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10 páginas.- 4 figuras.- 1 tablas.- referencias., [EN]: There is a need for tools to determine the origin of organic matter (OM) in Blue Carbon Ecosystems (BCE) and marine sediments to (1) facilitate the implementation of Blue Carbon strategies into carbon accounting and crediting schemes and (2) decipher changes in ecosystem condition over decadal to millennial time scales and thus to understand and predict the stability of BCE in a changing world. Pyrolysis-GC-compound specific isotope analysis (Py-CSIA) is applied for the first time in marine environments and BCE research. We studied Australian mangrove, tidal marsh and seagrass sediments, in addition to potential sources of OM (Avicennia, Posidonia, Zostera, Sarcocornia, Ecklonia and Ulva species and seagrass epiphytes), to identify precursors of different biomacromolecule constituents (lignin, polysaccharides and aliphatic structures). Firstly, the link between bulk δ13C and δ13C reconstructed from compound-specific δ13C showed that the pyrolysis approach allows for the isotopic screening of a representative portion of the OM. Secondly, for all samples, the C isotope fingerprint of the carbohydrate products (plant polysaccharides) was the heaviest (13C enriched), followed by lignin and aliphatic products. The differences in δ13C among macromolecules and the overlap in δ13C among putative sources reflect the limitations of bulk δ13C analyses for deciphering OM provenance. Thirdly, phanerogams specimen had the heaviest carbohydrate and lignin, confirming that seagrass-derived lignocellulose can be traced based on δ13C. Consistent differences for individual compounds were identified between seagrasses and between Avicennia and Sarcocornia using Py-CSIA. Fourth, ecosystem shifts (colonization of seagrass habitats by mangrove) on millenary time scales, hypothesized in previous studies on the basis of bulk δ13C and Py-GC–MS, were confirmed by Py-CSIA. We conclude that Py-CSIA is useful in Blue Carbon research to decipher OM sources in marine sediments, identify ecosystem transitions in palaeoenvironmental records, and to understand the role of different OM compounds in Blue Carbon storage., [ES]: Es necesario desarrollar herramientas para determinar el origen de la materia orgánica (MO) en ecosistemas de “Blue Carbon” (BCE) y en sedimentos marinos para (1) facilitar el desarrollo de estrategias de “Blue Carbon” en los esquemas de contabilidad y acreditación de C (2) descifrar cambios en las condiciones del ecosistema a escala de décadas a milenios y, por lo tanto, comprender mejor y predecir la estabilidad de BCE en escenarios de cambio climático. En este trabajo, aplicamos por primera vez el análisis de isótopos estables de C en compuestos específicos liberados por pirolisis (Py-CSIA) en entornos marinos y en la investigación de BCE. Estudiamos sedimentos de manglares, marismas y praderas marinas de Australia, además de las fuentes potenciales de MO (especies de Avicennia, Posidonia, Zostera, Sarcocornia, Ecklonia y Ulva y epífitas de praderas marinas), para identificar precursores de los diferentes constituyentes de las principales biomacromoléculas (lignina, polisacáridos y estructuras alifáticas). En primer lugar, la relación encontrada entre el δ13C total y el reconstruido a partir de los δ13C específicos de los compuestos, indica que el enfoque de pirólisis permite el cribado isotópico de una parte representativa de la MO. En segundo lugar, para todas las muestras, la huella isotópica de C de los productos de carbohidratos (polisacáridos vegetales) fue la más pesada (enriquecida en 13C), seguida de la lignina y los productos alifáticos. Las diferencias en δ13C entre los distintos tipos de macromoléculas y la superposición en δ13C entre las distintas fuentes putativas, pone de manifiesto las limitaciones de los análisis convencionales de δ13C totales (“bulk”) para descifrar la procedencia de la MO. En tercer lugar, las fanerógamas estudiadas mostraron la mayor proporción de carbohidratos y lignina, lo que confirma que la lignocelulosa derivada de pastos marinos se puede rastrear en base al δ13C de compuestos específicos. Mediante la Py-CSIA se identificaron diferencias consistentes para compuestos individuales entre las especies de praderas marinas y entre las de manglar (Avicennia y Sarcocornia). En cuarto lugar, mediante la Py-CSIA de δ13C confirmamos cambios en el ecosistema costero (colonización de hábitats de praderas marinas por manglares) ocurridos en los últimos milenios. Concluimos que la Py-CSIA es útil en la investigación de “Blue Carbon” y para descifrar las distintas fuentes de MO en los sedimentos marinos, identificar transiciones de ecosistemas en registros paleoambientales y para comprender mejor el papel de diferentes compuestos de la MO en el almacenamiento de C en el BCE., O.S. was supported by I+D+i projects RYC2019-027073-I and PIE HOLOCENO 20213AT014 funded by MCIN/AEI/10.13039/501100011033 and FEDER. L.M.S.-E. thanks MINECO pre-doctoral FPI fellowship BES-2017-079811 and J.A.G.-P. project PAIDI2020, PY20_01073. Both projects co-funded with EU FEDER funds. The laboratory personnel Alba M. Carmona and Desiré Monis are acknowledged for technical assistance. We are grateful to the anonymous reviewers for their effort and comments.

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).

12 páginas. 4 figuras.- 2 tablas.- 70 referencias.- Additional supporting information may be found in the online version of this article at http://onlinelibrary.wiley.com/doi/ 10.1002/ecy.2936/suppinfo .- Data are available from the Dryad Digital Repository: https://doi.org/10.5061/dryad.59zw3r23d, Recent studies have shown that invasive earthworms can dramatically reduce native biodiversity, both above and below the ground. However, we still lack a synthetic understanding of the underlying mechanisms behind these changes, such as whether earthworm effects on soil chemical properties drive such relationships. Here, we investigated the effects of invasive earthworms on soil chemical properties (pH, water content, and the stocks and fluxes of carbon, nitrogen, and phosphorus) by conducting a meta‐analysis. Invasive earthworms generally increased soil pH, indicating that the removal of organic layers and the upward transport of more base‐rich mineral soil caused a shift in soil pH. Moreover, earthworms significantly decreased soil water content, suggesting that the burrowing activities of earthworms may have increased water infiltration of and/or increased evapotranspiration from soil. Notably, invasive earthworms had opposing effects on organic and mineral soil for carbon and nitrogen stocks, with decreases in organic, and increases in mineral soil. Nitrogen fluxes were higher in mineral soil, whereas fluxes in organic soil were not significantly affected by the presence of invasive earthworms, indicating that earthworms mobilize and redistribute nutrients among soil layers and increase overall nitrogen loss from the soil. Invasive earthworm effects on element stocks increased with ecological group richness only in organic soil. Earthworms further decreased ammonium stocks with negligible effects on nitrate stocks in organic soil, whereas they increased nitrate stocks but not ammonium stocks in mineral soil. Notably, all of these results were consistent across forest and grassland ecosystems underlining the generality of our findings. However, we found some significant differences between studies that were conducted in the field (observational and experimental settings) and in the lab, such as that the effects on soil pH decreased from field to lab settings, calling for a careful interpretation of lab findings. Our meta‐analysis provides strong empirical evidence that earthworm invasion may lead to substantial changes in soil chemical properties and element cycling in soil. Furthermore, our results can help explain the dramatic effects of invasive earthworms on native biodiversity, for example, shifts towards the dominance of grass species over herbaceous ones, as shown by recent meta‐analyses., This project received support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement 677232). Further support came from the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, funded by the German Research Foundation (FZT 118).