Abstract :
The chemical composition of soil organic binders and their role in aggregate stability is largely unknown. The purpose of this study was to characterize soil organic matter (SOM) in soil macro and microaggregates by pyrolysis field ionization mass spectrometry (Py-FIMS). In comparison with a wheat-fallow (WF) rotation, a continuous wheat (CW) system stored more organic C, maintained a greater proportion of water stable macroaggregates > 250 μm and was characterized by greater molecular diversity of SOM. The highest concentration of molecular ions in all aggregate fractions were carbohydrates, lignin monomers, N compounds, and alkylaromatics (each representing from 9 to 15% of total detected molecular ions). Lipids, lignin dimers and sterols were the least abundant (each representing from 0.3 to 4% of total detected molecular ions). Linear regression models showed that the proportion of water stable macroaggregates was correlated with the concentration of lignin dimers (r = 0.98), sterols (r = 0.94), alkylaromatics (r = 0.94) and lipids (r = 0.90). Chemical classes of organic compounds were not correlated with the proportion of water stable microaggregates.
