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The effect of afforestation on the soil organic carbon (SOC) of a peaty gley soil using on-line thermally assisted hydrolysis and methylation (THM) in the presence of
C-labelled tetramethylammonium hydroxide (TMAH)
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Dr Geoffrey Abbott
Mason SL, Filley TR, Abbott GD
Journal of Analytical and Applied Pyrolysis
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In Britain substantial areas of both deep and shallow peatland have been afforested with conifers since the 1950s. However, information about the effects of afforestation on the properties of soil organic carbon (SOC) is lacking. Investigating the geochemical changes that take place when lignin- and tannin-derived phenols are degraded and incorporated into SOC will provide us with an insight into soil carbon dynamics at the molecular level. Here we compare the phenolic distributions in two different peaty gley soil profiles using on-line thermally assisted hydrolysis and methylation (THM) in the presence of both unlabelled and
C-labelled tetramethylammonium hydroxide (TMAH). The two soil profiles were beneath respectively an unforested moorland (ML) and a second rotation Sitka spruce (
) afforested moorland (SS), from Harwood (Northumberland, northeast England, UK). THM of these soils in the presence of
C-labelled TMAH enabled us to assess the relative contributions of lignin, demethylated lignin, and non-lignin phenolics. The lignin phenolic distributions differed in both soil profiles reflecting changing source and decay dynamics within and between the sites. A progressive degradation of syringyl (S) and guaiacyl (G) phenolics was observed in the ML soil, compared with an increase of such components in the organic/mineral horizons of the SS soil. A significant tannin input was observed, particularly in the upper horizons of the SS soil. The S/G ratio gradually decreased with increasing burial in the ML soil, whilst a change in vegetation input and land preparation was recorded by this ratio in the SS soil. Overall, this suggests that afforestation influences the phenolic compositional profiles in these peaty gley soils as a result of one or more of the following processes: changing vegetation input, horizon inversion prior to planting, root input or leaching. This highlights the potential of using lignin and tannins as molecular indicators to assess the effects of afforestation on SOC.
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