Search

Sponges produce distinct fatty acids (FAs) that (potentially) can be used as chemotaxonomic and ecological biomarkers to study endosymbiont-host interactions and the functional ecology of sponges. Here, we present FA profiles of five common habitat-building deep-sea sponges (class Demospongiae, order Tetractinellida), which are classified as high microbial abundance (HMA) species. Geodia hentscheli, G. parva, G. atlantica, G. barretti, and Stelletta rhaphidiophora were collected from boreal and Arctic sponge grounds in the North-Atlantic Ocean. Bacterial FAs dominated in all five species and particularly isomeric mixtures of mid-chain branched FAs (MBFAs, 8- and 9-Me-C16:0 and 10 and 11-Me-C18:0) were found in high abundance (together ≥ 20% of total FAs) aside more common bacterial markers. In addition, the sponges produced long-chain linear, mid- and a(i)-branched unsaturated FAs (LCFAs) with a chain length of 24‒28 C atoms and had predominantly the typical Δ5,9 unsaturation, although also Δ9,19 and (yet undescribed) Δ11,21 unsaturations were identified. G. parva and S. rhaphidiophora each produced distinct LCFAs, while G. atlantica, G. barretti, and G. hentscheli produced similar LCFAs, but in different ratios. The different bacterial precursors varied in carbon isotopic composition (δ13C), with MBFAs being more enriched compared to other bacterial (linear and a(i)-branched) FAs. We propose biosynthetic pathways for different LCFAs from their bacterial precursors, that are consistent with small isotopic differences found in LCFAs. Indeed, FA profiles of deep-sea sponges can serve as chemotaxonomic markers and support the conception that sponges acquire building blocks from their endosymbiotic bacteria.

Background: Since available arable land is limited and nitrogen fertilizers pollute the environment, cropping systems ought to be developed that do not rely on them. Here we investigate the rapidly growing, N2 -fixing Azolla/Nostoc symbiosis for its potential productivity and chemical composition to determine its potential as protein feed. Results: In a small production system, cultures of Azolla pinnata and Azolla filiculoides were continuously harvested for over 100 days, yielding an average productivity of 90.0-97.2 kg dry weight (DW) ha-1 d-1 . Under ambient CO2 levels, N2 fixation by the fern's cyanobacterial symbionts accounted for all nitrogen in the biomass. Proteins made up 176-208 g kg-1 DW (4.9 × total nitrogen), depending on species and CO2 treatment, and contained more essential amino acids than protein from soybean. Elevated atmospheric CO2 concentrations (800 ppm) significantly boosted biomass production by 36-47%, without decreasing protein content. Choice of species and CO2 concentrations further affected the biomass content of lipids (79-100 g kg-1 DW) and (poly)phenols (21-69 g kg-1 DW). Conclusions: By continuous harvesting, high protein yields can be obtained from Azolla cultures, without the need for nitrogen fertilization. High levels of (poly)phenols likely contribute to limitations in the inclusion rate of Azolla in animal diets and need further investigation. © 2018 The Authors. Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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.

Tannins account for a significant proportion of plant biomass and are likely to contribute to the residues formed by incomplete biomass combustion (black carbon, BC). Nonetheless, the molecular properties of thermally modified tannins have not been investigated in laboratory charring experiments. We applied conventional analytical pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and thermally assisted hydrolysis and methylation (THM-GC-MS) to investigate the effects of heat treatment with a muffle furnace on the properties of condensed tannins (CT) from Corsican pine (Pinus nigra) needles. Py-GC-MS showed a decrease in the relative abundance of the 1,2,3-trihydroxybenzenes (pyrogallols) at ≥300 °C and of the dihydroxybenzenes (mainly catechols) at ≥350 °C due to dehydroxylation of the CT B ring. Further dehydroxylation led to formation of monohydroxybenzenes (phenols), which showed a strong enrichment between 350 and 400 °C and, at higher temperatures, to a series of monocyclic and polycyclic aromatics [benzene, alkyl benzenes and polycondensed aromatic hydrocarbons (PAHs)]. Degradation of the A ring could not be recognized via Py-GC-MS, probably because of the poor chromatographic behavior of 1,3,5-trihydroxybenzenes (phloroglucinols). The progressive dehydroxylation and eventual polycondensation of the CT B ring was corroborated using THM-GC-MS. In addition, with THM-GC-MS the thermal rearrangement of CT A rings at 300 °C and higher was inferred from the relative abundance of 1,3,5-trimethoxybenzenes (methylated phloroglucinol derivatives). These compounds were observed at moderate/high temperature (up to 450 °C) and can not be produced from THM of lignin, suggesting that they may be markers of CT in natural BC samples. © 2012 Elsevier Ltd.

