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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.

We investigated the carbon (C) mineralisation and nitrogen (N) dynamics in litter from a Corsican pine forest in response to individual and combined additions of aluminium (Al), condensed tannin (extracted from fresh Corsican pine needles) and hydrolysable tannin (commercial tannic acid). Production rates of CO 2 , NH 4 + and NO 3 − concentrations, tannin concentrations and Al speciation were determined at various time intervals during a 28-day incubation experiment. The addition of Al decreased CO 2 production and shut down nitrification. Exchangeable NH 4 + strongly increased in the Al-amended litter, likely due to (i) decreased microbial uptake of NH 4 + , (ii) the inhibition of nitrification and (iii) competition for soil organic matter (SOM) binding sites by Al. Both tannin species affected C mineralisation and/or N dynamics, be it in different ways. Addition of tannic acid led to a strong increase of the C mineralisation rate and microbial uptake of N, caused by rapid degradation of this labile tannin and subsequent increased microbial nutrient demand. Net immobilisation of N occurred as long as one week after addition. Condensed tannin was not consumed but probably strongly bound to (nitrogenous) SOM compounds, forming recalcitrant complexes and decreasing net N mineralisation. Complexation of Al by tannins in solution before addition to the litter mitigated the Al-induced release of exchangeable NH 4 + . In the case of condensed tannin with complexed Al, this was due to detoxification of Al through complexation. Increased microbial demand for N likely played a major role in decreased NH 4 + accumulation in the samples to which tannic acid with complexed Al was added. Nitrification was shut down despite of the complexation of Al by either condensed tannin or tannic acid.

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.

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.

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

The speciation of titrated copper in a dissolved tannic acid (TA) solution with an initial concentration of 4 mmol organic carbon ((OC)/l was investigated in a nine-step titration experiment (Cu/oC molar ratio = 0.0030-0.0567). We differentiated between soluble and insoluble Cu species by 0.45 mu m filtration. Measurements with a copper ion selective electrode (ISE) and diffusive gradients in thin films (DGT) were conducted to quantify unbound Cu(II) cations ('free' Cu) and labile soluble Cu complexes. For the DGT measurements, we used an APA hydrogel and a Chelex 100 chelating resin (Na form). Insoluble organic Cu complexes (> 0.45 mu m) was the dominant Cu species for Cu/OC = 0.0030-0.0567 with a maximum fraction of 0.96 of total Cu. At Cu/OC > 0.0100, Cu-catalysed degradation of aggregate structures resulted in a strong increase of free Cu and (labile) soluble Cu complexes with a maximum fraction of 0.28 and 0.32 of total Cu, respectively. Labile (i.e. DGT-detectable) soluble Cu complexes had a relatively high averaged diffusion coefficient (D) in the APA hydrogel (3.50 x 10(-6) - 5.58 x 10(-6) cm(2) s(-1)).

Pine litter amended with either tannic acid (TA) or condensed tannins (CTs) was studied to assess the effects on C, N and P mineralization in relation to the fate of tannins by incubation experiments during various time intervals. TA induced a rapid short-term effect resulting in high C respiration and net N and P immobilisation. After one week of incubation, TA was decomposed and net C, N and P mineralization and net nitrification resembled that of the control (non-amended litter). CTs exhibited effects on net mineralization on longer terms, i.e. after several weeks of incubation until the end of the experiment (84 days). While net N and P mineralization were greatly reduced, net nitrification was only slightly affected. Most likely CTs formed complexes with organic N of the substrate thereby reducing net N mineralization, while such complexes were not involved in net nitrification processes. The reduction of net P mineralization is due to the lack of need for P by microbes when they cannot get access to N. The fact that decreasing amounts of extractable CTs were accompanied by increasing effects on mineralization processes with incubation time strongly suggests that CTs were incorporated into the litter in such a way that they were inextricable by the common solvents needed to measure tannins, such as for the Folin-Ciocalteu and HCl-butanol assays.

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.

Summary The processes governing the (im)mobilization of Al, Fe and dissolved organic matter (DOM) in podzols are still subject to debate. In this study we investigated the mechanisms of (im)mobilization of Al, Fe and organic matter in the upper and lower B horizons of two podzols from the Netherlands that are in different stages of development. We equilibrated batches of soil material from each horizon with DOM solutions obtained from the Oh horizon of the corresponding soil profiles. We determined the amount of (im)mobilized Al, Fe and DOM after addition of Al and Fe at pH 4.0 and 4.5 and initial dissolved organic carbon (DOC) concentrations of 10 mg C litre−1 or 30 mg C litre−1, respectively. At the combination of pH and DOC concentrations most realistic for the field situation, organic matter was retained in all horizons, the most being retained in the lower B horizon of the well-developed soil and the least in the upper B horizon of the younger profile. Organic matter solubility seemed to be controlled mainly by precipitation as organo-metal complexes and/or by adsorption on freshly precipitated solid Al- and Fe-phases. In the lower B horizons, at pH 4.5, solubility of Al and Fe appeared to be controlled mainly by the equilibrium with secondary solid Al- and Fe-phases. In the upper B horizons, the solubility of Al was controlled by adsorption processes, while Fe still precipitated as inorganic complexes as well as organic complexes in spite of the prevailing more acidic pH. Combined with a previous study of eluvial horizons from the same profiles, the results confirm the important role of organic matter in the transport of Al and Fe to create illuvial B horizons initially and subsequently deepening and differentiating them into Bh and Bs horizons.

