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

Elevated carbon dioxide (CO2) (eCO(2)) 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 eCO(2) on the N2O emission from agricultural soils remains poorly understood. This meta-analysis summarizes the effect of eCO(2) on N2O emission in agricultural ecosystems and soil physiochemical and biological characteristics using 50 publications selected. The eCO(2) effect values, which equal to the percentage changes of N2O emission under eCO(2), were calculated based on the natural logarithm of the response ratio to eCO(2). We found that eCO(2) significantly increased N2O emission (by 44%), which varied depending on experimental conditions, agricultural practices, and soil properties. In addition, eCO(2) 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, eCO(2) significantly increased soil microbial biomass carbon (by 28%) and soil microbial biomass nitrogen (by 7%) contents. Additionally, eCO(2) 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 eCO(2) 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.