The rewetting of drained peatlands alters peat geochemistry and often leads
to sustained elevated methane emission. Although this methane is produced
entirely by microbial activity, the distribution and abundance of
methane-cycling microbes in rewetted peatlands, especially in fens, is rarely
described. In this study, we compare the community composition and abundance
of methane-cycling microbes in relation to peat porewater geochemistry in two
rewetted fens in northeastern Germany, a coastal brackish fen and a
freshwater riparian fen, with known high methane fluxes. We utilized 16S rRNA
high-throughput sequencing and quantitative polymerase chain reaction (qPCR) on 16S
rRNA, mcrA, and pmoA genes to determine microbial community
composition and the abundance of total bacteria, methanogens, and
methanotrophs. Electrical conductivity (EC) was more than 3 times higher in
the coastal fen than in the riparian fen, averaging 5.3 and 1.5 mS cm−1,
respectively. Porewater concentrations of terminal electron acceptors (TEAs) varied
within and among the fens. This was also reflected in similarly high intra-
and inter-site variations of microbial community composition. Despite these
differences in environmental conditions and electron acceptor availability,
we found a low abundance of methanotrophs and a high abundance of
methanogens, represented in particular by Methanosaetaceae, in both
fens. This suggests that rapid (re)establishment of methanogens and slow
(re)establishment of methanotrophs contributes to prolonged increased methane
emissions following rewetting.</p