Lignin-derived phenols, carbon isotope

Prahl et al. (1994) also concluded that terrestrial OC contributes significantly to Washington Margin sediments. These authors determined bulk elemental and stable carbon isotopic compositions and concentrations of a range of vascular plant biomarkers (epicuticular wax-derived n-alkanes, lignin-derived phenols and cutin-derived hydroxy-alkanoic acids) for sediments from the Columbia... 

Upon oxidative degradation, the complex lignin polymers break down into a suite of simple lignin-derived phenols which are indicative of their source. Of these, p-coumaric acid occurs only in non-woody angiosperm and gymnosperm tissues ( 7), and is therefore, of considerable interest as a potential carrier of a carbon isotope signal for C3/C4 ratios in the catchment vegetation. Both... 

The pathways of carbon flow in eukaryotes are more complex than in prokaryotes, mainly because the C2 units produced within mitochondria can be exported (e.g. for lipid biosynthesis) only as part of a citrate unit produced in the citric acid cycle. The branch point in carbon flow to either isoprene or acetate can lead to additional isotopic fractionation. In general, it seems that n-alkyl hpids in a particular organism are depleted in 13C by c. 1.5%o relative to isoprenoids produced from the same substrate (Hayes 1993). In higher plants, the phenolic precursors of lignin derive from glucose (Fig. 2.29), so it is not surprising that the carbon isotopic composition of lignin reflects the major photosynthetic pathway involved (C3 or C4 Benner et al. 1987). 

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