AimsBacillus, a gram-positive bacterium, has multiple beneficial traits which help the plants in nutrients acquisition, either directly or indirectly. However, the mechanisms that mediate the positive or negative impact of Bacillus on exotic or native species are poorly understood. Our objective was to determine whether the quantitative and/ or qualitative differences in the Bacillus community present on the exotic Ambrosia artemisiifolia and the native Setaria viridis provide a competitive

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... ntage to the invader over native species. MethodsA. artemisiifolia monoculture, mixture of A. artemisiifolia and S. viridis and S. viridis monoculture were designed in the field experiment. Bacillus diversity in their rhizospheres was analyzed using 16S rRNA and their effects on the competitive growth of A. artemisiifolia and S. viridis were tested in greenhouse experiment.ResultsThe Shannon index, species richness, and evenness index of Bacillus diversity in the rhizosphere soil of A. artemisiifolia in the monoculture treatment were lower than in the mixture treatment. The relative abundance of Bacillus megaterium in the rhizosphere soil of A. artemisiifolia was higher than that in the rhizosphere soil of S. viridis. Whether Bacillus in the rhizosphere soil of A. artemisiifolia or B. megaterium inoculation enhanced the relative competitiveness of A. artemisiifolia and inhibited that of S. viridis by altering their carbon, nitrogen, and phosphorus concentrations. ConclusionsA. artemisiifolia invasion influenced Bacillus communities, especially B. megaterium. The higher abundance of B. megaterium in A. artemisiifolia rhizosphere creates higher levels of the available nutrient than that in native S. viridis.