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Soils constitute the major reservoir of mercury (Hg) in terrestrial ecosystems, whose stability may be threatened by wildfires. This research attempts to look at the effect of prescribed fire on the presence of Hg in a shrubland ecosystem from NE Portugal, delving into its relationship with soil aggregate size and the molecular composition of soil organic matter (SOM). During the prescribed fire, on average 347 mg Hg ha−1 were lost from the burnt aboveground biomass of shrubs and 263 mg Hg ha−1 from the combustion of the soil organic horizon. Overall, Hg concentration and pools in the mineral soil did not show significant changes due to burning, which highlights their role as long-term Hg reservoirs. The higher Hg concentrations found in smaller aggregates (<0.2 mm) compared to coarser ones (0.5–2 mm) are favored by the higher degree of organic matter decomposition (low C/N ratio), rather than by greater total organic C contents. The Hg-enriched finest fraction of soil (<0.2 mm) could be more prone to be mobilized by erosion, whose potential arrival to water bodies increases the environmental concern for the Hg present in fire-affected soils. The SOM quality (molecular composition) and the main organic families, analyzed by Fourier-transform infrared spectroscopy in combination with multivariate statistical analysis, significantly conditioned the retention/emission of Hg in the uppermost soil layers. Thus, before the fire, Hg was strongly linked to lipid and protein fractions, while Hg appeared to be linked to aromatic-like compounds in fire-affected SOM.

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.

Editorial on the Research Topic Wildfire severity and forest soils: impacts and post-fire restoration strategies to mitigate climate change Impacts of fire on forest soils have been widely studied in the last decades. Early studies compared burned and unburned areas, revealing that soil properties and dynamics are significantly affected by fire. Moreover, the advancements in soil and fire sciences revealed the importance of considering the variety of fire characteristics, ecosystem types and environmental pre- and post-fire conditions when studying fire effects on soils (Certini, 2005; Pereira et al., 2018; Fernández-García et al., 2020). Previous research has shown that the temperature reached in the soil and the residence time are critical factors that determine the effects of fire on soil properties. Biological and biochemical properties are generally altered at low temperatures (Fernández-García et al., 2020), while moderate temperatures cause shifts in soil organic matter and several nutrients (Marcos et al., 2007). High temperatures, on the other hand, can impact other chemical properties as well as ecologically relevant physical properties, such as soil structure and mineralogy (Santín and Doerr, 2016; Alcañiz et al., 2018; Fernández-García et al., 2019).

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.

Volcanic caves are priceless resources found worldwide. Recently, these environments and the life within have captured the attention of the world, due to the detection of numerous volcanic cave entrances on the Moon and Mars. The TUBOLAN and HIRES-SOM (funded by the Spanish Ministry of Science and Innovation), the MICROCENO (funded by the Portuguese Foundation for Science and Technology) and the MICROLAVA (funded by the Regional Government of Andalusia) research projects are extraordinary examples of the raising scientific interest in exploring lava tubes on Earth. The goals are the deep characterization of the highly complex subsurface microbial communities adapted to lava tubes from Lanzarote and La Palma (Canary Islands, Spain), and Selvagens Islands (Portugal), respectively, and understand their interactions with biotic and abiotic factors to provide clues on how microbial life has evolved. Recognizing biosignatures and reconstruct climate information recorded in siliceous speleothems from these volcanic caves are also key priorities of these ongoing projects. The interdisciplinary and international dimensions gleaned in these projects are crucial toward properly exploring and protect these unique underground resources. The objective of this multidisciplinary meeting was to gather European leading researchers involved in the study of volcanic caves to share their knowledge, results obtained thus far and discuss current development in their respective fields.

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.

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 degrees 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.

La repelencia al agua del suelo (RAS) se atribuye a la acumulación de compuestos hidrofóbicos (lípidos), pero su extracción no siempre elimina la RAS, lo que sugiere que componentes macromoleculares no extraíbles también pueden estar relacionados con una RAS. Se han estudiado suelos quemados (B) y control (UB) del Parque Nacional de Doñana (Huelva, España) bajo dos tipos de vegetación (alcornoque y brezo) y fracciones de suelo: gruesa (1–2 mm) y fina (<0.05 mm). La composición molecular de la materia orgánica del suelo (MOS) se analizó mediante espectrometría de masas de ultra-alta resolución. Además, se empleó la regresión por mínimos cuadrados parciales (PLS) para explorar la relación entre la RAS y la MOS definida por la abundancia de los 1221 compuestos orgánicos comunes. También se utilizaron índices para obtener gráficas que faciliten la identificación de biomarcadores de la RAS. En los suelos quemados, la RAS estaba significativamente relacionada (P<0.05) con compuestos aromáticos y condensados, mientras que, en los suelos control, la MOS incluía compuestos aromáticos y ligninas. En las fracciones finas, la RAS estuvo relacionada principalmente con lípidos, pero, no se encontró correlación en las fracciones gruesas. Los resultados permiten concluir que la hidrofobicidad depende de varias famílias de compuestos orgánicos. La combinación de la FT-ICR/MS con herramientas estadísticas ha facilitado la obtención de nuevos biomarcadores de RAS.

