Deciphering the Input from Fossil and Recent Organic Carbon to Soils in Recultivation Sites in Lusatia, Germany

Summary Previous studies from the recultivated open-cast mining sites of Lusatia differentiate only between the organic carbon pools. This enabled a rough estimation of the individual contributions but did not allow describing molecular differences between the pools nor molecular changes over time. Therefor our work aims to use Ultrahigh resolution mass spectrometry (Fourier transform ion cyclotron resonance mass spectrometry, FT-ICR-MS). It allows a deeper insight into the molecular composition of the different soil carbon pools in the recultivated open-cast mining sites. Negative ESI FT-ICR-MS measurements of the solvent extracts reveal a strong dominance of organo-oxygen compounds representing components with varying carboxylic and hydroxyl groups. The differences in the chemical compositions of the soil extracts from Bar-1 site allowed tracking the changes of the molecular composition of organic matter fractions. Higher amounts of lignite-derived compounds found in the lower part of the profile point to a reduced supply of recent organic carbon into the deeper parts of the profile and a low transformation of the recalcitrant lignite-derived OM at a depth below 40 cm due to missing melioration treatment and/or lacking roots. At Bar-2 site, the compositional inventory of the soil lipids is rather constant with depth completely lacking condensed aromatics.