Connecting molecular biomarkers, mineralogical composition, and microbial diversity from Mars analog lava tubes.

Lanzarote (Canary Islands, Spain) is one of the best terrestrial analogs to Martian volcanology. Particularly, Lanzarote lava tubes may offer access to recognizably preserved chemical and morphological biosignatures valuable for astrobiology. By combining microbiological, mineralogical, and organic geochemistry tools, an in-depth characterization of speleothems and associated microbial communities in lava tubes of Lanzarote is provided. The aim is to untangle the underlying factors influencing microbial colonization in Earth's subsurface to gain insight into the possibility of similar subsurface microbial habitats on Mars and to identify biosignatures preserved in lava tubes unequivocally. The microbial communities with relevant representativeness comprise chemoorganotrophic, halophiles, and/or halotolerant bacteria that have evolved as a result of the surrounding oceanic environmental conditions. Many of these bacteria have a fundamental role in reshaping cave deposits due to their carbonatogenic ability, leaving behind an organic record that can provide evidence of past or present life. Based on functional profiling, we infer that Crossiella is involved in fluorapatite precipitation via urea hydrolysis and propose its Ca-rich precipitates as compelling biosignatures valuable for astrobiology. In this sense, analytical pyrolysis, stable isotope analysis, and chemometrics were conducted to characterize the complex organic fraction preserved in the speleothems and find relationships among organic families, microbial taxa, and precipitated minerals. We relate organic compounds with subsurface microbial taxa, showing that organic families drive the microbiota of Lanzarote lava tubes. Our data indicate that bacterial communities are important contributors to biomarker records in volcanic-hosted speleothems. Within them, the lipid fraction primarily consists of low molecular weight n-alkanes, α-alkenes, and branched-alkenes, providing further evidence that microorganisms serve as the origin of organic matter in these formations. The ongoing research in Lanzarote's lava tubes will help develop protocols, routines, and predictive models that could provide guidance on choosing locations and methodologies for searching potential biosignatures on Mars.

Effects of Climate Change on Soil Organic Matter C and H Isotope Composition in a Mediterranean Savannah (Dehesa): An Assessment Using Py-CSIA.

Dehesas are Mediterranean agro-sylvo-pastoral systems sensitive to climate change. Extreme climate conditions forecasted for Mediterranean areas may change soil C turnover, which is of relevance for soil biogeochemistry modeling. The effect of climate change on soil organic matter (SOM) is investigated in a field experiment mimicking environmental conditions of global change scenarios (soil temperature increase, +2-3 °C, W; rainfall exclusion, 30%, D; a combination of both, W+D). Pyrolysis-compound-specific isotope analysis (Py-CSIA) is used for C and H isotope characterization of SOM compounds and to forecast trends exerted by the induced climate shift. After 2.5 years, significant δ13C and δ2H isotopic enrichments were detected. Observed short- and mid-chain n-alkane δ13C shifts point to an increased microbial SOM reworking in the W treatment; a 2H enrichment of up to 40‰ of lignin methoxyphenols was found when combining W+D treatments under the tree canopy, probably related to H fractionation due to increased soil water evapotranspiration. Our findings indicate that the effect of the tree canopy drives SOM dynamics in dehesas and that, in the short term, foreseen climate change scenarios will exert changes in the SOM dynamics comprising the biogeochemical C and H cycles.

Anthracological study of a Chalcolithic funerary deposit from Perdigões (Alentejo, Portugal): A new analytical methodology to establish the wood burning temperature.