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.

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.

The HIRES-SOM project is a multidisciplinary project funded by the Ministry of Science and Innovation of Spain, aimed at generating knowledge on soil organic matter (SOM) and microbiota to guide novel strategies for the sustainable management of volcanic soils. The investigation will be conducted within the framework of the recent Tajogaite eruption in La Palma Island, which constitutes an optimal benchmark both for scientific research on freshly erupted materials and for the management of affected soils of high added value. Insights into the generation and resilience of SOM and of the associated microbiota will be explored with advanced biogeochemical, microbiological, mineralogy and modelling techniques [1,2]. The main goals of the project are twofold. On the one hand, it intends to assess the state and evolution of the SOM and microbiota in soils calcined by the lava flows and covered by the pyroclastic ashes. On the other hand, fundamental understanding will be sought about the initial stages of pedogenesis and consolidation of organic matter on the eruptive materials. The project intends to identify primary microbial communities and molecular precursors of organic matter in volcanic ash, lava flows and eruption-affected soils. Moreover, accelerated microbial colonization of volcanic substrates under laboratory conditions will allow monitoring photoautotrophic microorganisms that colonize natural volcanic materials, with the ultimate innovative goal of devising methods for the rapid fertilization of porous pyroclastic ashes by indigenous microorganisms for sustainable soil regeneration. References: [1] Martinez-Haya et al, Energy Fuels 35 (2021) 8699; Talanta 185 (2018) 299; Phys. Chem. Chem. Phys. 22 (2020) 19725. [2] Miller A., et al, Sci Total Environ 426 (2012) 1; Geomicrobiol. J. 31 (2014) 236; Sedimentology 65 (2018) 1482; Sci Total Environ 698 (2020) 134321; Coatings 10 (2020) 1134.

Volcanic speleothems are cave formations found in lava tubes that are composed of minerals that have been deposited by volcanic activity. Siliceous speleothems are important to determine the timing and intensity of past volcanic eruptions, as well as assessing the environment conditions [1]. Another important contribution is the identification of biosignatures (organic compounds or microorganisms) preserved within the speleothems, which is relevant for astrobiology. However, for that, it is required the use of increasingly cutting-edge analytical molecular characterization techniques with the goal to analyze a remarkable number of different organic compounds. One of the most promising techniques is analytical pyrolysis coupled to ultra-high resolution mass spectrometry (Py-GC/Q-TOF). This advanced technique allows the analyze of more than 15,000 different organic compounds per sample, without any pre-treatment. However, this overwhelming number is not feasible to study each organic compound individually. Therefore, it is mandatory the development of novel graphical-statistical tools to help identifying their main biogenic families [2], as well as the alterations and adaptation of microorganisms to environmental (e.g., climate change, drought) or anthropogenic (e.g., oil spills, forest fires) factors [3,4]. In this communication, it will present the advantages of the combination of ultra-high resolution analytical pyrolysis technique and chemometrics as an innovative strategy for unsupervised classification and visual analysis of organic matrices preserved in siliceous speleothems. References: [1] Miller, A.Z., et al., Journal of Chromatography A 1461 (2016) 144-152. [2] Jiménez-Morillo, N.T., et al., Science of the Total Environment 817 (2022) 152957. [3] Miller, A.Z., et al., Science of the Total Environment 698 (2020) 134321. [4] Miller, A.Z., et al., IScience 25 (2022) 104556.

Pyrolysis (Py) is the thermochemical decomposition of organic materials (OM) at elevated temperatures without oxygen. The products of Py are amenable to chromatographic separation which, when combined with appropriate detectors, yields valid fingerprint information about the composition and molecular structure of complex mixtures of natural and synthetic macromolecules [1-2]. Analytical Py poses several advantages over other techniques for OM characterization: minimal or no sample preparation needed, the small sample size required, and the ability to detect and characterize a wide variety of organic materials in a single analysis, including recalcitrant and low solubility organic forms [3]. Therefore, this technique is convenient for relatively rapid analyses of scarce or precious organic samples such as those that may be found in extreme environments. In this communication, apart from the conventional Py techniques such as Py associated with gas chromatography and mass spectrometry (Py-GC/MS), will give examples of the application of other more advanced variants to speleothems analyses that provide complementary or more accurate information. These include pyrolysis associated with compound-specific isotope analysis (Py-CSIA) and ultra-high resolution analytical Py (Py-GC/Q-TOF) that are unique and available in our labs at IRNAS-CSIC MOSS Group. References: [1] González-Pérez, J.A., et al., Journal of Chromatography A 1388 (2015) 236–243. [2] San-Emeterio, L.M., et al., Applied Science 11 (2021) 6684. [3] Quénéa, K., et al., Journal of Analytical and Applied Pyrolysis 76 (2006) 271–279.

