| Hangzhou bay coastal wetland was the transition zone of coastal wetland from north to south in our nation, which played an extremely important role in maintaining the balance of regional ecological systems, providing habitat, conservation of biodiversity and to withstand and weaken the ocean natural disasters. It was an indispensable green barrier of region social and economic development, and it had an important significance of ecosystems and biodiversity protection. With the formation of Hangzhou bay industrial zone, the coastal tidal wetlands was rapidly reclaimed and utilized, the area of native wetland was sharply dropped, and the native wetlands vegetation was severely damaged, and in addition to the invasion of exotic species such as Solidago canadensis, Conyza canadensis, etc., the ecosystem integrity and security of nature and agriculture were under a serious threat. Therefore, to maintain wetland ecological environment and to restore and reconstruct degraded wetland ecosystem were important issue that currently facing our whole mankind. Phragmites communis was a rhizomatous herb-grass with strong ability of asexual reproduction and resistibility and competitiveness, and it was a native plant in Hangzhou bay. Through ongoing field investigation we found that a single P. communis communities keep a long-term stability and other weeds rarely invade in the communities, the phenomenon indicated that P. communis had a certain degree inhibition of the growth of other nearby plants, and that make it in a dominant position in the competition. However, it was not clear that whether the reason was related to the allelopathy of P. communis or not. And if it did have allelopathy, what were allelochemicals that affected other species? Therefore, the study of reeds allelopathic effects and isolation and identification of its potential allelochemicals conducive to further searching of the competitive mechanism between the P. communis and other wetland plants. And it had important guiding significance to the scientific management and ecosystem restoration of Hangzhou bay wetland and even global wetland. Besides, it could provide references for the rational use of P. communis resources and could help to develope new biogenic herbicides. In this thesis, we first studied the allelopathic effects of different tissues of P. communis on4plants(S. canadensis, Sesbania cannabina, C. canadensis and Taraxacum mongolicum) which were common in Hangzhou bay wetland, and explored the allelopathic potential and the main tissue that the allelochemicals came from. Then S. Canadensis which was the main invasive plant in Hangzhou bay was taken as a recipient for researching the allelopathical mechanism of P. communis. Finally, by biological testing for active tracking, and through leaching, extraction, separation by silica gel column chromatography and identification by gas chromatography-mass spectrometry(GC-MS), we isolated and identified the allelopathic active substances of P. communis, and then tested and verified their allelopathic activity. The main conclusions were followed as:(1) P. communis had allelopathic effects to these4recipient plants. S. canadensis, Taraxacum mongolicum and C. canadensis were sensitive to allelopathy, while Sesbania cannabina was insensitive. Allelopathic effect of P. communis with characteristics of double concentration effects, which is "low promoting high inhibiting"; In descending order, allelopathic effects in different tissues of P. communis is leaf> stem> root, leaves may be an important storage tissue of P. communis allelochemicals.(2) Allelopathy of P. communis affected on the photosynthesis of S. canadensis, including leaf stomatal openness and the light response capability. The net photosynthetic rate and stomatal conductance were not inhibited under lower concentration (2.5%) of leaves extracts, but they were significantly inhibited under higher concentration10.0%). And the effective photosynthetic function duration was shortened under higher concentration treatments. While with the concentration of extracts increasing, maximum net photosynthetic rate, light saturation point and apparent quantum efficiency presented a trend of promotion in lower concentration and inhibition in higher concentration. With the concentration increasing, the dark respiration rate decreased, although the dark respiration rates of each treatment were significantly higher than CK.(3) With the increase of extract concentration, cumulative growth of basal diameter and height of S. canadensis was significantly decreased while the amount of deaths was significantly increased; Chlorophyll content keep decreasing with processing time prolonged, and the higher concentration, the lower chlorophyll content, while carotenoid content was increased first and then decreased; When treated in a low concentration10.0%), the activities of peroxidase (POD) and superoxide dismutase (SOD) became stronger with processing time prolonged, but when the concentration continued to rise, they both presented an increased first and then decreased trend; Catalase activity (CAT) and malondialdehyde (MDA) content increased when the concentration of extract increased, and both increased with processing time prolonged; Soluble protein content and root activity decreased with higher concentration, and the trend was exacerbated with prolonged processing.(4) Allelochemicals in P. communis was extracted by sistilled water, then organic solvent extraction was carried out to make a preliminary separation. After biological testing from different extraction phases, we selected a high active phase, n-butanol phase. Further separation of n-butanol phase was conducted by silica gel column chromatography and eluting with organic solvents of different polarity. Using the bioassay method again to select the most active fractions Fr.5, Fr.6, Fr.7, Fr.9, Fr.10, and then use GC-MS to detect and identify the organic compounds contained in them. Allelochemicals from P. communis were initially identified. The results of isolation and identification showed that compounds wherein was very complex, mainly sugars, alcohols, benzene, organic acids, ketones, amides and esters. There mainly was11organic compounds in Fr.5, including organic acids, alcohols, sugars, etc., wherein the relative content of1,2,3,4-Butanetetrol is63.02%, which is the highest in Fr.5. There was15kinds of organic compounds in Fr.6, including organic acids, alcohols, sugars, esters, ketones, etc.. Similarly, the relative content of1,2,3,4-Butanetetrol is the highest, which is53.55%. There was15kinds of organic compounds in Fr.7, including organic acids, alcohols, sugars, esters, etc., wherein the relative content of1,2,3,4-Butanetetrol is24.22%, and which is the highest one. There was12kinds of organic compounds in Fr.9, including organic acids, esters, sugar, amide, etc., wherein the relative content of Dibutyl phthalate is27.79%, which is the highest one. There was22kinds of organic compounds in Fr.10, including organic acids, esters, sugar, amide, etc.. Similarly, the relative content of Dibutyl phthalate is the highest, which is18.69%.(5) According to GC-MS detection results,14kinds of suspected allelochemicals were selected. Applying the corresponding exogenous compounds as an alternative, their allelopathic activity was verified by biological testing methods. The results showed that the allelopathic activity of those14kinds of potential allelochemicals were different from each other. The allelopathic inhibition of Methyl hexadecanoate,(Z,Z)-9,12-Octadecadienoic acid, Phenethylamine and2-Methyl-2-propen-l-ol was stronger than the rest of allelochemicals. In addition, among the compounds identified by GC-MS, Dibutyl phthalate, Methyl hexadecanoate, Oleic acid,(Z,Z)-9,12-Octadecadienoic acid and Acetamide, N,N-diethyl-had been reported in some studies that were related with allelopathic substance, and was shown to have allelopathic effects. While Vanillomandelic acid, Phenethylamine, and2-Methyl-2-propen-l-ol these three kinds of allelochemicals had not been reported in related studies. |
PDF Full Text Request