Predominance of methanogens over methanotrophs in rewetted fens characterized by high methane emissions

Abstract

Abstract. 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.

Rewetting of Three Drained Peatlands Drives Congruent Compositional Changes in Pro- and Eukaryotic Soil Microbiomes through Environmental Filtering

“…Methanoperedens) which reduce CH4 by the reverse methanogenic pathway [20] were detected in the water-covered fen Alderwet. Although we did not find a clear correlation between methanogen and methanotroph abundance (see [16] for similar findings), we did find a strong distinction of anaerobic and aerobic methanotrophs depending on water content and therefore oxygen availability, between sites and depths.…”

“…Rewetting is a proven strategy to protect the large SOC stocks; however, it can also lead to increased emissions of the potent GHG CH4 and to the release of dissolved organic matter (DOM). While effects of peatland rewetting on GHG and DOM fluxes are comparably well studied [11][12][13][14][15], the impact on the peat microbiota, the primary driver of GHG production and emissions, is poorly understood, since it has been not well studied in temperate fens (see an exception in [16]). The major players in soil organic matter (SOM) decomposition in peat soils are microorganisms of the bacterial, archaeal and eukaryotic (e.g.…”

“…Wet peatlands are known to contribute a large share of the global CH4 emissions [1,52]. The higher mcrA abundance after rewetting ( Figure 5) could lead to increased CH4 emissions from peatlands, as is the case in rice paddy fields [16,53]. Interestingly, their abundance was high in the rewetted top soils, at least in Alderwet and Percowet, and not in the subsoils.…”

Eukaryotic rather than prokaryotic microbiomes change over seasons in rewetted fen peatlands

“…2), due to the high amount of sulfate reducers in CW which is regularly flooded with sea water. The higher abundance of methanogens in rewetted sites seems to be the main reason for the increase of CH 4 production and thus potentially emission after rewetting [36]. It has been shown that CH 4 dominated the balances of annual greenhouse gases in decades after rewetting a bog in Lower Saxony [16].…”

Carbon release and transformation from coastal peat deposits controlled by submarine groundwater discharge: a column experiment study

“…Peatlands along the coastal margins are also a major source of DOC to coastal and shelf areas (Freeman et al 2001; Mulholland 2003). Currently, the majority of experimental studies considering carbon transformation processes from wetland soil focus on onshore processes (Kalbitz et al 2000; Chambers et al 2011; Wen et al 2018; Säurich et al 2019). A number of experimental approaches have identified the ionic strength of the advective pore water as an important factor controlling DOC concentrations and mobilization, where increasing ionic strength results in decreasing DOC release from organic soils and vice versa (Tipping and Hurley 1988; Limpens et al 2008; Tiemeyer et al 2017).…”