Elevated CO₂ and Nitrogen Supply Boost N Use Efficiency and Wheat (T. aestivum cv. Yunmai) Growth and Differentiate Soil Microbial Communities Related to Ammonia Oxidization

Elevated CO₂ levels (eCO₂) pose challenges to wheat (Triticum aestivum L.) growth, potentially leading to a decline in quality and productivity. This study addresses the effects of two ambient CO₂ concentrations (aCO₂, daytime/nighttime = 410/450 ± 30 ppm and eCO₂, 550/600 ± 30 ppm) and two nitrogen (N) supplements (without N supply—N0 and with 100 mg N supply as urea per kg soil—N100) on wheat (T. aestivum cv. Yunmai) growth, N accumulation, and soil microbial communities related to ammonia oxidization. The data showed that the N supply effectively mitigated the negative impacts of eCO₂ on wheat growth by reducing intercellular CO₂ concentrations while enhancing photosynthesis parameters. Notably, the N supply significantly increased N concentrations in wheat tissues and biomass production, thereby boosting N accumulation in seeds, shoots, and roots. eCO₂ increased the agronomic efficiency of applied N (AE_N) and the physiological efficiency of applied N (PE_N) under N supply. Plant tissue N concentrations and accumulations are positively related to plant biomass production and soil NO₃⁻-N. Additionally, the N supply increased the richness and evenness of the soil microbial community, particularly Nitrososphaeraceae, Nitrosospira, and Nitrosomonas, which responded differently to N availability under both aCO₂ and eCO₂. These results underscore the importance and complexity of optimizing N supply and eCO₂ for enhancing crop tissue N accumulation and yield production as well as activating nitrification-related microbial activities for soil inorganic N availability under future global environment change scenarios.