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The quantity and quality of plant litter in the soil play an important role in the soil organic matter balance. Besides other pedo-climatic aspects, the content of recalcitrant molecules of plant residues and their chemical composition play a major role in the preservation of plant residues. In this study, we report that intrinsically resistant alkali-soluble bio-macromolecules extracted from maize plant (plant-humic acid) (plant-HA) contribute directly to the soil organic matter (OM) by its addition and conservation in the soil. Furthermore, we also observed that a high syringyl/guaiacyl (S/G) ratio in the lignin residues comprising the plant tissue, which modifies the microscopic structure of the alkali-soluble plant biopolymers, enhances their recalcitrance because of lower accessibility of molecules to degrading enzymes. These results are in agreement with a recent study, which showed that the humic substance of soil consists of a mixture of identifiable biopolymers obtained directly from plant tissues that are added annually by maize plant residues.

Humic acids have been widely investigated by spectroscopic methods, especially NMR and FTIR, and they are known to show significant differences according to their origin. Low resolution methods such as NMR and FTIR, however cannot easily distinguish different input sources or establish relations between SOM chemistry and vegetation or land use in general. High resolution methods, such as analytical pyrolysis and pyrolysis combined with methylation do offer such possibilities. Therefore, HAs from five reference soils called the Eurosoils, including a Vertic Cambisol (E1, Italy), a Rendzina (E2, Greece), a Dystic Cambisol (E3, Great Britain), an Orthic Luvisol (E4, France) and an Orthic Podzol (E5, Germany), that were previously characterized a.o. by NMR, FTIR and ESR, were also analyzed by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and thermally assisted hydrolysis and methylation (THM) and subsequent analysis by GC/MS. The Orthic Podzol sample showed the largest aliphaticity, and the strongest degradation of aliphatics and lignin. The Dystric Cambisol featured the least decomposed HA, which was reflected by a large content of long-chain alkanes, and little lignin degradation. Both the Dystric Cambisol and the Orthic Luvisol HAs contained a significant amount of microbial organic matter. Polyaromatics, which indicate the presence of charred material, were most abundant in the Vertic Cambisol and the Podzol HAs and lowest in the Dystric Cambisol and the Rendzina HAs. THM was able to distinguish between the various vegetations/land uses. Although quantifications by NMR and py-GC/MS are essentially different, the general results largely coincided. NMR appears to underestimate aromaticity and overestimate aliphaticity, but a molecular mixing model yielded reasonable correlations between NMR and pyrolysis data. Classification by ‘degradation state’ based on py-GC/MS largely coincided with acidity determined by titration, but FTIR data did not coincide. Py-GC/MS, with its much larger resolution, is a better tool to distinguish effects of vegetation, microbial input, and degradation. HA's produce the same variety of compounds upon pyrolysis as total SOM extracts and are therefore chemically not more simple than SOM. HA chemistry, however can be understood in the light of land use history and SOM dynamics.

To reconstruct past shifts in the upper forest line (UFL) in the Northern Ecuadorian Andes we are studying the applicability of plant-specific patterns of lipids preserved in soils as proxies for past vegetation along an altitudinal transect. Longer chain length n -alkanes, (C 19 –C 35 ) were previously found to occur in plant-specific patterns in the dominant vegetation in the area as well as in preliminary soil samples, and may serve as such a proxy. In the present study, we assessed the preservation of n -alkane patterns with depth in soils from five excavations along an altitudinal transect 3500–3860 m above sea level (m.a.s.l) in the area. We used the carbon preference index (CPI) as well as chain length distributions of n -alkanes and their most likely degradation products, n -methyl (Me) ketones, n -alcohols and n -fatty acids. Clear n -alkane patterns were found in all the soils and at all depths, while a clear relationship with the observed patterns of n -Me ketones identified them as the primary degradation product of the former. Very low average n -Me ketone/ n -alkane ratio values were found, ranging from 0.03 to 0.15 at the top of the mineral soil, to 0.05–0.20 at the interface with an underlying palaeosol several thousand years old. The concurrent high CPI values indicate very limited degradation of n -alkanes with depth. Except for C 33 , the shifts in n -Me ketone/ n -alkane values were similar for all chain lengths investigated, signifying an absence of preferential degradation of individual n -alkanes. With one exception, all the soils showed a similar increase in n -Me ketone/ n -alkane values with depth, indicating that the degradation rates were not influenced by altitude. This means that, even if the total concentration of n -alkanes decreases over time, the characteristic pattern remains intact, conserving their potential as a biomarker for past vegetation reconstruction in the area, as well as for investigation of degradation processes of soil organic carbon.

