Elevated carbon dioxide stimulates nitrous oxide emission in agricultural soils: A global meta-analysis

Elevated carbon dioxide (CO₂) (eCO₂) has been shown to affect the nitrous oxide (N₂O) emission from terrestrial ecosystems by altering the interaction of plants, soils, and microorganisms. However, the impact of eCO₂ on the N₂O emission from agricultural soils remains poorly understood. This meta-analysis summarizes the effect of eCO₂ on N₂O emission in agricultural ecosystems and soil physiochemical and biological characteristics using 50 publications selected. The eCO₂ effect values, which equal to the percentage changes of N₂O emission under eCO₂, were calculated based on the natural logarithm of the response ratio to eCO₂. We found that eCO₂ significantly increased N₂O emission (by 44%), which varied depending on experimental conditions, agricultural practices, and soil properties. In addition, eCO₂ significantly increased soil water-filled pore space (by 6%), dissolved organic carbon content (by 11%), and nitrate nitrogen content (by 13%), but significantly reduced soil pH (by 1%). Moreover, eCO₂ significantly increased soil microbial biomass carbon (by 28%) and soil microbial biomass nitrogen (by 7%) contents. Additionally, eCO₂ significantly increased the abundances of ammonia-oxidizing bacteria (AOB) amoA (by 21%), nirK (by 15%), and nirS (by 15%), but did not affect the abundances of ammonia-oxidizing archaea (AOA) amoA and nosZ. Our findings indicate that eCO₂ substantially stimulates N₂O emission in agroecosystems and highlight that optimization of nitrogen management and agronomic options might suppress this stimulation and aid in reducing greenhouse effect.