Rhizosphere Azotobacter Effect Of Eupatorium (Ageratina Adenophora) Invasion Force

Invasive plants commonly have caused severe damage to the local ecological system and produce huge economic losses. Therefore, exotic plant invasion has been becoming a global problem. Although there have been a lot of research works on plant invasion, so far the mechanism of the plant invasion has not yet to be clarified. In recent years, the research works have demonstrated that the invasive plants may change the rhizosphere soil microbial community by which to enhance themselves invasion power. For example,"Accumulation of local pathogens hypothesis, ALPH" predicts that exotic plants can accumulate pathogens for local plants in the invaded habitat and thus gain competitive advantage indirectly."Microbial positive feedback hypothesis, MPFH" shows that invasive plants can increase the number of the soil azotobacter, ammonia-oxidizing bacteria and fungi, by which to accelerate soil nutrient cycling and further to promote the growth of invasive plants.In this study, nitrogen-fixing bacteria (NFB) isolated from rhizosphere soil of invasive plant Ageratina adenophora and local plant species were subject to screen out their ability of producing indole compounds,siderophore and dissolving phosphate salts. Then their effects on germination and seedlings growth of A. adenophora, the native plants and the economic crops were detected using water agar culture. Several main conclusions were made:1.The ability of rhizosphere NFB producing indole compounds, siderophore and dissolving phosphate salts were related to their isolation sources and phylogenetic position.In total, the tested367NFB strains were distributed in47OTUs and phylogenetically close to22genera. Relatively, the ability of strains decreased to a less degree from producing indole compounds, producing siderophore and the ability of dissolving phosphate salts. Moreover, the NFB strains from A. adenophora showed higher level of above three indicators than those from other plant species.2.There are different effects of NFB strains on the germination and seedlings growth of A. adenophora, the native plants and the economic crops.The effects of NFB strains on the germination and seedlings growth of A. adenophora, the native plants and the economic crops were evaluated. Totally, the selected27strains from different OTUs showed adverse influence on the germination and growth of native plants and crops. Among them,7strains significantly inhibited the growth of Triticeae Dumort,10strains inhibited the growth of Nicotiana tabacum,14strains inhibited the growth of Isachne globosa (Thunb.) Kuntze and17strains for Polygonum multiflorum Thunb. On the contrast,47strains were tested for their ability to promote the growth of A. adenophora and most of them showed positive effects. Among of them,12strains significantly enhanced the growth of A. adenophora.3. Strains from the rhizosphere of A. adenophora had a better role in promoting itself growth than those from other plant species.Among those strains being able to promote the growth of A. adenophora,73%of strains were obtained from the rhizosphere of A. adenophora, but only27%of strains from the local plant species.In conclusion, our results showed that A. adenophora has changed soil microbial community structure during the invasive process and can accumulate a number of azotobacter by which benefits its own growth but harmful to the native plants, finally result in its successful invasion indirectly.