Impacts of Elevated CO 2 and a Nitrogen Supply on the Growth of Faba Beans ( Vicia faba L.) and the Nitrogen-Related Soil Bacterial Community.

Ecosystems that experience elevated CO 2 (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 CO 2 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 CO 2 concentrations did not significantly alter the soil NH 4 + -N or NO 3 - -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.