Establishing the origin of aromatic products from vascular and non-vascular vegetation inputs in surficial peats using ¹³C-labelled tetramethylammonium hydroxide (TMAH) thermochemolysis

Six cambic stagnohumic gley soil profiles located on marginal peatland between a gymnosperm plantation (Sitka spruce (Picea sitchensis (Bong.) Carr.)) and heather grassland in Wark Forest (northeast England), were analysed using 13C labelled tetramethylammonium hydroxide (TMAH) thermochemolysis to yield methylated phenolic and oxygenated aromatic products. The identification of aromatic compounds derived from the thermally assisted hydrolysis and methylation (THM) of vascular plant, Sphagnum and non-Sphagnum spp. allowed changes in vegetation both within the top 50 cm of peat (surficial peat) and across the site to be explored. Four sphagnum acid pyrolysis products reflected the presence of Sphagnum spp.; lignin phenols reflected the presence of vascular inputs; whilst 3,4-dimethoxybenzenepropanoic acid methyl ester reflected the presence of the non-Sphagnum moss Polytrichum commune. Pb-210 dating of the surficial peat suggests that a historic change in vegetation identified by the changes in aromatic compound distribution with depth, coincide with the adjacent plantation of coniferous woodland. The peat closest to the plantation has seen a shift from grass dominated vegetation, to a species diverse vegetation cover, including Sphagnum spp. and vascular vegetation. These results suggest that Sphagnum spp. are able to survive not only perturbing environmental conditions, but are also able to establish themselves amongst non-Sphagnum species. This study demonstrates the ability of C-13-TMAH THM to be utilised as a screening method for the rapid characterisation of aromatic biomacromolecules in peat to identify key historic and current vegetation inputs. This technique in combination with peat dating helps identify the degradation patterns of these inputs and associated carbon dynamics, providing information on the resilience of current peat deposits to climate change and changing peat conditions.