Rice is the world's most important agricultural plant and essential for the feeding of millions of people, whereas huge areas of flooded rice fields are the major source of the greenhouse gas methane, produced by methanogenic Archaea. Due to their ecological relevance the biodiversity and activity of Archaea in paddy soils have been thoroughly investigated by application of molecular biology methods. However, there are only few investigations which consider the spatial distribution and diversity of these microorganisms with respect to soil structural parameters. Soil structure is very important, since it influences the gas and water fluxes as well as the water retention capacity of soils. Especially paddy soils used for cropping of lowland rice have a rapidly changing structure due to the cycles of irrigation and drainage of rice fields. How this soil structure dynamic influences microbial biocoenoses under special consideration of methanogenic Archaea will be presented with this poster. With regard to the changing conditions in space and time, soil samples for microbial community and soil structure analysis will be taken from soil microcosms with three different soil textures. The sampling will range from the soil surface down to five cm, in steps of 0.5 cm. The sampling times will represent flooding or drainage stages respectively. Changes of the Archaeal community will be monitored by Restriction Fragment Length Polymorphism (RFLP) analysis of 16S rRNA genes. Structural changes of soil will be detected by cross sections of resin embedded soil samples. Using this approach of combined methods it is expected to gain a better understanding of the archaeal population dynamics in paddy fields in dependency of changing soil structure. Especially the investigation of these influences on methanogens can be useful to understand the methane production of paddy fields.