Composition of plant tissues and soil organic matter in the first stages of a vegetation succession

Differences in soil organic matter (SOM) composition in consecutive soil pr ofiles (under algae, grass, moss, heather and pine) from a primary vegetati on succession (central Netherlands) were investigated by Cross Polarization -Magic Angle Spinning (CPMAS) C-13 NMR, chemical degradation (acid hydrolys is of polysaccharides) and pyrolysis-GC/MS (Py-GC/MS) in relation to the ve getation. All mineral soil horizons had lower contents of polysaccharides t han the ectorganic layer and/or the fresh plant material as suggested by th e diminishing O-alkyl peaks by NMR. The monosaccharide distribution pointed to an increase of microbial sugars in the soil as suggested by the raising C-6/C-5 ratios. Soil polysaccharides may be accompanied by a significant c ontribution of carbohydrates from mosses in the first stages, because the u ndecomposed moss tissues have high C-6/C-5 ratios, which falsify the usual interpretation that such high ratios may be due to microbial sugars. Fresh litter and ectorganic layers under heather and pine had similar contents of aromatics, but the contribution of lignin (guaiacols and syringols) was lo wer in the ectorganic horizons. The degree of oxidation, as determined by t he acid/aldehyde ratio, increased with progressive humification. All Ah hor izons contained less aromatics, more oxidized lignin remnants and higher am ounts of aliphatic compounds than the litter. One or two macromolecules, wh ich produced n-alkenes/n-alkanes and branched alkenes/alkanes upon pyrolysi s and were derived from mosses, were mainly responsible for the accumulatio n of aliphatics in soil, although other aliphatic polymers, such as suberin , might also play an important role. Preservation of components from earlie r vegetation might significantly influence SOM composition. (C) 2001 Elsevi er Science B.V. All rights reserved.