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

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

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

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)

Global meta-analysis reveals positive effects of biochar on soil microbial diversity

Biochar has gained global attention due to its potential for climate change mitigation and soil quality improvement. Yet, the consequences of biochar additions for soil microbes-the major biotic drivers of soil function-remain unknown across global environmental gradients. We aimed to explore the responses of soil bacterial communities to biochar addition, and further investigate how biochar and soil properties impact these responses. We conducted a global meta-analysis and found that, in general, biochar has a limited impact on the proportion of major bacterial phyla, with only Acidobacteria and Gemmatimonadetes being largely impacted: the relative abundance of Acidobacteria decreased by 14.6%, while that of Gemmatimonadetes increased by 19.8%. Also, the experimental type played a role in shaping the response of microbial community to biochar application. In addition, biochar significantly promoted the diversity of soil bacteria, i.e., genetic richness and diversity. These changes were significantly associated with biochar load, C/N ratio, pyrolysis temperature, biochar pH, as well as soil C/N ratio and pH. We further found that the impacts of biochar on functional diversity, i.e., C substrate richness consumed by soil microbes increased with the biochar load, which might relate to increased genetic richness. Our work suggests that selecting key biochar properties can improve soil quality, microbial function, and climate change mitigation while maintaining the positive impacts of biochar on soil microbial diversity. Further research is needed to link the response of soil microbial composition at the genus level to biochar addition, with microbial functions

Trophic level drives the host microbiome of soil invertebrates at a continental scale

Background: Increasing our knowledge of soil biodiversity is fundamental to forecast changes in ecosystem functions under global change scenarios. All multicellular organisms are now known to be holobionts, containing large assemblages of microbial species. Soil fauna is now known to have thousands of species living within them. However, we know very little about the identity and function of host microbiome in contrasting soil faunal groups, across different terrestrial biomes, or at a large spatial scale. Here, we examined the microbiomes of multiple functionally important soil fauna in contrasting terrestrial ecosystems across China. Results: Different soil fauna had diverse and unique microbiomes, which were also distinct from those in surrounding soils. These unique microbiomes were maintained within taxa across diverse sampling sites and in contrasting terrestrial ecosystems. The microbiomes of nematodes, potworms, and earthworms were more difficult to predict using environmental data, compared to those of collembolans, oribatid mites, and predatory mites. Although stochastic processes were important, deterministic processes, such as host selection, also contributed to the assembly of unique microbiota in each taxon of soil fauna. Microbial biodiversity, unique microbial taxa, and microbial dark matter (defined as unidentified microbial taxa) all increased with trophic levels within the soil food web. Conclusions: Our findings demonstrate that soil animals are important as repositories of microbial biodiversity, and those at the top of the food web harbor more diverse and unique microbiomes. This hidden source of biodiversity is rarely considered in biodiversity and conservation debates and stresses the importance of preserving key soil invertebrates

Consistent responses of soil microbial taxonomic and functional attributes to mercury pollution across China

Background: The ecological consequences of mercury (Hg) pollution—one of the major pollutants worldwide—on microbial taxonomic and functional attributes remain poorly understood and largely unexplored. Using soils from two typical Hg-impacted regions across China, here, we evaluated the role of Hg pollution in regulating bacterial abundance, diversity, and co-occurrence network. We also investigated the associations between Hg contents and the relative abundance of microbial functional genes by analyzing the soil metagenomes from a subset of those sites. Results: We found that soil Hg largely influenced the taxonomic and functional attributes of microbial communities in the two studied regions. In general, Hg pollution was negatively related to bacterial abundance, but positively related to the diversity of bacteria in two separate regions. We also found some consistent associations between soil Hg contents and the community composition of bacteria. For example, soil total Hg content was positively related to the relative abundance of Firmicutes and Bacteroidetes in both paddy and upland soils. In contrast, the methylmercury (MeHg) concentration was negatively correlated to the relative abundance of Nitrospirae in the two types of soils. Increases in soil Hg pollution correlated with drastic changes in the relative abundance of ecological clusters within the co-occurrence network of bacterial communities for the two regions. Using metagenomic data, we were also able to detect the effect of Hg pollution on multiple functional genes relevant to key soil processes such as element cycles and Hg transformations (e.g., methylation and reduction). Conclusions: Together, our study provides solid evidence that Hg pollution has predictable and significant effects on multiple taxonomic and functional attributes including bacterial abundance, diversity, and the relative abundance of ecological clusters and functional genes. Our results suggest an increase in soil Hg pollution linked to human activities will lead to predictable shifts in the taxonomic and functional attributes in the Hg-impacted areas, with potential implications for sustainable management of agricultural ecosystems and elsewhere