Anthracological analyses of charcoal samples retrieved from Pit 16 of Perdigões (Reguengos de Monsaraz, Portugal), a secondary deposition of cremated human remains dated back to the middle of the 3rd millennium BC, enabled the identification of 7 different taxa: Olea europaea, Quercus spp. (evergreen), Pinus pinaster, Fraxinus cf. angustifolia, Arbutus unedo, Cistus sp. and Fabaceae. All taxa are characteristic of both deciduous and evergreen Mediterranean vegetation, and this data might indicate that the gathering of woods employed for the human cremation/s occurred either on site, or in its vicinity. However, considering both the large distribution of the identified taxa and data about human mobility, it is not possible to conclusively determine the origin of the wood used in the cremation(s). Chemometric analysis were carried out to estimate the absolute burning temperature of woods employed for the human cremation/s. An in-lab charcoal reference collection was created by burning sound wood samples of the three main taxa identified from Pit 16, Olea europaea var. sylvestris, Quercus suber (evergreen type) and Pinus pinaster, at temperatures between 350 and 600 °C. The archaeological charcoal samples and the charcoal reference collection were chemically characterized by using mid-infrared (MIR) spectroscopy in the 1800-400 cm-1 range, and Partial Least Squares (PLS) regression method was used to build calibration models to predict the absolute combustion temperature of the archaeological woods. Results showed successful PLS forecasting of burn temperature for each taxon (significant (P <0.05) cross validation coefficients). The anthracological and chemometric analysis evidenced differences between the taxa coming from the two stratigraphic units within the Pit, SUs 72 and 74, suggesting that they may come from two different pyres or two different depositional moments.

Soil Organic Matter Molecular Composition Shifts Driven by Forest Regrowth or Pasture after Slash-and-Burn of Amazon Forest.

Slash-and-burn of Amazon Forest (AF) for pasture establishment has increased the occurrence of AF wildfires. Recent studies emphasize soil organic matter (SOM) molecular composition as a principal driver of post-fire forest regrowth and restoration of AF anti-wildfire ambience. Nevertheless, SOM chemical shifts caused by AF fires and post-fire vegetation are rarely investigated at a molecular level. We employed pyrolysis-gas chromatography-mass spectrometry to reveal molecular changes in SOM (0-10, 40-50 cm depth) of a slash-burn-and-20-month-regrowth AF (BAF) and a 23-year Brachiaria pasture post-AF fire (BRA) site compared to native AF (NAF). In BAF (0-10 cm), increased abundance of unspecific aromatic compounds (UACs), polycyclic aromatic hydrocarbons (PAHs) and lipids (Lip) coupled with a depletion of polysaccharides (Pol) revealed strong lingering effects of fire on SOM. This occurs despite fresh litter deposition on soil, suggesting SOM minimal recovery and toxicity to microorganisms. Accumulation of recalcitrant compounds and slow decomposition of fresh forest material may explain the higher carbon content in BAF (0-5 cm). In BRA, SOM was dominated by Brachiaria contributions. At 40-50 cm, alkyl and hydroaromatic compounds accumulated in BRA, whereas UACs accumulated in BAF. UACs and PAH compounds were abundant in NAF, possibly air-transported from BAF.

Changes in soil organic matter molecular structure after five-years mimicking climate change scenarios in a Mediterranean savannah.

Mediterranean savannahs (dehesas) are agro-sylvo-pastoral systems with a marked seasonality, with severe summer drought and favourable rainy spring and autumn. These conditions are forecasted to become more extreme due to the ongoing global climate change. Under such conditions, it is key to understand soil organic matter (SOM) dynamics at a molecular level. Here, analytical pyrolysis (Py-GC/MS) combined with chemometric statistical approaches was used for the molecular characterization of SOM in a five-years field manipulative experiment of single and combined rainfall exclusion (drought) and increased temperature (warming). The results indicate that SOM molecular composition in dehesas is mainly determined by the effect of the tree canopy. After only five years of the climatic experiment, the differences caused by the warming, drought and the combination of warming+drought forced climate scenarios became statistically significant with respect to the untreated controls, notably in the open pasture habitat. The climatic treatments mimicking foreseen climate changes affected mainly the lignocellulose dynamics, but also other SOM compounds (alkanes, fatty acids, isoprenoids and nitrogen compounds) pointing to accelerated humification processes and SOM degradation when soils are under warmer and dryer conditions. Therefore, it is expected that, in the short term, the foreseen climate change scenarios will exert changes in the Mediterranean savannah SOM molecular structure and in its dynamic.

Soil pH and Soluble Organic Matter Shifts Exerted by Heating Affect Microbial Response.