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.

Summary Interactions with dissolved organic matter (DOM) are generally believed to play a crucial role in the translocation of Al and Fe in acid sandy soils. Binding of Al and Fe to DOM affects their mobility in soils by altering sorption equilibria of charged sites on solid soil material, inducing precipitation of organo-metallic complexes and preventing the formation of inorganic Al and Fe phases. The relative importance of the different processes, especially with respect to the translocation of Al, Fe and organic matter in podzols, remains unresolved. We determined the effect of the presence of solid soil material from the eluvial (AhE and AE, respectively) horizons of a Fimic Anthrosol and a Haplic Podzol on the metal-to-organic carbon (M/C) ratio in solution and the formation of dissolved organic Al and Fe complexes. Furthermore, we assessed the resulting influence on the mobilization of Al, Fe and DOM. Even under considerable metal loading, the M/C ratios and ‘free’ metal fractions in solution remained low and relatively constant, due to an apparent buffering by the solid phase and the formation of organo-metal complexes in solution. The M/C ratios remained so low that significant precipitation of organo-metal complexes due to saturation with metals was not found. The apparent buffering by the solid phase can be explained by a strong release of organic matter from solid soil material and adsorption of non-complexed Al and Fe on solid organic matter upon metal addition. Adsorption of organo-metal complexes most likely played only a minor role. The observations confirm the expected mobilization of Al, Fe and DOM in eluvial horizons and seem to indicate that even under fluctuating input of Al, Fe and DOM the soil solution will have a constant composition with respect to M/C ratios and percentage of Al and Fe present in dissolved organo-metal complexes.

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.

The interaction of Cu with dissolved organic matter (DOM, extracted from an organic forest floor) was investigated and the resulting data was evaluated in terms of their uncertainty. The speciation of Cu over free Cu (as analysed by diffusive gradients in thin films (DGT)), dissolved Cu–DOM complexes and precipitated Cu–DOM was determined as a function of pH (3.5, 4.0 and 4.5) and Cu/C ratio. The dissolved organically bound fraction was highest at pH 4.5, but this fraction decreased with increasing Cu/C ratio, which was observed for all pH levels. In the range of Cu=C ¼ 7 � 10 � 5 –2:3 � 10 � 2 (mol/mol) the precipitated fraction was very small. The speciation of both Al and Fe was not affected by increasing Cu concentrations. From a continuous distribution model using the Scatchard approach, we calculated the optimal fit and corresponding upper and lower 95% uncertainty bounds of the overall stability constants (Ko) with the shuffled complex evolution Metropolis (SCEM) algorithm. Although the optimal equation fitted the data very well, the uncertainty of the, according to literature, most reliable approach to establish stability constants, was still large. Accordingly, the usually reported intrinsic stability constants exhibited large uncertainty ranging from log Ki ¼ 6:0–7.1 (optimal 6.7) for pH 3.5, log Ki ¼ 6:5–7.1 (optimal 6.8) for pH 4.0, and log Ki ¼ 6:4–7.2 (optimal 6.8) for pH 4.5 and showed only little effect of pH. 2002 Elsevier Science Ltd. All rights reserved.

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.

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.

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.

Fossil remnants of benthic foraminifera consist of carbonate tests and their organic linings. The macromolecular and stable isotopic composition of these benthic foraminiferal organic linings was characterized to evaluate their potential use as paleoclimate proxies. Using Curie point pyrolysis–GC–MS (Py–GC–MS) we show that benthic foraminiferal organic linings consist of protein and polysaccharides, bound together in a complex macromolecular structure. Both chitin derivatives and traces of guaiacols and syringols, usually assigned to lignin are found. Although the five species of benthic foraminifera all contain chitin derivatives and proteins, the relative contribution of these compounds tends to vary considerably. Oxygen stable isotopic analyses of the organic linings of the benthic foraminiferal species Ammonia tepida indicates that ∂ 18 O OL values are in line with fractionation between seawater and organic matter. In contrast a ∂ 13 C deliberate tracer experiment showed that metabolic carbon is the main source for the carbon fixed in the organic lining. The different pathways of carbon and oxygen stable isotopes into the foraminiferal linings have important implications for future proxy development as they reflect different components of the environment compared to the carbonate bound stable isotopes. Still, the future application of benthic foraminiferal organic linings and their isotopic values critically relies on improvements in calibration and sample size required for isotopic analyses.