Microbial resistance promotes plant production in a four-decade nutrient fertilization experiment

There is a current lack of mechanistic understanding on the relationships between a soil microbial community, crop production, and nutrient fertilization. Here, we combined ecological network theory with ecological resistance index to evaluate the responses of microbial community to additions of multiple inorganic and organic fertilizers, and their associations with wheat production in a 35-year field experiment. We found that microbial phylotypes were grouped into four major ecological clusters, which contained a certain proportions of fast-growers, copiotrophic groups, and potential plant pathogens. The application of combined inorganic fertilizers and cow manure led to the most resistant (less responsive) microbial community, which was associated with the highest levels of plant production, nutrient availability, and the lowest relative abundance of potential fungal plant pathogens after 35 years of nutrient fertilization. In contrast, microbial community was highly responsive (low resistance) to inorganic fertilization alone or plus wheat straw, which was associated with lower crop production, nutrient availability, and higher abundance of potential fungal plant pathogens. Our work demonstrates that the response of microbial community to long-term nutrient fertilizations largely regulates plant production in agricultural ecosystems, and suggests that manipulating these microbial phylotypes may offer a sustainable solution to the maintenance of field productivity under long-term nutrient fertilization scenarios. © 2019 The Author

UV index and climate seasonality explain fungal community turnover in global drylands

Aim: Fungi are major drivers of ecosystem functioning. Increases in aridity are known to negatively impact fungal community composition in dryland ecosystems globally; yet, much less is known on the potential influence of other environmental drivers, and whether these relationships are linear or nonlinear. Time period: 2017–2021. Location: Global. Major taxa studied: Fungi. Methods: We re-analysed multiple datasets from different dryland biogeographical regions, for a total of 912 samples and 1,483 taxa. We examined geographical patterns in community diversity and composition, and spatial, edaphic and climatic factors driving them. Results: UV index, climate seasonality, and sand content were the most important environmental predictors of community shifts, showing the strongest association with the richness of putative plant pathogens and saprobes. Important nonlinear relationships existed with each of these fungal guilds, with increases in UV and temperature seasonality above 7.5 and 900 SD (standard deviation x 100 of the mean monthly temperature), respectively, being associated with an increased probability of plant pathogen and unspecified saprotroph occurrence. Conversely, these environmental parameters had a negative relationship with litter and soil saprotroph richness. Consequently, these ecological groups might be particularly sensitive to shifts in UV radiation and climate seasonality, which is likely to disturb current plant–soil dynamics in drylands. Main conclusions: Our synthesis integrates fungal community data from drylands across the globe, allowing the investigation of fungal distribution and providing the first evidence of shifts in fungal diversity and composition of key fungal ecological groups along diverse spatial, climatic and edaphic gradients in these widely distributed ecosystems. Our findings imply that shifts in soil structure and seasonal climatic patterns induced by global change will have disproportionate consequences for the distribution of fungal groups linked to vegetation and biogeochemical cycling in drylands, with implications for plant–soil interactions in drylands.C.C. is supported by the European Commission under the Marie Sklodowska-Curie Grant Agreement No. 702057 (DRYLIFE). C.C. acknowledges funding from the Italian National Program for Antarctic Research (PNRA) and is supported by a PNRA postdoctoral fellowship. E.E. is supported by an Australian Research Council DECRA (Discovery Early Career Researcher Award) fellowship (DE210101822). M.D-B. is supported by a project from the Spanish Ministry of Science and Innovation (PID2020-115813RA-I00), and a project PAIDI (Andalusian Research, Development and Innovation Plan) 2020 from the Junta de Andalucía (P20_00879). Microbial distribution and colonization research in B.K.S.'s lab is funded by the Australian Research Council (DP210102081). E.G. is supported by the European Research Council Grant agreement 647038 (BIODESERT)