Fire-induced alterations to soil pH and organic matter play an important role in the post-fire microbial response. However, the magnitude of which each parameter affects this response is still unclear. The main objective of this work was to determine the magnitude in which soil pH and organic matter fire-induced alterations condition the response of viable and cultivable micro-organisms using laboratory heating, mimicking a range of fire intensities. Four heating treatments were applied to unaltered forest soil: unheated, 300, 450, and 500 °C. In order to isolate the effect of nutrient or pH heating-induced changes, different culture media were prepared using soil:water extracts from the different heated soils, nutrient, and pH amendments. Each medium was inoculated with different dilutions of a microbial suspension from the same original, unaltered soil, and microbial abundance was estimated. Concurrently, freeze-dry aliquots from each soil:water extract were analyzed by pyrolysis-gas chromatography/mass spectrometry. The microbial abundance in media prepared with heated soil was lower than that in media prepared with unheated soil. Nutrient addition and pH compensation appear to promote microbial proliferation in unaltered and low-intensity heated treatments, but not in those heated at the highest temperatures. Soil organic matter characterization showed a reduction in the number of organic compounds in soil-heated treatments and a marked increase in aromatic compounds, which could be related to the observed low microbial proliferation.

Organic geochemistry and mineralogy suggest anthropogenic impact in speleothem chemistry from volcanic show caves of the Galapagos.

The network of lava tubes is one of the most unexploited natural wonders of the Galapagos Islands. Here, we provide the first morphological, mineralogical, and biogeochemical assessment of speleothems from volcanic caves of the Galapagos to understand their structure, composition, and origin, as well as to identify organic molecules preserved in speleothems. Mineralogical analyses revealed that moonmilk and coralloid speleothems from Bellavista and Royal Palm Caves were composed of calcite, opal-A, and minor amounts of clay minerals. Extracellular polymeric substances, fossilized bacteria, silica microspheres, and cell imprints on siliceous minerals evidenced microbe-mineral interactions and biologically-mediated silica precipitation. Alternating depositional layers between siliceous and carbonate minerals and the detection of biomarkers of surface vegetation and anthropogenic stressors indicated environmental and anthropogenic changes (agriculture, human waste, and cave visits) on these unique underground resources. Stable isotope analysis and Py-GC/MS were key to robustly identify biomarkers, allowing for implementation of future protection policies.

Hydrophobicity of soils affected by fires: An assessment using molecular markers from ultra-high resolution mass spectrometry.

Soil water repellency (SWR) is a physical property due to a complex interaction of factors (e.g., fire, soil organic matter, soil texture) that reduces the soil water infiltration capacity. Traditionally, SWR is attributed to the accumulation and redistribution of hydrophobic compounds within soil profile. To obtain further insight into chemical compounds, which could be associated with SWR, a study was done on coarse (1-2 mm) and fine (< 0.05 mm) granulometric fractions of burned and unburned sandy soils under two Mediterranean vegetation biomes from Doñana National Park (Spain). The water drop penetration time (WDPT) test was used to assess the SWR. The molecular composition of extracted humic substances from the soil organic matter (SOM) was determined by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS). Partial least squares (PLS) regressions showed that the SWR can be predicted (P = 0.006) solely based on the abundances of approximately 1200 common compounds determined by FT-ICR/MS. This model confirmed the significant correlation between a specific SOM molecular composition and the SWR. The comparative analysis revealed that the SWR in the burned samples was significantly (P < 0.05) related to the abundance of aromatic and condensed compounds, while in the unburned samples there was a significant influence of aromatic hydrocarbons and lignin compounds. In the fine fraction, lipid compounds were significantly associated with the SWR. Contrastingly, the coarse fraction did not show any correlation. Alternatively, soils with a high SWR were significantly related to the presence of lipids and lignin. This analysis showed that combining FT-ICR/MS molecular characterizations with statistical treatments is a powerful approach for exploratory analysis suggesting that the structural features associated with SWR in the studied soils are different depending on the types of vegetation or the soil physical fractions with different particle size.

