Temporal and vertical organic matter differentiation along a vegetation succession as revealed by pyrolysis and thermally assisted hydrolysis and methylation

The origin and chemical nature of soil organic matter (SOM) in the ectorganic (L, F and H) horizons from four profiles from different stages of a primary vegetation succession on drift sand was studied to evaluate the impact of the vegetation on organic matter formation. In addition, the main sources of SOM, Le, needles, leaves and (fine) roots of the covering species were analysed. Using conventional pyrolysis, virtually no differences were found between profiles in the same pine forest but with (chemically) different undergrowths. (Deschampsia flexuosa vs. Empetrum nigrum) that clearly delivered leaf and root litter to SOM. Thermally assisted hydrolysis and methylation (THM) of the same samples released compounds that were not detected by conventional pyrolysis without methylation. These compounds included methyl ethers and methyl esters of ((poly)hydroxy)alkanoic acids and were identified as building blocks of cutin and suberin. Both biopolymers appeared to be better tracers of the various inputs of plant material than lignin, particularly in case of the most humified SOM. Although there was evidence of alteration of cutin and suberin compositions in the course of the succession in the beech forest, an inventory was still possible of above- and below ground litter as sources of SOM. (C) 2001 Elsevier Science B.V. All rights reserved.