LAUSR

Changes in the structure and abundance of plant rhizosphere microbial communities have direct correlation with plant health and fitness. Extensive studies have been carried out on growth inhibition effects of consecutive monoculture on several medicinal plants but there is paucity of information about its effect on Achyranthes bidentata Blume, a suitable species for consecutive monoculture. Our objective was to evaluate the shifts of soil microbial community structure under consecutive monoculture of A. bidentata. The 16S rDNA sequencing results showed that the bacterial communities in 10-year (10 Y) and 30-year (30 Y) monocultured soil samples were different in diversity and abundance from those in newly planted soil (1 Y) and control soil. There was significant enhancement in the abundance of Pseudomonas and Bacillaceae. Furthermore, DGGE profiles revealed distinct changes in Pseudomonas spp. with the increasing years of monoculture. The abundance of Pseudomonas aeruginosa was distinctly higher in consecutively monocultured plots than in the newly planted plot. The results from the LC-MS/MS analysis and in vitro interaction found that phytosterones were one of main substances in root and soil samples, and the allochemicals showed the positive interaction with the dominant beneficial species of P. aeruginosa W9. It is therefore suggested that consecutive monoculture of A. bidentata led to a distinct shift in rhizosphere bacterial community, with the enhancement of the plant beneficial bacteria. The result obtained from the studies are expected to be helpful to unravel the rhizo-biological mechanism of A. bidentata under consecutive monoculture and provide the basis for further understanding the roles of microbiome in overcoming continuous cropping obstacles for other monocultured plants.