Elevated CO2 results in modified N2O emissions from paddy rice fields

Elevated atmospheric CO2 concentrations (e[CO2]) represent an undeniable climate trend, under which the potential response of rice field N2O flux emissions may have been oversight and necessitated a mechanistic explanation for their linkage. During the 3-year rice growth period, two treatments were implemented, including the ambient CO2 concentration (AC) and an increase in the CO2 concentration by 200 mu mol mol-1 (EC). The trends and variations in N2O emissions were monitored, and soil physicochemical properties and enzyme activities during critical growth stages were collected and analyzed. The correlation between environmental factors was explored, and ultimately, the rice yields were measured. The findings suggest that in comparison to AC, EC significantly augmented the cumulative N2O emissions by 17.18-28.83% over a 3-year period. Notably, the N2O flux reached its peak during the initial stages of field solarization and irrigation, contributing to substantial cumulative emissions; furthermore, EC exacerbated these emissions. The EC significantly enhanced the soil pH, dissolved organic carbon, NH4+-N content, and three types of enzyme activities, which were particularly pronounced during the early growth stage, while reducing the soil NO3--N content. The relationships between N2O flux and temperature as well as between N2O flux and soil moisture exhibited an exponential pattern, with a stronger correlation observed between soil moisture. EC not only mitigated the sensitivity to temperature but also enhanced the association between soil moisture content. The growth of rice plants was enhanced by e[CO2]; however, its impact on grain yield remains limited. The aforementioned findings have significant theoretical implications for understanding the response of paddy field N2O emissions to e[CO2].