Speleothems represent a valuable archive of paleoclimatic information. In order to identify environmental changes that occurred in the past [1] and to establish protocols for valid models in searching for signs of life in lava tubes, the TUBOLAN and MICROCENO projects study the composition of the organic matter remains preserved in siliceous speleothems in lava tubes from Lanzarote and Selvagens islands, respectively. However, the small size of the samples, their nature, and the challenges of extracting the organic components trapped in them and analyzing with conventional methods, have hindered their use for reconstructing environmental changes [2]. Lanzarote Island offers an extraordinary variety of lava tubes and siliceous speleothems formed through different post-volcanic processes. In addition, Selvagens Islands (Madeira, Portugal) constitute an isolated and undisturbed ecosystem, and consequently, its volcanic caves are a promising model system for investigating pristine biosignatures preserved in siliceous speleothems. Here we show the results of thermal analyses performed on a gypsum core collected in the Inferno Cave (Selvagen Grande Island) and on sediments sampled on the floor of Naturalistas, Las Breñas, and Pescadores caves (Lanzarote). The gypsum core showed the presence of thermostable organic compounds preserved mainly in layers H3-H5 and H7, matching the highest organic carbon contents of the whole profile. The H6 layer shows the presence of organic constituents with contrasting composition. Sediments from Lanzarote lava tubes exhibit a high abundance of organic compounds derived from micro-organisms and the remains of higher plants (leached from the soil above the cave). A complete characterization of the samples, including geochronology, is being performed to relate changes in the speleothems composition to historical episodes of environmental disturbance or/and climatic events. References: [1] Miller, A.Z., De la Rosa, JM, Jimenez-Morillo, NT, Pe

La agricultura actual se enfrenta al reto de garantizar el suministro de alimentos a una población en continuo crecimiento mientras la actividad humana ya ha deteriorado sobre el 40% de los suelos cultivables del planeta, aumentando la dependencia de los fertilizantes minerales. En este contexto, la valorización de residuos agrícolas para utilizarlos como sustratos o suplementos del suelo se propone como alternativa, creando además una solución a la generación masiva de residuos orgánicos agro-ganaderos. Este trabajo muestra las propiedades físicas de interés agrnómico y la composición (macro y micronutrientes) de biochars, composts y cenizas producidas a partir de restos vegetales de las agroindustrias olivadera y des arroz, y los efectos de su aplicación a los suelos calcáreos (Xerochrept y Luvisol) bajo condiciones de clima mediterraneo. Las enmiendas mostraron atributos apropiados para mejorar las propiedades agronómicas del suelo. El biochar mostró una alta aromaticidad y abundancia de C orgánico estable. Las enmiendas ricas en ceniza mostraron altos contenidos en P y K y micronutrientes. El compost presento una elevada capacidad de retención de agua y un adecuado balance de C y N. Todas las enmiendas orgánicas redujeron la hidrofobicidad del suelo. La aplicación de biochar consiguió aunmentar la humedad del suelo en los primeros 10 cm y reducir su compactación, los que se evidencio por la reducción significativa de la resistencia del suelo a la penetrabilidad. Las plantas de las parcelas enmendadas mostraron un mejor potencial hídrico foliar. Además, los valores de la tasa de fotosíntesis neta, la eficiencia media de uso del agua intrínseca y la tasa máxima del transporte de electrones en el momento de la cosecha mejoraron significativamente en los árboles de las parcelas enmendadas con una dosis de biochar de 40 t ha-1. En relación al ciclo de C, la adición de compost incrementó de manera significativa la respiración (emisión de CO2) y la cantidad de C proced

