Climatic vulnerabilities and ecological preferences of soil invertebrates across biomes.

Unlike plants and vertebrates, the ecological preferences, and potential vulnerabilities of soil invertebrates to environmental change, remain poorly understood in terrestrial ecosystems globally. We conducted a cross-biome survey including 83 locations across six continents to advance our understanding of the ecological preferences and vulnerabilities of the diversity of dominant and functionally important soil invertebrate taxa, including nematodes, arachnids and rotifers. The diversity of invertebrates was analyzed through amplicon sequencing. Vegetation and climate drove the diversity and dominant taxa of soil invertebrates. Our results suggest that declines in forest cover and plant diversity, and reductions in plant production associated with increases in aridity, can result in reductions of the diversity of soil invertebrates in a drier and more managed world. We further developed global atlases of the diversity of these important soil invertebrates, which were cross-validated using an independent database. Our study advances the current knowledge of the ecological preferences and vulnerabilities of the diversity and presence of functionally important soil invertebrates in soils from across the globe. This information is fundamental for improving and prioritizing conservation efforts of soil genetic resources and management policies

Vegetation structure determines the spatial variability of soil biodiversity across biomes

The factors controlling the spatial variability of soil biodiversity remain largely undetermined. We conducted a global field survey to evaluate how and why the within-site spatial variability of soil biodiversity (i.e. richness and community composition) changes across global biomes with contrasting soil ages, climates and vegetation types. We found that the spatial variability of bacteria, fungi, protists, and invertebrates is positively correlated across ecosystems. We also show that the spatial variability of soil biodiversity is mainly controlled by changes in vegetation structure driven by soil age and aridity. Areas with high plant cover, but low spatial heterogeneity, were associated with low levels of spatial variability in soil biodiversity. Further, our work advances the existence of significant, undescribed links between the spatial variability of soil biodiversity and key ecosystem functions. Taken together, our findings indicate that reductions in plant cover (e.g., via desertification, increases in aridity, or deforestation), are likely to increase the spatial variability of multiple soil organisms and that such changes are likely to negatively impact ecosystem functioning across global biomes

Efectos del cambio climático sobre la dinámica del nitrógeno en zonas áridas a distintas escalas espaciales