Combination of Stable Isotope Analysis and Chemometrics to Discriminate Geoclimatically and Temporally the Virgin Olive Oils from Three Mediterranean Countries.

The knowledge of the isotopic composition of virgin olive oil (VOO) allows the evaluation of authenticity and geographical origin, being an important tool against fraud. This study aimed to assess if VOOs produced in three Mediterranean regions could be discriminated on the basis of multivariate statistical analysis of geoclimatic and isotopic data. A total of 138 geo-referenced VOO samples from Portugal, France and Turkey from two different cultivation years were collected. The isotopic composition (δ13C, δ2H and δ18O) of VOOs was obtained using an elemental analyzer coupled to an isotope ratio mass spectrometer (EA-IRMS). One-way analysis of variance for δ13C, δ2H and δ18O showed some significant differences either between crop years or geoclimatic conditions. Based on multiple regression analyses using meteorological and geographical parameters, a meteoric water line for olive oil from Portugal, France and Turkey, in two harvest years, were created to assess the impact of climate change on their δ2H and δ18O values. Principal component analysis and Linear Discriminant Analysis, used to sort samples according to geoclimatic origin, performed best for French and Portuguese olive oils. In light of the results, multivariate isotopic analysis of VOO samples may discriminate not only between geoclimatic regions but also among cultivation years.

Fire effects on C and H isotopic composition in plant biomass and soil: Bulk and particle size fractions.

This work studies carbon (C) and hydrogen (H) isotope composition of plant biomass and soil organic matter (SOM) in an attempt to assess both, changes exerted by fire and possible inputs of charred materials to the soil after a wildfire. Isotope composition of bulk soil, soil particle size fractions and biomass of the dominant standing vegetation in the area (Quercus suber) from Doñana National Park (SW-Spain) were studied by isotope ratio mass spectrometry (IRMS). SOM C isotope composition indicates the occurrence of two SOM pools with different degree of alteration. Coarse soil fractions (>0.5 mm) were found 13C depleted with δ13C values close to those in leaf biomass, pointing to a predominance of poorly transformed SOM. Conversely, fine fractions (<0.1 mm) were found enriched in 13C as corresponds to a more humified SOM. The fire produced no changes in this trend, although a consistent 13C enrichment (c. 1‰) was observed in all soil fractions with decreasing size. Concerning H isotopes, the coarse fractions (>0.5 mm) displayed significant lower δ2H values than the intermediate and fine ones (<0.5 mm), again similar to those in leaf biomass (c. -80‰), whereas the fine fractions were found deuterium (2H)-enriched with significant higher δ2H values (c. 50‰), suggesting physical speciation of H depending on soil particle size. The fire produced a significant 2H depletion (Δ2H c. -10‰) in the finer fractions (<0.1 mm). The study of stable isotope analysis added new information and complements the results obtained by other proxies to better understand the effect of fire on SOM.

Effect of a wildfire and of post-fire restoration actions in the organic matter structure in soil fractions.

The impact of wildfires and of restoration actions on soil organic matter (SOM) content and structure was studied in a soil under pine (Pinus pinea) from Doñana National Park (SW Spain). Samples were collected from burnt areas before (B) and after post-fire restoration (BR) and compared with an unburnt (UB) site. Analytical pyrolysis (Py-GC/MS) was used to investigate SOM molecular composition in whole soil samples and in coarse (CF) and fine (FF) fractions. The results were interpreted using a van Krevelen graphical-statistical method. Highest total organic carbon (TOC) was found in UB soil and no differences were found between B and BR soils. The CF had the highest TOC values and FF presented differences among the three scenarios. Respect to SOM structure, the B soil was depleted in lignin and enriched in unspecific aromatics and polycyclic aromatic hydrocarbons, and in all scenarios, CF SOM consisted mainly of lignocellulose derived compounds and fatty acids. In general, FF SOM was found more altered than CF. High contribution of unspecific aromatic compounds and polycyclic aromatic hydrocarbons was observed in B-FF whereas BR-FF samples comprised considerable proportions of compounds from labile biomass, possibly due to soil mixing during rehabilitation actions. The fire caused a defunctionalisation of lignin-derived phenolics and the formation of pyrogenic compounds. The van Krevelen diagram was found useful to-at first sight-differentiate between chemical processes caused by fire and of the rehabilitation actions. Fire exerted SOM demethoxylation, dealkylation and dehydration. Our results indicate that soil management actions after the fire lead to an increase in aromaticity corresponding to the accumulation of lignin and polycyclic aromatic compounds. This suggests additional inputs from charred lignocellulosic biomass, including black carbon, that was incorporated into the soil during rehabilitation practices.

