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7 páginas.- 5 figuras.-- 1 tabla.- 42 referencias.- Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.scitotenv.2019.07.229, 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., This study is part of the results of the FUEGONEO (CGL2016-76620-R) and INTERCARBON (CGL2016-78937-R) projects funded by the Spanish “Ministerio de Economía y Competitividad”. Girona-García, A. was funded by an FPI research grant (BES-2014-068072) of the “Ministerio de Economía y Competitividad” (Spanish government). Thanks are due for the financial support to CESAM (UID/AMB/50017 - POCI-01-0145-FEDER-007638), to FCT/MCTES through national funds (PIDDAC), and the co-funding by the FEDER, within the PT2020 Partnership Agreement and Compete 2020. We also thank the Aragonese Agents for Nature Protection (APN) of the Moncayo Natural Park for their collaboration and for issuing the sampling permits.

20 páginas.- 8 figuras.- 1 tabla.- 94 referencias.- Supplemental information can be found online at https://doi.org/10.1016/j.isci.2022.104556, 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., This research work received funding from the European Commission’s 7th Framework Programme under the Marie Curie Intra-European Fellowship PIEF-GA-2012-328689-DECAVE. The financial support from the Spanish Ministry of Science and Innovation (MCIN) under the research project TUBOLAN PID2019- 108672RJ-I00 funded by MCIN/AEI/10.13039/501100011033 is also acknowledged. In addition, this work received support from: i) the Portuguese Foundation for Science and Technology (FCT) under the MICROCENO project (PTDC/CTA-AMB/0608/2020), the EROFIRE project (PCIF-RPG-0079-2018) and the project UID/Multi/04449/2019 for HERCULES/UE. A.Z.M. was supported by the CEECIND/01147/2017 contract from FCT, and the Ramón y Cajal contract (RYC2019-026885-I) from the MCIN. M.L.C. and N.T.J.M. were supported by CEECIND/00349/2017 and 2021/00711/CEECIND contracts, respectively, funded by FCT. F.G. was financially supported by the ‘‘HIPATIA’’ research program of the University of Almería and a Ramón y Cajal Fellowship (RYC2020-029811-I) of MCIN.

9 páginas.- 5 figuras.- 1 tabla.- referencias.- Supplementary data to this article can be found online at https://doi.org/10.1016/j.scitotenv.2022.159288, 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., Projects EU-EJC 2nd Call Projects MIXROOT-C and MAXROOT-C, Ministerio de Ciencia Innovación y Universidades (MICIU) INTERCARBON project (CGL2016-78937-R) & DECAFUN (CGL2015-70123-R). L. M. San Emeterio also thanks MICIU for funding FPI research grants (BES-2017-07968).

páginas.- 7 figuras.- 4 tablas.- 87 referencias, Estuaries are dynamic interfaces between land, rivers and the ocean that play major roles in the global carbon cycle. These coastal wetlands store huge amounts of organic carbon (OC), commonly known as “blue carbon” and excellent places to study C cycling. The Guadiana river estuary is among the most important tidal salt marshes in the South - Iberian coastal margin. Here, a detailed organic geochemical study is described that includes the identification of sedimentary OM composition at a molecular and isotopic level. Total organic carbon content (TOC) of core sediments ranged from 0.39 to 2.23% and stable carbon isotope composition (δ13C) also showed a wide range between −22.4 and −27.0‰. A13C depletion trend observed from the surface to bottom in the core sediments profiles, reflects loss of labile biogenic 13C enriched compounds i.e. polysaccharides and a selective preservation of more depleted compounds with depth i.e. lignin and lipids in the core sediments. Series of n-alkanes were found in the range from C10 to C31. Carbon preference index ratio (CPI) calculated for long-chain n-alkanes (C24–C31) that ranged between 1.17 and 1.94 reflecting diverse OM inputs to the sediments. A study of the lignin-derived phenolic composition pointed to a recalcitrant OM derived from both gymnosperm and angiosperm plants. Moreover, high abundance of vinyl phenol and vinyl guaiacol points to a dominant contribution of lignins from grasses and aquatic macrophytes to the sediments. A well-resolved series of long-chain linear alkyl benzenes (LABs from C4 to C22) were recorded in all core sediment samples indicating direct discharge of untreated domestic and/or industrial effluents to the estuary. Polycyclic aromatic hydrocarbons (PAHs) with more than 3 rings reflects the pyrogenic origin of a portion of the sedimentary OM. This study highlights the importance of different OM sources to the lower Guadiana estuarine sediments and contributes to a better knowledge about its origin, dynamics and fate. © 2020 Elsevier Ltd, Research was supported by EU contract numbers FP7-ENV-2011, Grant agreement no: 282845 and FP7- 534 ENV-2012 Grant agreement No: 308392 and also from MINECO project INTERCARBON (CGL 2016-78937-R). We acknowledge the funding by an EU Erasmus Mundus Joint Doctorate fellowship administered by FUECA, University of Cadiz, Spain for Mukesh Kumar.

9 páginas.- 5 figuras.- referencias., 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., We would like to thank the three anonymous reviewers for their helpful comments on the first version of this paper. Following their suggestions,we included several improvements in the manuscript. We are also grateful to projects MarkFire (PAIDI2020, PY20_01073), co-funded by Junta de Andalucía and EU FEDER funds, and EROFIRE (PCIF/RPG/0079/2018) funded by Fundação para a Ciência e a Tecnologia (FCT, Portugal). The Spanish Ministry of Science and Innovation is acknowledged for funding the project PID2019-108672RJ-I00 and the “Ramón y Cajal” postdoctoral contract of Ana Z. Miller [grant number RYC2019-026885-I]. Espacio Natural de Doñana and Estación Biológica de Doñana are acknowledged for technical and logistic support through Project INTERCARBON (2017/19).

