Litter decomposition and humification in acidic forest soils studied by chemical degradation, IR and NMR spectroscopy and pyrolysis field ionization mass spectrometry

Abstract

Two forest soils (Typic Dystrochrept, Entic Haplorthod) with mor and moder were investigated by chemical degradation, IR and CPMAS I3C NMR spectroscopy and pyrolysis (Py) field ionization (FI) mass spectrometry (MS). Chemical analyses show that during litter decomposition, humification, and podzolisation, cellulose and lignin structures decrease considerably, whereas no distinct changes were found for the hemicellulose and protein fractions. These results are consistent with current hypotheses on the conversion of plant residues to stable humic substances, but the sum of chemically identified organic soil components of the litter layers only accounts for 40-50% of total organic carbon. The amounts of different carbon types were estimated by the integration of CPMAS "C NMR spectra. For the L layers this calculation assigns 56-58 % as 0-alkyl-C, 20-22 % as alkyl-C, 14-16 % as aryl-C, and 6-8 % as carboxyl-C. With increasing soil depth 0-alkyl-C (with polysaccharides as main source) decrease to 31-42 %, aliphatic C increases to 3 6 4 3 %, and aryl-and carboxyl-C show no distinct changes. The hypothesis of an increasing aromaticity during humification in soils therefore is questionable. Data from Py-FIMS confirm and extend the results of chemical methods as well as IR and "CNMR spectroscopy. In particular, the FI mass spectra of the generated pyrolysates show that the increase in polymethylene carbon during the biodegradation and humification of beech and spruce litter is partly due to an increase of saturated fatty acids. This means, Py-FIMS is able to describe the structure of wet-chemically unaccounted, individual humus constituents and thus improves the knowledge about the genesis of humic substances. Humifizierung in sauren Waldhumusprofilen mit chemischem Abbau, IR und NMR Spektroskopie und Pyrolyse Feldionisation-MassenspektrometrieZwei Waldboden (Typic Dystrochrept, Entic Haplorthod) mit Rohhumus und Moder wurden chemisch, spektroskopisch (IR, CPMAS I3C NMR) und thermisch (Py-FIMS) untersucht. Die Ergebnisse der chemischen Analyse zeigen, daB wahrend der Streuzersetzung, Humifizierung und Podsolierung Cellulose und Lignin abnehmen, wahrend sich Hemicellulosen und Proteine kaum verandern. Diese Ergebnisse stimmen mit den bekannten Vorstellungen bezuglich Streuzersetzung und Humifizierung iiberein, jedoch erklart die Summe der chemisch identifizierten organischen Bodeninhaltsstoffe der Streulagen nur 40-50 % des gesamten organischen Kohlenstoffs. Die Summe der verschiedenen Bindungsformen des Kohlenstoffs wurde durch Integration der I3C NMR Spektren errechnet. Fur die L-Lagen gilt: 56-58 % 0-Alkyl-C, 20-22 % Alkyl-C, 14-16 % Aryl-C und 6-8 % Carboxyl-C. Mit zunehmender Bodentiefe nehmen die Polysaccharide auf 31-42 % ab, der Aliphatenanteil steigt auf 3 6 4 3 %, Aryl-C und Carboxyl-C zeigen keine deutlichen Veranderungen. Die Hypothese der zunehmenden Aromatisierung wahrend der Humifizierung in Boden wird dadurch grundsatzlich in Frage gestellt. Die Ergebnisse der Py-FIMS bestatigen und erweitern sowohl die che...

Micromorphological and 13C NMR characterization of a Humic, Lignic, and Histic Folisol from British Columbia

“…Increasing alkyl C intensity with decomposition has been observed in peats (Preston etal. 198'7,1989;Nord6n et al 1992) and forest litter and humus (Hempfling et al 1987; Kcigel-Knabner et al 1988;Zech et al 1987Zech et al , 1990 similar to the levels seen in the Hr2, Oco …”

Organic Carbon Chemistry in Soils Observed by Synchrotron-Based Spectroscopy

“…This analytical approach can be used to increase the understanding of the spatial (microscale) distribution of soil organic C at the molecular level and improve understanding of organomineral interactions and C sequestration in soils (Lehmann et al, 2007) that would not be possible without the use synchrotron radiation. However, investigation of the structural composition of organic C in soils using FTIR spectromicroscopy and subsequent qualitative and quantitative interpretation of the spectra to describe the changes in organic matter chemistry is at times difficult due to the influence of O-H stretching and bending of sorbed water, clay minerals, and metal oxides, Si-O-Si stretching, carbonates, and other inorganic soil constituents that lead to overlap between individual absorption bands of organic and inorganic soil components (Table 10.1) and the preponderance of poorly defined baselines (Hempfling et al, 1987;Rumpel et al, 2001). These need to be considered to avoid incorrect attribution and allow relative quantification.…”

Comparison of humus horizons from two ecosystem phases on northern Vancouver Island using 13C CPMAS NMR spectroscopy and CuO oxidation

“…The spectra in Fig. 2 (a-d) (Hempfling et al 1987;Preston et al 1987Preston et al , 1989K<igel-Knabner et al 1988); this and the good resolution in the spectra suggest that the O-alkyl C most likely derives from original plant inputs.…”