Preliminary Study On Invasion Mechanisms Of Three Asteraceae Plants And Biological Control Of Alternanthera Philoeroides

In order to investigate the soil physical and chemical properties and biochemical activity invased by three asteraceae plants and their possible invasion mechanisms, we collected soil samples from the rhizosphere of Ageratina adenophora,Mikania micrantha and Bidens pilosa to measure their physical and chemical properties and strength of the biochemical activity in Yunnan Province. From the results, we can find that there are no significant difference on PH and water content. Determination of soil physical and chemical properties showed that the organic matter, total N, available K levels of invased soil samples of three asteraceae invasive plants were significantly higher than that of mixed native plants. And soil samples which invaded by Ageratina adenophora have the highest organic matter content of 30.42g/kg, mixed native plants have the lowest organic matter content of 16.35g/kg. All values of physical and chemical properties of soil samples which invaded by Ageratina adenophora were significantly higher than that of other samples. Organic matter, total N and available K content of soil samples of Mikania micrantha invasion area were significantly higher than that of Mikania micrantha and mixed native plants; Organic matter, total N, available N and available K content of soil samples of Bidens pilosa invaded area were significantly higher than samples of mixed native plants. The results of biochemical activity of soil samples show that:The nitrification potential and ammonification intensity of soil samples of areas invaded by three invasive asteraceae plans were higher than that of mixed native plants soil samples. Ihe nitrification potential of soil sample of Mikania micrantha invasion area has the highest value, followed by Ageratina adenophora, but the ammonification of soil sample invaded by Ageratina adenophora has the highest intensity; the denitrification of soil sample of Bidens pilosa invasion area has the highest intensity, while the sample of mixed native plants area has the second highest intensity and the soil sample of Ageratina adenophora has the lowest denitrification intensity. Overall, the physical and chemical and biochemical parameters of the soil sample of mixed native plants were generally lower than that of the invaded soil samples. Present study suggests that the invasion by Ageratina adenophora,Mikania micrantha and Bidens pilosa had more significant effects on soil ecology than that of local plants. The invasion of alien plants can cause changes in soil physical and chemical properties. Alien plants can also improve the level of soil nutrients in invasion areas, plunder of resources and crowd out native plants.Interaction between invasive plant and soil microbial community is an important aspect to understand the plant invasiveness and susceptibility of receptive communities. In present study, PCR-DGGE was conducted to analyze the bacterial community in the rhizospheric soil, which were heavily invaded, newly invaded or non-invaded by two alien invasive weeds, Mikania micrantha and Bidens pilosain in Haikou and Guangzhou city. China. The analysis of DGGE showed some regularity .Firstly, we analysed soil samples invased by different invasive plants. From the samples of Mikania micrantha, we found that the soil samples from heavily invaded site and newly invaded site by Mikania micrantha in Haikou have the highest similarity. From the samples of Bidens pilosa, samples from heavily invaded site and non-invaded site by Bidens pilosa in Haikou have the highest similarity. Secondly, we analysed samples from different invaded sites. From the samples of Guangzhou, we found that the soil samples from non-invaded site by Bidens pilosa and non-invaded site by Mikania micrantha had the highest similarity. From the samples of Haikou, we found that the samples from heavily invaded site and newly invaded site by Mikania micrantha had the highest similarity. From the results of sequencing and alignment of the specific bands, we can infer that invasion of Mikania micrantha and Bidens pilosa in Guangzhou and Haikou may modified soil microbial community composition. The bacteria's quantity of Bacilli,Proteobacteria and some other bacteria in the soil were changed. All those results suggested that the invasion of Mikania micrantha and Bidens pilosa can modify soil microbial community composition, probably creating favorable soil environment to benefit their invasion.From the natural Alternanthera leaves, we obtained 11 strains of pathogenic fungi. Among them, one strain named NT008 has a strong pathogenicity to Alternauthera. Under the control condition, we assayed the virulence of strain NTOO8, testing the influence of herbicides on NT008 mycelia growth and spore germination, and testing the influence of herbicide mixed with the pathogenic fungi. The results show that, strain NT008 has a strong virulence on Alternanthera. Different kinds of herbicides or differernt concentrations of one herbicide produced different virulence to Alternanthera. According to manufacturer's recommendation, optimal concentration of 3 herbicides (glyphosate 200mL/mu. Butyl 2,4-dichlorophenoxy acetate 300mL/mu Starane 50mL/mu) were tested. With concentration of 2050μg/mL glyphosate,2867μg/mL 2,4-D dimethyl ammonium and 166.7μg/mL Starane, the inhibition rate on mycelia growth of strain NT008 were 43.23%,96.30% and 37.07%, respectively. The inhibition rate 2,4-D dimethyl ammoniumon on spore germination of strain NT008 was 20.4%, while the inhibition rate of glyphosate and Starane were 8.1% and 3.1%, respectively. The results of strain NT008 spores mixed with herbicides indicated that glyphosate mixed with strain NT008 spores had a good effect, and 2,4-D dimethyl ammonium agent second.