10 páginas.- 4 figuras.- 1 tabla.- 40 referencias.- Supplementary Materials: The following are available online at https://www.mdpi.com/article/10.3390/agronomy11122560/s1, Soil water repellency (hydrophobicity) prevents water from wetting or infiltrating soils, triggering changes in the ecosystems. This physical property is directly correlated to the erodibility grade of a soil. Wildfire events may develop, enhance, or destroy soil hydrophobicity, modifying the erodibility grade of a soil and increasing the loss of its most reactive layer (organic matter). To assess the main organic family of compounds (biomarkers) surrogates to fire-induced water repellency, a study was carried out on a fire-affected soil under eucalyptus canopy at two depths (0–2 and 2–5 cm) from Portugal. The potential soil water repellency was measured using the water drop penetration time (WDPT) test. The molecular characterization of hydrophobic biomarkers was carried out using analytical pyrolysis (Py-GC/MS) in combination with multivariate statistical analysis (PCA, MLR). The upper burned soil layer (0–2 cm) displayed a significant contribution of fresh biomass (lignin and polysaccharides), while the deepest (2–5 cm) one showed more humified organic matter (lipids). The soil hydrophobicity was directly correlated to non-polar organic compounds, such as lipids and polycyclic aromatic hydrocarbons (PAHs), and inversely to unspecific aromatic compounds. The combination of mass spectrometry techniques and chemometric analysis allowed obtaining a preliminary forecast model of hydrophobicity degree in fire-affected soil samples under eucalyptus canopy. This analytical approach opens the door to developing more sensitive mathematical models using molecular organic compounds to predict the alteration of hydrophobicity and other soil physical properties induced by fires. View Full-Text, The Portuguese Foundation for Science and Technology (FCT) and the Spanish Ministry of Science and Innovation are acknowledged for funding the CEECIND/01147/2017 and “Ramón y Cajal” (RYC2019-026885-I) post-doctoral contracts, respectively).

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. © 2020 Elsevier B.V., To projects INTERCARBON, CARBOSOIL, and POSTFIRE Projects (CGL2016-78937-R, CGL2013-43845-P and CGL2013-47862-C2-1-R, respectively) funded by the Spanish Ministry for Economy and Competitiveness. The authors also thank project EROFIRE (PCIF/RPG/0079/2018) funded by Fundação para a Ciência e a Tecnologia (FCT, Portugal). N.T. Jiménez-Morillo was funded by an FPI research grant ( BES-2013-062573 ).

8 páginas.- 5 figuras.- 1 tabla.- 27 referencias.- Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.fpsl.2019.100410, Natural preservatives are used in food packages to improve the shelf life of perishable products. Carvacrol and thymol, the main components of oregano essential oil (OEO), are used in active packaging due to their antimicrobial and antioxidant properties. Here, the effect of a bioactive polylactic acid (PLA)/polybutylene succinate (PBS) package in the conservation of lettuce compounds with dietetic value is studied. Analytical pyrolysis (PyGC/MS) was used to detect changes in dietary components such are phytosterols (PHSTs) and polyunsaturated fatty acids (PUFAs) after 1, 4 and 8 days of packaged in PLA/PBS (95:5%) films containing different OEO concentrations (2-10%). Lettuce PUFAs and PHSTs content decreased when packed in films without OEO. However, when packed in films containing 5 and 10% OEO, these bioactive components were preserved during the estimated lettuce shelf life, for up to 8 days of storage., Projects CSIC10-1E-448, AGL2012-38357-C02-01 and INTERCARBON (CGL2016-78937-R) co-financed by FEDER Funds, and AGR-7252 Junta de Andalucía. M. Llana-Ruiz-Cabello wish to acknowledge ‘Junta de Andalucía’ grant associated to AGR-7252 project. Alba Carmona Navarro and Desire Monis Carrere are recognized for their technical assistance

Comunicación oral presentada en el 1st Iberian Meeting in Separation Sciences & Mass Spectrometry, XIX Conference of the Spanish Society of Chromatography and Related Techniques (SECyTA), IX Conference of the Spanish Society of Mass Spectrometry (SEEM), VI Conference of the Mass Spectrometry Group of the Portuguese Society of Chemistry (SPQ). Santiago de Compostela, October 8th-11th (2019)., Changes in climatic and environmental conditions can affect both, plant chemical and isotope composition. Nowadays, many studies use bulk isotope values, which represent a weighed mean average of the different plant compounds. An isotopic characterization of individual biogeochemical compounds is desirable in order to differentiate the isotopic composition of the main plant components. However, biomass is composed mainly of high MW biopolymers i.e. polysaccharides (celluloses), polypeptides (lignin), polypeptides (proteins), polyesters (waxes), etc. not amenable to most chromatographic techniques without the use of more or less previous intense extraction and sample preparation. Here, a particular analytical pyrolysis technique combining Py‐GC with a continuous flow isotope ratio mass spectrometer (IRMS) (Py‐CSIA) is described and validated. Isotopic values obtained by Py‐CSIA of standard n‐alkanes mixtures (dissolved C16 to C30 series with increasing concentrations along three pentads, Indiana Univ. SIL mix. Type B), fitted well to a straight line (R2 > 0.999). No induced thermal cracking nor deviations from the acclaimed isotope composition (fractionation) was observed up to high pyrolysis temperature (< 400 °C). Results linking detailed molecular and isotope composition obtained by the direct analysis of various biomass types and biopolymers will be discussed. In general, our results show that Py‐ CSIA can reveal major differences between biomass components from different biogenic origin with high precision. In addition, despite that biomass pyrolysates from different origins may yield very similar Py‐GC/MS patterns, Py‐CSIA can make the difference providing additional valuable isotopic information., Ministerio de Ciencia Innovación y Universidades” INTERCARBON project (CGL2016‐78937‐R). N.T. Jiménez‐Morillo and L. San Emeterio thanks the MICIU for funding FPI research grants (BES‐2013‐062573 and Ref. BES‐2017‐07968). Desiré Monis is acknowledged for technical assistance

