystis wesenbergii,which are main cyanobacteria species in cyanobacterial bloom.In addition,we also explored the allelopathic inhibition of juglone on the growth and photosynthetic performance in eukaryotic green algae,Scenedesmus obliquus.And the effects of juglone on inter-specific competiton between were Microcystis aeruginosa and Scenedesmus obliquus.The results are provid the theoretical support for the screening of allelopathic induced by plant which can inhibite harmful algae.Also they can help assess the ecological safety of allelochemicals.The main conclusions of this study are as follows:1.Allelopathic inhibition of juglone on the growth and physiological performance in Microcystis.The present study evaluated the allelopathic effects of juglone on the toxic Microcystis aeruginosa and notoxic Microcystis wesenbergii.Results showed that 0.3-0.9 mg L-1 juglone notably depressed the population proliferation and photosynthetic performance of M.aeruginosa and M.wesenbergii.The growth inhibition rate of M.aeruginosa and M.wesenbergii treated by 0.9 mg L-1 juglone reached to 75% and 67% after 11 day exposure.The antioxidant enzyme activity(SOD and CAT)in juglone groups changed significantly,suggesting the juglone-induced oxidant stress in M.aeruginosa and M.wesenbergii cells.Also cell membrane and organelle were damaged.In addition,juglone exposure enhanced the intracellular microcystins production per cell,but had no impact on the extracellular microcystins release.Combined with the decreased cell abundance,the total amount of microcystins did not increase in cyanobacterial culture medium.2.Allelopathic inhibition of juglone on the growth and photosynthesis in S.obliquus.The cell density of S.obliquus without juglone constantly increased exponentially during the experimental period.Juglone were decreased the cell density of S.obliquus.The higher the juglone concentration was,the more S.obliquus cell density was inhibited.At the end of the experiment,the inhibition rate of S.obliquus cell density was 40% at 0.9 mg L-1 juglone.There was also different inhibition regulation on different biomass of algae cell.The population size of S.obliquus was changed by juglone,but it has no effect on the photosynthesis.Generally speaking,trade-offs existed between the defense of juglone and colony formation.3.Effect of juglone on interspecific competitionThe inhibition effect on Microcystis aeruginosa by juglone is stronger than Scenedesmus obliquus in both monocultures and co-culture system.The cell density of M.aeruginosa and S.obliquus were both decreased in co-culture system.The higher the juglone concentration was,the more cell density was inhibited.Juglone had no significant effect on the growth rates and competition outcome of mixed cultures of Microcystis and Scenedesmus.When mixed at different initial ratios,the two algae have different competitive advantages and are density dependent.In photosynthesis,juglone had no effect on the photosynthetic activity of M.aeruginosa,but promoted the photosynthetic activity of S.obliquus.In conclusion,the harmful cyanobacteria Microcystis was inhibited by the juglone while adversely affecting the Scenedesmus.The above results provide a scientific basis for the screening algal allelochemicals and assess the safety of juglone.