Comparison of solid-state carbon-13 nuclear magnetic resonance and organic matter biomarkers for assessing soil organic matter degradation

Soil organic matter (SOM) is a heterogeneous mixture of compounds that are derived from a number of sources. Therefore, trying to assess the stage of SOM alteration is challenging. Recently, our research has proposed a number of degradation parameters based on the measurement of SOM biomarkers. These biomarkers, which can be attributed to a specific organism source and the stage of alteration (oxidation) of a compound can provide information regarding the stage and rate of SOM degradation. The previously developed biomarker ratios for assessing SOM degradation have not been tested with degradation parameters derived from other molecular methods. This study investigates the use of solid-state [13.sub.c] nuclear magnetic resonance (NMR) and organic matter biomarker methods for the assessment of SOM degradation in four soils from Western Canada. Total solvent extraction was used to isolate free lipids, base hydrolysis was used to extract bound lipids, and copper (II) oxide (CuO) oxidation was used to liberate lignin monomers and dimers from the soil. The presence of plant sterols and their oxidative degradation products facilitated the analysis of SOM alteration. Cutin and suberin degradation parameters were applied to study the relative amounts of suberin versus cutin inputs into soil as well as the stage ofcutin and suberin degradation. The extent of oxidation for lignin-derived compounds was also tabulated. The trends observed by solid-state [13.sub.c] NMR (alkyl/O-alkyl ratios) were consistent with those found with the biomarker techniques, however, it should be noted that the biomarker methods provide detailed information on specific compounds whereas solid-state [13.sub.c] NMR only provides information on the 'bulk' structure of SOM. Because only a small portion of SOM components are amenable to analysis by biomarker methods, it is advantageous to use these methods in tandem with solid-state [13.sub.c] NMR spectroscopy and other molecular techniques when investigating SOM sources and biogeochemistry. Abbreviations: SOM, soil organic matter, NMR, nuclear magnetic resonance.