Póster presentado en el 1st Iberian Meeting in Separation Sciences & Mass Spectrometry, XIX Conference of the Spanish Society of Chromatography and Related Techniques (SECyTA), IX Conference of the Spanish Society of Mass Spectrometry (SEEM), VI Conference of the Mass Spectrometry Group of the Portuguese Society of Chemistry (SPQ). Santiago de Compostela, October 8th-11th (2019)., In less than 50 years the area occupied by peat bogs in the Gulf of Cádiz (SW‐Spain) has been reduced by more than 90%. The peat bog studied here may well be considered as relict and one of the last and more Meridional still in existence in the Northern hemisphere. The vertical molecular composition of a 85 cm peat bog from Ribetehilo lagoon (Doñana National Park; SW‐Spain 37° 7'30.81"N; 6°37'50.19"O) is studied using analytical pyrolysis (Py‐GC/MS) and ultra‐high resolution mass spectrometry (ESI‐FT‐ICR/MS). The results obtained by the two techniques were similar, showing as shallow OC composition was dominated by fresh material from upper vegetation cover, while more transformed and humified material was accumulated in the bottom layers. This may be due to i) intense microbial activity combined with large fluctuations of the water table occurring during the year; and/or ii) anaerobic rocesses. In general, the lack of peat preservation in depth is probably a sign of bog degradation processes, probably linked with climate changes to which Mediterranean wetlands are particularly responsive., MICIU INTERCARBON Project (CGL2016‐78937‐R UE/FEDER). N.T. Jiménez‐Morillo and L. San Emeterio thanks the MICIU for funding FPI research grants (BES‐2013‐062573 and Ref. BES‐2017‐07968 UE/FEDER). Prof. P. Hatcher (Old Dominion Univ., USA) for advice and access to the COSMIC ESI‐FT‐ICR/MS instrument. Desiré Monis for technical assistance.

Póster presentado en el 1st Iberian Meeting in Separation Sciences & Mass Spectrometry, XIX Conference of the Spanish Society of Chromatography and Related Techniques (SECyTA), IX Conference of the Spanish Society of Mass Spectrometry (SEEM), VI Conference of the Mass Spectrometry Group of the Portuguese Society of Chemistry (SPQ). Santiago de Compostela, October 8th-11th (2019)., Environmental research about causes and effects of progressive soil desertification is attracting the attention of the scientific community. Factors that accelerate soil organic matter (SOM) mineralization may also induce structural changes in its molecular composition, but the specific impact of different climatic factors (annual precipitation, number of days with precipitations, temperature…) has not yet been the subject of systematic research. This study attempts to identify potential climatic molecular proxies in SOM, i.e., pyrolytic compounds correlated with specific climatic indices. A set of 16 Spanish soils under differing climatic conditions were selected. Molecular characterization of SOM was done by pyrolysis‐gas chromatography/mass spectrometry (Py‐GC/MS) applied to whole soil samples. Up to 193 compounds were identified corresponding to alkanes, alkylbenzenes, N‐compounds, olefins, phenols and carbohydrate derivatives. Simple and multiple correlations between pyrolytic and climatic ariables showed that the concentration of several compounds was significantly correlated (P < 0.05) with particular climatic variables. In a second stage, using van Krevelen [1,2] diagrams, it was possible to display different patterns of pyrolytic compounds responsive to specific climatic characteristics. Finally, extrapolation functions were applied to simulate SOM molecular composition under future climatic scenarios, e.g., changes in temperature, evapotranspiration, rainfall, etc. This study demonstrates the potential of Py‐GC/MS in identifying specific molecules and compound families useful for predicting climate impact on SOM, as well as for monitoring soil quality in terms of the progress of desertification, References [1] D.W. van Krevelen, Fuel 29, 269–284 (1950). [2] G. Almendros, Z. Hernández, J. Sanz, S. Rodríguez‐Sánchez, M.A. Jiménez‐González, J.A. González‐Pérez, J. Chromatogr. A. 1533, 164–173 (2018)., t Financial support by Spanish CICyT (grants CGL2013‐43845‐P & CGL2016‐78937‐R) is acknowledged. M.A.J.G. thanks Spanish MINECO (pre‐doctoral FPI fellowship BES‐2014‐069238).

