Elevated CO2 has a significant impact on denitrifying bacterial community in wheat roots

Elevated CO2 (eCO2) stimulates plant growth and photosynthesis, which affect root deposition, leading to altered structure and function of the root microbiome. We studied the effect of eCO2 on wheat-root microbiome composition and plant development, with an emphasis on denitrifying communities. Wheat plants were grown in a greenhouse with continuous fertigation for 6 weeks under ambient CO2 (400 ppm) or eCO2 (850 ppm). The total bacterial community was quantified using qPCR with universal 16S rRNA gene primers, and denitrifying genes (nirK, nirS, nosZ) were measured. In addition, total (16S-based) and N2O-reducing (nosZ-based) bacterial community compositions in the soil and roots were analyzed by amplicon sequencing during plant growth. eCO2 had a significant impact on abundance of the studied denitrifying genes, particularly during the late stages of wheat growth before spike formation. Moreover, eCO2 had a significant impact on N2O-reducing community structure in roots. This effect was more pronounced on Burkholderiales and Rhizobiales, with a minor effect on Pseudomonadales. In addition, as expected, bacterial community structure (total and N2O-reducing bacteria), and denitrifying gene abundance, were primary influenced by habitat (soil vs. roots), and secondarily by plant developmental stage. In summary, it is suggested that eCO2 may change root microbiome, enhance wheat development and N demand without an increase in N2O emission.