Page 127 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Plant succession is comparable in northern and southern regions of the study area
The patterns of vegetation succession at the Max Gundelach and Fredricksborg NE sites showed comparable local vegetation evolution, based on macro-analysis, and domination by mosses. The two plant successions of the Max Gundelach and Fredricksborg NE sites do not disagree with the local plant succession documented by Wolters et al. (2010), located latitudinally (54°06.00’, 06°46.70) between the Max Gundelach and Fredricksborg NE sites. The site of Wolters et al. (2010) was established with birch woodland, leading to carr vegetation during paludification, Salix and reeds during the establishment of a lagoonal environment, and finally Chenopodiaceae indicates the inundation of the marine environment. The Wolters et al. study was supplemented by macrofossil samples but did not assess changes in mosses, the primary peat-forming vegetation type.
The parallel sequences observed at the Max Gundelach and Fredricksborg NE sites begin and end at different times, suggesting that a comparable geomorphological context was present at both sites but during different periods. Moreover, the sequence of vegetation succession spanned c. 3000 years at the Max Gundelach site but only 800 years at the Fredricksborg NE site, indicating that the changes in geomorphological conditions occurred at vastly differing rates. These periods are aligned with the peat growth described by Wolters et al. (2010) which prevailed for 1,300 years before inundation occurred. The differences in the duration and rate of peat accumulation are likely the result of the differences in the rate of sea-level rise between these two locations, in addition to other, largely unknown, palaeoenvironmental factors. The variation in CH4 concentrations between sites is large and may reflect the types of organic matter available to in situ microbial communities and subsequent mineralization rates.
Dominance of Bathyarchaeia suggests a central role in organic matter turnover
Bathyarchaeia dominated the archaeal communities of the peat sediments, with an average relative abundance of 70%. This phylum is an evolutionary diverse microbial group that is found in a wide range of organic-rich environments, including deep sea and freshwater sediments (Evans et al. 2015). Bathyarchaeia often dominate marine subsurface archaeal communities, with relative abundances ranging from 10% to 100% (Fry et al. 2008; Zhou et al. 2018). Peat deposits are rich in cellulose and lignins (Mcmorrow et al. 2004), which are eventually converted to fluvic and humic acids that are more accessible to the microbial
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