The chronology of polycyclic driftsand sequences in cultural landscapes has mainly been based on the combination of radiocarbon (14C) dating of intercalated organic horizons and pollen analysis. This approach, however, yields indirect age information for the sediment units. Also, as soils are dynamic systems, the pedogenetical interpretation of the 14C ages is often quite difficult.To improve the results of radiocarbon dating, we applied fractionated 14C dating, sustained by soil micromorphology and pyrolysis-gas chromatography/mass spectrometry. The results indicate the complexity of the sources and decomposition processes of SOM, and, consequently, provide information as to why radiocarbon dates are not always reliable for the geochronology of driftsand deposits. We then performed an optically stimulated luminescence (OSL) dating study of the driftsand beds in the sequence. This approach yields direct sedimentation ages, and allows differentiating the instable (sand drifting) period from the stable (soil formation) period in each individual cycle of the sequence. Post-depositional mixing of the sands, however, may upset the reliability of the OSL chronology.

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.

Molecular identification of aged black carbon (BC) is problematic owing to potential interference of non-charred aromatic organic matter and to a general lack of techniques that are capable of providing detailed chemistry of it. Pyrolysis-GC/MS is thought to be unsuitable for analysis of BC because the pyrolysis step itself causes molecular rearrangements that may interfere with the thermal modifications by natural burning, and because a significant fraction of BC is not pyrolysable. We optimised a coil probe pyrolysis method for BC by analysing both a lignin-rich peat sample and an aged legume-derived charcoal at various temperatures (400–1200 °C). Pyrolysis at 750 °C for 10 s combined acceptable thermal modifications to the pyrolysed peat with high-quality chromatograms from charcoal. Using this method we analysed 91 samples of up to >11,000 yrs old oak, birch and legume charcoal from a colluvial soil in NW Spain. The charcoal produced a large suite of aromatic compounds that can be considered characteristic of BC in this study: benzene, toluene, PAHs (naphthalene, biphenyl, fluorene and phenanthrene) and N- and O-containing (poly)aromatics (e.g. dibenzofuran and benzonitrile). A series of N-containing compounds that had not been previously reported in charcoal pyrolysates were found (C1-benzoxazole, benzene dicarbonitriles, 2-phenylpyridine, naphthalenecarbonitrile, 2-biphenylcarbonitrile). Small amounts of short-chain n-alkane/n-alkene pairs indicated some aliphatic material had survived the fire. Uncharred or weakly charred carbohydrate substances in the charcoal were identified as levoglucosan, levoglucosenone, furans and furaldehydes. Charcoal fragments from different plants produced similar pyrolysates. Markers of ‘thermolabile’ (non-charred or weakly charred) biomass disappeared as sample age increased. Nonetheless, signal intensity improved with age, suggesting that the pyrolysability of the relatively ‘thermostable’ (condensed) BC fraction increased. We postulate that gradual oxidation of the condensed aromatic backbone of BC enhanced its susceptibility to pyrolysis.

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.

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.

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.

Aged black carbon (BC) from biomass burning is difficult to identify chemically when it is mixed with other forms of soil organic matter (SOM). As a consequence, the natural abundance of aged and degraded BC is unknown. We carried out a molecular characterisation of up to ∼7000 yr old charcoal and NaOH-extractable SOM obtained from a colluvial soil in NW Spain using Curie point pyrolysis-GC/MS and THM. Black C was tentatively quantified using solid state 13 C CP and DP NMR in conjunction with a molecular mixing model (MMM), and the use of BPCAs. Not surprisingly, the charcoal consisted for the most part of chemically distinctive BC moieties, as concluded from CP and DP NMR–MMM (>72% BC-inherent C) and the BPCA method (30–40%). Charcoal produced mainly benzene, toluene and polycyclic aromatic hydrocarbons (PAHs) upon pyrolysis and THM. The SOM was a mixture of BC-derived (producing benzene, toluene, PAHs and benzonitrile on pyrolysis) and non-BC lipid, carbohydrate and protein-derived OM. Benzenes, PAHs and benzonitrile accounted for 41–54% (pyrolysis-GC/MS) and 34–58% (THM) of total identified peak area in extractable SOM, comparable with the 32–41% BC obtained using DP NMR–MMM. Combined results suggested that the SOM BC was a partially oxidised, N-containing, weakly condensed aromatic network. Apart from increased oxidation with age, ∼700 and 7000 yr old BC gave similar molecular fingerprints. The results contribute to our knowledge of the chemistry of BC, a potential climate mediator, and its fate in the terrestrial environment.

