Elevated CO2 alters the structure of the bacterial community assimilating plant‐derived carbon in the rhizosphere of soya bean

© 2019 British Society of Soil Science Elevated CO2 (eCO2) increases rhizodeposits, which in turn alters the soil microbial community. However, it is not really known how the microbial community metabolizes plant-derived carbon (C) in the rhizosphere under eCO2, especially in agricultural soils. This study used a 13CO2 labelling technique combined with DNA-stable isotope probing (SIP) to fractionate the 13C-DNA and 12C-DNA from the rhizosphere of soya bean plants (Glycine max (L.) Merr. cv. Suinong 14) grown for 54 days under ambient CO2 (aCO2) (390 ppm) or eCO2 (550 ppm). The DNA fractions were then subjected to Illumina Miseq sequencing. The results showed that eCO2 decreased the richness and diversity of the 13C-assimilating bacterial community compared to aCO2 (p < 0.05). Elevated CO2 decreased the abundances of genera, including Pseudarthrobacter, Gaiellales_uncultured, Microlunatus, Gemmatimonas, Gemmatimonadaceae_uncultured, Ramlibacter, Massilia, Luteimonas, Acidobacteriaceae_uncultured, Bryobacter and Candidatus_Solibacter. These genera were probably fast-growing bacteria and sensitive to labile C. In contrast, eCO2 stimulated the growth of genera Novosphingobium, Acidimicrobiales_uncultured, Bacillus, Flavisolibacter and Schlesneria, which were able to assimilate complex C compounds. Moreover, the increased population of Novosphingobium under eCO2 might have accelerated electron flow from the oxidation of organic C. Correspondingly, eCO2 did not affect the concentration of the dissolved organic C but increased the plant-derived 13C in the rhizosphere. These results indicated that an eCO2-induced increase in non-labile C in rhizodeposits contributed to the increase in population size of a number of the plant-C-metabolizing genera that might become the mechanism for the turnover of fresh C in the rhizosphere, modifying the soil C cycle under eCO2 environments.