Changes in CH4 and CO2 emissions from soils under flooded conditions after being exposed to FACE (free-air CO2 enrichment) for three years

To evaluate the variations of CO2 and CH4 emissions from FACE (free-air CO2 enrichment, F) soils three years after rice-wheat rotation FACE treatment, incubation experiments in the laboratory with laboratory and elevated CO2 concentration (1000 μl L−1) were carried out under flooded conditions at 25°C. Results show that soil organic carbon is increased by 11% after exposure to FACE treatment for three years. The results indicate that at laboratory and elevated CO2, the cumulative CO2 emissions from FACE soils are 35% and 22% higher than those from the ambient soils, whereas the cumulative CH4 emissions from FACE soils are 2.6 and 2.3 times that of ambient soils. Thus, there is a larger ratio of cumulative emissions of CH4 to CO2 in the soil F. The elevated CO2 concentration during the incubation stimulates the cumulative CO2 emission significantly, but its stimulation on CH4 emission is not statistically significant. The results indicate that the elevated atmospheric CO2 concentration stimulates the turnover rates of soil organic matter, with a net increase in soil organic matter content, and alters the CH4/CO2 ratio.