The volcanic ash soils in the Guandera region in northern Ecuador exhibit a typical accumulation of organic matter. However, while accumulated, the organic matter present in the mineral soil bears hardly any resemblance with the covering vegetation and its litter. A strong degradation of the ligno-cellulose complex and a large accumulation of aliphatic components were the main characteristics. The accumulation of aliphatic moieties coincided with an excellent preservation of the solvent extractable n-alkanes and n-alcohols as evidenced by large carbon preference indexes (CPIs) and, consequently, a typical plant-derived signature. Although well-preserved, the n-alkanes underwent β-oxidation yielding n-methyl ketones in a somewhat different distribution. The differences observed between n-alkanes and n-methyl ketones were attributed to a relatively more rapid oxidation of alkanes derived from the grass Calamagrostis effusa as compared to the more woody roots of Neurolepis aristata. From top to bottom of the profile, and therefore with time, all lipid signals had rather similar compositions with limited (microbial) degradation implying their significant value as potential biomarkers.

Tannin, condensed and hydrolysable, and lignin are two of the most abundant natural biopolymers in the environment. Yet it is still not possible using one analytical technique to simultaneously track each of their dynamics in litter and soils. Thermally assisted hydrolysis and methylation (THM) using tetramethylammonium hydroxide (TMAH) has been employed to investigate the cycling of tannin and lignin forms in one analysis, but sometimes with equivocal results as many of the products released may originate from both biopolymers. In this study we applied 13 C-labeled TMAH in the analysis of soil organic matter in a soil profile under Corsican pine, an input lacking in hydrolysable tannins, to show the potential of this tool in tracking complex phenol chemistry. This method successfully allowed for a qualitative distinction among tannin and lignin input as well as permitting the inference of ring specific decay of condensed tannins.

Soil organic matter in a chronosequence of Michigan soils (Spodic Udipsamments and precursors) was studied in thin section and by pyrolysis-gas chromatography/mass spectrometry (GC/MS). The Michigan soils were compared with a well-drained Dutch Typic Haplorthod that was studied with the same methods. Both techniques indicate that most B-horizon organic matter in the Michigan sequence is root- and char-derived and not due to illuviation. Microbial matter contributes significantly to B-horizon chemistry. Although charcoal is common in A horizons, it hardly contributes to soil organic matter (SOM) chemistry in this horizon, while it constitutes a significant part of B-horizon C. This suggests that silt-size particulate charcoal is transported downward. Nitrogen-containing pyrolysis fragments are abundant, which, together with significant amounts of aromatic components, points to contribution of proteins. The Michigan soils are far less rich in alkyl C than the Dutch counterpart. This suggests a much lower residual accumulation of recalcitrant compounds in the former, probably due to a larger contribution of root litter and a more efficient decomposition. Faster decomposition (shorter mean residence time) in the Michigan soils is also suggested by the low accumulation of SOM in the B horizon. Thus we can conclude that in the Michigan soils, dissolved organic matter contributes significantly to transport of Al and Fe, but essentially without illuviation of organic matter in the B. In the Dutch Spodosol, on the other hand, both transport of dissolved organic C to the B horizon and accumulation of SOM through decomposition of roots play important roles. Pyrolysis-GC/MS is a powerful tool in deciphering organic-matter-related aspects of soil genesis. The formation of many soils is organic matter driven, and this aspect is still poorly understood.