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.

Contiene 6 figuras, 2 tablas., Posidonia oceanica forms extensive peat-like deposits (mats) in Mediterranean coastal waters, which have a potential as carbon sinks and archives of environmental change. Nonetheless, the organic chemistry of both P. oceanica plant materials, as well as the environmental and diagenetic effects on the composition of its detritus, is poorly understood. We analyzed plant organs of P. oceanica and the coarse organic matter from a mat core spanning 750 yrs using pyrolysis techniques (PY-GC-MS and THM-GC-MS) to improve our understanding of their molecular properties and their preservation upon mat development. It appeared that leaf sheaths, roots and the outer parts of rhizomes were composed predominantly of phenolic constituents based on p-hydroxybenzoic acid (p-HBA), which is atypical for vascular plants, in addition to carbohydrates and lignin. The inner rhizome and leaf blades had a different composition, with predominance of carbohydrates. The seagrass detritus in the mat was composed mainly of p-HBA phenolic material and carbohydrates, confirming earlier studies showing that the coarse detritus in the mat originates largely from Posidonia sheath, root and rhizome debris. The intermolecular arrangement of the p-HBA remains unclear, as they seem to correspond to ester-bound phenols yet their persistence in the mat attributes them a refractory nature. Variations in molecular composition within the mat are probably associated with diagenetic alteration of P. oceanica detritus, such as the decomposition of minor amounts of fatty acids, chlorophyll and syringyl lignin, and selective preservation of p-HBA relative to carbohydrates. This work lays the foundations for a molecular understanding of carbon storage within the mats and the environmental changes recorded therein., The pyrolysis experiments and J.K. were funded by the project CGL2010-20662 (Plan Nacional de I+D+i, Ministerio de Economía y Competitividad, España) and grant GPC2014/009 (Xunta de Galicia). O.S. was supported by the ECU Faculty Research Grant Scheme and the CSIRO Flagship Marine & Coastal Carbon Biogeochemical Cluster (Coastal Carbon Cluster). The field work and sample preparation were funded by the SUMILEN project “Advances in sampling techniques, biogeochemical characterization, and quantification of the millenary deposits of seagrasses” (Plan Estatal CTM2013- 47728-R) and PALEOPARK project “Millenary changes in the insular Spanish National Parks: perturbations, resilience and trends after the seagrass archives” (Parques Nacionales 1104/2014). This is a publication of the Group of Benthic Ecology 2014 SGR 120.

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.

We performed solid state 13C cross-polarization magic angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectroscopy and pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) on the Penido Vello peat deposit located in Galicia, NW Spain. Often regarded as complementary techniques, solid state 13C NMR and Py–GC/MS are widely used for the characterisation of organic matter. Recently, a molecular mixing model (MMM) was proposed to predict the distribution of C in biochemical components (carbohydrate, protein, lignin, lipid, char) from the 13C NMR spectral distribution, thereby allowing a quantitative comparison with Py–GC/MS product abundances. We discuss the application of this model to a peat core, by comparing NMR-MMM results with Py–GC/MS data. The core represents ∼5000 yr accumulation and ranges from fibric (at the surface) to hemic (bottom). The amounts of carbohydrates and lipids predicted by the MMM and calculated from the quantified Py–GC/MS chromatograms are in close agreement. However, the well known low capability of the conventional Py–GC/MS method to provide structural information on proteins from bulk soils, the poor GC amenability of polar compounds and many other possible sources of inaccuracy in Py–GC/MS and NMR-MMM caused discrepancies with predictions made with the MMM. Also, the MMM failed to give good prediction of the C/N ratio of the peat material. Although the NMR-MMM approach does not account for molecular transitions during decomposition, this oversimplification proved to be acceptable. The MMM seems to be a useful tool for the interpretation of NMR spectral distributions in peat material.

