Abstract: The CH₄ and N₂O emissions from rice field in northern China were measured in situ by chamber technique from March to December 1995～1996,and their relationship was discussed.Soil temperature,pH,moisture and Eh in the rice field were also determined.The results showed that there was a significant teade off between CH₄ and N₂O emissions(R²=-0.494).During the period of monitoring,soil temperature,pHand Eh varied between 0 and 24℃,6.87 and 7.02,adn 415 and 300mv,respectively.Soil moisture was 38～72% FC during the non-flooding period.Among these impacting factors,soil Eh was very important functionally on CH₄ and N₂Oemissions.Six related bacteria groups in this rice field,fermenters,H₂ producing acetogens,methanogens,methanotrophs,nitrifiers and denitrifiers,were obsered,All of them had their own dynamic patterns in their numbers and enzyme activities during the period of observation.The trade off between CH₄ and N₂O emissions from rice field could be controlled by the dynamics of the numbers and enzyme activities of these related microorgamisms.

Key words: Rice field, CH₄ and N₂O emissions, Microorganisms, Soil Eh, soil chemical property, Three Gorges Reservoir, temporal and spatial dynamics, canyon landform area, water level fluctuation zone