Bacterial communities incorporating plant-derived carbon in the soybean rhizosphere in Mollisols that differ in soil organic carbon content

- We investigated the composition of the bacterial communities incorporating rhizodeposits at the OTU level.
- The path of root-derived C into rhizospheric bacterial communities was soil-specific.
- The difference in rhizodeposits metabolizing bacteria between soils mainly occurred in genera affiliated to Proteobacteria and Actinobacteria.
- Soil Corg had the greatest influence on this difference.

A primary factor regulating the composition of the microbial community in the rhizosphere is carbon (C) efflux from root systems, which fundamentally influences microbial functions in the rhizosphere, such as biodegradation, plant growth, and rhizosphere signalling. However, information regarding the incorporation of plant-C by the bacterial community in the rhizosphere is limited, particularly in soybean. Soybean plants were grown in rhizo-boxes containing low- or high-organic C (Corg) Mollisols and labelled with 13CO2 at the flowering stage. After soil DNA was extracted from the rhizosphere, 13C-DNA was separated from 12C-DNA using the stable isotope probing method, followed by pyrosequencing analysis. Between soils, significant differences in the abundance of genera incorporating 13C in the rhizosphere were observed, with Aquincola, Dechloromonas, Massilia, Amycolatopsis, Delftia, Magnetospirillum, Psychrobacter, Ochrobactrum, Pseudoxanthomonas and Niastella showing greater relative abundances in low-Corg soil (p < 0.05) compared to high-Corg soil. However, the opposite trend was observed for Enhydrobacter, Flavisolibacter, Propionibacterium and Staphylococcus. Correspondingly, the number of operational taxonomic units in each genus varied between soils. Soil type greatly affected the flow of plant-C into rhizospheric bacterial community. The plant-C metabolizing bacteria may contribute to the transformation of rhizodeposits in the soil and soil C sequestration.