Studies On The Allelopathy Of Several Submerged Potamogetonaceae Species On Planktonic Algae

The release of allelopathically compounds is an important trait developed by macrophytes against planktonic algae. Several submerged plants of Potamogetonaceae such as Potamogeton maackianus A. Benn., Potamogeton malaianus Miq., Potamogeton crispus L., were studied the allelopathically effects on algae Scenedesmus obliquus and Microcystis aeruginosa. By compared the intensive changes of allelopathy on different initial concentration of algae in co-exist systems in laboratory, threshold value of the allelopathy from the plants were evaluated for the first time. It was found that allelopathic effects depended on the algal initial concentration. Based on the antialgal function, the apolar ethyl acetate extracts of P. malaianus and P. maackianus were isolated, purified and identified. According to the algal bioassay, a new antialgal hydroxylated fatty acid was isolated successively from P. malaianus. In order to certify the allelopathic chemicals in the planting water, the apolar extraction of planting water of P. maackianus were analyzed, too. Furthermore, the allelopathic influences on algae enzymes and isoenzyme of POD, SOD, CAT, COD were investigated by means of PAGE. The main results are summarized as following: 1. The allelopathic effects of P. maackianus on S. obliquus at different initial concentrations were not the same though all tests presented algal growth inhibiting. 15±5g/8L P. maackianus performed significant growth inhibiting on S. obliquus at the initial concentrations of 10⁵,10⁶,10⁷ cell·L^-1, while less effects were observed when algal initial concentrations below or above this range. The allelopathic effects of P. maackianus on M. aeruginosa depended on the algal initial concentration more sensitively. 15±5g/8L P. maackianus performed significant growth inhibiting on M. aeruginosa at the initial concentrations of 10⁶,10⁷ cell·L^-1, while no effects were observed when the algal initial concentrations below or above this range. 2. The allelopathic effects of P. malaianus on different algae depended on algae specie and the algal initial concentration. 15±5g/8L P. malaianus performed significant growth inhibiting on S. obliquus at the initial concentrations of 10⁷,10⁸ cell·L^-1, while no effects were observed at the algal initial concentrations of 104 cell·L-1. P. maackianus with the same biomass performed significant growth inhibiting on M. aeruginosa at the initial concentrations of 108 cell·L-1, while no effects were observed at the algal initial concentrations of 105, 109 cell·L-1. 3. 15±5g/8L P. crispus presented significant growth inhibiting on S. obliquus at the algal initial concentrations of 106,107 cell·L-1, while no effects were observed at the algal initial concentrations of 105 cell·L-1. 15±5g/8L P. maackianus performed significant growth inhibiting on M. aeruginosa at algal initial concentrations of 105,106 cell·L-1. 4. A hydroxylated fatty acid was isolated from the ethyl acetate extract of P. malaianus. The compound was assigned the molecular formular of C18H30O2 which was speculated to be linolenic acid. The inhibition rate of Selenastrum capricornutum was up to 25% when the concentration of this compound was 24.2mg/L. 5. According to the identification of apolar extracts from P. maackianus and its planting water, some common compounds were found both in the planting water and the three antialgal eluant components: (1) m/z 395.4 [M+H]+, which was found to be the main compound in the planting water, No.1 eluant component and No.2 eluant component; (2) m/z 515.4 [M+H]+, which was found to be the main compound in the planting water and No.7 eluant component; (3) m/z 557.6 [M+H]+, which was found to be the main compound in the planting water and No.1 eluant component. These compounds or one of them would be the allelochemical from P. maackianus. 6. By means of PAGE, algal antioxidant enzyme, cytochrome-oxidase and their isoenzyme were investigated. Compared with the control, the enzyme levels of S. obliquus under the allelopathy from P. malaianus were influenced evidently. The electrophoretic band of POD varied and its activity declined, but the new electrophoretic band indicated that POD had resistant against allelopathy stress. SOD was more sensitive to allelopathy since its activity significantly declined and several electrophoretic band disappeared. The activity of CAT increased a little. All the results showed the injury of O2.-from allelopathy. The analyses of COD presented electrophoretic band disappearing and color fading, which indicated the influences on the process of oxidative phosphorylation.