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

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 (C-org) Mollisols and labelled with (CO2)-C-13 at the flowering stage. After soil DNA was extracted from the rhizosphere, C-13-DNA was separated from C-12-DNA using the stable isotope probing method, followed by pyrosequencing analysis. Between soils, significant differences in the abundance of genera incorporating C-13 in the rhizosphere were observed, with Aquincola, Dechloromonas, Massilia, Amycolatopsis, Delftia, Magnetospirillum, Psychrobacter, Ochrobactrum, Pseudoxanthomonas and Niastella showing greater relative abundances in low-C-org soil (p < 0.05) compared to high-C-org 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.