Revisiting 3D van Krevelen diagrams as a tool for the visualization of volatile profile of varietal olive oils from Alentejo region, Portugal.

This paper aims to study the volatile composition of monovarietal extra-virgin olive oils from different varieties from Alentejo region (Portugal). Volatile profile of 82 olive oils was performed by head-space solid phase micro-extraction hyphenated with gas chromatography/mass spectrometry (HS-SPME-GC/MS). A total of 107 volatile compounds, belonging to several class of compounds, like aldehydes, hydrocarbons, alcohols, terpenoids, ketones, sulphurous compounds, acids and esters were identified, assigned to a specific biogenic origin and total abundances were plotted in modified 3D van Krevelen diagrams. The 3D plots showed that there are compositional differences among olive oil varieties. Discriminant analysis confirmed that the pattern of volatile compounds includes enough information to group sample variety amongst discrete monovarietal olive oil. Combining statistical analysis (t-Student) and graphical-tools (van Krevelen diagram) seems to be a powerful tool to determine what molecular families were characteristic of each olive oil variety, contributing to the valorization of monovarietal Portuguese olive oil.

Impact of wildfires on subsurface volcanic environments: New insights into speleothem chemistry.

Siliceous speleothems frequently reported in volcanic caves have been traditionally interpreted as resulting from basalt weathering combined with the activity of microbial communities. A characteristic feature in lava tubes from Hawaii, Azores and Canary Islands is the occurrence of black jelly-like speleothems. Here we describe the formation process of siliceous black speleothems found in a lava tube from La Palma, Canary Islands, Spain, based on mineralogy, microscopy, light stable isotopes, analytical pyrolysis, NMR spectroscopy and chemometric analyses. The data indicate that the black speleothems are composed of a hydrated gel matrix of amorphous aluminum silicate materials containing charred vegetation and thermally degraded resins from pines or triterpenoids from Erica arborea, characteristic of the overlying laurel forest. This is the first observation of a connection between fire and speleothem chemistry from volcanic caves. We conclude that wildfires and organic matter from the surface area overlying caves may play an important role in the formation of speleothems found in La Palma and demonstrate that siliceous speleothems are potential archives for past fires.

Quantitative forecasting black (pyrogenic) carbon in soils by chemometric analysis of infrared spectra.

A detailed and global quantitative assessment of the distribution of pyrogenic carbon (PyC) in soils remains unaccounted due to the current lack of unbiased methods for its routine quantification in environmental samples. Conventional oxidation with potassium dichromate has been reported as a useful approach for the determination of recalcitrant C in soils. However, its inaccuracy due to the presence of residual non-polar but still non-PyC requires additional analysis by 13C solid-state nuclear magnetic resonance (NMR) spectroscopy, which is expensive and time consuming. The goal of this work is to examine the possibility of applying infrared (IR) spectroscopy as a potential alternative. Different soil type samples (paddy soil, Histic Humaquept, Leptosol and Cambisol) have been used. The soils were digested with potassium dichromate to determine the PyC content in environmental samples. Partial Least Squares (PLS) regression was used to build calibration models to predict PyC from IR spectra. A set of artificially produced samples rich in PyC was used as reference to observe in detail the IR bands derived from aromatic structures resistant to dichromate oxidation, representing black carbon. The results showed successful PLS forecasting of PyC in the different samples by using spectra in the 1800-400 cm-1 range. This lead to significant (P < 0.05) cross-validation coefficients for PyC, determined as the aryl C content of the oxidized residue. The Variable Importance for Projection (VIP) traces for the corresponding PLS regression models plotted in the whole IR range indicates the extent to which each IR band contributes to explain the aryl C and PyC contents. In fact, forecasting PyC in soils requires information from several IR regions. In addition to the expected IR bands corresponding to aryl C, other bands are informing about the patterns of oxygen-containing functional groups and the mineralogical composition characteristic of the soils with greater black carbon storage capacity. The VIP traces of the charred biomass samples confirm that aromatic bands (1620 and 1510 cm-1) are the most important in the prediction model for PyC-rich samples. These facts suggest that the mid-IR spectroscopy could be a potential tool to estimate the black carbon.

