Nitrogen-regulated effects of free-air CO sub(2) enrichment on methane emissions from paddy rice fields

Using the free-air CO sub(2) enrichment (FACE) techniques, we carried out a 3-year mono-factorial experiment in temperate paddy rice fields of Japan (1998-2000) and a 3-year multifactorial experiment in subtropical paddy rice fields in the Yangtze River delta in China (2001-2003), to investigate the methane (CH sub(4)) emissions in response to an elevated atmospheric CO sub(2) concentration (200 plus or minus 40 mmol mol super(-1) higher than that in the ambient atmosphere). No significant effect of the elevated CO sub(2) upon seasonal accumulative CH sub(4) emissions was observed in the first rice season, but significant stimulatory effects (CH sub(4) increase ranging from 38% to 188%, with a mean of 88%) were observed in the second and third rice seasons in the fields with or without organic matter addition. The stimulatory effects of the elevated CO sub(2) upon seasonal accumulative CH sub(4) emissions were negatively correlated with the addition rates of decomposable organic carbon (P