Microbial community structure and its temporal changes in Rehmannia glutinosa rhizospheric soils monocultured for different years

• Microbial community was affected by both monoculture years and developmental time.
• A significant correlation existed between microbial biomass and metabolic activity.
• The ratio of cyclopropyl PLFAs to precursors was higher in monocultured soils.
• The amounts of pathogenic fungi increased with the extended monoculture.

Consecutive monoculture leads to a substantial decline in both yield and quality for Rehmannia glutinosa. The diversity of microbes in rhizosphere can affect plant health. The objective was to investigate the effects of consecutive monoculture of this plant on rhizospheric microbial community composition and catabolic diversity at different stages of plant growth. The results showed that the microbial communities were significantly affected by both longevity of monoculture and plant growth stage. The amounts of phospholipid fatty acids indicative of most microbial functional groups differed significantly between the newly planted and monocultured soils. In addition, a significant correlation was observed between the microbial biomass and the community metabolic activities. The cyclopropyl-to-precursor ratio (cy/pre), an indicator of physiological stress in microbial communities, was significantly higher in the monocultured soils than in the newly planted soil at both the root elongation and expansion stages. Furthermore, the amounts of two pathogenic fungi (Fusarium oxysporum and Aspergillus flavus) significantly increased with increasing years of monoculture. In conclusion, we revealed characteristic differences in the microbial community composition and functions in R. glutinosa rhizosphere after monoculture, which might be attributed to the changes in plant performance and root exudates.