Effect of winter-flooding on methanogenic archaeal community structure in paddy field under organic farming

Paddy field is a major emission source of methane. Methane is the terminal product of anaerobic decomposition of organic matter and generated by methanogenic archaea under flooded conditions in paddy fields. This study aimed to reveal the effect of winter flooding on methanogenic archaeal community structure in paddy fields of Andosols under organic farming. Soil samples were collected from experimental paddy fields in the Field Science Center, Tohoku University, for two years. They were under flooding conditions during winter with organic farming, under non-flooding conditions during winter with organic farming and under non-flooding conditions during winter with conventional farming (non-organic farming). Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis of methanogenic archaeal 16S rRNA gene revealed that the DGGE patterns were nearly the same irrespective of the treatment and sampling times. Twenty-three bands were observed from each treatment and 4, 13 and 6 sequences were closely related to Methanomicrobiales, Methanosarcinales and Methanocellales, respectively. Real-time quantitative PCR analysis indicated that the abundance of methanogenic archaeal 16S rRNA gene and mcrA gene, encoding alpha subunit of methyl-coenzyme M reductase, was not significantly different among the paddy fields. This study first revealed a methanogenic archaeal community in an Andosol paddy field and showed that the community was not affected by winter flooding under organic farming.