Vertical distribution of the methanotrophic community after drainage of rice field soil

Anoxic soils, such as flooded rice fields, are major sources of the greenho use gas CH4 while oxic upland soils are major sinks of atmospheric CH4. Nev ertheless, CHI is also consumed in rice fields where up to 90% of the produ ced CH4 is oxidized in a narrow oxic zone around the rice roars and in the soil surface layer before it escapes into the atmosphere. After 1 day drain age of rice field soil, CH4 oxidation was detected in the top 2-mm soil lay ers, but after 8 days drainage the zone of CH4 oxidation extended to 8 mm d epth. Simultaneously, the potential For CH4 production decreased, but some production was still detectable after 8 days drainage throughout the soil p rofile. The vertical distribution of the methanotrophic community was also monitored after and 8 days drainage using denaturing gradient gel electroph oresis after PCR amplification with primer sets targeting two regions on th e 16S rRNA gene that are relatively specific for methylotrophic alpha- and gamma -Proteobacteria, and targeting two functional genes encoding subunits of key enzymes in all methanotrophs, i.e. the genes for the particulate me thane monooxygenase (pmoA) and the methanol dehydrogenase (mxaF). Drainage stimulated the methanotrophic community. Eight days after drainage, new met hanotrophic populations appeared and a distinct methanotrophic community de veloped. The population structure of type I and II methanotrophs was differ ently affected by drainage. Type II methanotrophs (alpha -Prorteobacteria) were present throughout the soil core directly after drainage (1 day), and the community composition remained largely unchanged with di Dth. Only two new type II populations appeared after 8 days of drainage. Drainage had a m ore pronounced impact on the type I methanotrophic community (gamma -Proteo bacteria). Type I populations were not or only weakly detected 1 day after drainage. However, after 8 days of drainage, a large diversity of type I me thanotrophs were detected, altough they were not evenly distributed through out the soil core but dominated at different depths. A distinct type I comm unity structure had developed within each soil section between 0 and 20 mm soil depth, indicating the widening of suitable habitats For methanotrophs in the rice field soil within 1 week of drainage, (C) 2001 Federation of Eu ropean Microbiological Societies. Published by Elsevier Science B.V. All ri ghts reserved.