MOLECULAR COMPOSITION AND CHEMOMETRIC DIFFERENTIATION AND CLASSIFICATION OF SOIL ORGANIC-MATTER IN PODZOL B-HORIZONS

Whole soils from nine different Podzol B-horizons were analysed by wet -chemistry, solid-state cross-polarization/magic-angle spinning (CPMAS ) C-13-NMR spectroscopy and pyrolysis-field ionization mass spectromet ry (Py-FIMS). The wet-chemical analyses referred to site-specific cont ents of polysaccharides, lipids, lignins, fulvic acids, humic acids an d humins in the organic matter of each horizon. All CPMAS C-13-NMR spe ctra for soils were characterized by intense signals from O-alkyl carb on and alkyl carbon. Aryl carbon and carboxyl carbon were less abundan t. Correspondingly, the Py-FIMS spectra were dominated by signals from carbohydrates and lipids, especially sterols such as ethylcholestapen taene, ethylcholestatetraene, dehydroergosterol, ergosterol, stigmaste rol, taraxerone and a-tocopherol. Lower relative abundances were regis tered for lignins and alkylaromatics. Both intact and microbially alte red lignins accumulated in the B-horizons. Temperature-resolved Py-FIM S enabled two organic matter pools with different thermal stability to be detected. The thermolabile pool (evolution under 450 degrees C) co nsists mainly of carbohydrates, sterols and N-containing compounds, wh ereas the thermostable pool (evolution above 450 degrees C) is largely made up of condensed lignins, lipids and alkylaromatics. To visualize differences and/or similarities between the nine Podzol B-horizons ac cording to their organic matter composition, the data sets obtained by wet-chemistry, CPMAS C-13-NMR spectroscopy and Py-FIMS were evaluated by chemometric methods. Using principal component analysis (PCA), nei ther the wet-chemical data nor the C-13-NMR spectra enabled the Podzol B-horizons to be classified according to vegetation or Podzol type. I n contrast, PCA of 200 FISHER-weighted Py-FIMS signals clearly separat ed the B-horizons according to the composition of SOM. Soils with weak Podzol features are characterized mainly by signals from carbohydrate s, phenols/lignin monomers, fatty acids, and constituents of plant wax es (e.g., nonacosanedione, nonacosanediol). Haplic Podzols show strong signals from lignin dimers, long-chain lipids and sterols. The result s obtained by cluster analysis (CA) of the 200 FISHER-weighted Py-FIMS signals were visually well correlated with those derived from PCB. Bo th chemometric techniques enabled the classification of the nine Podzo l B-horizons according to their degree of podzolization.