Variability in depth-mediated shifts in methanogen and methanotroph communities across tropical Andean mountain peatlands

Abstract

The balance between methane producing and methane consuming microorganisms is partially responsible for the magnitude and direction of soil-atmosphere methane fluxes. Therefore, understanding the effects of vegetation and land use on relative abundance, community structure and vertical distribution of methane cycling microorganisms should help us interpret patterns of net emissions of methane. Mountain peatlands in the tropics are abundant and are important in global carbon cycling, but little is known about the communities of methane-cycling microorganisms in these ecosystems. We sampled peat from eight Andean peatlands in Peru, Ecuador and Colombia and described the dominant vegetation, grazing intensity and other site characteristics at each site. We characterised the microbial community of each peat sample at different depths and identified the methane cycling microorganisms. We observed a higher proportion of methanogens and methanogen:methanotroph in the shallow peat of grazed sites than ungrazed sites. At ungrazed sites we found relatively high methanotroph abundance relative to methanogens, even at the deepest sampling depths, suggesting plant aerenchymal oxygen transport structures communities at depth. We found changes in the methane cycling microbial communities among sites and with depth, e.g., in the superficial peat the hydrogenotrophic methanogens were more abundant but at depth there was more metabolic diversity. Our study provides new insights into the community structure of methane cycling microorganism of the tropical mountain peatlands, and raises interesting questions regarding the drivers of methanotroph abundance deeper in peat.