|Other Abstract||The release of allelochemicals was an important trait developed by macrophytes against planktonic algae. It was believed that allelopathy existed only between foreign plants and native life-forms from the chemical ecological point of view. The allelopathical effects of Eloeda nuttallii (Hydrocharitaceae), which was one of the typical foreign plants, on Mycrocystis aeruginosa (FACHB905)，a local isolated species, were studied in this paper. In parallel, researches to identify the allelopathical effects of Vallisneria spiralis on M. aeruginosa were conducted. The experiments were performed in co-existing systems under different scale, together with cultivating M. aeruginosa in the liquor cultured with plants. The results showed that E. nuttallii could effectively inhibit the growth of M. aeruginosa in laboratory, while V. spiralis did not have obvious allelopathical effect on M. aeruginosa. The allelochemicals stigmasta-4, 22-dien-3-one, 4-methyl-, stigmast-4-en-3, 6-dione and its homolog were separated, identified and quantified from E. nuttallii. The relationship between the amount of allelochemicals excreted from E. nuttallii and the right living environment was demonstrated qualitatively. Some comments on how to use the allelopathical effects of E. nuttallii to improve the environment quality were suggested in conclusion. The results were summarized as followed:
1. The co-existing test of E. nuttallii and M. aeruginosa (FACHB905) showed that E. nuttallii could effectively inhibit the growth of M. aeruginosa. At the end of the 10-day period, the EC50 was 3.0 g (fresh weight) of E. nuttallii for 8 L M. aeruginosa liquor with the initial concentration of 105 cell / mL. As for 400 mL M. aeruginosa liquor, the EC50 was 0.2 g (fresh weight) of E. nuttallii. The results indicated that the allelopathical effect between E. nuttallii and (FACHB905) was repeatable in a certain range.
2.Under different nutrient levels and the luminous intensity, the liquor cultured with V. spiralis have no obvious allelopathical effects on M. aeruginosa. The result was consistent with the opinion of Alastair (2003) who proposed that allelopathy existed only between foreign plants and native life-forms.
3.The allelochemicals excreted to the surrounding water from E. nuttallii in non-volatile status.
4.Stigmast -4-en-3, 6-dione (molecular formula was C29H46O2, molecular weight was 426), its homolog (MF was C28H42O2, MW was 412) and stigmasta-4, 22-dien-3-one, 4-methyl- (MF was C30H49O, MW was 424) as allelochemicals from E. nuttallii were successfully separated and identified by thin-layer chromatography (TLC), gas chromatography-mass spectrometer (GC-MS), liquid chromatography-mass spectrometer (LC-MS) and nuclear magnetic resonance (NMR) for the first time. Stigmast -4-en-3, 6-dione was the main allelochemical extracted from E. nuttallii. The concentration could reach 4 ppm in dry powder. The inhibition rate was 48% with 96-well plate method.
5.Under different environmental conditions, inhibitory effects of the liquor cultured with E. nuttallii on M. aeruginosa indicated that the amount of allelochemicals excreted from E. nuttallii was regulated by the surroundings. Under stress, e.g. restricted light or limited nutrients, the allelochemicals excreted from E. nuttallii would increase in amount. Therefore, it is essential to decrease the eutrophic level first and foremost, then make use of phyto-allelopathy against excess reproduction of algae in eutrophic lakes. It would be a long-term and slow process to control algae by phyto-allelopathy.|