Several thousand of tank bromeliads per hectare of neotropical forest create a unique wetland ecosystem that harbors diverse communities of archaea and bacteria and emit substantial amounts of methane. Since there is only little information about the microbiology within bromeliad wetlands, we studied the spatial distribution and potential functions of microbial communities and methane (CH4) cycling and their drivers in tank bromeliad wetlands. We selected tank bromeliads of six different species and two functional types (terrestrial and canopy) in a neotropical montane forest of Southern Ecuador and sampled organic tank slurry. Archaeal and bacterial communities were characterized using terminal-restriction fragment length polymorphism (T-RFLP) and Illumina MiSeq sequencing, respectively, and linked with physico-chemical tank-slurry properties. Additionally, we performed tank-slurry incubations to measure CH4 production, stable carbon isotope fractionation and pathway of CH4 formation.
Archaeal and bacterial community composition in bromeliad wetlands were dominated by methanogens and by Alphaproteobacteria and Bacteroidetes, respectively, and did not differ between species but between functional types. Hydrogenotrophic Methanomicrobiales were the dominant methanogens among all bromeliads but also characteristic for canopy bromeliads. Aceticlastic Methanosaetaceae were characteristic for terrestrial bromeliads. Complementary, hydrogenotrophic methanogenesis was the dominant pathway of CH4 formation. The relative contribution of aceticlastic to total produced CH4 increased in terrestrial bromeliads and led to a concomitant increase in total CH4 production. Rhodospirillales and Clostridiales were characteristic for canopy bromeliads. Planctomycetales and Actinomycetales were characteristic for terrestrial bromeliads. While nitrogen concentration and pH explained 32% of the archaeal community variability, 29% of the bacterial community variability was explained by concentrations of nitrogen, acetate and propionate. Bromeliad functional types, associated with different forest strata, and their constrained environmental characteristics, e.g light availiability and tank organic matter quality and quantity, may be most important drivers for spatial distribution of archaeal and bacterial communities and microbial CH4 cycling in neotropical forest canopies.