Programa de doctorado en Estudios MedioambientalesA lo largo de este doctorado se llevaron a cabo una serie de experimentos de laboratorio y de campo para evaluar el impacto de distintos agentes de cambio ambiental global (en lo sucesivo cambio global) sobre el ciclo del nitrógeno en zonas áridas a distintas escalas espaciales (local, regional y global). En primer lugar llevamos a cabo un estudio observacional en 224 zonas áridas a nivel global, situadas en todos los continentes menos la Antártida, para evaluar los impactos del incremento de la aridez derivado del cambio climático sobre los ciclos biogequímicos del nitrógeno (N), carbono (C) y fósforo (P). Los resultados obtenidos indicaron que este aumento de la aridez conllevará una disminución del control biótico (ej. menor cobertura vegetal) y un incremento del abiótico (p. ej. mayor dominio de la meteorización mecánina) sobre los ciclos biogeoquímicos en las zonas áridas. De este modo, los nutrientes asociados a procesos biológicos como el C y N (p. ej. fotosíntesis, descomposición de materia orgánica y fijación de N atmosférico) disminuirán con el incremento de aridez, mientras que nutrientes como el P, asociados con procesos geoquímicos (p. ej. meteorización de la roca), se verán favorecidos, generando desacoples entre los ciclos biogeoquímicos del C, N y P. Debido a la fuerte dependencia estequiométrica que los seres vivos tienen sobre los ciclos biogeoquímicos del C, N y P, su desacople podría acarrear un impacto negativo sobre la producción primaria, la respiración o la descomposición de la materia orgánica a nivel global. En segundo lugar, evaluamos el papel de la vegetación como elemento modulador de los efectos del incremento de aridez que se espera en zonas áridas en respuesta al cambio climático sobre el N total disponible y la abundancia en el suelo de genes de bacterias (AOB) y arqueas (AOA) nitrificantes a lo largo de un gradiente regional mediterráneo (desde España a Túnez). Conforme aumentó la aridez en este gradiente, disminuyeron la disponibilidad total de N y el ratio AOB: AOA. Los micrositios con vegetación favorecieron un incremento de AOB, mientras que suelos desnudos favorecieron la abundancia de AOA, más resistentes al estrés ambiental. Los resultados obtenidos indican que la vegetación podría reducir los impactos del incremento de aridez derivado del cambio climático sobre el N disponible del suelo y los microorganismos implicados en la nitrificación, debido a la acumulación de matera orgánica que ésta promueve, y a los nichos que proporciona a diferentes grupos de bacterias y arqueas nitrificantes. Por último, evaluamos el papel de la costra biológica del suelo (CBS), comunidades dominadas por líquenes, musgos y cianobacterias, en la resistencia y resiliencia de variables del ciclo del N a cambios en temperatura, contenido de agua en suelo y en la disponibilidad de C, N y P a escala local mediante incubaciones en el laboratorio. En general, los suelos bajo CBS mostraron una mayor resistencia a los cambios en temperatura y una mayor resiliencia a las adiciones de C y N. Sin embargo, los cambios en humedad edáfica no afectaron a las variables del ciclo del N, sugiriendo que procesos tales como la mineralización en zonas áridas pueden ser llevados a cabo en un rango amplio de humedad. Posteriormente, llevamos a cabo un experimento en cámara de cultivo para evaluar el papel modulador de la CBS sobre el ciclo del N en respuesta a pequeños pulsos de agua (1% de la capacidad de campo), similares a los producidos por los eventos de rocío. La CBS favoreció una acumulación de N total disponible en suelo en respuesta a estos pequeños pulsos de agua, siendo el mecanismo descrito en este trabajo uno de los posibles responsables del incremento de los contenidos de N típicamente observado bajo la CBS en zonas áridas. En su conjunto, la investigación realizada en el marco de esta tesis doctoral, ha profundizado nuestro conocimiento sobre los papeles que juegan la costra biológica y la vegetación como moduladores de los impactos del cambio global sobre el ciclo del N en zonas áridas. Del mismo modo, concluimos que un incremento de aridez a nivel mundial podría llevar a un desacople de los ciclos del C, N y P en suelo en los ecosistemas más áridos, lo que posiblemente afectará a los procesos y servicios ecosistémicos que prestan estos ambientes. Asimismo, el trabajo realizado en esta tesis pone de manifiesto que el estudio de los impactos del cambio global requiere del entendimiento de atributos y procesos ecosistémicos ligados a distintas escalas espaciales, que van desde patrones generales ligados a escala global a los mecanismos y factores concretos que actúan a escalas regionales y locales.Universidad Pablo de Olavide. Centro de Estudios de Postgrad

Global ecological predictors of the soil priming effect.

Identifying the global drivers of soil priming is essential to understanding C cycling in terrestrial ecosystems. We conducted a survey of soils across 86 globally-distributed locations, spanning a wide range of climates, biotic communities, and soil conditions, and evaluated the apparent soil priming effect using 13C-glucose labeling. Here we show that the magnitude of the positive apparent priming effect (increase in CO2 release through accelerated microbial biomass turnover) was negatively associated with SOC content and microbial respiration rates. Our statistical modeling suggests that apparent priming effects tend to be negative in more mesic sites associated with higher SOC contents. In contrast, a single-input of labile C causes positive apparent priming effects in more arid locations with low SOC contents. Our results provide solid evidence that SOC content plays a critical role in regulating apparent priming effects, with important implications for the improvement of C cycling models under global change scenarios

Forest plantations reduce soil functioning in terrestrial ecosystems from South Africa

The role of forest plantations in regulating soil ecosystem functions remains poorly understood in terrestrial ecosystems from Africa. Here, we evaluated the importance of forest plantations in regulating soil microbial functional profiles, community-level physiological profiles (CLPPs) and activities of soil microbial communities compared with native forests in two contrasting seasons. We found that forest plantations consistently reduced the rates of multiple soil functions associated with soil nutrient and carbon (C) cycling and shifted the activity and functional profile of microbial communities in two contrasting seasons and two independent regions from South Africa. Our results suggest land use changes from natural forests to plantations to maintain a continuously growing human population will have important negative consequences for soil functions in forest ecosystems from Africa with implications for ecosystem functioning under changing environments

Microbial regulation of the soil carbon cycle: evidence from gene-enzyme relationships.