Volcanic eruptions are geological events spewing large amounts of magma-derived products such as hot lava, volcanic ash, water, and gases. Among the most iconic features of effusive eruptions are lava tubes, which have also been detected on the Moon and Mars. On Earth, these cavities are rapidly colonized by specialized microorganisms, whose growth is fueled by surface-derived organic matter transported via percolation water or by CO2 fixed in situ by chemolithoautotrophic organisms. The likelihood presence of essential life-supporting molecules on Mars, coupled with the interconnection between the origin of life and volcanic eruptions, leads to an intriguing possibility: the existence of specialized chemoautotrophic life within planetary caves. This notion fuels excitement regarding the potential preservation of microbial life within the lava tubes of Mars. Combining microbiological, mineralogical, and organic geochemistry tools, an in-depth characterization of speleothems and associated microbial communities in lava tubes of Lanzarote (Canary Islands, Spain) is provided. The aim is to untangle the underlying factors influencing microbial colonization in Earth’s subsurface in order to gain insight into the possibility of similar subsurface microbial habitats on Mars and to unequivocally identify biosignatures preserved in lava tubes. In this sense, analytical pyrolysis, stable isotope analysis and chemometrics were conducted to characterize the complex organic fraction preserved in speleothems from Lanzarote lava tubes, one of the best terrestrial analogues to Martian volcanology. Our data show 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. Thus, our research will lay the foundation

Forest fires are a recurrent ecological phenomenon in the Mediterranean basin. They induce molecular changes in soil organic matter (SOM) leading to immediate and long-term environmental consequences [1]. The SOM is of paramount importance as indicator of soil health [2]. Fire-induced changes in SOM include the alteration of biogenic chemical structures and the accumulation of newly formed ones, enhancing dynamics in the complex balance between the different C-types [2,3]. Therefore, understanding SOM molecular composition, before and after fire, is fundamental to monitor changes in soil health, as well as its natural or man-mediated recovery [3,4]. Our aim was to assess the molecular composition of organic matter in fire-affected leptosols, at two depths (0-2 and 2-5 cm) under different vegetation types located in the southwestern of Portugal (Aljezur, Algarve). The SOM characterization was conducted by analytical pyrolysis (Py-GC/MS), a technique based on the thermochemical breakdown of organic compounds in the absence of oxygen at elevated temperatures [5]. The Py-GC/MS has been found suitable for the structural characterization of complex organic matrices [4], providing detailed structural information of individual compounds considered fingerprinting of SOM. However, due to the relative high number of molecular compounds released by analytical pyrolysis, the use of graphical-statistical methods, such as van Krevelen diagrams, are usually applied to help monitoring SOM molecular changes produced by fire [3,4]. This work represents the first attempt to evaluate the fire effects in SOM using a detailed molecular characterisation of SOM under different vegetation canopies, recently affected by wildfire, in southern Portugal. References:[1] Naveh, Z., 1990. Fire in the Mediterranean - a landscape ecological perspective. In: Goldammer, J.G., Jenkins, M.J. (Eds.), Fire in Ecosystems Dynamics: Mediterranean and Northern Perspective. SPB Academic Publishing, The Hague.[2

Siliceous speleothems, formed by mineral deposition in lava tubes, are vital for understanding past volcanic eruptions, assessing environmental conditions, and investigating extreme life forms. Molecular characterization of cave samples is also relevant, needing the use of cuttingedge analytical techniques. The analytical pyrolysis (Py) coupled with exact-mass spectrometry (Py-GC/Q-TOF) is a promising one. Analytical Py involves thermal decomposition of organic matter (OM) at high temperatures without oxygen, enabling chromatographic separation and providing valuable information about complex mixtures’ composition and molecular structure, including natural and synthetic macromolecules. Advantages of analytical Py include minimal sample preparation, small sample sizes, and detection of various organic materials, even those with low solubility or resistance to degradation. This technique facilitates rapid analysis of scarce or unique organic samples found in extreme environments and Mars analogues. Ultra-high resolution analytical pyrolysis (UH-Py) allows the identification of numerous distinct organic molecules in a sample without pre-treatment. However, due to the large number of chemical structures discovered, investigating each molecule separately is unfeasible. To address this, novel graphical-statistical tools are needed to identify primary chemical and biogenic families in a sample and investigate microorganisms’ adaptations to environmental or anthropogenic factors. This communication introduces the integration of UH-Py with multivariate statistical analysis and graphic-statistical tools as an innovative strategy for unsupervised classification and visual analysis of preserved organic matrices in siliceous speleothems from diverse lava tubes. The study focuses on samples from Selvagens Islands, La Palma (Canary Island), Easter Island, and the Galapagos Islands. By combining these analytical techniques, it becomes possible to identify biosignatures, such as mic

