Decomposition of Juncus seeds in a valley mire (Faroe Islands) over a 900 year period

Abstract

The influence of past depositional environments on the chemistry of sub-fossil Juncus seed coats (testa) from the top 1 m (corresponding to ca. 900 years of peat accumulation) of a peat bog in the Faroe Islands was examined. The chemistry of the testa of fresh Juncus seeds were characterised using thermally assisted pyrolysis and methylation (THM) in the presence of tetramethyl ammonium hydroxide (TMAH) and 'type' compounds were identified, representative of the major chemical groups in the testa (cellulose-related sugars, lignin-related phenolics, fatty acids). The abundance of the 'type' compounds in the products from sub-fossil testae (the internal tissues of the seeds do not survive beyond the very early stages of decomposition) was then quantified at contiguous 1 cm depth intervals. Major losses of C 18 unsaturated fatty acid methyl esters and sugars were associated with the fresh to sub-fossil transition at ca. 7 cm depth. The preservation of the phenolic ferulic acid in the seed testa appears to be favoured by the input of small basaltic particles from the nearby stream channel. The mechanism by which inwash of inorganic material may be responsible for the improved chemical preservation of the Juncus seed testa is, however, unclear. The sugars were easily metabolised by microorganisms under aerobic conditions of low water table and preserved under anoxic conditions with high water table, suggesting that a drier mire surface may result in the more efficient depletion of polysaccharides and cellulose during the initial stage of decomposition in the acrotelm.

Molecular composition of plant parts and sediment organic matter in a Mediterranean seagrass (Posidonia oceanica) mat

“…A similar mass spectrum was presented by Yeloff et al (2008) and Spaccini et al (2013) in Juncus seed coats and soil organic matter from agricultural sites, respectively. This compound was tentatively identified as a tetramethyl-substituted glucopyranoside derivative (Yeloff et al 2008).…”

“…A similar mass spectrum was presented by Yeloff et al (2008) and Spaccini et al (2013) in Juncus seed coats and soil organic matter from agricultural sites, respectively. This compound was tentatively identified as a tetramethyl-substituted glucopyranoside derivative (Yeloff et al 2008). The NIST '05 library gave a very good correlation with phenyl-O-2,3,4,6-tetra-O-methyl-α-D-glucopyranoside as well, which implies that this compound possibly corresponds to an aromatic glycoside, with a structure similar to that of phloridzin, present in Posidonia leaf extracts (Cuny et al 1995).…”

N deposition and elevated CO2 on methane emissions: Differential responses of indirect effects compared to direct effects through litter chemistry feedbacks

“…The relative abundance of major groups of macromolecular organic compounds, like saturated fatty acids, guaiacyl lignin, syringyl lignin, and p‐hydroxyphenyl lignin, was determined through chemolysis of thermally assisted hydrolysis and methylation, as the number of detected ions in the mass spectrometer is linearly related to the amount of material [ Blokker et al , 2005]. Organic compounds were chosen to represent the components relevant for decomposition and were classified on the basis of their mass spectra, applying the commercial databases Wiley 6 and NIST98 [ Yeloff et al , 2008]. To 200 μ g of sample, 5 μ l of a 25% TMAH solution in methanol was added.…”

Recent applications in analytical thermochemolysis

“…Sub-fossil Juncus seed coats (testa) from a peat bog (900 years of peat accumulation) in Faroe Islands were investigated by thermochemolysis-TMAH [182]. One of the findings focused on the main chemical composition of the testa which was grouped as cellulose-related, lignin-derived phenolics and fatty acids.…”