T-RFLP pattern of 16S rDNA extracted from anoxic rice field soil at 10°C. The numbers indicate the length of the fragment in base pairs. Mm, Methanomicrobiaceae; Mb, Methanobacteriaceae; Msr, Methanosarcinaceae; Msa, Methanosaetaceae; RC I, Rice cluster I; RC III, Rice cluster III; RC IV, Rice cluster IV.