Abstract: The effect of different cultivation conditions on the release of methane, the amounts of methanogens and methane-oxidizing bacteria in rice paddy soil are reported. After rice seedlings was transplanted, the amount of methane released from rice plant was gradually increased with rice plant growth and reached to the maximum at flourishing tillering stage. After this stage it was gradually decreased. The amount of methanogens in rice paddy soil was 2-3 orders of magnitude lower during the earlier stages than that during the latter stages in earlier rice. However, the amount of methanogens was slighly higher during the middle stage than that during the earlier and latter stages. The predominant methanogenic bacteria isolated from rice paddy soil belonged to Methanobacterium and Methanosarcina. The amount of methane-oxidizing bacteria was about 103-104/g dry soil during the earlier stage and 108/g dry soil during the latter stage in earlier rice. Then, it was kept at about 108/g dry soil in latter rice. Four strains of methane-oxidizing bacteria were isolated and belonged to faculative heterotrophic methylotrophs.

Key words: rice paddy soil, rice plant, methane release, methanogens, methane-oxidizing bacteria