Characterization of rhizosphere bacterial microbiota under Robinia pseudoacacia plantations during long-term vegetation restoration on ex-arable land

Rhizosphere microbiota are intimately linked with plant growth and defense, but the microbial response to long-term vegetation restoration remains unclear. Here, soil samples were collected from Robinia pseudoacacia stands of different ages (7–35 years old) and a wheat field (control) for a comparative study of rhizosphere bacterial microbiota. The potential influencing factors were identified using principal coordinate analysis, partial least squares discriminant analysis, and partial least squares path modeling. Afforestation influenced soil environmental conditions and bacterial microbiome structure. Microbiota differentiation was mainly explained by niche compartments at the horizontal level. Age-related differences in the rhizosphere microbiota were not prominent, whereas soil samples of different niche compartments were clustered separately. The rhizosphere microbiota exhibited remarkable convergence with increasing stand age. The rhizosphere microbiota dynamics were inconsistent with those of the bulk soil microbiota. Soil organic carbon and available phosphorus contents were the major environmental factors influencing rhizosphere bacterial richness. Accordingly, rhizosphere niche predominantly drove microbiota differentiation along horizontal gradients depending on the soil environment. Growth of R. pseudoacacia trees played a non-significant role in the structuring of rhizosphere microbiota in the restored ecosystem. Results of this study enable a broader understanding of how rhizosphere microbiota respond to long-term afforestation, which could facilitate vegetation restoration.