Impacts of Elevated CO2 and a Nitrogen Supply on the Growth of Faba Beans (Vicia faba L.) and the Nitrogen-Related Soil Bacterial Community

Ecosystems that experience elevated CO2 (eCO(2)) are crucial interfaces where intricate interactions between plants and microbes occur. This study addressed the impact of eCO(2) and a N supply on faba bean (Vicia faba L.) growth and the soil microbial community in auto-controlled growth chambers. In doing so, two ambient CO2 concentrations (aCO(2), daytime/nighttime = 410/460 ppm; eCO(2), 550/610 ppm) and two N supplement levels (without a N supply-N0-and 100 mg N as urea per kg of soil-N100) were applied. The results indicated that eCO(2) mitigated the inhibitory effects of a N deficiency on legume photosynthesis and affected the CO(2 )assimilation efficiency, in addition to causing reduced nodulation. While the N addition counteracted the reductions in the N concentrations across the faba beans' aboveground and belowground plant tissues under eCO(2), the CO2 concentrations did not significantly alter the soil NH4+-N or NO3--N responses to a N supply. Notably, under both aCO(2) and eCO(2), a N supply significantly increased the relative abundance of Nitrososphaeraceae and Nitrosomonadaceae, while eCO(2) specifically reduced the Rhizobiaceae abundance with no significant changes under aCO(2). A redundancy analysis (RDA) highlighted that the soil pH (p < 0.01) had the most important influence on the soil microbial community. Co-occurrence networks indicated that the eCO(2) conditions mitigated the impact of a N supply on the reduced structural complexity of the soil microbial communities. These findings suggest that a combination of eCO(2) and a N supply to crops can provide potential benefits for managing future climate change impacts on crop production.