Plastic production has skyrocketed since the 1950s, resulting in over 8.3 billion tons of plastic generated and a projected 1500 million tons by 2050. Plastics have become pervasive but also environmentally impactful, contributing to CO2 emissions and marine pollution. Every year, 4.8 to 12.7 million metric tons of plastic waste enter the ocean, microplastics are small fragmented pieces (< 5 mm) of fragmented plastic debris, microbeads, and fibres, becoming a persistent pollutant in the sea and beaches. They absorb persistent organic pollutants (POPs) and Polybutylene terephthalate (PBTs) and can harm marine life by acting as carriers for pollution. Land-based sources account for 80% of microplastic pollution, while the fishing industry contributes 18%. In this work, we have sampled polluted sand at two depths (0–10 and 10–20 cm) at two sites in Lagoas de Santo André e da Sancha Nature Reserve, Alentejo coast (Portugal): close to the sea (P) and close to the lagoon (L) within a transect of 1.3 km with a separation of 150 m among sites. The main goal of this study was to monitor and identify the type of plastic at the molecular scale to understand its occurrence, composition, and impact to aid in the development of mitigation strategies and a better understanding of their environmental impact. In identifying microplastics techniques such as Fourier-transform infrared spectroscopy, Raman spectroscopy, and Thermogravimetry are commonly used. Another technique widely used in microplastic molecular characterization is nominal mass analytical pyrolysis (Py-GC/MS). Pyrolysis techniques have well-known advantages such as the requirement of small sample size with little or no preparation, being therefore convenient for inexpensive and relatively rapid analyses of scarce or little samples. Here, a novel exactmass high-resolution analytical pyrolysis (Py-GC/Q-TOF) technique is described and -to the best of our knowledge- for the first time used to identify the constituent mono

For temperate regions in forests and scrublands, a 5-level categorization was established to operationally define soil burn severity (SBS). This classification is important for estimating post-fire erosion risks and scheduling post-fire rehab activities [1]. This work describes the relationships between field SBS and molecular-level changes in the soil organic matter (SOM). Direct analytical pyrolysis [2] was used to study unburned (SBS-0) and burned soils (SBS 1 to 5) at two scenarios: 1) wildfire, and 2) burning laboratory experiment. The pyrolysis compounds were identified and plotted in modified 3D van Krevelen diagrams [3]. Moderate chemical changes occurred between stages SBS-0 to SBS-3, such as, dehydration, demethylation, depletion of polymethylene structures, carbohydrate rearrangements, lignin demethoxylation and triterpene preservation. Clear SOM transformations occurred at SBS-4 onwards with concentration of alkyl structures (triterpenes). Progressive changes in terms of SBS were not linear for all compounds. The subtraction surfaces suggest two major stages: SBS (0–1) generation of pyrolytic anhydrosugars; and SBS (3–4) generation of condensed compounds. Molecular-level changes in SOM after wildfire and laboratory experiment were similar. Nonetheless, the former showed incorporation of alkyl compounds and methoxyphenols, probably inputs of charred biomass from the vegetation. References: [1] Vega, JA. et al. 2013. Plant Soil 369, 73–91 [2] Jiménez-Morillo, NT. et al. 2016. Catena 145, 266–273 [3] Almendros, G. et al. 2018. J. Soils Sediments 18, 1303-1313

Olive cultivation is a crucial driver of the economy in the European Mediterranean basin, particularly in Spain, where it occupies about 2.75 million ha [1]. In recent years, there has been an expansion of super-intensive olive farming, which ensures high productivity but requires irrigation and is expected to increase organic waste generation and water demand. Consequently, it is imperative to adopt more sustainable approaches to manage the agricultural waste generated during olive harvesting and agro-industrial processing. To tackle that challenge, there is a renewed emphasis on utilizing organic amendments derived from agricultural residues. Biochar (B), a highly aromatic carbon obtained through biomass pyrolysis, has the potential to sequester carbon in the soil for extended periods and its unique physical properties increase soil porosity [2]. Nevertheless, B effects on SOM composition and functionality in the medium and long term are largely unknown. Additionally, green compost (Cp) is rich in nutrients and labile organic carbon, making it a valuable soil amendment for improving soil fertility, structure, and moisture retention. The two main goals of this study are: i) To discern the effects of transforming traditional olive orchards into bushrow olive cultivation on soil organic matter (SOM) composition, which plays an essential role in the carbon cycle and on soil quality, and ii) To assess the effects of of B and Cp on SOM composition two years after application. With such purposes, soil samples were taken from super-intensive olive orchards (1650 trees/ha; irrigated 30% water needs) amended with (B), green compost (Cp), a combination of B+Cp, as well as control plots [3]. Soil samples were also collected from traditional olive orchards in the same farm (La Hampa, Coria del Río) for comparative purposes. The free lipid fraction and volatile SOM were studied by using GC/MS and analytical pyrolysis (Py-GC/MS) respectively. Control soils, particularly those fr