Photosynthetically fixed CO 2 is converted into terrestrial bio(macro)molecules and sequestered as soil organic matter (SOM) by (bio)chemical and physical stabilization processes. SOM is generally divided in arbitrary pools for modeling SOM dynamics. Biochemically recalcitrant SOM fractions are enriched with alkyl carbon (C) structures and resist decomposition due to intrinsic molecular properties. The proportion of alkyl C and the mean age of SOM increase with increase in soil depth. Precursors of these recalcitrant bio(macro)molecules such as glycerides, waxes, and terpenoids occur in plants, microorganisms and animals. The intrinsic biochemical stability of naturally occurring recalcitrant aliphatic biomacromolecules may enhance the terrestrial storage of atmospheric CO 2 . Also, aliphatic macromolecules may be formed in soils upon non-enzymatic polymerization of low-molecular-weight lipids. In this review we propose that increasing the soil organic carbon (SOC) pool by land-use and management practices should also include strategies to increase the proportion of aliphatic compounds in the belowground biomass. Thus, collaborative research is needed to study the fate of plant-, microbial- and animal-derived aliphatic C as precursors for stabilized aliphatic SOC fractions, in particular in deeper soil horizons.

Pioneer plant species were observed growing on mined areas despite unfavourable conditions such as extreme pH, high salinity and phytotoxic levels of several elements. This study evaluated the contribution of pioneer species to the accumulation of soil organic matter (SOM). We collected 51 samples from 17 non-vegetated, natural and pioneer-vegetated sites in five highly saline mined areas in the Sierra de Cartagena (Spain). The composition of SOM was determined using total C, N and S elemental anlayzer, pyrolysis and solid state (13)C NMR spectroscopy. Results showed that pioneer species like Lygeum spartum had contributed approximately 11 kg SOM kg(-1) soil into the Balsa Rosa sites since 1991; it will take approximately 120 years of continuous growth for this plant to increase the SOM level comparable to natural site. In the Portman Bay area, Sarconia ramosissima and Phragmites australis can contribute SOM equivalent to present day SOM in natural sites in the next 30 years. Low quality SOM (C/N>20) deposited by pioneer plants was dominated by lignin-derived organic compounds such as phenols, guaiacols, syringols and aromatics while polyssacharides and alkyls were the major components in high quality SOM (C/N

Extractable and solvent insoluble, ester-bound lipids were analysed in an acid, sandy soil profile under Corsican pine. The n-alkanes and alkanoic acids from the soil profile showed rather poor correlations with those from the pine needles and roots, while the n-alkanol composition in the mineral horizons strongly indicated the presence of lipids derived from a previous grass vegetation. Although the ester-bound lipids (ω-hydroxyalkanoic acids and α,ω-alkanedioic acids (>C24)) suggested that plant sources other than pines were present in the mineral soil horizons their composition was less contaminated and a clear distinction between needle and root input could be discerned. The divergent clustering of soil horizons and plant materials by individual and combined compound classes emphasized the usefulness of both extractable lipids and cutin/suberin in unravelling (past) vegetation and tissue history and contributions to soil organic matter.

Total lipid extracts (TLEs) of subsoils from under oak, had been subjected to natural acidification, were analysed to trace the effects of soil pH on their composition. In addition, roots were analysed as being the main source of SOM in the deeper mineral soil horizons. The TLE of the roots comprised largely triterpenoids and steroids that were barely present in the subsoils. Conversely, only small amounts of alkanoic acids, and no alkanols, ω-hydroxyalkanoic acids or α,ω-alkanedioic acids were detected in the root TLE, whereas in soil TLEs these compounds were highly abundant. The compounds are suggested to be derived from hydrolysed suberin, from the previous grass vegetation and most likely illuviated lipids (i.e. immobilised lipids that moved downwards in dissolved form from overlying horizons) from upper, organic matter-rich horizons and oxidation of lipids mediated by microorganisms. In the course of the soil acidification the amounts of TLE increased and within this fraction long-chain (>C20) alkanoic acids, alkanols, ω-hydroxyalkanoic acids and α,ω-alkanedioic acids increased relatively with respect to short chain (

The base-hydrolysable fraction of roots and soil organic matter (SOM) in mineral subsoils from oak forests (coastal dunes, The Netherlands) with a soil pH varying from pH (CaCl2) 6.9 to 3.5 were analysed both quantitatively and qualitatively. Comparison of thermally assisted hydrolysis and methylation (THM) using tetramethylammonium hydroxide (TMAH) with base hydrolysis data confirmed that base hydrolysis is an efficient way of analysing ester-linked compounds in soils. The compounds released from SOM upon base hydrolysis comprised largely suberin-derived lipids, which were clearly related to the oak vegetation and, in particular, to oak roots. Compared with fresh (fine) roots, which are largely responsible for the input of SOM in the subsoils, unsaturated and epoxy compounds decreased in soil, probably due to oxidation. The amounts of the saponifiable fraction increased upon acidification, whilst hardly any changes were observed in their composition. This accumulation, without significant compositional alteration of ester-bound moieties in acidic soils, indicates that these chemically labile compounds can be preserved in soils.

