Age, turnover and molecular diversity of soil organic matter in aggregates of a Gleysol

We used an integrated approach to describe soil organic matter (SOM) dynamics through known inorganic and organic components in aggregates of adjacent forested and cultivated Gleysolic soil. Mineral and SOM components were examined in water stable macroaggregates (>250 µm), microaggregates 1 (50–250 µm) and microaggregates 2 (<50 µm) fractions. SOM was characterized by pyrolysis-field ionization mass spectrometry (Py-FIMS), and soil minerals by X-ray diffraction analysis. The mean residence time of organic-C (OC) was determined using radiocarbon dating. OC turnover was determined using the natural abundance of native 13C and that derived from corn residue. We found that OC in macroaggregates was young (<100 yr), turned over in 14 yr, and consisted of OM typical of that found in tissues of plants and soil organisms. Chemical classes of compounds in macroaggregates consisted mainly of carbohydrates, lignin monomers and phenols, lignin dimers, lipids (alkanes, alkenes, n-alkyl esters), fatty acids, sterols, ...