Póster presentado en el 1st Iberian Meeting in Separation Sciences & Mass Spectrometry, XIX Conference of the Spanish Society of Chromatography and Related Techniques (SECyTA), IX Conference of the Spanish Society of Mass Spectrometry (SEEM), VI Conference of the Mass Spectrometry Group of the Portuguese Society of Chemistry (SPQ). Santiago de Compostela, October 8th-11th (2019)., The measurement of stable isotopes has become an important tool within the field of archaeology. The isotopic trace of human and animal tissues and components (bone, collage, keratin, muscle, fat etc.) allowed insight into the diet of our ancestors in a specific period of time, as well as its relationship with various human pathologies. Furthermore, this technique informs about food origin and possibly also their commercial routes, as well as population migrations. Pyrolysis‐compound specific isotope analysis (Py‐CSIA) is a cutting‐edge analytical approach able to provide, not only a precise identification of organic compounds in different complex matrices, but also additional valuable information about nature and origin of the materials based on their isotope composition. This technique is based on the coupling of a micro‐furnace pyrolysis unit to a gas chromatograph equipped with an isotope ratio mass spectrometer (IRMS) as detector. The individual volatile pyrolysis products separated by gas chromatography are directed to a combustion or pyrolysis micro‐reactor (GC‐Isolink system) and finally the isotope composition of the gases produced measured in a continuous flow IRMS via a interface unit. With this technique it is possible to make direct determinations of stable isotope ratios (i.e. δ13C, δ15N, and δ2H) of specific compounds with minimum sample handling and pre‐treatment, thus minimizing the chance of contamination and artefacts productions. In this communication, we introduce the Py‐CSIA technique into the field of archaeology by studying the direct determination of the isotopic composition of human skeletons buried in medieval necropolises from Center and South of Portugal, The authors thanks to TRANSCULTURAL (POCI‐01‐0145‐FEDER‐031599) and INTERCARBON (CGL2016‐78937‐R) projects. L. San Emeterio thanks the MICIU for funding FPI research grants (BES‐2017‐07968). Desiré Monis is acknowledged for her technical assistance.

11 páginas.- 7 figuras.- 1 tabla.- 73 referencias.- Supplementary data to this article can be found online a https://doi.org/10.1016/j.scitotenv.2019.134321, 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., A.Z. Miller acknowledges the support from the Marie Curie Intra-European Fellowship of the European Commission seventh Framework Fig. 6. Contour van Krevelen density plots displaying cumulative abundances of pyrolysis compounds identified in Table S2 for: A) Erica arboreabiomass, B) Andosol topsoil, C) Black jelly-like speleothem 1 (BS1), and D) Black jelly-like speleothem 2 (BS2).9A.Z. Miller et al. / Science of the Total Environment 698 (2020) 134321 Programme (grant PIEF-GA-2012-328689) and the CEECIND/01147/2017 contract funded by Fundação para a Ciência e a Tecnologia (Portugal). The authors acknowledge the Spanish Ministry of Economy and Competitiveness (project CGL2013-41674-P) and ERDF funds forfi-nancial support. The authors are grateful to the speleologist OctavioFernández (GE Tebexcorade–La Palma) for the assistance during thefield trip and photographic documentation in the lava tubes from LaPalma Island

8 páginas. 4 figuras.- 2 tablas.- referencias.- Supplementary data to this article can be found online at https:// doi.org/10.1016/j.jenvman.2019.109567, 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, José M. De la Rosa and Marco A. Jiménez-González thank the Spanish Ministry of Economy and Competitiveness (MINECO, Spain) for funding the “Ramón y Cajal” post-doctoral contract (RYC2014-16338) and the pre-doctoral FPI fellowship (BES-2014-069238) respectively. Nicasio T. Jiménez-Morillo was funded by the scholarship PosDoc/Por 3O/OUT17 (FCT, Portugal).

26 páginas.- 22 figuras.- referencias.- URL de libro https://www.publish.csiro.au/book/7743/, Wildfires are a global phenomenon occurring in tropical, temperate and boreal regions that affect 300-460 Mha every year (Randerson el al. 2012; Giglio el al. 2013) (Chapter 1). Temperate regions have been affected historically by wildfires (Pausas el al. 2008; Lasheras-Álvarez el al. 2013) and during the 20th century a drastic increase in the extent and severity of burnt areas has occurred. This has made wildfires one of the main threats for ecosystems, particularly those in Mediterranean areas. The obvious consequence of a wildfire is the partial or complete loss of the vegetation. However, wildfires may also cause changes in the physical, chemical and biological properties of soil (González-Pérez el al. 2004; Certini, 2005). The alteration of geomorphological and hydrological processes of the topsoil following a wildfire (de la Rosa el al. 2013a; Faria el al. 2015a) can boost erosion processes that, in turn, are often associated with quantitative and qualitative changes in soil organic matter (SOM) (Chapters 3, 4, 5, 6, 7, 8, 9, 10 and 11). In fact, desertification risk in connection with increased wildfire recurrence is very high in Mediterranean ecosystems (Shakesby, 2011) and the design and application of proper post-fire restoration strategies is paramount for reducing such risk. Restoration of both quality and quantity of SOM is important for soil rehabilitation after a wildfire. Nevertheless, many studies have focused only on the effects of fire in the total amount of SOM, with only scarce the attention paid to the SOM chemical composition and molecular structure, despite its relevance (Almendros el al. 1984a,b; González Pérez el al. 2004, 2008; Certini el al. 2011, de la Rosa el al. 2013a; Faria el al. 2015a,b; Aznar el al. 2016; Jiménez-González el al. 2016; Jiménez-Morillo el al. 2016a, 2017)., J. M. de la Rosa thanks The Spanish Ministry of Economy and Competitiveness (MINECO) for his 'Ramón y Cajal' post-doctoral contract (RYC2014-16338). M.A. Jiménez-González and N.T. Jiménez Morillo thank MINECO for funding their predoctoral FPI fellowships (BES-2014-069238 and BES-2013-062573).