Subsurface horizons contain considerable amounts of soil organic matter (SOM), which has generally a relatively recalcitrant nature and may be an important key in the examination of the role of soils in the sequestration of carbon. Nonetheless, this part of SOM is hardly studied. This paper focuses on the effects of soil acidification on the formation of SOM in sandy subsurface horizons under Corsican pine ( Pinus nigra var. maritime ) and common oak ( Quercus robur L.) forests in coastal dunes (The Netherlands) as characterized by pyrolysis and thermally assisted hydrolysis and methylation. In the pine forests of 50–70 y old SOM appeared to be only slightly affected by soil pH, whereas SOM from oak forests (100–200 years) showed pronounced changes upon soil acidification. With decreasing soil pH in the oak forests, lignin was more degraded (decrease in syringyl/guaiacyl ratio, reduction of the relative concentration) and the contribution of suberin-derived aliphatic moieties increased. The latter compounds may therefore play an important role in the formation of SOM in the studied subsoils.

Pyrolysis of an alkanol, an alkanoic acid and a wax ester is shown to be affected by the presence of clay and/or ammonium. The alkanol dehydrates and is mainly converted into an 1-alkene, trans and cis 2-alkenes, and a variety of mid-chain alkenes due to double bond migration (‘scrambling’). The alkanoic acid is less affected than the alkanol, although a series of alkenes, alkanes and alkanones is produced in the presence of clay. Furthermore, a large portion is converted into the corresponding alkyl nitrile due to reaction with ammonium, which is promoted by clay. Pure clay does not cause bond breaking of the wax ester upon pyrolysis, but in the presence of ammonium ions the ester bond is cleaved to some extent yielding the alkanol and the alkanoic acid moieties. The products released (i.e. alkanol and alkanoic acid) undergo subsequent reactions. Comparison of pyrolysates of a mixture of grass material and clay with a soil sample taken from the grassland showed great resemblance in the aliphatic part consisting mainly of n-alkenes and n-alkanes, while a large difference with the pyrolysate of grass leaves (alkanols and alkanoic acids) alone was observed. This suggests that mineral particles, especially clay, present in soil samples, can generate compounds upon pyrolysis not directly derived from plant biopolymers.

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, i.e. 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.

Differences in soil organic matter (SOM) composition in consecutive soil profiles (under algae, grass, moss, heather and pine) from a primary vegetation succession (central Netherlands) were investigated by Cross Polarization-Magic Angle Spinning (CPMAS) 13C NMR, chemical degradation (acid hydrolysis of polysaccharides) and pyrolysis-GC/MS (Py-GC/MS) in relation to the vegetation. All mineral soil horizons had lower contents of polysaccharides than the ectorganic layer and/or the fresh plant material as suggested by the diminishing O-alkyl peaks by NMR. The monosaccharide distribution pointed to an increase of microbial sugars in the soil as suggested by the raising C6/C5 ratios. Soil polysaccharides may be accompanied by a significant contribution of carbohydrates from mosses in the first stages, because the undecomposed moss tissues have high C6/C5 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 lower in the ectorganic horizons. The degree of oxidation, as determined by the acid/aldehyde ratio, increased with progressive humification. All Ah horizons contained less aromatics, more oxidized lignin remnants and higher amounts of aliphatic compounds than the litter. One or two macromolecules, which produced n-alkenes/n-alkanes and branched alkenes/alkanes upon pyrolysis and were derived from mosses, were mainly responsible for the accumulation of aliphatics in soil, although other aliphatic polymers, such as suberin, might also play an important role. Preservation of components from earlier vegetation might significantly influence SOM composition.

