Abstract: Methane is one of the most important greenhouse gases and clean energy sources. With the highest abundance of active metals on Earth, iron oxides exert significant influences on the conversion of organic matter to methane under anaerobic conditions. Low-crystallinity, easily reducible Fe(III) oxides could inhibit methanogenesis in three ways: (1) Fe(III)reducing bacteria competed with methanogens for common electron donors such as acetate and H₂; (2) methanogens reduced Fe(III) oxides with H₂ oxidation, diverting the electron flow from methanogenesis to Fe(III) reduction; (3) Fe(III) oxides might increase the redox potential of their surrounding environments to inhibit methanogenesis. Recently, the conductive iron oxides have been demonstrated to facilitate methanogenesis from organic matter, in which iron oxides function as electron conduits and create direct interspecies electron transfer between syntrophic bacteria and methanogens. This review summarizes the mechanisms of inhibition or promotion effect of iron oxides on syntrophic methanogenesis. Furthermore, we highlight the research trends of the influence of iron oxides on methanogenesis, which would be helpful for the practical applications in greenhouse gases mitigation and bioenergy production.

Key words: alpine forest, headwater stream, soluble nitrogen, soluble phosphorus.