Póster presentado en EGU 2019, Viena (Austria) 7 al 12 de abril de 2019. Puede ver el Abstract en https://meetingorganizer.copernicus.org/EGU2019/EGU2019-17062.pdf, Given the artistic, social and economic value of cultural heritage, its conservation is of upmost importance for being preserved for future generations. Through accurate characterization of organic materials, such as alteration products and biopolymers used in the past as construction, supporting or protective materials of in monuments and artistic artifacts, it would be possible to ameliorate the conservation practices for controlling deterioration. Pyrolysis-compound specific isotope analysis (Py-CSIA) is a novel analytical technique able to provide, not only an accurate identification of organic compounds in different complex matrices, but also additional valuable information about nature and origin of the materials based on their isotopic composition. This technique is based on the coupling of a micro-furnace pyrolyser (F.Lab 3030i) to a gas chromatograph (GC) and using an isotope ratio mass spectrometer (IRMS) as detector. The individual volatile pyrolysis products separated by gas chromatography are directed to a combustion or a pyrolysis micro-reactor (GC-Isolink system) and finally the isotope composition of the gases produced measured in the IRMS (Thermo Fisher Delta V Advantage) via an appropriate interface (ConFlo IV universal interface unit). With this technique it is possible to make direct measures of stable isotope ratios (i.e. [U+1D6FF]13C, [U+1D6FF]D, , [U+1D6FF]15N and also [U+1D6FF]18O) of specific compounds with minimum sample handling. In this communication we will introduce the Py-CSIA technique in the field of cultural heritage as a novel technique for the direct determination of the isotopic composition of polymers and biopolymers. Case studies on the characterization of biopolymers using Py-CSIA will be presented and the potential application in the field of cultural heritage conservation discussed., [1] González‐Pérez et al. (2016). Compound‐specific stable carbon isotopic signature of carbohydrate pyrolysis products from C3 and C4 plants. Journal of the Science of Food and Agriculture, 96(3), 948-953. [2] González-Pérez et al.. (2015). Pyrolysis-gas chromatography–isotope ratio mass spectrometry of polyethylene. Journal of Chromatography A, 1388, 236-243. [3] Gil et al. (2011). Stable isotopes and human diet in central western Argentina. Journal of Archaeological Science, 38(7), 1395-1404. [4] Mottram et al.. (1999). New chromatographic, mass spectrometric and stable isotope approaches to the classification of degraded animal fats preserved in archaeological pottery. Journal of Chromatography A, 833(2), 209-221. [5] Tambakopoulos, D., & Maniatis, Y. (2017). The marble of the Cyclades and its use in the Early Bronze Age. Early cycladic sculpture in context. Oxbow: Oxford and Philadelphia, 468-82. [6] von Holstein, I. C., & Makarewicz, C. A. (2016). Geographical variability in northern European sheep wool isotopic composition (δ13C, δ15N, δ2H values). Rapid Communications in Mass Spectrometry, 30(12), 1423-1434., This research has been funded by the Spanish Gov. ‘Ministerio de Ciencia , Innovación y Universidades’ under grant ref. BES–2017–079811 . Project CGL 2016 -78937 –Co-financed by FEDER Funds .

Comunicación oral presentada en EGU 2019, Viena (Austria) 7 al 12 de abril de 2019. Puede ver el Abstract en https://meetingorganizer.copernicus.org/EGU2019/EGU2019-18932-1.pdf, Changes in climatic and environmental conditions can affect both, plant chemical and isotope composition. Therefore, biomass carbon isotope composition is frequently used to gain information about the environmental conditions at the time a plant was growing [1]. In this field, the majority of studies use isotope values obtained from bulk samples. However, these values are a weighed mean average of the different plant compounds. The Isotopic characterization of individual biogeochemical compounds represents a relevant analytical advance able to differentiate the isotopic composition of the main plant components i.e. polysaccharides, lignin, polypeptides, lipids and waxes, etc. Here, we investigate the link between molecular and isotope composition of bark from three Eucalyptus species (E. grandis, E. dunni and a hybrid E. grandis x E. dunni) using Py-CSIA. Bulk samples and lignin extracted were analysed by Py-CSIA; this technique, although not widely used, has been previously developed and applied, with different variants [2-7], to characterize plant products including lignin [8], sugars [9] and terpenes [10]. Our results support the idea that the pyrolysis compound specific isotope analysis (Py-CSIA) can provide valuable and accurate isotopic fingerprinting of biomass. Despite that wood/bark from different origins provide very similar pyrolysis pattern, isotopic composition of relevant specific compounds can make the difference giving additional valuable information., [1] Michenerand Lajtha (Eds). Stable Isotopes in Ecology and Environmental Science (2nd Ed.) Blackwell Publishing Ltd (2007) 566p. [2] Gonñi and Eglinton, J. High Resol. Chromat. 17 (1994), 476. [3] Pulchan et al., J. Anal. Appl. Pyrolysis 42 (1997), 135. [4] Gleixner and Schmidt. In Nitrogen-containing Macromolecules in the Bio- and Geosphere. Stankiewicz and van Berger (Eds), ACS Symposium Series 707 (1998), pp. 34–46. [5] Gleixner et al. Rapid Commun. Mass Spectrom. 13 (1999) 1278. [6] Schulten and Gleixner Water Res. 33 (1999) 2489. [7] Gleixner et al. Organic Geochemistry 33 (2002) 357. [8] Steinbeiss et al. J. Anal. Appl. Pyrolysis 75 (2006) 19. [9] González-Pérez et al. J. Sci. Food Agric. 96 (2016) 948. [10] Llana-Ruíz-Cabello et al. J. Chrom A 1525 (2017) 145., FPI grant funded by the Spanish Government (Ref. BES-2017-07968)