Summary Podzols tend to form on drift sands in The Netherlands given sufficient time. Differences in organic matter (OM) composition relate to vegetation succession on drift sand that evolves eventually into a micropodzol. We examined the relation between the water-soluble organic matter (WSOM) and the total OM composition in the Ah horizons of the first vegetation stages, under grass (Corynephorus canescens), moss (Polytrichum piliferum), heather (Calluna vulgaris) and pine (Pinus sylvestris), as determined by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and analysis of polysaccharides after acid hydrolysis. Polysacharides dominate the OM in the Ah horizons under grass and moss. Lignin and aliphatic compounds are minor compounds in these profiles, but are more important under heather and pine. The Py-GC traces of the WSOM under grass and moss contain abundant products derived from polysaccharides. The water-soluble fraction is enriched in phenolic and aliphatic compounds in comparison with their contents in pyrolysates of the total OM. In the WSOM fractions under heather and pine, phenols dominate the pyrolysates, whereas lignin-derived methoxyphenols are rare. Remarkably large amounts of alkenes and alkanes are present in the pyrolysates of these water-soluble fractions, most probably derived from aliphatic biopolymers. Their presence in water might be explained through the formation of colloids, which are stabilized by micelle-like arrangements.

11 páginas, 7 figuras, 3 tablas., The heating effect on the soil organic matter (SOM) of a Mediterranean soil was studied in two fractions (macro- and microaggregates) and in two environments (soil under canopy of Quercus coccifera and bare soil between plants). Samples were heated under laboratory conditions at different temperatures (220, 380 and 500 degrees C) to establish their effects on the SOM quality and quantity by comparison with unheated control samples (25 degrees C). The SOM content in the soil under canopy was higher than in the bare one and in the microaggregate fractions than in the macroaggregate ones. Increasing temperatures caused, in general. the decrease of SOM content in both soils as well as in both aggregate classes. The quality of SOM was determined after extraction with 0.1 M NaOH and analysed by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Obtained pyrolysates were characterized by the presence of polyphenols and other aromatic pyrolysis products (lipids, polysaccharides, proteins and lignin derivatives). Some of the products in these control samples, and furthermore the presence of black carbon (BC) markers (e.g. benzene, pyridine and toluene), confirmed the occurrence of past wildfires in the study zone. The composition of the SOM extracted from the soils heated at 220 degrees C, was quite similar to that obtained from unheated soils. The products derived from polysaccharides and lignin, and some coming from polyphenols, were not detected in the pyrolysates of the soil heated at 380 and 500 degrees C., This study was supported by the Conselleria d’Educació de la Generalitat Valenciana and its program “Beca para estancias de becarios y contratados predoctorales en centros de investigación fuera de la Comunidad Valenciana” (BEFPI/2008/018)and the Agreement Generalitat Valenciana – CSIC (2005020112)“Impacto de los incendios forestales repetidos sobre los procesos de erosión hídrica del suelo y la recuperación de la cubierta vegetal. Seguimiento y evaluación en una estación permanente de campo”. We also thank Leo Hoitinga and Joke Westerveld in the University of Amsterdam for helping in the SOM extraction and Py-GC/MS use, and Elizabeth Barrachina and Dolores Rius in the CIDE laboratory for SOM content determinations and Eugenia Gimeno-García for statistics assistance. Comments from two anonymous reviewers prompted significant improvements in the presentation of results.

Volcanic ash soils contain very large stocks of soil organic matter (SOM) per unit area. Consequently, they constitute potential sources or sinks for the greenhouse gas carbon dioxide. Whether soils become a net carbon source or sink with climate and/or land-use change depends on the stability of SOM against decomposition, which is influenced by stabilization mechanisms in the soil. To quantify organic carbon stocks and to clarify the importance of chemical and physical soil characteristics for carbon stabilization in volcanic ash soils, we applied selective extraction techniques, performed X-ray diffraction analysis of the clay fraction and estimated pore-size distribution of soils under natural upper montane forest and grassland (páramo) in the Ecuadorian Andes. Our results show that organic carbon stocks under both vegetation types are roughly twice as large as previously reported global averages for volcanic ash soils. SOM stabilization is suggested to be dominantly influenced by the following chemical and physical soil characteristics: (i) direct stabilization of SOM in organo-metallic (Al-humus) complexes, explaining at most 40% of carbon accumulation, (ii) indirect protection of SOM (notably aliphatic compounds) through low soil pH and toxic levels of Al, and probably also (iii) physical protection of SOM caused by a very large micro-porosity. Moreover, in the case of the forest soils, inherent recalcitrance of OM itself was responsible for substantial accumulation in ectorganic horizons. Both vegetation types contributed to soil acidification, thus increasing SOM accumulation.

