Abstract: There exist two pathways for methane formation in mires,which are acetate fermentation and H ₂/CO ₂ reduction.In principle,the process of acetate fermentation driven by acetoclastic methanogens can produce much more methane than that of H ₂/CO ₂ reduction driven by H ₂/CO ₂ utilizing methanogens.In some specific environments,which one will play a more important role in bacterial methane formation depends on the content of active or labile organic carbon,especially newly fixed organic compounds such as root exudates.Mires,e.g.marsh,fen and swamp,rich in active/labile organic carbon,will produce much more methane through acetate fermentation and mires,such as bog, poor in active organic carbon,will form and emit less methane through H ₂/CO ₂ reduction.The reason why there exist differences in the dominant pathway and amount of methane formed in different types of mires is that the type of methanogens has changed because of changes in the concentration of acetate or H ₂ and temperature and so on in mire porewater.