Hydrogenotrophic methanogenesis is the dominant methanogenic pathway in neotropical tank bromeliad wetlands.

Several thousands of tank bromeliads per hectare of neotropical forest create a unique wetland ecosystem that emits substantial amounts of CH . Tank bromeliads growing in the forest canopy (functional type-II tank bromeliads) were found to emit more CH than tank bromeliads growing on the forest floor (functional type-I tank bromeliads) but the reasons for this difference and the underlying microbial CH -cycling processes have not been studied. Therefore, we characterized archaeal communities in bromeliad tanks of the two different functional types in a neotropical montane forest of southern Ecuador using terminal-restriction fragment length polymorphism (T-RFLP) and performed tank-slurry incubations to measure CH production potential, stable carbon isotope fractionation and pathway of CH formation. The archaeal community composition was dominated by methanogens and differed between bromeliad functional types. Hydrogenotrophic Methanomicrobiales were the dominant methanogens and hydrogenotrophic methanogenesis was the dominant methanogenic pathway among all bromeliads. The relative abundance of aceticlastic Methanosaetaceae and the relative contribution of aceticlastic methanogenesis increased in type-I tank bromeliads probably due to more oxic conditions in type-I than in type-II bromeliads leading to the previously observed lower in situ CH emissions from type-I tank bromeliads but to higher CH production potentials in type-I tank bromeliad slurries.