Abstract: By the method of static opaque chamber/ modified gas chromatography,a oneyear field experiment was conducted to measure in situ the CH₄ and N₂O emission from a winter-time flooded paddy field in a hilly area of Southwest China.Gas samples were taken simultaneously from rice-involved and riceuninvolved plots.The results showed that during rice growth period,the CH₄ emission from the winter-time flooded paddy field was higher than that from other paddy fields,but largely lower than many previous reports for the similar regions in Southwest China.The average flux of CH₄ emission from riceinvolved plots was 22.76±2.76 mg CH4·m^-2·h^-1 during rice growth period,9.64±1.17 mg CH₄·m^-2·h^-1 per year,and 1.43±0.20 mg CH₄·m^-2·h^-1during non-rice growth season; while that from riceuninvolved plots was only 2.03±0.18 mg CH₄·m^-2·h^-1 per year,markedly lower than those from riceinvolved plots.During rice growth season,the mean emission rate of CH₄ and N₂O was 4.53±0.38 mg CH₄·m^-2·h^-1and 32.01±5.02 μg N₂O·m^-2·h^-1 from rice-uninvolved plots,but reached to 22.76±2.76 mg CH₄·m^-2·h^-1 and 73.04±5.03 μg N₂O·m^-2·h^-1 from rice-involved plots,respectively.Rice involvement resulted in 302% increment of CH₄ and 128% increment of N₂O mission.There was a clear trade-off between CH₄ and N₂O emission in paddy fields.Even with a span of 500 years,our calculation showed that in this winter-time flooded paddy field,the GWP contributed by N₂O production was 7.9% of the CH₄ contribution,and thus,the greenhouse effect of N₂O production from this field was very small.

Key words: UV-B, Competition, Ozone depletion, Wheat