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Hydrophobic organic compounds in soils, mainly derived from plants, cause soil water repellency (SWR). The relation between such hydrophobic compounds, which we call SWR-markers, and SWR has been rarely known. We aim to understand these relations and trace the possible origin of SWR-markers. Sandy soils were collected from the field under various vegetation at different depths. Of the bulk soil characteristics, total organic carbon (TOC) strongly correlated to SWR. A new sequential extraction and hydrolysis approach was applied to our sandy soils to obtain three individual organic fractions that were analysed by gas chromatography–mass spectrometry: the D fraction was extracted from soils by DCM/MeOH, which was used to eliminate free lipids; the residual soils were extracted by IPA/NH3 and were separated into a DCM/MeOH soluble fraction (AS) and an insoluble fraction (AI) which was depolymerised by trans-methylation. SWR increased after DCM/MeOH extraction and disappeared almost after IPA/NH3 extraction. According to the chemical composition of each fraction, the D fractions and the AS fractions mainly originated from plant leaf waxes. Suberin-derived compounds were most abundant in the AI fractions. Based on the composition of the extracted fractions and the behaviour of SWR upon these extractions, we speculate that high molecular weight suberins were stronger SWR-markers than the low molecular weight (free) lipids. As suberin is an aliphatic biopolyester typically existing in plant roots, the influence of roots on SWR may be more important than previously thought. The results suggest that our approach is useful to extract the essential SWR-markers and enable the identification of their main sources: plant leaf waxes and roots. In particular roots may have a strong influence on SWR to affect water infiltration and, therefore, plant growth.

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.

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.

The volcanic ash soils along an altitudinal transect in Guandera Biological Station in northern Ecuador have been developed under varying vegetation around the upper forest line. Generally, the soils currently covered by forest are composed of Fulvic Andosols (melanic index >1.7) while those under paramo (tropical alpine grasslands) have developed into Melanic Andosols. This vegetation effect on soil formation is believed to be associated with differences in organic matter composition. In this study, we examined whether Fulvic Andosols differed from Melanic Andosols in organic matter composition. Using analytical pyrolysis techniques, we found hardly any differences in the organic matter characteristics related to vegetation cover, not even between soils that supposedly have been covered by forest and paramo for millennia. Small differences were found within the lipid compounds, while the polysaccharides and lignin were virtually absent from the (deeper) mineral soil horizons. The low abundance of polysaccharides in soils that have undergone severe organic matter decomposition is not unusual for most soils, but is uncommon in other Andosols studied with the same pyrolysis techniques.

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.

We investigated the ability of accelerated solvent extraction (ASE) to extract selected lipid biomarkers (C-19=C-34 n-alkanes, n-alcohols and n-fatty acids as well as dehydroabietic acid and P-sitosterol) from a sandy soil profile under Corsican pine. Two organic layers (moss and F1) as well as two mineral soil horizons (EA and Cl) were sampled and extracted with DCM/MeOH (93:7 v/v) by ASE at 75 degrees C and a pressure of 6.9 x 10(6) Pa or 17 x 10(6) Pa. Soxhlet extractions were used as the established reference method. After clean-up and derivatization with BSTFA, the extracts were analyzed on GC/MS.Using Soxhlet as a reference, we found ASE to extract all compounds adequately. The n-alkanes, especially, were found to be extracted very efficiently from all horizons studied. Only the n-fatty acids and P-sitosterol from the organic layers seemed to be extracted at a slightly lower efficiency by ASE. In all but two instances the relative abundance of extracted lipids within a component class was the same regardless of the extraction method used.Using a higher pressure in the ASE extractions significantly increased the extraction efficiency for all component classes in the moss layer, except P-sitosterol. The effect was most pronounced for the n-alkanes. In the EA horizon, a higher pressure slightly reduced the extraction efficiency for dehydroabietic acid. The observed differences between ASE and Soxhlet extractions as well as the pressure effect can be explained by a decrease in polarity of the extractant due to the elevated pressure and temperature applied during ASE extractions as compared to Soxhlet extractions. This would mainly increase the extraction efficiency of the least polar biomarkers: the n-alkanes as was observed. In addition, a better penetration of still partially water-filled micro pores under elevated pressure and temperature may have played a role.

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 (

This paper intends to shed light on the interactions between tannin and mineral soil particles. For that purpose, aqueous solution of condensed tannin (CT) (derived from Black pine (Pinus nigra var. maritima)) and commercially available tannic acid (TA) were added to purified quartz (Qtz) sand and quartz sand coated with either goethite (Gt) or ferrihydrite (Fh). After solvent removal by evaporation the samples were extracted by water. The extracts were analysed for organic carbon, total phenolics and CT. The extractability of the two tannins was small and increased in the order Qtz-Fh < Qtz-Gt < Qtz. For all mineral samples, TA was more extractable than CT. Bonding of tannins to the mineral samples and the partial peptisation of the Fe oxide coatings upon the binding resulted in complex tannin release curves. Our results suggest that the inextractability of tannins from natural soils and the absence of tannins in soil leachates might be caused by strong adsorption on soil minerals such as Qtz and Fe (oxy)(hydr)oxides. The results of competition experiments with mixtures of both tannins demonstrate that the CTs, and TA in particular, can release large amounts of Fe (oxides), suggesting that the tannins are excellent metal-mobilising agents. We therefore suggest that the fate of tannins in the mineral soil environment is highly dependent on the abundance of weakly bonded secondary oxides.

