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Lookup NU author(s): Dr Geoffrey AbbottORCiD, Eleanor Swain, Dr Aminu Muhammad
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A much improved understanding of how water-table fluctuations near the surface affect decomposition and preservation of peat-forming plant litter and surficial peats is needed in order to predict possible feedbacks between the peatland carbon cycle and the global climate system. In this study peatland plants (bryophytes and vascular plants), their litter and peat cores were collected from the Ryggmossen peatland in the boreonemoral zone of central Sweden. The extracted residues from whole plant tissues were depolymerized using thermally assisted hydrolysis and methylation (THM) in the presence of both unlabelled and 13C-labelled tetramethylammonium hydroxide (TMAH) which yielded both vascular plant- and Sphagnum-derived phenols. Methylated 4-isopropenylphenol (IUPAC: 1-methoxy-4-(prop-1-en-2-yl)benzene), methylated cis and trans 3-(4’-hydroxyphen-1-yl)but-2-enoic acid (IUPAC: (E/Z)-methyl 3-(4-methoxyphenyl)but-2-enoate), and methylated 3-(4’-hydroxyphen-1-yl)but-3-enoic acid (IUPAC: methyl 3-(4-methoxyphenyl)but-3-enoate) (van der Heijden et al., 1997) are confirmed as TMAH thermochemolysis products of sphagnum acid and also as being specific to Sphagnum mosses. These putative biomarkers were also significant components in the unlabelled TMAH thermochemolysis products from the depolymerization of samples from eight peat cores, one from a hummock and one from a hollow at each of the four stages along the bog plateau-to-swamp forest gradient. We have proposed and measured two parameters namely i) σ which is defined as the total amount of these four molecules normalised to 100 mg of TOC; and ii) an index (SR%) which is the ratio of σ to the Λ parameter giving a measure of the relative amounts of sphagnum acid to the vascular plant phenols in peat moss and the surficial peat layers. Changes in σ and SR% down the bog plateau (BP), bog margin (BM) and fen lagg (FL) cores in the Ryggmossen mire indicates that the sphagnum acid bound into the peat is being degraded in the unsaturated and seasonally saturated layers. There is then a stabilisation of Sphagnum-derived phenols in the deepest horizons of the seasonally saturated layer and into the permanently-saturated layer. These results suggest that sphagnum acid will be stabilised in peatlands shifting to a wetter and more variable precipitation regime whereas it will be gradually stripped away in surficial peats shifting to a drier climate, such that any subsequent rewetting of the peat could lead to anaerobic hydrolysis and fermentation of the newly exposed carbohydrates. This highlights the sensitivity of Sphagnum surficial peats to climate-induced changes in water levels albeit there may be differences in the extent of degradation along the bog-fen gradient.
Author(s): Abbott GD, Swain EY, Muhammad AB, Allton K, Belyea LR, Laing CG, Cowie GL
Publication type: Article
Publication status: Published
Journal: Geochimica et Cosmochimica Acta
Year: 2013
Volume: 106
Pages: 177-191
Print publication date: 01/04/2013
Online publication date: 27/12/2012
ISSN (print): 0016-7037
ISSN (electronic): 1872-9533
Publisher: Elsevier B.V.
URL: http://dx.doi.org/10.1016/j.gca.2012.12.013
DOI: 10.1016/j.gca.2012.12.013
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