Changes in soil organic matter composition after Scots pine afforestation in a native European beech forest revealed by analytical pyrolysis (Py-GC/MS).

The introduction of coniferous species in former deciduous forests may exert changes in soil organic matter, particularly in its molecular composition. In this work, pyrolysis-gas chromatography-mass spectrometry was used to study changes in SOM quality related to the centennial afforestation of Scots pine in an area formerly covered by European beech forest in the NE-flank of the Moncayo Natural Park (NE-Spain). For each soil profile three organic layers (fresh litter, fragmented litter and humified litter) and mineral soil horizons (Ah, E, Bhs and C) were studied. A total of 128 compounds were identified in the pyrograms, and composition differences were detected among the organic and mineral soil layers as well as between soils under beech and pine, for the main compound classes: nitrogen compounds, aromatics, lignin methoxyphenols, polycyclic aromatic hydrocarbons, lipids and polysaccharide-derived moieties. Such chemical differences were found to be derived from the biomass composition of the predominant vegetation type that was incorporated into the soil and from its progression into the soil profile. The analysis of the distribution of alkanes indicated higher SOM stabilization in the native beech forest soil. The signal of beech biomarkers (long chain n-alkanes C31-C33) found in the pine E horizon indicates the permanence of SOM derived from the natural forest ca. 100 years after the afforestation.

Mulching-induced preservation of soil organic matter quality in a burnt eucalypt plantation in central Portugal.

Mulching has amply proven its effectiveness to mitigate post-fire soil erosion but its impacts on soil organic matter (SOM) quality and quantity continue poorly studied. The present study addressed this knowledge gap for a eucalypt plantation in central Portugal that had been burnt and, immediately after the wildfire, mulched with 13.6 Mg ha-1 of eucalypt logging residues some five years before. This was done by performing a range of analytical techniques (elemental and isotope analyses, analytical pyrolysis and 13C NMR spectroscopy) not only on the bulk soil samples but also on their humic acids (HAs) and free organic matter (FOM) fractions. While mulching reduced soil and SOM losses with 91 and 93%, respectively, it also improved SOM quality of the topsoil, in particular in terms of HAs and FOM. At 0-4 cm depth, both HAs and FOM contents were roughly twice as high in the mulched plots as in the control plots. The effects of mulching on the molecular composition of HAs and FOM fractions, however, varied markedly. Analytical pyrolysis (Py-GC/MS) revealed that mulching had led to a noticeable accumulation of labile, aliphatic SOM constituents such as carbohydrate-derived and alkyl compounds (fatty acids and n-alkanes) but that it hardly affected the composition of HAs. Even so, solid-state 13C NMR spectroscopy showed that mulching had resulted in a relative increase in aryl C in the FOM fraction, suggesting an enhanced preservation of the pyrogenic OM. Overall, the combined use of a range of analytical techniques allowed to conclude that, five years after their application, the forest logging residues had led to a greater preservation of the fire-derived pyrogenic OM (mainly aromatic compounds) in the topsoil as well as to higher contents of SOM's most labile molecular constituents (mainly carbohydrates and n-alkyl compounds). The former reflected the reduced erosion rates, while the latter was probably due to a combination of reduced erosion rates with the additional input of fresh organic matter.