Despite the potentially large contribution of black carbon (BC) to the recalcitrant soil organic matter pool, the molecular-level composition of aged BC has hardly been investigated. Pyrolysis-GC/MS, which provides structural information on complex mixtures of organic matter, was applied to the NaOH-extractable organic matter of an acidic colluvial soil (Atlantic ranker) sampled with high resolution (5 cm) that harbours a fire record of at least 8.5 ka. Additionally, 5 charcoal samples from selected soil layers were characterised using pyrolysis-GC/MS for comparison. Pyrolysis-GC/MS allowed distinguishing between BC and non-charred organic matter. It is argued that a large proportion of the polycyclic aromatic hydrocarbons (PAHs), benzenes and benzonitrile in the pyrolysates of the extractable organic matter, together accounting for 21–54% of total identified peak area, derived from BC. In charcoal samples, these compounds accounted for 60–98% of the pyrolysis products. The large quantity of BC in almost all samples suggested a key role of fire in Holocene soil evolution. The high C content of the soil (up to 136 g C kg−1 soil) may be attributed to the presence of recalcitrant organic C as BC, in addition to the sorptive preservation processes traditionally held responsible for long-term C storage in acid soils. Interactions between reactive Al hydroxides and BC could explain the longevity of BC in the soil. This work is the first thorough pyrolysis-GC/MS based study on ancient fire-affected organic matter.

NaOH and Na4P2O7 extractable organic matter fractions of two volcanic ash profiles (Azores Islands) were studied by pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). The soils did not have melanic horizons and were not affected by burning. The pyrolysates of all samples were dominated by polysaccharide-derived compounds. The Na4P2O7 extractable fractions were relatively enriched by markers of lignin, proteins, and lipids. Only in the topsoils (A horizons) did lignin appear to be present in significant amounts and, although present with a high degree of side-chain oxidation, the distribution of lignin-derived products could be related to the overlying vegetation. A similar trend was observed for lipids, in particular the high abundance of C26 alkanol in profile EUR05 clearly reflecting grass. Below the topsoils, lignin and lipids were hardly detectable. With depth, markers of intact polysaccharides decreased relatively to smaller polysaccharide pyrolysis products. The same is true for chitin. Compared with other soils, the relative abundance of lignin and lipids was remarkably low. The occurrence of large amounts of polysaccharides including chitin points to an important in situ production of soil organic matter by fungi and/or arthropods. There is no indication of preservation of plant-derived organic matter by allophane or Al3+, but the presence of large amounts of (microbial) polysaccharides and chitin suggests that these secondary organic matter products are indeed stabilized.

Differences in agricultural management and land use lead to differences in soil structure, soil organic matter (SOM) dynamics and composition. We investigated the SOM composition at three depth layers in a permanent pasture (PP), an organic arable (OA) and a conventional arable (CA) field within one soil series in marine loam deposits in The Netherlands. Both arable fields were in the grass phase of the rotation. The chemical composition of SOM was determined by a combination of conventional pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and of thermally assisted hydrolysis and methylation (THM) with tetramethylammonium hydroxide (TMAH). In PP, SOM was composed of relatively little decomposed, mainly grass-derived material comprising polysaccharides, lignin, aliphatic compounds (extractable lipids, cutin, suberin) and proteins. With depth, plant-derived constituents decreased, whereas microbial and humified material predominated. Both arable soils contained mainly strongly humified plant material and microbially altered proteineous material that showed heterocyclic N-compounds together with alkylbenzenes and phenols upon pyrolysis. With THM small traces of plant-derived alkanols and cutin/suberin were observed in the arable soils. The upper layers of OA contained little lignin, which can only be derived from the grass vegetation or manure inputs since last ploughing (2 years before) since it was not found in the whole plough layer. Overall SOM composition is therefore hardly affected by organic farming compared to conventional management. The differences in SOM content and composition between the pasture and arable fields can be ascribed to differences in input and depth distribution of fresh organic materials. But a difference in physical protection of easily mineralisable SOM between pasture and arable soils is also likely to contribute.