[Introduction]: Caves are exceptional habitats for highly specialized microorganisms that can interact with minerals, allowing us to better understand the role of microorganisms in biogeochemical cycles and biomineralization processes. These priceless subterranean resources can be found all over the world, but they are one of the least explored habitats on Earth. Yet, lava caves have recently received special attention due to the discovery of numerous volcanic cave entrances on the Moon and Mars [1]. Such subsurface geological settings, characterized by stable physicochemical conditions, may support microbial activity over geological timescales, resulting in the preservation of traces of life in the rock record, recognized as biosignatures. These subterranean environments and the microbial life within thus provide a unique opportunity to study extremely specialized microorganisms, novel metabolic strategies, and interactions with igneous rocks relevant to astrobiology and planetary sciences., [Methods]: The diversity and function of microbial communities dwelling on speleothems from volcanic caves of Selvagens Islands (Madeira, Portugal), La Palma and Lanzarote (Canary Islands, Spain) have been investigated using portable cutting-edge DNAbased analysis, complemented by in-depth metagenomics and field emission scanning electron microscopy (FESEM), to understand which microorganisms grow in these extreme ecosystems, which functional properties they have, and their role in constructive and/or destructive mineral processes. In addition, advanced chromatography, and mass spectrometry techniques, such as GC/MS, PyrolysisGC/Q-TOF and Pyrolysis-compound specific isotope analysis (Py-CSIA) have been employed for an indepth biogeochemical characterization of the siliceous speleothems and for the assessment of biosignatures preserved in the samples, as described in Miller et al. [2,3]., [Results and Discussion]: Bacterial communities showed heterogeneity in composition among lava tubes, with the Actinomycetota, Bacillota and Bacteroidota phyla as the most abundant, exceeding 50% for most of the sampling sites. Using FESEM, we described the morphology of microbial cells and their interactions with the mineral substrate. FESEM images showed abundant actinobacteria-like cells and other morphotypes, resembling those reported by Riquelme et al. [4] in lava tubes from USA, Canada, Portugal and Spain, and in Etna lava tubes [5]. Observations conducted on microbial mat samples from a lava tube in Lanzarote revealed the presence of Ca-rich spheroids closely associated with filamentous cells of Crossiella sp.. The functional profile of microbial communities predicted by PICRUSt showed the presence of urease enzyme, that has been identified as responsible for the microbial precipitation of CaCO3 via urea hydrolysis [6], suggesting that this genus could promote speleothem formation. Similar biogenic-like CaCO3 microspheres were reported in colored microbial mats from Kipuka Kanohina lava cave in Hawaii, USA [4]. The presence of short-chain n-alkanes (C<20) and methylated fatty acids identified in the organic fraction of the siliceous speleothems are recognized as biosignatures of microbial origin (membrane lipids and/or microbial metabolites). High molecular weight lipid compounds (e.g., sterols and long-chain nalkanes) are indicative of vegetation biomarkers derived from lixiviation processes of the soil overlying caves

Today's agriculture faces the challenge of guarantee food supply of a growing population while human activity has already degraded nearly 40 % of the world's soils [1], which lose productive capacity and increase dependence on mineral fertilizers. In this context, the valorization and recycling of mineral and agricultural waste for use as substrates or soil amendments promotes the local and sustainable economy as well as the implementation of activities based on closing the soil nutrients’ cycle. Moreover, pyroclastic rocks and volcanic ashes formed by volcanic eruptions are usually rich in Si, Ca, Mg, Al, Fe, K, P and S [2], so they can be used in agriculture as inorganic mulch. Looking for an effective solution to the great waste generation and the current challenges of sustainable agriculture [3], this study addresses the agronomic effects of the application of contrasting inorganic and organic materials including green compost, wood biochar, rice husk ash and volcanic ash released in the recent eruption of the Tajogaite volcano (La Palma Island, Spain) as amendments of an alkaline soil typical of the Mediterranean basin. For this purpose, barley seeds were planted and grown under controlled conditions in a greenhouse for 60 days on a Luvisol amended with the above-mentioned materials. The organic amendments improved soil physical properties, such as the reduction of bulk density and of the soil resistance to penetration, and increased the organic carbon content. Biochar increased the amount of refractory organic matter of the Luvisol. The application of rice husk ash, volcanic ash, and to a lesser extent the green compost, increased the nutrient content of the soil. Nevertheless, no significant differences were observed on germination rates, productivity and abiotic markers of stress of the barley plants. Acknowledgements: Authors thank the financial support from the Spanish Ministry of Science and Innovation (MCIN) under the projects RES2SOIL (PID2021-126349OB

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

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 Donana 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 C-13 depleted with delta O-13 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 C-13 as corresponds to a more humified SOM. The fire produced no changes in this trend, although a consistent C-13 enrichment (c. 1 parts per thousand) was observed in all soil fractions with decreasing size. Concerning H isotopes, the coarse fractions (>0.5 mm) displayed significant lower delta H-2 values than the intermediate and fine ones (<0.5 mm), again similar to those in leaf biomass (c.-80 parts per thousand), whereas the fine fractions were found deuterium (H-2)-enriched with significant higher delta H-2 values (c. 50 parts per thousand), suggesting physical speciation of H depending on soil particle size. The fire produced a significant H-2 depletion (Delta H-2 c. -10 parts per thousand) 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. (C)2020 Elsevier B.V. All rights reserved.

