Soil organic matter in nano-scale structures of a cultivated Black Chernozem

Abstract

We report on the spatial arrangement, chemical composition and stabilization of soil organic matter (SOM) in nano-size structures isolated from a clay fraction of a cultivated Black Chernozem of Canada. Both soil fractions were characterized by Transmission Electron Microscopy (TEM), Pyrolysis Field Ionization Mass Spectrometry (Py-FIMS) and radiocarbon dating, which assisted to better understand the role of SOM and inorganic colloids in the stabilization of carbon and nitrogen at the nm scale. Observations made by TEM indicated that SOM in nano-size fractions occurred mainly in organo-mineral complexes but also in solitary structures of humic substances that formed a carbonaceous network of single strands linking clusters of humic materials and minerals, ranging from a few nm to μm in size. Observations by TEM indicate that humic substances facilitated the spatial arrangement of minerals, thus contributing to physical and physico-chemical stabilization of SOM in nano-size structures. The thermal products evolved during Py-FIMS analyses showed that SOM had greater thermal stability in nano-size structures than in the clay fraction, indicating differences in physical adsorption, cross-linking, polymerization, and/or polycondensation reactions. The SOM in nano-size structures accumulated carbohydrates, N-heterocyclics, peptides, alkylaromatics but was depleted in fatty acids, whereas SOM in the clay fraction was enriched in phenols, lignin monomers, lipids and fatty acids.