FORMATION AND MOBILIZATION PATHWAYS OF DISSOLVED ORGANIC-MATTER - EVIDENCE FROM CHEMICAL STRUCTURAL STUDIES OF ORGANIC-MATTER FRACTIONS IN ACID FOREST FLOOR SOLUTIONS

Citation
G. Guggenberger et al., FORMATION AND MOBILIZATION PATHWAYS OF DISSOLVED ORGANIC-MATTER - EVIDENCE FROM CHEMICAL STRUCTURAL STUDIES OF ORGANIC-MATTER FRACTIONS IN ACID FOREST FLOOR SOLUTIONS, Organic geochemistry, 21(1), 1994, pp. 51-66
Citations number
70
Categorie Soggetti
Geosciences, Interdisciplinary
Journal title
ISSN journal
01466380
Volume
21
Issue
1
Year of publication
1994
Pages
51 - 66
Database
ISI
SICI code
0146-6380(1994)21:1<51:FAMPOD>2.0.ZU;2-8
Abstract
Dissolved organic matter (DOM) is well recognized to influence the geo chemistry of ecosystems. This study was conducted to determine the pat hways of DOC mobilization in the forest floor of coniferous forests. D OM from the forest floor of two acid forest soils in the Fichtelgebirg e (Germany) was fractionated into hydrophobic acids and neutrals, and hydrophilic acids and neutrals. Carbon distribution at both sites was similar: 53 and 52% hydrophobic acids, 23 and 22% hydrophilic acids, 1 0 and 11% hydrophobic neutrals, and 7 and 8% hydrophilic neutrals, res pectively. Structural composition of the DOM fractions was determined using chemical degradation, FT-IR and C-13 NMR spectroscopy, as well a s pyrolysis-field ionization mass spectrometry. Results indicate diffe rent chemical composition of the DOM fractions within each site. Hydro phobic acids show high concentrations of carboxyl and hydroxyl groups, and a high ratio of vanillic acid to vanillin (ca 1.0), both indicati ng a high degree of biodegradation of plant-derived compounds. Carbohy drates are covalently bound to apolar moieties and from carbohydrate c omposition a lignocellulose nature of the hydrophobic acid fraction is suggested. Hydrophilic acids can be differentiated from the hydrophob ic acids by their higher degree of oxidative biodegradation. The hydro philic acid fraction also exhibits a higher ratio of microbially relea sed polysaccharides versus plant-derived polysaccharides. Hydrophobic neutrals show the closest relationships to the refractory soil humin, with less degraded dimeric 'condensed' lignin subunits and relatively high contents of non-carbohydrate aliphatics. Hydrophilic neutrals are enriched in carbohydrates mobilized by enzymatic cellulose and hemice llulose breakdown, as well as from microbial origin. We conclude that DOM release into forest floor solution is related to microbial activit y by oxidative degradation of plant-derived organic matter (e.g. water -soluble lignin and lignocellulose fragments) and by production of mic robial metabolites (e.g. polysaccharides). Overall evidence suggests t hat hydrophobic acids (i) represent intermediates in organic matter de composition, which can be further degraded to hydrophilic acids and CO 2, and (ii) are precursors of humic substances in illuvial horizons af ter precipitation/adsorption.