| Erigeron canadensis is an exotic, invasive species from North American, which has now spread into many regions of China. This plant shows strong allelopathy to native species, which endangers agricultural production, biodiversity and so on. So it is very important to research its chemical invasion mechanism to prevent its spread to more zones. On the other hand, finding methods of rational development and sustained utilization of E. Canadensis may be a more scientific approach to controlling this rich natural resource.Therefore, both the allelopathy and the utilization of E. Canadensis, as well as the results, are discussed below.1. To establish a formal bioassay of eluviated matter, the effect of osmotic stress on biossay of allelopathy was first studied. Taken its results as a premise,the allelopathic potential of water extracts of Erigeron canadensis (WEEC) was investigated, using several receptors. The results showed that WEEC had many adverse effects on seeds and seedlings, such as a decline in germination rate, a delay in germination time; growth inhibition of roots; high concentrations caused the caulicle to be inhibited, while low concentrations caused the caulicle either to be inhibited or to be accelerated, depending on the species of the specimen.The stems of adult plants were lower and more slender when irrigated with WEEC; the distribution of photosynthetic products in root, stem, leaves and other parts was changed, and the dry matter accumulation was also restrained. Take maize as an example, the influence of WEEC on different growing development periods was:seedling stage>silking stage>filling period>ripening period> seed germination.Allelopathy of volatilility from E. canadensis was studied in a semi-closed container, and the effects of its allelochemicals released with volatilization or eluviations on acceptor plants were compared. The results showed that the seed germination and seedling growth were affected differently by volatile oil (VOEC) and its eluviations (abbreviate:aqua aromatic, AAEC). The acceptors’stem lengths were accelerated with low VOEC concentration and inhibited with high concentration, and the inhibitation of the stems was significantly smaller than that of the radix. In the treatment of AAEC, both stems and roots were strongly inhibited. Brassica cantpestris spp. Chinens was the most sensitive plant to the chemical components of VOEC, while the Sonchus oleraceus L. was the most easily influenced by AAEC. All these showed that the allelochemicals released with different modes could result in different responses of acceptors.The effects of naturally decomposed of E. canadensis plants on soil microbial communities, seed germination and seedling growth were also studied. It was found that, compared with th control samples, allelochemicals of decaying substance (DSEC) changed microbial communit structures with a decrease of bacteria ratio, and an increase of actinomyces and fungi ratios. Th results indicated that soil mixed with DSEC had a tendency to be changed from "bacteria-rich’ to "fungi-rich". Furthermore, the acceptors cultured on the soil with DSEC showed a decrease o germination rate and stem height, but the leaf area and biomass increased significantly.The results above indicated that WEEC, VOEC, AAEC, DSEC had different allelopathic potential, and the releasing mode of E. canadensis was various.2. Allelopathy dynamic changes of 3 main allelochemicals in E. canadensis (WEEC, VOEC, AAEC) were investigated with 3 acceptors,3 indexes during the growing season, and the relativity was analyzed between the changes and influence factors. It was found that the 27 curves were dissimilar, they were changed with the acceptors, indexes, growing periods. In general, the period that main stem growing quickest stage had the strongest allelopathy, and the bud stage was the weakest period. It also found that, besides the influence factors mentioned above, there some other factors showing significant correlated relationship with dynamic changes of allelochemicals in E. canadensis, such as solution concentration, releasing mode, interaction of allelochemicals, growth of different plant parts, mineral elements in soil and plants, and weather.3. The population structure and dynamics with which E. canadensis invaded was analyzed. The result indicated that Simpson index, Shannon index, Brillouin index of quadrats increased when allelopathy of E. Canadensis decreased, which suggested the allelopathy of E. Canadensis participated in the self-regulation of population. The correlation analysis showed significant or highly significant negative correlations between allelopathy and indexes. The relationship between them was exponential(p<0.05), which means the eluviated matter of E. Canadensis was an influential factor in the change of evenness and species diversities in plant communities having a dominant presence of E. canadensis.Photosynthetic capacity of E. canadensis was one reason for its marked dominance in various plant communities.Thoughitsnet photosynthetic rate was not any greater than that of accompanying species, such as Lactuca sibicica, the water use efficiency of E. canadensis increased and its transpiration rate decreased with its growth, which means the plant had strong photosynthetic ability and drought resistance, it was more adapted to high temperatures and dry environmental conditions in summer, thus showing a greater biological invasion ability.4. Allelochemicals extraction and separation of E. canadensis withthe bioactivity-guided fractionation and isolation principle were carried out. The result showed that there were abundant terpenoids, especially monoterpene, in VOEC. The most important allelochemicalwas limonene with the relative content of 55.49%. Allelochemicals in WEEC were benzoic acid and its derivatives, including phenylacetic acid, vanillin, vanillic acid, syringaldehyde, syringic acid, etc. Four compounds were isolated from water extract of E. canadensis with HSCCC, HPLC and repeating column chromatography. Thestructures of 3 compounds were determined by using chemical and spectral methods as syringaldehyde, luteolin, quercetin.5. Allelopathy mechanisms of E. canadensis were investigated. The result suggested the allelopathy mechanism on seedlingsincluded the restraint of water-absorbing capacity in seed germination, a decline in the content of soluble proteins, activity of SOD, POD, CAT and plant hormones (GH、GA、CTK、ABA) level changed. The effect on adult plants were the damage of photosynthesis, including the influence on the content of photosynthetic pigments, structure parameter and gas exchange parameters of leaves, and distribution of photosynthate.6. Except the activity of weed controlling, water extract of E. Canadensis showed an antagonistic activity on bacterial and fungal growth. The antibacterial activities of chloroform extract on streptococcus, acetone extract on salmonella, n-butanol extract on fungi, were the best. The inhibitory percentage of 20 g/L n-butanol extract on Alternaria anax Whetz was 88.63%, which showed similar bacteriostatic effects with 10 g/L mancozeb.The results of the antimicrobial test of essential oil showed that VOEC had a significant broad spectrum of antimicrobial activity against all 6 food-borne pathogens and 2 fungi tested. Especially, Shigella dysenteriae, Alternaria panax Whetz and Rhizoctonia solani were most sensitive to it. The inhibitory percentage of 20 g/L VOEC on Rhizoctonia solani was 100%, and 10,20 g/L VOEC showed similar bacteriostatic effect with 5,10 g/L mancozeb to Alternaria panax Whetz. |
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