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.