Recent advances in the spectroscopic characterization of soil humic substances and their ecological relevance

Non destructive spectroscopic methods such as ¹³C- and ¹⁵N-NMR provide new insights into the structure of humic substances. Solid state NMR is capable of studying complete native soils by the CPMAS-technique. By means of nitrogen 15-enriched composts it is suggested that nitrogen in soil organic matter is mainly located in amide and peptide structures. Most probable assignments are given. The investigation of humification processes in forest soils is possible via an approach which uses several fractionation techniques in combination with degradative and non-degradative analytical techniques. Besides structure analysis, the ¹³C-NMR-spectroscopy provides important information about the functions of humic substances. By using ¹³C-enriched xenobiotics the binding mechanism to organic matter can be elucidated on a molecular basis. Molecular fluorescence spectrometry, a non-invasive method, is a powerful tool for the quantitative characterization of metal ion complexation by dissolved organic matter in aqueous leaf litter extracts in terms of conditional stability constants and metal binding capacities.