Changes in N2-fixation activity, abundance and composition of diazotrophic communities in a wheat field under elevated CO2 and canopy warming

Abstract Global climate change with elevated atmospheric CO2 concentrations and warming may potentially influence microbial function and nitrogen (N) cycling in various ecosystems. Despite the significance of diazotrophic mediation in soil N cycling within agricultural ecosystems, little is known about the impacts of climate change on diazotrophic abundance and community composition. An open-air field experiment growing wheat was conducted under four treatments: ambient condition (CK), CO2 enrichment up to 500 ppm (CE), warming of canopy air by 2 °C over ambient (WA), and the combined CO2 enrichment and canopy warming (CW). Quantitative real-time PCR and high-throughput pyrosequencing were used to analyze diazotrophic abundance and community composition in the bulk and rhizosphere soils. Results showed that both N2-fixation activity and nifH gene abundance were higher in the rhizosphere than those in bulk soil. N2-fixation activity and nifH gene abundance were significantly increased under elevated CO2 treatments, while no significant change was observed under warming treatment. Elevated CO2 levels altered the diazotrophic community composition and increased the alpha diversity. A redundancy analysis indicated that soil organic carbon, total nitrogen and available potassium were the most important factors in shaping diazotrophic communities in the wheat rhizosphere and bulk soil. These findings suggest that N2-fixation and diazotrophic community in wheat soil are more impacted by elevated CO2 compared with warming. Therefore, understanding how simultaneous elevated CO2 and temperature levels influences the microbial ecology of soil diazotrophs, can provide novel insights into the sustainability of agricultural production under future climate scenarios.