Carbohydrates as proxies in ombrotrophic peatland: DFRC molecular method coupled with PCA

Abstract

Understanding organic matter (OM) dynamics in peat remains challenging as molecular-level carbohydrate studies of organic geochemistry are still generally rare. Herein, neutral monosaccharides derived via the newly developed derivatisation followed by reductive cleavage (DFRC) method were investigated for an ombrotrophic peatland in France for assessing their potential application as proxies in peat OM dynamics.The concentrations of major neutral monosaccharides, namely, glucose, xylose, arabinose, galactose, mannose, rhamnose (Rha) and fucose (Fuc), were determined via gas chromatography for 24 depth records collected from an ombrotrophic peatland in Sagnes, France. Depth records were distributed along the ecological layers of a peatland, i.e. acrotelm, mesotelm and catotelm. Mechanistic features of DFRC were employed to develop a new proxy ‘∆’ to decipher the lignocellulosic input in recent sediments. Additionally, principal component analysis (PCA) was applied to the molecular monosaccharide composition. This combination of the multi-dimensional statistical technique and the molecular fingerprint yielded a better understanding of the carbohydrate geochemistry along an ombrotrophic peatland. In case of DFRC, PCA was used to separately cluster deoxyhexoses (Rha and Fuc) from Rib. A comparison of these two groups of monosaccharides with a vegetation indicator (C/N) and microbial indicator (total amount of phospholipids) confirmed that the discrepancy obtained using PCA is due to the fact that deoxyhexoses are more likely a vegetation indicator and ribose is more likely a microbial indicator.