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.

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.

Forest fires are a recurrent ecological phenomenon in the Mediterranean basin. They induce molecular changes in soil organic matter (SOM) leading to immediate and long-term environmental consequences [1]. The SOM is of paramount importance as indicator of soil health [2]. Fire-induced changes in SOM include the alteration of biogenic chemical structures and the accumulation of newly formed ones, enhancing dynamics in the complex balance between the different C-types [2,3]. Therefore, understanding SOM molecular composition, before and after fire, is fundamental to monitor changes in soil health, as well as its natural or man-mediated recovery [3,4]. Our aim was to assess the molecular composition of organic matter in fire-affected leptosols, at two depths (0–2 and 2–5 cm) under different vegetation types located in the southwestern of Portugal (Aljezur, Algarve). The SOM characterization was conducted by analytical pyrolysis (Py-GC/MS), a technique based on the thermochemical breakdown of organic compounds in the absence of oxygen at elevated temperatures [5]. The Py-GC/MS has been found suitable for the structural characterization of complex organic matrices [4], providing detailed structural information of individual compounds considered fingerprinting of SOM. However, due to the relative high number of molecular compounds released by analytical pyrolysis, the use of graphical-statistical methods, such as van Krevelen diagrams, are usually applied to help monitoring SOM molecular changes produced by fire [3,4]. This work represents the first attempt to evaluate the fire effects in SOM using a detailed molecular characterisation of SOM under different vegetation canopies, recently affected by wildfire, in southern Portugal. References: [1] Naveh, Z., 1990. Fire in the Mediterranean – a landscape ecological perspective. In: Goldammer, J.G., Jenkins, M.J. (Eds.), Fire in Ecosystems Dynamics: Mediterranean and Northern Perspective. SPB Academic Publishing, The Hague.

The direct effect of fire on soil microorganisms is quite evident and is directly related to the temperatures reached. Temperatures above 200 °C are enough to sterilize the soil [1], but normally these temperatures are limited to the first few centimetres of the soil profile [2, 3]. In spite of the elimination of some groups of microorganisms caused by low and moderate severity fires, other surviving groups in the microbial community will be also affected by side indirect fire effects such as soil organic matter and pH shifts. Here soils from two close-by areas in the Sierra Nevada National Park, under similar weather conditions and altitude (c. 2000 m. a. s. l.) were studied. To evaluate vegetation influence, a Pinus sylvestris reforested and a high mountain shrubs sites were sampled at each pH zone. Composite samples (8 sites) from each vegetation and pH zone were taken and used for a laboratory heating experiment (300 º C, 20 min). The treatments were: low pH soil under Pinus sylvestris (PSI-H) and unheated (PSI-C) and under Juniperus oxycedrus heated (ENE-H) and unheated (ENE-C); soil under Pinus sylvestris at high pH heated (PCA-H) and unheated (PCA-C) and under Juniperus sabina heated (SAB-H) and unheated (SAB-C). After the laboratory heating application, soil samples were cooled and both, heated and unheated samples, were reinoculad with unaltered fresh soil. Microbial response was monitored during 28 days and soil organic matter alteration studied by analytical pyrolysis (Py-GC/MS). Microbial respiration after heating was faster and reached higher values at high pH compared with low pH samples, and the vegetation influence was patent at heated and unheated treatments; thereby Juniperus sp. samples showed higher values of microbial respiration than those collected under Pinus sylvestris. Microbial biomass in unaltered samples also evidenced the influence of soil pH and vegetation with similar tendency as that described for respiration. Results obtained with a

