Impacts of atmospheric CO₂ enrichment on nitrous oxide emissions in wheat and rice cropping systems at global and local scales

Human activity is boosting atmospheric carbon dioxide (CO₂), which further compounds the contributions to climate change through interaction effects with other greenhouse gases, especially nitrous oxide (N₂O). However, the global-scale role of elevated CO₂ (eCO₂) in shaping N₂O emissions across major cereal systems remains insufficiently studied. This effect can be especially important in cereal crops such as rice and wheat, which are among the most predominant crops on the planet and require different management strategies. Here, we combined meta-analysis of a global database (including rice and wheat cropping systems) with a two-year rice-wheat cropping experiment in eastern China; and found that eCO₂ consistently promotes N₂O emissions both at local and global scales in wheat cropping systems. For meta-analysis, we show that wheat cropping increased eCO₂-induced N₂O emissions by 19.6 %, whereas rice cropping showed no significant changes. Local experiments supported the global results and revealed a potential functional mechanism for the positive relationship between eCO₂ and N₂O emissions, where eCO₂ experimentally increased the ratio of microbial nitrite reductase gene abundances (nirK, nirS) to N₂O reductase gene abundance (nosZ) in soil. Taken together, our study highlights the potential positive feedback among eCO₂ and N₂O, as well as the crucial role of cereal type in governing the eCO₂ effect on N₂O emissions, which is an important consideration for management to both mitigate climate change under global change and promote agricultural sustainability.