Assessing Plant and Microbial Biomarker Contributions to Soil Organic Matter Using Two Methods of Pyrolysis-Gas Chromatography-Mass Spectrometry (py-GC/MS).

Plant biochemical characteristics influence decomposition rates and subsequently the biochemical composition soil organic matter. Pyrolysis gas chromatography-mass spectrometry (py-GC/MS) is a method that analyzes biochemical fragments of samples and may be used to infer probable source molecules and structures (i.e. lignins, aromatics, proteins ect.) Methylation combined with py-GC/MS improves detection of lignin-derived acids as well as fatty acid methyl esters.  We used both methods (py-GC/MS and TMAH-py-GC/MS) to characterize three fern and two angiosperm species live tissues, litter and soils beneath them in Kohala, Hawaii. Py-GC/MS provided a broad biochemical overview of the samples including lignin, polysaccharide, lipid, and N-bearing compound fragments while TMAH-py-GC/MS provided detailed lignin and lipid-derived fatty acids at the expense of the other categories.  We found distinct differences in lignin biomarkers between the ferns and angiosperms using both methods, although TMAH-py-GC/MS as necessary to observe intact p-coumaryl lignin acids of the ferns.  Although known polysaccharide composition differs between polypod and non-polypod fern clads and angiosperms, we observed no distinct differences in biomarkers, due to the lack of specificity and charring of the samples. Large concentrations of plant-derived epicuticular waxes were evident in the live tissues of all samples and we observed no selective preservation of these compounds in soils beneath the ferns. Py-GC/MS and TMAH-py-GC/MS are compound-specific methods useful to track decomposition dynamics in ecosystems, but most useful used in tandem.