Influence of the mineral matrix on the formation and molecular composition of soil organic matter in a long-term, agricultural experiment

Abstract

Abstract. The formation of soil organic matter from grass residues was studied in a 34-yearold pot experiment with grass cultivation on loamy marl using pyrolysis-field ionization mass spectrometry (Py-FIMS). For whole soils, the Py-FI mass spectra indicated clear changes in the molecular-chemical composition during SOM formation from grass residues. In particular, the enrichment of heterocyclic N-containing compounds with time was remarkable.For organomineral size fractions, even larger differences in the composition of SOM were found. The changes between the 13th and 34th experimental year are partly explained by a net transfer of phenols, lignin monomers und lignin dimers from medium silt to fine silt. Moreover, it is demonstrated that temperature-resolved Py-FIMS enables the determination of the thermal energy required for the evolution of individual compound classes which is a measure of the strength of humic-and organomineral bonds. At lower temperatures (<400 C), the enrichment of thermally less stable and/or loosely bound organic matter with cultivation time in clay and fine silt is due to carbohydrates, N-containing compounds, phenols and lignin monomers. Shifts of evolution maxima toward a higher pyrolysis temperature (> 400 °C) in clay, fine silt and medium silt are explained by a higher thermal stability of humic and/or organomineral bonds of lignin dimers, alkylaromatics and lipids, that developed during the last two decades of the experiment.

The nature and dynamics of soil organic matter: Plant inputs, microbial transformations, and organic matter stabilization

“…Today's theories of SOM stabilization postulate direct adsorption of amino acids to clays (Sollins et al, 2006;Yuan and Theng, 2012) and the general belief that most soil N is composed of proteinacous-derived and cell wall constituents (Stevenson, 1994;Di Costy et al, 2003;Nannipieri and Paul, 2009). Pyrolysis analysis (Schulten and Leinweber, 1993;Schulten, 1996) shows significant concentrations of cyclic N monomers in soil. The possibility that these are formed during analysis has been considered (Schulten and Leinweber, 1999); however, it is now believed that considerable quantities of these non-plant N compounds do occur in soil (Gillespie et al, 2014).…”

Thermal stability and composition of mineral‐bound organic matter in density fractions of soil

“…1998 ). Leinweber & Schulten (1992) and Schulten & Leinweber (1993) interpreted shifts in such thermograms to higher pyrolysis temperatures as indicating stronger organic–organic and organic–mineral bonds. This view was supported by Py‐FIMS of mixtures when compared with complexes of fulvic acid (FA) with certain clay minerals ( Schnitzer et al .…”

Pyrolysis-molecular beam mass spectrometry to characterize soil organic matter composition in chemically isolated fractions from differing land uses

“…Shulten, Schnitzer and colleagues (HempXing and Schulten 1990;Schnitzer 1991;Schnitzer and Schulten 1992;Schulten 1993;Schulten and Leinweber 1993;Sorge et al 1993) have previously identiWed marker signals for several classes of compounds (Table 1). While relative intensities of each of the marker signals may diVer between py-FIMS and py-MBMS, we assume that the identiWcation of compounds by their m/z should be the same in py-MBMS compared to py-FIMS.…”