Bacterial community dynamics in the rhizosphere of a long-lived, leguminous shrub across a 40-year age sequence

Numerous studies have investigated rhizosphere soil microbial communities. However, the question on how composition and diversity of rhizosphere communities shift with plant age has received far less attention. We collected rhizosphere and bulk soils from replicated plots representing 1, 8, 14, 31, and 40-year-old stands of the leguminous perennial shrub Caragana liouana at a research site in Shanxi, China. The bulk soils were used to analyze physicochemical properties. The rhizosphere soils were used to analyze the diversity and structure of rhizosphere bacteria communities by using barcoded pyrosequencing of the 16S rRNA gene. We found that different stages of plant development harbored unique rhizosphere bacterial communities. The α-diversity showed a significantly positive correlation with stand age suggesting that the rhizosphere bacterial community benefits from the establishment and development of C. liouana. We also found that the composition of the bacterial community was shaped primarily by stand age. The bacterial rhizosphere community composition did not change much from 8- to 31-year-old stands, but then dramatically changed at the 40-year-old stand. Further, we found a negative correlation between stand age and the abundance of Proteobacteria, while the abundances of Chloroflexi were positively correlated with age. Our results indicated that stand age exerted strong influences on the composition of the rhizosphere bacterial community explaining almost 30% of community variances among samples. These results shed new light on the dynamic interactions between long-lived plants and rhizosphere bacteria under field conditions.