Tannic acid (TA) and condensed tannin (CT) are strongly retained by mineral phases consisting of quartz (Qtz) with or without coatings of either goethite (Gt) or ferrihydrite (Fh). We investigated the impact of evaporation of the carrier solvent after addition of solutions of TA and CT to the mineral phases on tannin retention. These experiments were performed in solutions ranging from acidic to alkaline pH to study the effect of pH on tannin retention and the release of Fe from the mineral phases. It was found that pH had little influence on the interactions between the tannins and the minerals under natural soil pH conditions (pH 4–8) and that evaporation of the carrier solvent followed by re-extraction resulted into stronger retention of the tannins than if the evaporation step was omitted, especially for CTs. Tannins promoted the release of Fe, Al and Si from the mineral phases into the solution, with Fe concentrations increasing in the order Qtz > Qtz–Fh > Qtz–Gt. Qtz–Fh was the strongest adsorbent, and CT was retained stronger than TA. These results confirm that TA and the CTs used are efficient Fe, Al and Si mobilising agents. In natural soil, the fate of tannins after entering the mineral soil is probably affected by the soil's moisture regime and especially by the abundance and type of Fe (oxy)(hydr)oxides. Also, in quartzitic soil poor in secondary oxides, tannins may be tightly bound to Qtz surfaces. We suggest that under natural conditions, where evaporation and rewetting occur continuously, tannins can be attenuated by mineral soil constituents but can also act as carriers of metals or metal (hydr)oxides.

Large-scale clear-cutting and burning caused the altitude of the natural upper forest line (UFL) in the Northern Ecuadorian Andes to decline to the point that its ‘natural’ position is now uncertain. To obtain a detailed reconstruction of the dynamics of the UFL over the last few thousand years, traditional proxies alone do not suffice. For instance, pollen analysis suffers from a low altitudinal resolution due to the large wind-blown component. In an attempt to find new, additional proxies to study past UFL dynamics in the Ecuadorian Andes, we investigated the occurrence of isoprenoids (diterpenes, phytosterols and pentacyclic triterpenoids) in the roots and leaves of 19 plant species responsible for the dominant biomass input in soil and peat records along altitudinal transects covering approximately 500 m above and below the current UFL in two locations in the Northern Ecuadorian Andes. Isoprenoids can serve as biomarker if they are uniquely present in a relevant plant species and preserved well enough in chronological order in suitable records. Such biomarkers could help establish past vegetation dynamics including the UFL position. For an isoprenoid to be a biomarker in soils normally it must be absent from the roots of a plant species as roots do not enter soils in chronological order. For peat deposits this criteria only needs to be met for the peat species themselves as only roots from peat species will be present. Two diterpenes, four phytosterols and six pentacyclic triterpenoids met the criteria for biomarker in peat records. Of these, one diterpene, two phytosterols and three pentacyclic triterpenoids also met the criteria for biomarker in soils. Samples from a soil under forest, a soil under the adjacent paramo and a nearby peat deposit, 14C dated at approximately 1500 cal. AD and 200 cal. AD, were tested for the presence of isoprenoids that meet the criteria for biomarker. Such isoprenoids were only found in the peat bog samples. However, we found that changes of number and concentrations of isoprenoids with depth might provide additional information related to past vegetation changes. In conclusion, isoprenoids show potential for use in a multi-proxy approach to reconstruct past UFL locations in the Northern Ecuadorian Andes and other ecosystems with similar vegetation and soils.

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

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)).

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.

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.

A problem inherent in analytical procedures where thermochemolyis or pyrolysis is coupled with in situ methylation by tetramethylammonium hydroxide is the inability to determine if an observed aromatic methoxyl group was originally present as a hydroxyl or a methoxyl functionality. This analytical insensitivity makes it impossible to ascertain relative inputs of fresh lignin, demethylated lignin and polyphenols (hydrolysable) into natural organic matter pools. 13C-TMAH thermochemolysis, however, methylates using a 13C-labeled methyl group permitting the differentiation of original and analytically-added methyl groups and therefore the potential source of many 'lignin' phenols. Common oak root, senescent leaf, wood, and bark as well as brown rot decayed oak wood are compared herein to test if the 13C-TMAH modification can be used to differentiate sources of phenols. Oak was chosen as it exhibits extremely high contents of hydrolysable tannins which interfere with the study of wood decomposition but also confound any comparative studies of the fate of lignin and tannin in soil profiles, dissolved organic matter, and sediments when using the unlabeled TMAH thermochemolysis technique. The average % monohydroxyl (i.e. 3,5-dimethoxyl, 4-hydroxyl in source) content of syringyl compounds for each sample varies as leaves (70%) < root (75%) < bark (77%) < brown rot wood (85.9%) < wood (89%). Some compounds such as permethylated syringic acid were almost 90% 3,4,5-trihydroxyl benzoic acid in origin as was determined for oak leaf, or, put another way, S6 was derived almost exclusively from gallic acid. Similarly, what was assumed to be permethylated ferulic acid in roots turned out to be predominantly caffeic acid with a 3,4-dihydroxyl substitution rather than the 3-methoxy, 4-hydroxy substitution. When individual compound concentrations are corrected for the polyhydroxyl content to better reflect 'true' lignin, or at least lignin predominantly bound via a ß-O-4 configuration as is released by this chemolysis procedure, the values for lignin proxies changed substantially. As such, it must be considered that many unlabeled TMAH methylated compounds released from natural systems and ascribed to a 'lignin' source may in fact be from tannins or other fresh or degraded phenolics.