9 páginas.- 5 figuras.- 56 referencias, 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., This was supported by MINECO projects INTERCARBON (CGL2016-78937-R), FUEGONEO (CGL2016-76620-R), and Paisaje y Sociedad. El valle medio del Ebro entre el 6000 y el 500 cal ANE (HAR2015-65620-P).

Póster presentado en el EGU General Assembly 2017, 23–28 April 2017, Vienna, Austria, INTRODUCTION The Swan Coastal plain of Western Australia is dominated by fire-prone banksia woodland (Burrows and McCaw, 1990). In these areas, prescription burning is often used to reduce the risk of wildfires, by reducing available fuels (Boer et al., 2009). Little research has been conducted on the effects of prescription burning on Banksia woodlands, and, in particular, information on the impacts on soil properties and soil water repellency (SWR) is carce. Here, we have studied the impact of fire on SWR in a Banksia woodland and monitored its evolution in the medium-term. It is expected that results are useful for management and restoration of fire-affected Banksia woodlands. METHODS An experimental fire was conducted on May 7th 2015 in Kings Park, Perth, Western Australia. The fire affected an area of 6 ha of mixed Banksia/Allocasuarina woodland under moderate fire intensity. At the time of ignition, the wind speed below the canopy was 1.2 km/h. During the prescribed burning, air temperatures were on average 20 ± 1◦C and relative humidity ranged between 45 and 55% (measured using a Kestrel portable weather station). Fuel moisture averaged 11.8% (measured using Wiltronics moisture meter) and soil moisture at 1 cm deep ranged from 0.1% to 8.6% (measured with a PR2 soil profile probe attached to a HH2 data logger). Temperatures greater than 120 ◦C were measured 1 cm below the soil surface using iButton temperature sensors. SWR was measured under lab conditions in oven-dry samples (48 h, 105 ◦C) with the water drop penetration time (WDPT) test. Soil microbial activity was determined with the 1-day CO2 test that is based on the measurement of the CO2 burst produced after moistening dry soil (Muñoz-Rojas et al., 2016)., PRELIMINARY RESULTS AND DISCUSSION SWR was severe in the control (mean WDPT = 2608 s) and pre-burned areas (2722 s). One week after the prescribed fire, persistence of soil water repellency remained stable in the burned area (2402 s). In contrast, extreme SWR was observed in the burned area (3750 s). This may be explained by a reduction of water repellency by burning (Zavala et al., 2009; Jordán et al., 2014), as environmental conditions led to an increase in control areas. Although prescribed burning usually do not produce high severity fires, evidences of high severity were found, due to prolonged smouldering caused by subsurface Banksia root clusters. In some cases, this led to release of iron oxides, observed as red spots in the surface. Fire in Mediterranean and semi-arid environments has a significant effect on microbial biomass and the composition of soil microbial communities during the post-fire period, when soil nutrients become available (Bárcenas-Moreno et al., 2011; Muñoz-Rojas et al., 2016). In our study, microbial activity increased sharply in the burned area and most likely contributed to a decrease of organic hydrophobic substances in the first centimetres of the soil profile. Bárcenas-Moreno et al. (2011) observed that bacterial activity increases immediately after fire, while fungi decreased and recovered slowly. These processes may contribute to explain differences in SWR following fire, since this soil property may be influenced by fungal activity (Lozano et al., 2013)., This research has been partly funded by the University of Western Australia through the project "Soil water repellence in biodiverse semiarid environments: new insights and implications for ecological restoration" (UWA Research Collaboration Awards, Ref. ENV.2013.6.2-4) and the Spanish Ministry for Economy and Competitiveness through the research projects GEOFIRE (Ref. CGL2012-38655-C04-01) and POSTFIRE (Ref. CGL2013-47862-C2-1-R).

Póster presentado en el EGU General Assembly 2017, 23–28 April 2017, Vienna, Austria, Post-fire rehabilitation actions and recovery attempts of burned soils include a range of management practices (tillage, tree logging, reforestation . . . ), in some cases producing an additional damage to that directly caused by fire. Among negative impacts derived from unappropriated rehab practices are the increase soil erosion, loss of soil fertility and alterations in the hydrological cycle. Analytical pyrolysis (Py-GC/MS) is an appropriate technique to study organic matter characteristics within complex matrices. Here this technique is used to study the alterations caused by burning and post-fire rehab plans to soil organic matter (SOM). Fire and post-fire rehab actions impact on SOM is studied in a sandy soil under pine (Pinus pinea) forest that was affected by a severe fire in August 2012 in Doñana National Park (SW Spain). Bulk samples as well as its sieved soil fractions (coarse, 1–2 mm, and fine, This study is part of the results of the GEOFIRE and POSTFIRE Projects (CGL2012-38655-C04-01 and CGL2013-47862-C2-1-R respectively) funded by the Spanish Ministry for Economy and Competitiveness. N.T Jiménez-Morillo is funded by a FPI research grant (BES-2013-062573).

