Search

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.

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.

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

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.

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 (

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.

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.

Publisher Summary Molecular chemistry reveals significant differences between extracted and non-extractable (residue) peat. In the extracts, lignin and other aromatic fragments, nitrogen-containing moieties are more abundant whereas aliphatics, methyl ketones and lipids are more abundant in the non-extractable fraction. This is not astonishing, since partly oxidized lignin and proteins are hydrophilic and extractable with NaOH, whereas for the extraction of lipids one needs organic solvents. Short-chain straight aliphatics are more abundant in the extractable fraction, and there appears to be a regular decay series of alkanes and alkenes from n -C 28, 28:1 to n -C 10 . One branched alkane that is predominantly present in the extractable fraction is possibly of microbial origin. Some polysaccharide moieties are specifically associated with the extractable fraction and some with the residues. This probably reflects a predominantly microbial origin for the first and predominantly plant-derived for the second, because the plant-derived polysaccharides may still be present in larger molecular units.

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).