Pyrogenic organic matter from palaeo-fires during the Holocene: A case study in a sequence of buried soils at the Central Ebro Basin (NE Spain).

We studied the fire record and its environmental consequences during the Holocene in the Central Ebro Basin. This region is very sensitive to environmental changes due to its semiarid conditions, lithological features and a continuous human presence during the past 6000 years. The study area is a 6 m buried sequence of polycyclic soils developed approximately 9500 years ago that is exceptionally well preserved and encompasses four sedimentary units. The content and size distribution of macroscopic charcoal fragments were determined throughout the soil sequence and the analysis of the composition of charcoal, litter and sediments via analytical pyrolysis (Py-GC/MS). The high amount of charcoal fragments recovered in most horizons highlights the fire frequencies since the beginning of the Neolithic, most of which were probably of anthropogenic origin. In some soil horizons where charcoal was not found, we detected a distribution pattern of lipid compounds that could be related to biomass burning. On the other hand, the low number of pyrolysates in the charcoal could be attributed to high-intensity fires. No clear pattern was found in the composition of pyrolysates related to the age of sediments or vegetation type. The most ancient soil (Unit 1) was the richest in charcoal content and contains a higher proportion of larger fragments (>4 mm), which is consistent with the burning of a relatively dense vegetation cover. This buried soil has been preserved in situ, probably due to the accumulation of sedimentary materials because of a high-intensity fire. In addition, the pyrogenic C in this soil has some plant markers that could indicate a low degree of transformation. In Units 2-4, both the amount of charcoals and the proportions of macrofragments >4 mm are lower than those in Unit 1, which coincides with a more open forest and the presence of shrubs and herbs. The preservation of this site is key to continuing with studies that contribute to a better assessment of the consequences of future disturbances, such as landscape transformation and climate change.

Ultra-high resolution mass spectrometry of physical speciation patterns of organic matter in fire-affected soils.

Fire is one of the most important modulating factors of the environment and the forest inducing chemical and biological changes on the most reactive soil component, the soil organic matter (SOM). Assuming the complex composition of the SOM, we used an ultra-high resolution mass spectrometry analysis technique to assess the chemical composition and fire-induced alterations in soil particle size fractions (coarse and fine) from a sandy soil in a Mediterranean oak forest at Doñana National Park (Southwest Spain). Electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) showed that the coarse fraction of soils not affected by fires consisted mainly of polyphenolic compounds consistent with little-transformed SOM and fresh biomass, whereas the fine fraction was enriched in protein and lipid like homologues suggesting microbially reworked SOM. In fire-affected SOM, the coarse fraction contained a high proportion of aromatic compounds, consistent with inputs of charred litter or in situ chemical transformation of the SOM. Analysis of the fine fraction revealed two differentiated chemical families pointing to the existence of two carbon pools; a native microbial-derived moiety composed of lipids and polypeptide compounds, and a secondary, pyrogenic or thermally-altered moiety rich in aromatic compounds. This work represents the first application of ultra-high resolution mass spectrometry to study the chemical composition of SOM in different particle size fractions.

Laccase SilA from Streptomyces ipomoeae CECT 3341, a key enzyme for the degradation of lignin from agricultural residues?

The role of laccase SilA produced by Streptomyces ipomoeae CECT 3341 in lignocellulose degradation was investigated. A comparison of the properties and activities of a laccase-negative mutant strain (SilA-) with that of the wild-type was studied in terms of their ability to degrade lignin from grass lignocellulose. The yields of solubilized lignin (acid precipitable polymeric lignin, APPL) obtained from wheat straw by both strains in Solid State Fermentation (SSF) conditions demonstrated the importance of SilA laccase in lignin degradation with the wild-type showing 5-fold more APPL produced compared with the mutant strain (SilA-). Analytical pyrolysis and FT-IR (Fourier Transform Infrared Spectroscopy) confirmed that the APPL obtained from the substrate fermented by wild-type strain was dominated by lignin derived methoxyphenols whereas those from SilA- and control APPLs were composed mainly of polysaccharides. This is the first report highlighting the role of this laccase in lignin degradation.