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.

Some well-drained podzols on quartz sands in the Netherlands and neighbouring Belgium and Germany show mottling in all horizons due to selective removal of organic matter. Phospholipid analysis and morphology of the mottles suggests that this removal is due to a combination of bacteria, fungi, and actinomycetes. Investigation by pyrolysis-GC/MS of organic matter in the depleted zones as compared to their surroundings indicates (1) selective decay of relatively palatable components, (2) residual accumulation of aliphatic biopolymers such as cutan and suberan that produce alkanes, alkenes and methylketones upon pyrolysis, and (3) accumulation of microbial polysaccharides and N-containing compounds. Although the selective organic matter decay in the depleted mottles is similar to the process that causes degradation of organic matter at the top of the B-horizon and its conversion to an E-horizon, the essential difference is that, while decay at the E–B-horizon transition in podzols is governed by the presence or absence of aluminium and iron, the micro flora that is responsible for the decay mottles acts independently from metal concentrations.

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.

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).

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.

In a primary vegetation sequence on wind blown sands in the Netherlands, podzolization becomes evident under pine forest with various undergrowth and is more expressed under the subsequent beech forest. Recognizable podzol-B horizons appear together with H (humified O) horizons. In order to investigate whether the vegetation influences H horizon composition and the water-soluble fraction of this horizon, H horizons of three subsequent succession stages ( Pinus/Empetrum–Fagus/Vaccinium–Fagus without undergrowth) were sampled, fractionated, and analysed with 13 C CPMAS-NMR, pyrolysis-GC/MS, and by pollen analysis. Water soluble and NaOH soluble fractions of the three H horizons were very similar, suggesting that the humified material in the H horizon was formed exclusively from pine litter and that beech litter, yearly added to the soil surface in large amounts, did not influence the composition of the H horizon. The fact that the input of beech litter into the H horizon under beech was small was supported by very low amounts of Fagus pollen in all H layers. Humin fractions of the three H horizons were remarkably different, which was mainly due to varying amounts of beech root litter. The similarity of the water soluble organic matter fractions suggested that a direct relation between vegetation and organic matter mobilized by humification in the H horizon only exists under pine forest. Hence, increased podzolization under beech was probably not due to changing organic matter input, but to the factor time.

The TEX 86 is a proxy based on a ratio of pelagic archaeal glycerol dibiphytanyl glycerol tetraether lipids (GDGTs), and used for estimating past sea water temperatures. Concerns exist that in situ production of GDGTs lipids by sedimentary Archaea may affect its validity. In this study, we investigated the influence of benthic GDGT production on the TEX 86 by analyzing the concentrations and distributions of GDGTs present as intact polar lipids (IPLs) and as core lipids (CLs) in three sediment cores deposited under contrasting redox conditions across a depth range from 900 to 3000 m below sea level in and below the Arabian Sea oxygen minimum zone (OMZ). Direct analysis of IPLs with crenarchaeol as CL via HPLC/ESI-MS 2 revealed that surface sediments in the OMZ were relatively depleted in the phospholipid hexose, phosphohexose (HPH)-crenarchaeol compared to suspended particulate matter from the water column, suggesting preferential and rapid degradation of this IPL. In sediment cores recovered from deeper, more oxic environments, concentrations of HPH-crenarchaeol peaked at the surface, probably due to in situ production by ammonia-oxidizing Archaea, followed by a rapid decrease with increasing depth. No surface maximum was observed in the sediment core from within the OMZ. In contrast, the glycolipids, monohexose-crenarchaeol and dihexose-crenarchaeol, did not change in concentration with depth in the sediment, indicating that they were relatively well preserved and likely mostly derived from fossil pelagic GDGTs. These results suggest that phospholipids are more sensitive to degradation, while glycolipids might be preserved over longer time scales, in line with previous incubation and modeling studies. Furthermore, in situ produced IPL-GDGTs did not accumulate as IPLs, and did not influence the CL-TEX 86 . This suggests that in-situ produced GDGT lipids were more susceptible to degradation than fossil CL and IPL and did not accumulate as CL. In agreement, no significant changes of TEX 86 with sediment depth in the core lipids were observed. However, consistent differences between IPL-derived TEX 86 and CL-TEX 86 were found. These could be explained by a different composition of CL-GDGT of the glyco- and phospholipids, in combination with dissimilar degradation rates of phospholipids vs. glycolipids. We also observed consistent differences in both IPL-derived and CL-TEX 86 between the different cores, equivalent to 3 °C when converted to temperature, despite the proximity of the core locations. These differences may potentially be due to a larger addition of GDGTs produced in deeper, colder waters to the (sub)surface-derived GDGTs for the deeper core sites.