Changes in the molecular composition of ester-linked aliphatic compounds with depth in an acid andic forest soil are studied. Thermally assisted hydrolysis and methylation (THM) using tetramethylammonium hydroxide in combination with gas chromatography/mass spectrometry revealed a dominance of cutin over suberin-derived THM products in the top 5 cm. From 5 to 20 cm, a strong increase in the contribution of suberin-derived THM products was observed. From 20–50 cm, suberin-derived C22, C24 (and C26) ω-hydroxy acids were found to decrease relatively strongly with depth compared with other suberin building-blocks. Their decrease with depth in the ester-bound fraction is ‘reversely’ linked with a strong increase of these compounds in the free extractable lipid fraction which would justify their use as main indicators of a root-derived input to the free extractable lipid fraction. In addition, their relatively strong decrease in the ester-bound fraction suggests that these compounds are more easily released from the suberin structure in soils than other ester-bound aliphatic building-blocks.

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.

The mobility of Al and Fe in acidic sandy forest soils is greatly influenced by interactions with dissolved organic matter (DOM). We determined the distribution of Al, Fe(II) and Fe(III) over dissolved ‘free’ metal, dissolved metal–DOM complexes and metal–DOM precipitates as influenced by solution pH, redox potential and metal/organic carbon (M/C) ratios. For this, we used water extracts of the Oh horizon of a Fimic Anthrosol brought at pH=3.5, 4.0 and 4.5, and added increasing amounts of Fe(II), Fe(III) and Al. For all three metals, soluble metal–DOM complexes were dominant at low M/C ratios (

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.

The composition of amorphous and condensed soil/sediment organic matter (SOM) domains was investigated for one soil sample and four sediment samples. These samples were oxidized with persulfate to remove amorphous SOM, before and after which the composition of SOM was studied by thermogravimetric analysis, pyrolysis-GC/MS, and cross polarization magic angle spinning 13C-NMR. Comparison of the SOM composition before and after oxidation showed that condensed SOM was more thermostable and less polar than amorphous SOM. Condensed SOM was relatively low in O–alkyl C and carboxyl C and it was likely to contain only small amounts of labile organic components (carbohydrates, peptides, fatty acids). Apart from these general characteristics, the composition of the condensed and amorphous domains appeared to be highly dependent on the origin and nature of the SOM investigated. Condensed domains in relatively undecomposed SOM were enriched in aliphatic C, whereas condensed domains in relatively weathered SOM were enriched in aromatic C. Altogether, the compositional changes upon persulfate oxidation were similar to the compositional changes upon humification, which supports the idea that weathered SOM is more condensed than the original material.

Soluble complexation of Al(III), Fe(II) and Fe(III) with dissolved organic matter (DOM) greatly influences the bioavailability and mobility of the metals as well as the DOM itself in acidic forest soils. A scarcity of analytical tools to distinguish between ‘free’ Al(III), Fe(II) and Fe(III) and soluble organic complexes in acidic soil solutions has limited research in this area. We further tested diffusive gradients in thin films (DGT) for this purpose and used it to assess the influence of pH, redox potential and metal/organic carbon (M/C) ratios on soluble organic complexation of Al(III), Fe(II) and Fe(III). We used water extracts of an organic soil (H) horizon from a Fimic Anthrosol at pH 3.5, 4.0 and 4.5 to which we sequentially added the three metal species. DGT worked well for all but Fe(II) at pH 3.5 where a correction for proton competition was needed. For all three metal species, the ‘free’ fraction increased with increasing M/C ratios. The order of soluble complexation strength was Fe(III)>Al(III)>Fe(II). At low M/C ratios the ‘free’ fraction was highest at the lowest pH value due to more deprotonated functional groups, at high M/C ratios increased (organic) precipitation at higher pH reversed this effect. Both reduction of Fe(III) and oxidation of Fe(II) were found. Selective precipitation of Fe(III) complexes led to predominantly soluble Fe(II)–DOM complexes at higher M/C ratios. Therefore, in studies of the mobility and bioavailability of Fe and Al in acidic forest soils, both M/C ratios and Fe(II)/Fe(III) speciation in solution must be determined.