Each plant species has a unique chemical composition, and also within a given plant the various tissues differ from one another in their chemistry. These different compositions can be traced back after decay of the plant parts when they are transformed into soil organic matter (SOM). As a result, the composition of SOM reflects not only the plant origin, but also the various tissues, and the composition consequently provides an estimate of the contribution of above-ground vs. below-ground litter. From the latter distribution the extent of bioturbation (mixing of above-ground litter with the mineral soil) can be assessed. Application of thermally assisted hydrolysis and methylation (THM) using tetramethylammonium hydroxide (TMAH) and subsequent analysis by gas chromatography/mass spectrometry (GC/MS) releases all typical cutin- and suberin-derived aliphatic monomers (mono-, di- and trihydroxyalkanoic acids, alpha,omega-alkanedioic acids) as their methyl esters and/or ethers in a rapid manner. Using the distribution of omega-hydroxyalkanoic acids that are present in pine needle cutin (C(12) and C(14)) and not in root suberin, and those that are present in roots but not in needles (C(20) and C(22)), the extent of bioturbation (mixing of above-ground plant litter with the mineral soil) can be assessed. Similarly, the (9,16-dihydroxyhexadecanoic acid+9,10,18-trihydroxyoctadecanoic acid)/(C(20) + C(22) alpha,omega-alkanedioic acids) ratio reflects the degree of bioturbation. Three mineral soil profiles under Corsican pine with an A horizon that exhibited extensive bioturbation phenomena, and underlying C horizons with hardly any or no bioturbation, were investigated in order to examine the applicability of such an approach. It appeared that the A horizons contained all four mentioned omega-hydroxyalkanoic acids, while the C horizons contained virtually only the C(20) and C(22) members. The results not only suggest that bioturbation occurs in the A horizons, but also that possible illuviation or other transport mechanisms of omega-hydroxyalkanoic acids seem hardly ever or never to occur, which is a prerequisite for applying this biomarker approach in assessing degrees of bioturbation.

11 pages, 8 figures, 3 tables, 58 references., The application of lime in a mature Norway spruce (Picea abies [L.] Karst.) forest in southern Germany induced major changes in the activity of soil organisms and root growth. Since this may influence the chemical compostion of the soil organic matter (SOM) of the organic surface layer, its composition and changes due to the treatment were examined in this study. Fine roots of Norway spruce have a relatively low content of extractable lipids, a low alkyl C content (13C CPMAS NMR) and a high ratio of non-cellulosic to cellulosic carbohydrates (NC/CC, carbohydrate determination by MBTH and gas chromatography analyses) as compared to needles. Furthermore, they show high ratios of suberin/cutin compounds (thermally assisted hydrolysis and methylation, (THM)) and high ratios of eicosanic acid/phytadiene I in their lipid extracts (pyrolysis-GC/MS). Liming (4 t ha21 dolomite) of a Norway spruce organic surface layer decreased the proportion of alkyl C, the alkyl C/O-alkyl C ratio, and the content of extractable lipids. The NC/CC ratio and the abundance of suberin relative to cutin components increased. The contribution of the chlorophyll component phytadiene I decreased in relation to eicosanic acid. These changes are attributed to increased fine root formation in the organic layer after liming. Furthermore, the presence of less degraded lignin (THM, peak ratio of 3,4-dimethoxybenzoic acid, methyl ester/3,4-dimethoxy-benzaldehyde) on the limed plot is explained by the increased input of relatively fresh fine root material. On the other hand, the decrease in the carbon-to-nitrogen ratio may be attributed to the higher microbial activity after liming., This part of the Hoeglwald research was supported by the Ministry for Education and Science, Germany, and by the European Community activity Large-Scale Facility Wageningen NMR Centre (ERBFMGECT950066).

The aliphatic organic matter fraction in a forest soil in the Leuvenum Forest (central Netherlands) was examined by pyrolysis–GC/MS and thermochemolysis. In addition, roots were analyzed for their aliphatic composition. Pyrolysis of soil organic matter and the roots revealed an alkene and alkane pattern, usually attributed to cutan or suberan, whereas thermochemolysis elucidated the presence of suberin. The origin of the soil organic matter could be largely ascribed to root input.