Forest soil organic matter: structure and formation

Soil organic matter represents a major component of the world surface carbon reserves. The total carbon in dead organic matter in the forest floor and in the underlying mineral soil has been estimated to be 1450 x 10"9t C, exceeding the amount stored in living vegetation by a factor of two or three (Schlesinger 1977; Meentemeyer et al., 1982; Jenkinson, 1988). Mineralization and humification represent important processes in the terrestrial carbon cycle. Schlesinger (1990) estimated that about 0.7% of the annual terrestrial net primary production is sequestered in refractory humic substances carbon. Organic matter of forest soils is composed of a mixture of above- and belowground plant residues (primary resources), microbial residues (secondary resources), and humic compounds (Swift et al., 1979). Humic compounds are formed concomitantly during the microbial decomposition of primary and secondary resources. The conceptual view of soil organic matter in the present study is that of a continuum ranging from fresh plant litter to humic substances, the final products of humification. A complete separation of plant remains and humic compounds is not possible, due to the fact that organic matter at all stages of degradation and humification is present simultaneously in natural soils, albeit at different amounts. The way in which the objective of this research will be addressed is the study of the chemical structural changes during humification of major plant components, namely lignin and aliphatic biomacromolecules. This is achieved by the analysis of bulk samples in comparison with different fractions. The fractionation procedure is chosen according to the suitability for the compound class under investigation. The data obtained in this way reveal that previous hypotheses on the humification processes in soils are unrealistic. In a final step the results obtained on the structural chemical trends of the individual components are combined with evidence from the literature and a hypothesis is proposed for the major humification processes in forest soils. (orig.)SIGLEAvailable from TIB Hannover: RO 9287(24) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman