| Microcystis aeruginosa was overspreading all over the world, especially in severely eutrophicated water bodies. The heptapeptide compound produced by single cell cyanobactcria not only caused human liver cancer, but also affected regular growth of aquatic plant and animal, at least leaded to the serious ecosystem unbalance. Therefore, control of the"ecology cancer"was taken seriously by many countries in recent years. However, breakthrough development in this aspect has not been made as yet, in spite of substantive investments and abundant research work.With studies on algae allelopathy developed, some researchers suggested this may be the effective approach to solve harmful algae blooms lately. Current research work focused more on the impact of aquatic plants on algae, but the study of terrestrial plants was less emphasized. The purpose of this study was aimed to explore a novel approach in biological control of Microcystis by terrestrial plant.Our preliminary experiment showed that the water-soluble extract of leek can inhibit the growth of Microcystis aeruginosa (FACHB-905) effectually, especially when the extract was treated by high temperature. This study was conducted to investigate the effects and mechanisms of the water-soluble extract of leek on Microcystis aeruginosa under different designed conditions including pH, light intensity, aeration, initial concentration of algae, and the allelochemicals of leek was preliminary isolated. In additon, the qualitative relationship between the allelochemicals extracted from leek and the working conditions was analyzed. The effective uses of the allelopathical effects of leek extract to improve the water environment quality were also suggested and discussed in the paper.The results obtained were summarized as follows:(1)The inhibitory effect of single allelochemicals without pretreatment on Microcystis aeruginosa growth was not obvious, and the type and amount of solvent played a very important role when the allelochemicals took effect.(2)The water-soluble extract of fresh leek treated by high temperature inhibited Microcystis aeruginosa (FACHB-905) growth effectually. After 7 days incubation, the log-linear correlation existed between the inhibition rate and the concentration of the extract, and the EC50 was 0.808 g /L .(3)The inhibitory effect of leak extract treated with high temperature was affected by pH, light intensity, aeration and initial concentration of algae, which indicated that the apparent inhibitory effect of leak extract during incubation period was integrated with the interaction between such factors. In this experiment, the optimum conditions for the allelopathy were as follows: pH9.5, low light intensity (1000Lx), aeration, initial concentration of algae 106,107 ind / L.(4) The water-soluble extract of leek treated by high temperature obviously affected cell structure and some physiological indexes which contributed to inhibition of Microcystis aeruginosa growth. Under leak extrat treatment, cell ultra-structure of Microcystis aeruginosa was destroyed and finally disintegrated. Chlorophyll a content and photosynthetic rate declined evidently from the beginning of the treatment while respiratory rate, SOD activity and the content of soluble protein increased during early period then decreased;. Membrane permeability andMDA accumulation was consistent with the degrees of cell membrane destruction under leak extract treatment.(5)The allelochemicals of leek was preliminary isolated, and the best inhibitory effects were observed in N-hexane phase. The inhibition rate of N-hexane during incubation period reached higher than 90%; and that of the aqueous phase was also higher than 80%. The EC50 of N-hexane phase and aqueous phase were 0.26mg / L and 0.81mg / L, respectively. The inhibitory effects of N-hexane phase on algae growth were better than previously reported allelochemicals. Therefore,N-hexane phase of leak extract will have a promising application in algae control.
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