Methanogen communities along a primary succession transect of mire ecosystems

Peat accumulating mires are important sources of the greenhouse gas methane. Methane emissions and methanogenic Archaea communities have been shown to differ between fens and bogs, implying that mire succession includes an ecological succession in methanogen communities. We investigated methane production and the methanogen communities along a chronosequence of mires (ca. 100-2500 years), which consisted of five sites (1-5) located on the land-uplift coast of the Gulf of Bothnia. Methane production was measured in a laboratory incubation experiment. Methanogen communities were determined by amplification of a methyl coenzyme M-reductase (mcr) gene marker and analyzed by terminal-restriction fragment length polymorphism. The terminal-restriction fragment length polymorphism fingerprinting resulted in 15 terminal restriction fragments. The ordination configuration of the terminal restriction fragments data, using nonmetric multidimensional scaling, showed a clear gradient in the methanogen community structure along the mire chronosequence. In addition, fingerprint patterns of samples from the water table level and 40 cm below differed from one another in the bog site (site 5). Methane production was negligible in the three youngest fen sites (sites 1-3) and showed the highest rates in the oligotrophic fen site (site 4). Successful PCR amplification using mcr gene primers revealed the presence of a methanogen community in all five sites along the study transect.