Condensed tannins are a major component of litter inputs, but little is known about the effects of tannin structural variations on soil biological processes and organic matter development. Four different condensed tannins (CTs) extracted from balsam fir, western red cedar, kalmia and black spruce were added to Corsican pine litter and subsequently incubated for 16 weeks in order to investigate the effect of the B ring hydroxylation pattern on C, N and P transformations. While for C mineralization the chain length and stereochemistry of the CTs seemed to be a more important parameter, net N and P mineralization rates were clearly reduced compared with non-amended litter. With regard to the B ring hydroxylation, the prodelphinidin (PD) CTs having predominantly three hydroxy groups at the B ring (balsam fir and western red cedar) exhibited significantly lower mineralization rates than the procyanidin (PC) CTs having two OH groups (kalmia and black spruce). The same was true for net nitrification, but this process was only slightly affected by the CTs. Although based on only four CTs, this study indicates that B ring hydroxylation is an important variable determining net N and P mineralization rates. Our results support previous suggestions that PD tannins bind to or react more strongly with soil organic matter. Therefore, more than PC tannins, they reduce the availability of organic N for mineralization as well as their own detectability by standard methods for soil CT.

A collection of tannins extracted from various plant species was subjected to thermally assisted hydrolysis and methylation (THM) using tetramethylammonium hydroxide. The products obtained included 1,3,5-trimethoxybenzenes, derived from A rings of condensed tannins (CTs), and 1,2-dimethoxybenzene, 1,2,3-trimethoxybenzene, and derivatives as major products from the B ring. 1,2,4-Tri- and two tetramethoxybenzenes were also detected in most analyses. Correlation analyses revealed that they were derived from the B ring, with 1,2,4-trimethoxybenzene being derived from a procyanidin (PC) B ring and 1,2,3,5-tetramethoxybenzene from a prodelphinidin (PD) ring. Tannins from species that contained both CT and hydrolyzable tannin (HT) produced mainly permethylated gallic acid moieties upon THM, and the products derived from CTs were less abundant. Most likely, the ester-bound HTs are more easily transmethylated than the cleavage and methylation of the C-C and C-O linked CTs. Statistical analyses of the THM products and 13C NMR data of the tannins showed good correlations between the B ring hydroxylation and the di- and trimethoxybenzenes observed. Using the ratio of the methyl esters of 3,4-dimethoxybenzoic acid and 3,4,5-trimethoxybenzoic acid only provided good correlations of the percent PC as well. Furthermore, the 1,3,5-trimethoxybenzenes may serve as good markers of tannins in plant, soil, sediment or other samples as analyzed by THM.

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.

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.

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 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.

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 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.

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.

Burial of organic matter (OM) plays an important role in marine sediments, linking the short-term, biological carbon cycle with the long-term, geological subsurface cycle. It is well established that low-oxygen conditions promote organic carbon burial in marine sediments. However, the mechanism remains enigmatic. Here we report biochemical quality, microbial degradability, OM preservation and accumulation along an oxygen gradient in the Indian Ocean. Our results show that more OM, and of biochemically higher quality, accumulates under low oxygen conditions. Nevertheless, microbial degradability does not correlate with the biochemical quality of OM. This decoupling of OM biochemical quality and microbial degradability, or bioavailability, violates the ruling paradigm that higher quality implies higher microbial processing. The inhibition of bacterial OM remineralisation may play an important role in the burial of organic matter in marine sediments and formation of oil source rocks.

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.