Forest fires exert variable effects on the soil organic carbon (SOC) pool [1], and such effects are dependent on many factors including fire and soil characteristics, predominant vegetation and fuel [2]. An interpretation of the changes induced in SOC is relevant in order to predict possible fire derived adverse effects on soil characteristics such as water repellence and erodibility. In this work, soils from two large wildfires that occurred in the summer 2018, in the same biogeographical region (SE Iberian Peninsula, Monchique and Casares) and, hence, sharing similar climatic and physiographic conditions, were studied. The Monchique high severity wildfire (Agarve region, Portugal), destroyed 27.000 ha of eucalypt forest and shrubland. The Casares moderate severity wildfire (Andalusia region, Spain) consumed 300 ha of Mediterranean forest (cork and evergreen oak, pine and carob tree) and shrubland. Soil samples were collected immediately after the fire at 0-5 cm depth in both the unburnt (organic and mineral layer) and burnt (charred and mineral layer) areas. Direct analytical pyrolysis (Py-GC/MS, 400 °C, 1 min, 0.5 or 5.0 mg) was used to fingerprint SOC molecular structure. Unburnt samples from Monchique and Casares soils, showed distinct but well resolved and complex chromatograms reflecting the dominant vegetation (eucalyptus and Mediterranean bush), composed mainly of molecules derived from polysaccharides, lignin, fats, waxes and phytosterols. The effect of fire was clearly observed in both, quantity and quality of the SOC, but was different in the two forest fires. The Monchique site burnt soils showed a sharp decrease (destruction) of soil pyrolizable organic matter, with the almost complete disappearing of SOC in the surface (charred) but preserving the general SOC structure in the mineral layer. For the Casares soil, the fire slightly reduced the soil pyrolizable organic matter but a conspicuous SOC transformation was apparent in both the charred and the m

Biomass denotes all biological produced matter. This includes plant and animal products, agricultural crops, aquatic plants, algae and all types of wastes and waste byproducts such as forest, agricultural and animal wastes or municipal and industrial organic waste. Biomass, mainly wood, was humanity’s earliest source of energy and is still the most widespread renewable energy source alternative to fossil fuel consumption [1]. Biomass is also a source of many valueadded products, including biofuels, sugar and sugar alcohols, solvents, flavors and aromas and other industrial chemicals [2]. The chemical structure of biomass is complex, heterogeneous, diverse and relatively insoluble, posing difficulties for their detailed analysis [3]. Analytical pyrolysis has been proven an appropriate for biomass direct and rapid characterization [4]. In this study, a novel analytical pyrolysis hyphen technique that combines a micro-furnace multishot pyrolysis unit (Py; Frontier Lab. Fukushima, Japan. Mod 3030D) with gas chromatography (GC: Agilent Technologies, Sta. Clara, CA, USA; Mod. 8890) coupled to ultra-high resolution quadrupole time-of-flight mass spectrometry (Q-TOF MS) is described and used to characterize biomasses from different plant species. Detailed fingerprints were obtained and the main biomass biogenic components identified with exact masses. These included main structural biopolymers from lignin and holocellulose, as well as peptides and proteins, waxes and other extractives like terpenes, terpenoids and phytosterols. For accurate identification, the instrument was operated at high (HI) and low ionization (LI) energy of 70 and 15 eV respectively. References [1] Demibras, A. (2004). The Importance of Biomass. Energy Sources, 26:361–366. DOI:10.1080/0090831049077406 [2] Deswarte C.J.F. (2015). Introduction to Chemicals from Biomass. 2nd ed. Chichester: Wiley. 114–281 pp. DOI: 10.1002/9781118714478 [3] Dayton D.C; Foust T.D. (2019). Analytical Methods for Biomass Cha

Lignin is known as the most abundance, stabilized and protective soil organic matter (SOM) component, playing a significant role in the stabilization, mineralization or biodegradation [1]. The study of the main mechanisms driven by environmental factors such as future scenarios of climate change may certainly result in a better understanding of the link between SOM molecular structure and carbon turnover in soils [2]. This communication describes and validates a methodology based on analytical pyrolysis (Py-GC/MS) for the direct measure of lignin-derived phenols and its cleavages status directly from bulk soil samples taken in a five-years field experiment mimicking future extreme warming and drought events. Several proxies, based in molecular features of main lignin components, were calculated and used to explain ongoing processes of SOM transformation. These included the oxidation degree of the diverse lignin moieties and semi-quantification of aldehyde, ketones and acids. During the studied period a selective preservation of lignin in soil was observed, mainly affected by the effect of tree canopy. Also, an indirect effect over time of the different climate treatments and highlighted outside the tree canopy, could be attributed to the production of oxidative enzymes leading to enhanced decomposition. Lastly, forecasted soil warming is spotted as the most contributing climatic scenario to lignin degradation through a preservation/enrichment of lignin, identified by a higher oxidation degree of the lignin methoxyphenols. We will discuss how this aspect would affect soil carbon storage. Py-GC/MS technique is an important tool for characterizing and assessing lignin biopolymers in SOM that may provide detailed understanding of how climate change can alter soil organic C sequestration mechanisms. References [1] Bahri, H.et al., (2006). Soil Biology and Biochemistry, 38(7), 1977-1988 [2] Dungait et al (2008). Rapid Communications in Mass Spectrometry, 22(11), 1631-1639