Factors influencing the population of methanogenic bacteria and the initiation of methane production upon flooding of paddy soil

Exposure of dry oxic paddy sol to submerged anoxic conditions resulted in a decrease of the soil redox potential and initiation of CH 4 production. However, the most probable numbers (MPN) of hydrogenotrophic and acetotrophic methanogens did not change upon flooding the soil and upon initiation of CH 4 production, and stayed constant at 10 5 −10 6 and 10 4 −10 5 g −1 d.w. soil, respectively. Cells of Methanobacterium strain Bab1 added to anoxic soil suspensions mostly survived drying and storage under an air atmosphere. Initiation of CH 4 production was not affected by storage of dry soil under N 2 , air, or O 2 atmosphere. However, it was negatively affected by storage under the air at high negatively affected by storage under air at high relative humidities, under moist conditions, or by using only the small (< 100 μ m) soil particle fraction. All these treatments also resulted in decreased contents of dissolved organic carbon (DOC). The soil's capacity for initiation of CH 4 production could be regenerated either by addition of glucose or by exposure to H 2 and addition of reducing agents. The establishment of decreased redox potentials and the provision of methanogenic substrates by heterotrophic bacteria, but not the number of methanogenic bacteria, seemed to be the essential factors for initiation of CH 4 production after submergence of oxic paddy soil. CH 4 production could also be initiated in forest and arable soils. Here, however, the population of methanogenic bacteria (MPN) increased from about 10 3 to 10 5 −10 6 g −1 d.w. when methanogenesis started.