Póster presentado en el EGU General Assembly 2017, 23–28 April 2017, Vienna, Austria, Introduction Banksia woodlands (BW) are iconic ecosystems of Western Australia (WA) composed by an overstorey dominated by Proteaceae, e.g. Banksia menziesii and Banksia attenuata, in combination with other species, such as Eucalyptus spp., Verticordia spp. or Melaleuca spp. Although located in very poor dune soils, BW provide numerous ecosystem services and sustain a high biodiversity. In this area, annual rainfall is relatively high (about 800 mm) but permeability of the sandy substrate leads to a functionally arid ecosystem. Currently, BW are threatened by sand mining activities and urban expansion; therefore conservation and restoration of these woodlands are critical. Despite numerous efforts, the success of restoration plans is usually poor mostly due to the high sensitivity to drought stress and poor seedling survival rates (5-30%) (Benigno et al., 2014). A characteristic feature of BW is their root architecture, formed by a proteoid (cluster) system that spreads to form thick mats below the soil surface, favouring the uptake of nutrients (especially, P), and preventing soil erosion. Root exudates are related to numerous plant functions, as they facilitate penetration of roots in soil and enhance the extraction of scarce mineral nutrients and its further assimilation. Exudates may also interact directly with soil or indirectly through microbial mediated events being also related to soil water repellency (SWR; Lozano et al, 2014). Knowledge about the specific compounds able to induce SWR is limited (Doerr et al., 2000), but it is generally accepted that is caused by organic molecules coating the surface of soil mineral particles and aggregates (Jordán et al., 2013). Proteaceae release short-chained organic acids to enhance phosphate acquisition, which have been also reported to be related with SWR (Jiménez-Morillo et al., 2014). It is hypothesized that disruption of water dynamics in mature BW soils is underlying the failure of restoration plans. This research aims to study SWR and its impact on water economy in relation with soil functioning and plant strategies for water uptake in pristine BW. Results are expected to shed light on the origin and implications of SWR in the area and provide useful information for improving ongoing restoration plans. Materials and methods The study was conducted in natural BW of WA. Soil samples were collected at different soil depths (0-1, 1-10, 20-30 and 40-50 cm). Rationale for sampling depths was based on the different severities of SWR at each layer under field conditions. Soil water repellency was assessed under laboratory conditions in oven-dry samples (48 h, 105 ºC) and the chemical organic assemblage of bulked soil subsamples from each layer was analysed by direct analytical pyrolysis (Py-GC/MS)., Results and discussion Soil water repellency distributed discontinuously through the soil profile. The first thin layer (0-1 cm) composed of coarse sand and litter, located immediately above Banksia root clusters, showed wettable conditions. In contrast, the relatively well aggregated soil layer where the Banksia cluster root system is located (1-10 cm) was severely water-repellent. The 20-30 and 40-50 cm deep layers rendered wettable or subcritically water-repellent. After Py-GC/MS analysis, major compounds were identified and grouped according to their probable biogenic origin (lignin, polysaccharides, peptides, etc.). Among other soil organic compounds, well r esolved bimodal alkane/akene (C8-C31, maxima at C13 and C26) and fatty acids series (short-chained, C5-C9, and long-chained even-numbered C12-C18) were associated to the root cluster soil layer (1-10 cm). Also, a relatively high contribution of fire-derived polycyclic aromatic hydrocarbons (PAHs) was observed (7%), which is consistent with frequent fires occurring in BW. These results point to possible indirect links between organic substances released by roots and soil wettability involving soil microorganisms. Further discussion should shed light on possible ecological plant strategies and specific adaptations for water uptake in such arid ecosystems of WA., This research has been funded by the University of Western Australia (Research Collaboration Award 2015: ‘Soil water repellence in biodiverse semi arid environments: new insights and implications for ecological restoration’) and the Spanish Ministry of Economy and Competitiveness (research projects GEOFIRE, CGL2012-38655-C04-01, and POSTFIRE, CGL 2013-47862-C2-1-R.