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 To elucidate the mechanism of podzolization in its first stages we studied the fate of the water-soluble organic matter (WSOM) in incipient podzols in sandy soils by comparing the composition of the WSOM from L, F and H horizons with that in the bulk of the Bh horizons and fibres of three profiles. The WSOM appeared to consist significantly of ligno-cellulose and proteins, but these biopolymers were hardly present in the Bh horizons. The material of the fibres, however, greatly resembled the WSOM composition, thereby suggesting that in these soils most of the WSOM is transported through the B horizon and accumulates hardly changed in thin bands where the water stops moving. This implies that in the early steps of podzolization, accumulation of organic matter in the B horizon is not likely to be caused by water-soluble material.

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.

Thermally assisted Hydrolysis and Methylation was used to analyse in more detail the aromatic and aliphatic building blocks of the organic matter of two soil profiles from the Azores. Both Ah horizons showed significant contributions of lignin, tannins, cutin and suberin, which were virtually absent from the underlying horizons. Alkanoic acids were present throughout both soil profiles, with long-chain acids (>C20) decreasing with depth in comparison with short-chain acids in EUR05, whereas having a relative minimum in AB2 and 2Bw1 horizons in EUR06. Despite the huge potential of Andosols to store carbon, the studied soils did not exhibit a great preservation potential of plant-derived molecules (lignin, cutin/suberin-derived lipids, C26 alkanol) in comparison with other soils as studied by THM. By contrast, bacterial-derived branched alkanoic acids are better preserved than the plant-derived alkanoic acids, which confirms the high degree of microbial and insect-derived OM in the Andosols studied.

Tannins are ubiquitous in higher plants and therefore also in litter and soils where they affect many biogeochemical processes. Despite this well recognized role, the fate of tannins in litter and mineral soils is hardly known as often only trace amounts, if any, of tannins are measured. In this study we conducted an incubation experiment using Corsican pine litter to which known amounts of tannic acid (TA) or condensed tannins (CTs) from Corsican pine were added. Using Folin-Ciocalteu as a measure for total phenolics and HCl-butanol as an assay specific for CTs, acetone/water extractable phenolics and tannins decreased with time towards very low levels. Application of Thermally assisted Hydrolysis and Methylation to litter before and after acetone/water extraction revealed that revealed that TA concentration decreased. By contrast, CTs remained to a great extent in the litter and could not be extracted suggesting that they were tightly bound.

For a detailed reconstruction of historic upper forest line (UFL) positions, new proxies in addition to traditional pollen and vegetation analyses are needed. If the straight-chain lipid composition in plant leaves and roots is specific enough to allow distinction, their records in soils and peat bogs might be used for this purpose. We tested for such distinctiveness by analyzing the n-alkane, n-alcohol, n-aldehyde and wax ester composition in lipid extracts from the leaves and roots of the 19 plant species responsible for the dominant biomass input into soils and peat bogs along two altitudinal transects in the Ecuadorian Andes. We found the combined n-alkane and n-alcohol composition of the leaves of the studied plants to be unique enough in theory to allow for a distinction of the various plant species. The extractable straight-chain lipid concentrations in the roots were generally much lower than in the leaves of the same species, and were in many cases less specific. The n-fatty acids, n-aldehydes and wax ester compositions in leaves as well as roots appeared to be less suited as biomarkers, due to a lower specificity of the n-fatty acids and the absence of the n-aldehydes and wax ester from a significant number of plant species. Furthermore, using cluster analysis we found the combination of n-alkanes and n-alcohols from leaves to give the most meaningful clustering from the point of view of an UFL reconstruction, with all but one páramo grassland species and all but one peat bog species clustering separately from forest species. In addition, a large C31/C27 n-alkane ratio as well as a large C26/C30 n-alcohol ratio were found to be indicative of páramo vegetation (grasses). Both clustering and ratios can help reconstruct past UFL positions if discerning individual species from soil or peat records proves unfeasible. The preservation of the straight-chain lipid signal was tested in soil and peat samples from the study area predating 4910 ± 40 14C years B.P. and 2110 ± 40 14C years B.P., respectively, and found to be excellent.

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.

Changes in amount and characteristics of humic acids (HA) were studied during the composting of a biowaste in an 80 l composting device. HA was extracted by NaOH, purified with HCl–HF and dialysed. Freeze-dried HA was characterised by UV-285, elemental analysis, 13C NMR and pyrolysis-GC/MS. Composting of biowaste resulted in the degradation of 65% of the organic matter. The amount of HA decreased in the initial stage of composting but started to increase again after 20 days. At the start, HA was mainly composed of aliphatic compounds which were replaced by aromatic compounds during composting. Characterisation of HA revealed that the contribution of the condensation route was significant for HA formation during composting. Maturity indexes based on NaOH-extracted HA were inappropriate and moreover, beneficial effects of compost amendments to soils cannot be studied by organic matter analysis of bulk compost, but the amount and characteristics of available HA should be determined.

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.