Mountain peatlands of the tropical and subtropical Andes are numerous and play a key role in carbon cycling because they contain large stocks of carbon stored as peat and can sequester and emit greenhouse gases, especially carbon dioxide and methane (CH4). Whether a peatland is a source or sink of CH4 depends on the balance between methanogens and methanotrophs. These CH4 related microbial communities are affected by the redox potential and substrate availability and quality. Tropical Andean mountain peatlands are characterised by cushion and graminoid plants. Sparse data suggest these peatlands have low methane fluxes, although these plants possess aerenchyma which can transport CH4, perhaps because they supress CH4 emissions by transporting oxygen into peat. The dominant plant functional type and alterations caused by disturbances such as grazing can impact the soil microbial communities, altering the balance of methanogens and methanotrophs. Our objective was to assess the differences and potential drivers of the methanogens and methanotrophs microbial communities across a gradient of Andean tropical peatlands. We collected peat cores from seven mountain peatlands from Colombia, Ecuador and Peru and used high throughput sequencing of the small subunit ribosomal DNA (SSU rDNA) to determine bacterial and archaeal community composition in soils. Methanogens and methanotrophs represented less than 5% of the relative read abundance of the studied sites. With increasing soil depth, the abundance of methanogens and methanogen:methanotroph ratios increased except in one heavily grazed site where methanogens were abundant near the surface. We also found changes in the community composition of methanogens and methanotrophs amongsites and with soil depth. The dominant methanogen class observed in the surface varied among sites and were Methanomicrobia or Methanobacteria. However, the community on the surface of the heavily grazed site formed a cluster separated from the other studied sites and depths, perhaps driven by enteric microbes or labile inputs from cattle. Previous studies on CH4 fluxes carried in the heavily grazed site and and in a non-grazed site, showed low CH4 emissions (8.1 mg CH4 m-2 d -1) in the non-grazed site and high CH4 emissions (132.3 mg CH4 m-2 d -1) in the heavily grazed. The high grazing could be the driver of the changes in the methanogen and methanotroph community that we observed and matches the previously described high CH4 fluxes measured at this site. Further co-analyses of microbial communities and CH4 fluxes will test the generality of these ptterns.
Mountain tropical peatlands, methane, methanogens, methanotrophs, microbial community composition