Allelopathic Inhibitory Effects Of Hydrodictyon Reticulatum On Microcystis Aeruginosa

At present, the problem of global water eutrophication is getting worse. It stimulates algae aquatic phytoplankton to grow explosively, which results in water blooms, broking the balance and stability of aquatic ecosystem and threatening human health. Therefore how to control the growth of algae effectively has become a hot research topic recently. The method of making use of botanical allelopathy to removal algae has become increasingly popular due to its advantages of high efficiency, low cost and environmental friendly. It is largely significant to remedy eutrophic water.This paper briefly introduced the current situation, formation reason, harms of eutrophication and the incentive, harms of water bloom. The primary algal removal and control technologies were expounded. In the experimental section Hydrodictyon reticulatum and Microcystis aeruginosa which is typical of harmful algal bloom was taken as objects for study. The effects of H. reticulatum on the growth of M. aeruginosa were studied in both isolated culture and co-culture conditions. Nitrogen and phosphorus removal capacity of H. reticulatum was also tested. On this basis the inhibitory effects of the liquor cultured with H. reticulatum on the growth of M. aeruginosa were investigated further to prove H. reticulatum with allelopathy. At last, the allelopathic mechanisms of H. reticulatum on M. aeruginosa were studied by detecting the chlorophyll a contents, the superoxide anion radical (O2-) contents, the malonaldehyde (MDA) contents, the superoxide dismutase (SOD) activities of algae cells and the electric conductivity (EC), the OD260 value of algal extracellular fluid.The results showed that H. reticulatum could inhibit the growth of M. aeruginosa obviously as the highest suppression ratio was 98%. The inhibitory effects of H. reticulatum at different concentrations on M. aeruginosa were different. In the isolated culture and co-culture the strongest inhibitory effect occurred with 3g/L and 4g/L H. reticulatum, separately. The inhibitory validity was related to the comparative biomass of them. The inhibitory effects of H. reticulatum with the same concentration in the isolated culture were stronger than those in the co-culture. H. reticulatum had strong removal capacity on nitrogen and phosphorus. The decrease speed of the concentrations of nitrogen and phosphorus was in direct proportion to the concentrations of H. reticulatum. The highest decrease of nitrogen and phosphorus was 93.4mg/L and 4.58mg/L in 10 days, respectively. The growth of M. aeruginosa was inhibited by the liquor cultured with H. reticulatum markedly, and the inhibitory effects enhanced with the increasing of H. reticulatum concentration. The allelochemicals which released from H. reticulatum could hinder the generation of chlorophyll a and damaged the photosynthesis. Meanwhile, it induced algal cells to generate plenty of O2-, which caused lipid peroxidation and damaged the cellular membrane structure when it exceeded the clearance ability of SOD. The main product (MDA) of lipid peroxidation also altered the membrane permeability and made intracellular compounds (cytoplasm, nucleic acid, et al) release out, which resulted in the disintegration of M. aeruginosa.