| The release of allelochemicals is an important trait developed by aquatic plants against planktonic algae, and use of allelochemicals derived from plants may become a promising approach to control harmful algae blooms in eutrophicated water bodies. In this study, incubation experiments were conducted to investigate the allelopathical effects of the extracts from three typical foreign plants, Magnolia grandiflora, L, Sophora japonica cv. Pendula and B. s. var. sinica, on Mycrocystis aeruginosa. All these woody plants could effectively inhibit the growth of M.aeruginosa (FACHB-905)in laboratory. Then the allelochemicals derived from Magnolia grandiflora, which produced the best inhibitory effect against Mycrocystis aeruginosa were extracted, isolated and identified. The inhibition experiments indicated that the active allelochemicals belonged to the families of alcohols, ketones and esters. The main objective of this study was to provide more information for screening and development of new algaecides with high efficiency, economical feasibility and ecological safety. Results obtained in this study showed as follows.(1) The extracts of Magnolia grandiflora L, Sophora japonica cv. Pendula and B. s. var. sinica could effectively inhibit the growth of M.aeruginosa and the inhibitory effect increased gradually with the concentration of the extracts added. When the working concentration was 8g/L, after seven days incubation, the inhibition rates of the extracts from the three woody plants could reach 97.75%, 90.29% and 96%, respectively.(2) The allelochemicals of Magnolia grandiflora were preliminary isolated by the means of ethanol solvent extraction, and the best inhibitory effects were observed in N-hexane phase and N-butanol phase. The inhibition rate of N-hexane phase during incubation period reached 96.03%; and that of the N-butanol phase was also up to 98.04%. The inhibition rate of allelochemicals of Sophora japonica cv.Pendula during incubation period reached 99.89%, which was observed in N-hexane phase. The allelochemicals of B. s. var. sinica was also isolated, and the best inhibitory effects were observed in ethyl acetate phase and aqueous phase. The inhibition rate of ethyl acetate phase during incubation period reached94.59%; and that of the aqueous phase was up to 90.08%.(3) The extracts of Magnolia grandiflora obviously affected cell structure and some physiological indexes which contributed to inhibition of Microcystis aeruginosa growth. Under Magnolia grandiflora extract treatment, cell ultra-structure, especially the chloroplast and mitochondria, of Microcystis aeruginosa was destroyed and finally disintegrated. Membrane permeability was consistent with the degrees of cell membrane destruction under Magnolia grandiflora extract treatment.SOD activity increased during early period then decreased; The content of soluble protein in algae body decreased in almost a straight line.(4) The allelochemicals of Magnolia grandiflora were extracted by the means of ethanol solvent. By the phytochemical analysis, 33 compounds were isolated using silica gel column and Sephadex LH-20 column and identified by GC-MS. Following compounds were included in the active allelochemicals: 1-Heptatriacotanol; Chlestan-3-ol; 9,10-Secocholesta-5,7,10(19)-3?25,26-triol; 2H-cyclohepta[b]furan-2-one; 3,3a,4,7,8,8a-hexahydro-7-methyl-3-methylene-6-(3-oxobutyl)-; 6-[1-Hydroxymethylvinyl]-4,8a-dimethyl-4,8a-hexahydro-4a,5,6,7,8,8a-naphthalen-2(1H)-one and Mono(2-ethyl)phthalate. |