A lack of empirical evidence for the microbial regulation of ecosystem processes, including carbon (C) degradation, hinders our ability to develop a framework to directly incorporate the genetic composition of microbial communities in the enzyme-driven Earth system models. Herein we evaluated the linkage between microbial functional genes and extracellular enzyme activity in soil samples collected across three geographical regions of Australia. We found a strong relationship between different functional genes and their corresponding enzyme activities. This relationship was maintained after considering microbial community structure, total C and soil pH using structural equation modelling. Results showed that the variations in the activity of enzymes involved in C degradation were predicted by the functional gene abundance of the soil microbial community (R2>0.90 in all cases). Our findings provide a strong framework for improved predictions on soil C dynamics that could be achieved by adopting a gene-centric approach incorporating the abundance of functional genes into process models

Multifunctionality debt in global drylands linked to past biome and climate

Past vegetation and climatic conditions are known to influence current biodiversity patterns. However, whether their legacy effects affect the provision of multiple ecosystem functions, that is, multifunctionality, remains largely unknown. Here we analyzed soil nutrient stocks and their transformation rates in 236 drylands from six continents to evaluate the associations between current levels of multifunctionality and legacy effects of the Last Glacial Maximum (LGM) desert biome distribution and climate. We found that past desert distribution and temperature legacy, defined as increasing temperature from LGM, were negatively correlated with contemporary multifunctionality even after accounting for predictors such as current climate, soil texture, plant species richness, and site topography. Ecosystems that have been deserts since the LGM had up to 30% lower contemporary multifunctionality compared with those that were nondeserts during the LGM. In addition, ecosystems that experienced higher warming rates since the LGM had lower contemporary multifunctionality than those suffering lower warming rates, with a ~9% reduction per extra degree Celsius. Past desert distribution and temperature legacies had direct negative effects, while temperature legacy also had indirect (via soil sand content) negative effects on multifunctionality. Our results indicate that past biome and climatic conditions have left a strong “functionality debt” in global drylands. They also suggest that ongoing warming and expansion of desert areas may leave a strong fingerprint in the future functioning of dryland ecosystems worldwide that needs to be considered when establishing management actions aiming to combat land degradation and desertification.China Scholarship Council; National Natural Science Foundation of China, Grant/Award Number: 31570467; Horizon 2020 Framework Programme, Grant/Award Number: 702057, 242658 and 647038; Ramón y Cajal contract, Grant/Award Number: RYC-2016-20604; European Research Counci

D'Annunzio sulla scena lirica: libretto o "Poema"?

Australia Direct Action climate change policy relies on purchasing greenhouse gas abatement from projects undertaking approved abatement activities. Management of soil organic carbon (SOC) in agricultural soils is an approved activity, based on the expectation that land use change can deliver significant changes in SOC. However, there are concerns that climate, topography and soil texture will limit changes in SOC stocks. This work analyses data from 1482 sites surveyed across the major agricultural regions of Eastern Australia to determine the relative importance of land use vs. other drivers of SOC. Variation in land use explained only 1.4% of the total variation in SOC, with aridity and soil texture the main regulators of SOC stock under different land uses. Results suggest the greatest potential for increasing SOC stocks in Eastern Australian agricultural regions lies in converting from cropping to pasture on heavy textured soils in the humid regions

Humidity and low pH boost occurrence of Onygenales fungi in soil at global scale

Soils are important reservoirs for potential human pathogens and opportunistic fungi such as the dermatophyte or dimorphic fungi in the order Onygenales. In soils, these taxa are decomposers but many of them have the potential to cause respiratory and skin diseases in humans and, in some cases, systemic infections. Even so, the factors that determine the biogeography and ecology of order Onygenales remain largely undocumented. To address this knowledge gap, we surveyed members of Onygenales from topsoil fungal communities at 235 sites across six continents and provided a first global atlas. We retrieved 4.3% of the total fungal sequences (∼420 Onygenales) across nine biomes ranging from deserts to tropical forests. This work advances our knowledge on the ecology and global distribution of order Onygenales and suggests the hypothesis that wet and acid soils support the larger proportions of these fungi, while their richness is constrained by aridity.C.C. and L.S. wish to thank the Italian National Program for Antarctic Research (PNRA) for supporting their research. M.D-B. is supported by a project from the Spanish Ministry of Science and Innovation (PID2020-115813RA-I00), and a project PAIDI 2020 from the Junta de Andalucía (P20_00879). Microbial distribution and colonization research in B.K.S. lab is funded by Australian Research Council (DP190103714). E.G. is supported by the European Research Council grant agreement 647038 (BIODESERT)