Neutral monosaccharides as biomarker proxies for bog-forming plants for application to palaeovegetation reconstruction in ombrotrophic peat deposits

The application of molecular approaches to palaeovegetation reconstruction in peat is still relatively rare, with molecular level studies of carbohydrate organic geochemistry being generally uncommon. In this report, neutral monosaccharides derived via acid hydrolysis were investigated in modern bog-forming plants in order to assess their potential application as biomarkers in peat palaeovegetation reconstruction. The concentrations of major neutral monosaccharides, i.e. glucose (Glu), xylose (Xyl), arabinose (Ara), galactose (Gal), mannose (Man), rhamnose (Rha) and fucose (Fuc), were determined using gas chromatography (GC) for 7 lichens, 10 Sphagnum species and 7 vascular plants collected from three ombrotrophic mires across northern Europe. Based on factor analysis of the modern plant monosaccharide compositions, two carbohydrate proxies: [(Man + Gal):(Ara + Xyl)] and % contributions of Rha and Fuc in total Glu-free monosaccharides [%(Rha + Fuc)], were selected as biomarkers for bog-forming plants. The three plant groups could be separated by [(Man + Gal):(Ara + Xyl)], which showed decreasing values following the order: lichens > Sphagna > vascular plants. The high [%(Rha + Fuc)] in Sphagna allowed their separation from lichens and vascular plants. These two factors were applied as plant group-specific indices to investigate vegetation change in a peat core from Kontolanrahka Bog, Finland. Our findings show strong correspondence with fossil plant abundances from the same core, thereby confirming the potential of carbohydrate compositional parameters as proxies for palaeovegetation reconstruction in peat bogs.