A comparative study of methanogenic and methanotrophic microbial community dynamics between natural and restored boreal peatlands

Wetlands are unique ecosystems delivering essential ecosystem services to society. During the last decades, restoring the historically drained wetland has become a prioritized environmental protection action in many European countries, including Sweden. Nonetheless, the process of wetland restoration also induces significant alterations in soil biogeochemical characteristics, mostly attributed to the substantial fluctuations in water table levels (WTLs). Specifically, the restoration of WTLs creates ideal circumstances for diverse anaerobic microbial processes. One such process of special concern is production and coupled emission of the potent greenhouse gas methane. This study aims to describe the spatial distribution of the overall microbial community in boreal peatlands, with a focus on investigating methanogenic and methanotrophic microbial community structure dynamics between natural and restored boreal peatlands. The sampling sites included both natural and adjacent restored peatlands where samples for peat depth profiles down to 45cm were collected from nine different locations across Sweden. Due to high variation between peatlands, no significant overall difference was measured in methane porewater concentrations between restored and natural peatlands. Still, there were systematic differences in methane porewater concentrations between some restored and natural peatlands in specific depth. To assess the distribution of methanogenic and methanotrophic communities, we quantified 16S rRNA genes for methanogens and a key functional marker gene for methanotrophs (mxaF) from the peat soil depth profiles. These quantitative assays combined with compositional microbial community analysis from 16S rRNA analysis revealed distinct differences in microbial community structure over depth and between the different locations. There was also a distinct separation in microbial community structure between each pair of restored and natural peatlands, mainly observed in deeper layers, i.e., earlier-formed peat. The present study clearly showed that the extensive drainage and land use practices spanning over a century have had profound and long-lasting effects on the peatland microbial communities with responses that are unlikely to be fully recovered after merely a decade of peatland restoration efforts.