Stability of needle and root derived biomarker during litter decomposition

For nearly two decades, biomarker analysis has been widely used to draw conclusions about carbon dynamics and organic matter cycling in soil ecosystems. However, several of the fundamental assumptions underlying this approach had remained empirically untested. This thesis critically examines these foundations and calls some established practices into question.
A central contribution is the first direct comparison of two established depolymerization methods — base-catalyzed methanolysis with KOH and curie-point pyrolysis with TMAH — for analyzing plant- and root-derived molecular biomarkers. The comparison revealed that both the identity of detected molecules and their degradation trends depend strongly on the analytical method employed. Consequently, results obtained by these two approaches are not directly comparable, which has significant implications for cross-study interpretation.
The litter decomposition experiments — conducted over one year under controlled laboratory conditions and three years in a Finnish forest field setting — further demonstrated that the suitability of individual monomers as biomarkers is species-dependent. No universally root-specific molecule could be identified across the six studied species, and degradation dynamics differed considerably between species. These findings show that generalizing about litter input quantities based on measured biomarker concentrations in soil lacks an empirical foundation.
Overall, the molecular marker approach is best understood as a qualitative tool capable of providing broad indications of sample origin rather than precise quantitative estimates. This potential was effectively demonstrated in the final chapter, where the method was applied to a frozen mammoth dung sample from Alaska dating to approximately 12,300 BP. Combining molecular marker analysis with pollen spectra, macroremains, and ancient DNA, the study reconstructed both the paleoenvironment — an open, treeless mammoth steppe dominated by Poaceae and Artemisia — and aspects of the mammoth's paleobiology, including evidence for coprophagy derived from the presence of coprophilous fungal fruiting bodies. This case illustrates that, when used with appropriate caution and in combination with complementary methods, the molecular approach can yield meaningful insights into the provenance and context of organic material across deep time.