Póster presentado en el EGU General Assembly 2017, 23–28 April 2017, Vienna, Austria, Introduction Soil water repellency (SWR) has critical implications for restoration of vegetation in degraded areas as it is responsible of poor plant establishment and a high incidence of erosion processes. Different organic substances are capable of inducing SWR but polar molecules such as certain fatty acids, and waxes i.e. esters and salts of fatty acids, appear to be the main constituents of hydrophobic coatings on soil mineral particles (Doerr et al., 2005). Plant species most commonly associated with SWR are evergreen trees with a considerable amount of resins, waxes or aromatic oils such as eucalypts and pines. Most of these substances are abundant in ecosystems and are released to soil by plants as root exudates or decaying organic debris, and by soil fauna, fungi and other microorganisms, but a thorough knowledge of substances capable of inducing hydrophobicity in soils is still not complete (Jordan et al., 2013). Although SWR has been reported in most continents of the world for different soil types, climate conditions and land uses, there are still many research gaps in this area, particularly in semi-arid areas largely affected by this phenomenon. Materials and methods This research was conducted in three dominant ecosystems of Western Australia (WA), e.g. semi-arid grassland in the Pilbara region (North WA), Banksia woodland, and a coastal dune (both located in South WA). These environments have different climate characteristics and soil types but similar vegetation communities. Soil samples were collected under the canopy of a broad range of plant species that compose the dominant vegetation communities of these ecosystems, and SWR was measured under lab conditions in oven-dry samples (48 h, 105 ºC). Soil microbial activity was measured with the 1-day CO2 test, a cost-effective and rapid method to determine soil microbial respiration rate based on the measurement of the CO2 burst produced after moistening dry soil (Muñoz-Rojas et al., 2016). Soil pH and electrical conductivity (EC) were determined in deionised water (1:2.5 and 1:5 w/v, respectively). The structural characterization of soil organic matter (SOM) was analysed by direct analytical pyrolysis (Py-GC/MS) performed at 500 ◦C (González-Vila et al., 2009). Only chromatogram peaks with an area higher than 0.2 % were identified and used to obtain the relative abundance of main chemical families in each vegetation cover., Results Our results show that soil water repellence is strongly correlated to microbial activity, pH and electrical conductivity. After Py-GC/MS analysis, soil organic matter in the Banksia woodland and the coastal dune showed a high heterogeneity. In the Banksia woodland two different patterns were observed. Samples under Banksia spp. showed a SOM with clear signs of altereation (humified) that included a high contribution of stable families like unspecific aromatic compounds and alkane/alkene pairs whereas under Eucalyptus spp. showed a less altered SOM with a high relative contribution from lignocellulose (lignin and carbohydrates), together with a low relative content of recalcitrant families. However in the soil samples from coastal dunes a very similar SOM chemical composition was found in all cases. The dominant family was unspecific aromatic compounds (>30%), followed by alkane/alkene pairs and a high relative contribution from N bearing peptide compounds. This, together with a low relative amount of carbohydrate and lignin derived (methoxyphenols) compounds points to a SOM that undergoes great alteration processes, possible because of high turn-over rates. Very low contents of SOM were found in the Pilbara system, under Py-GC/MS detection levels, and therefore it was not possible to establish its chemical composition. A principal components analysis (PCA) axes based on the relative abundances of chemical families of compounds released after SOM pyrolysis (70.9 % of total variation explained in the two first axes) indicate that water repellence is closely related with fatty acids and the presence of short chain hydrocarbons., This research has been funded by the University of Western Australia (Research Collaboration Award 2015: ‘Soil water repellence in biodiverse semi arid environments: new insights and implications for ecological restoration’) and the Spanish Ministry of Economy and Competitiveness (research projects GEOFIRE, CGL2012-38655-C04-01, and POSTFIRE, CGL 2013-47862-C2-1-R.

Diapositiva de la comunicación oral presentada presentado en el EGU General Assembly 2015, 12-17 April 2015, Vienna, Austria, Soil microbial response after fire is controlled by numerous variables which conclude with a mosaic of results depending on organic carbon alterations or pH fire-induced changes. This fact has complicated the studies focused on post-fire microbial response, compiling high variability of opposite result in the bibliography. Soil laboratory heating cannot emulate a real wildfire effect on soil but lead us the possibility to control several variables and it is a valid tool to clarify the relative weight of different factors controlling microbial response after soil heating. In this preliminary study different heated treatments were applied to unaltered forest soil samples, obtaining 4 different heating treatments to simulate a range of fire intensities: unaltered-control (UH), and soil heated at 300, 450 and 500 ºC. In order to isolate possible nutrient availability or pH heating-induced changes, different culture media were prepared using soil:water extract from each heating treatments and adding different supplements to obtain the total of 11 different culture media: unheated soil without supplements (UH-N-), unheated soil with nutrient supplement (UH-N+), soil heated at 300 ºC without supplements (300-N-), soil heated at 300 ºC with nutrient supplement (300-N+), soil heated at 300 ºC with nutrient supplement and pH-buffered (300-N+pH); soil heated at 450 ºC without supplements (450-N-), soil heated at 450 ºC with nutrient supplement (450-N+), soil heated at 450 ºC with nutrient supplement and pH-buffered (450-N+); soil heated at 500 ºC without supplements (500-N-), soil heated at 500 ºC with nutrient supplement (500-N+), soil heated at 500 ºC with nutrient supplement and pH-buffered (500-N+). Each media was inoculated with different dilutions of a microbial suspension from the original unaltered soil, and the abundance of viable and cultivable microorganisms were measured by plate count method. In addition, the analysis of heating-induced soil organic matter alteration by mean of pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) technique was applied to soil samples and soil:water extract in order to obtain a deeper understanding of soil organic matter-microorganisms interaction after fire. Heating effect on soil:water extract media was evident since the number CFU in those media prepared by mean of heated soil was lower than those counted in media prepared with unaltered soil and inoculated with the same dilution. Nutrient addition appear to promote microbial proliferation in unaltered and 300 ºC treatments, while nutrient and pH compensation appear to attenuate heating effect in samples heated at 300 and 450 ºC. While, media prepared with soil:water extract form soil heated at 500ºC showed similar CFU abundance in all supplement treatments. Soil organic matter analyses evidences difference in the pyrogram obtained from each heating treatment sample, with a marked diminution of peaks with increased temperature. This preliminary study shows us the importance of soil organic matter fire-induced alterations in soil microbial response after soil heating process beyond the C content diminution or changes in C availability.