Allelopathic Inhibition Of Cyanobacteria By Barley Straw And Its Mechanism

Algae blooms, in particular cyanobacterial blooms as a result of eutrophication have been a worldwide phenomenon. Seeking for an environmental-friendly, low-cost and high-efficient emergency control method for cyanobacteria blooms is one of the key issues to be solved in the field of Environmental Science and Engineering. The Allelopathic inhibition of algae by plants has showed enormous application potential in eutrophication and algae bloom control. Among them, the use of barley straw is by far the most successful application example.In this dissertation, applications and mechanisms of allelopathic algae control by plants, especially by the straw of vascular plant barley were reviewed. To give a broad background and offer comparisons to barley straw, the separation and identification of allelochemicals from natural plants and common algal inhibition mechanisms by these allelochemicals were investigated. Comparing to the widely reported validity of algal inhibition effects by occidental type of barley, effects and action modes of their oriental relative--Tibetan barley were studied; algicidal effects of eight different kinds of barley straw decomposings prepared by different procedures were systematicly compared, and by the use of non-linear mathematical model the general laws of this allelopathy were discussed; a estimatation of the potential algicidal effects of using oriental barley straw in typical eutrophic lakes and reservoirs in China was also performed. The natural chemicals in barley straw were screened, and key allelochemicals which could effectively inhibite cyanobacteria growth were isolated and identified by multipal chemistry analytical tools, and its mechanism was also studied on the single cell level. The oberservations in this work will provide a theoretical gist and technology guide for the use of barley straw methods in algal control filed; meanwhile this work could also contribute to the recycle and reuse of agricultural wastes like straws. The main original conclusions of this work are drawn as following:(1) Tibetan barley straw decomposing can effectively inhibit algae growth while the dosage was more than2.0g (dry weight)/L. Based on the single cell level study using flow cytometry, such inhibition was more algistatic mode rather than algicidal. The preparation process of decomposing was also optimized, a procedure of "cutting barley straw into about2cm long--high pressure heat sterilization--aerobic degradation under light" could give a best algal inhibition effect.(2) For the first time the mathematical modeling method was introduced into allelopathic algal inhibition research area, and the "An-Johnson-Lovett" model considering ecological limiting factors was used to describe inhibition effects of barley straw decomposings. Using Labview software and the nonlinear regression programme developed by this work, the allelopathic "dose-effect" relationship of eight different barley straw decomposings was found to fit well to this model, and the allelopathic effect curve was U-shaped, which indicated that high doses of barley straw decomposing can effectively inhibit the growth of algae, while the low dose could stimulate algal growth slightly. The result of estimatation predicted that the use of oriental barley straw in typical eutrophic lakes and reservoirs in China could efficiently inhibite the growth of cyanobacteria.(3) Using multi chemical analysis methods of plant natural products chemistry, the key allelochemicals were isolated from barley straw, and their structures were identified to be a couple of chiral chemicals (C27H26O11), namely salcolin A and salcolin B. The study of inhibition mechanism on a single cell level showed a difference between them:Salcolin A mainly inhibited the algal intracellular esterase activity and lead to membrane depolarization; while Salcolin B directly attacked the cell membrane of the algal cells. However, unlike inhibition mechanisms of other allelochemicals, both Salcolin A and B showed no directly influence on the center of photosynthesis, and did not cause a change of oxidative activity in algal cells.