Showing papers by "Manuel Delgado-Baquerizo published in 2020"

Multiple elements of soil biodiversity drive ecosystem functions across biomes.

Abstract: The role of soil biodiversity in regulating multiple ecosystem functions is poorly understood, limiting our ability to predict how soil biodiversity loss might affect human wellbeing and ecosystem sustainability. Here, combining a global observational study with an experimental microcosm study, we provide evidence that soil biodiversity (bacteria, fungi, protists and invertebrates) is significantly and positively associated with multiple ecosystem functions. These functions include nutrient cycling, decomposition, plant production, and reduced potential for pathogenicity and belowground biological warfare. Our findings also reveal the context dependency of such relationships and the importance of the connectedness, biodiversity and nature of the globally distributed dominant phylotypes within the soil network in maintaining multiple functions. Moreover, our results suggest that the positive association between plant diversity and multifunctionality across biomes is indirectly driven by soil biodiversity. Together, our results provide insights into the importance of soil biodiversity for maintaining soil functionality locally and across biomes, as well as providing strong support for the inclusion of soil biodiversity in conservation and management programmes.

Global ecosystem thresholds driven by aridity

Abstract: Aridity, which is increasing worldwide because of climate change, affects the structure and functioning of dryland ecosystems. Whether aridification leads to gradual (versus abrupt) and systemic (versus specific) ecosystem changes is largely unknown. We investigated how 20 structural and functional ecosystem attributes respond to aridity in global drylands. Aridification led to systemic and abrupt changes in multiple ecosystem attributes. These changes occurred sequentially in three phases characterized by abrupt decays in plant productivity, soil fertility, and plant cover and richness at aridity values of 0.54, 0.7, and 0.8, respectively. More than 20% of the terrestrial surface will cross one or several of these thresholds by 2100, which calls for immediate actions to minimize the negative impacts of aridification on essential ecosystem services for the more than 2 billion people living in drylands.

Rare microbial taxa as the major drivers of ecosystem multifunctionality in long-term fertilized soils

Abstract: Soil microbial communities play an essential role in driving multiple functions (i.e., multifunctionality) that are central to the global biogeochemical cycles. Long-term fertilization has been reported to reduce the soil microbial diversity, however, the impact of fertilization on multifunctionality and its relationship with soil microbial diversity remains poorly understood. We used amplicon sequencing and high-throughput quantitative-PCR array to characterize the microbial community compositions and 70 functional genes in a long-term experimental field station with multiple inorganic and organic fertilization treatments. Compared with inorganic fertilization, the application of organic fertilizer improved the soil multifunctionality, which positively correlated with the both bacterial and fungal diversity. Random Forest regression analysis indicated that rare microbial taxa (e.g. Cyanobacteria and Glomeromycota) rather than the dominant taxa (e.g. Proteobacteria and Ascomycota) were the major drivers of multifunctionality, suggesting that rare taxa had an over-proportional role in biological processes. Therefore, preserving the diversity of soil microbial communities especially the rare microbial taxa could be crucial to the sustainable provision of ecosystem functions in the future.

The proportion of soil-borne pathogens increases with warming at the global scale

Abstract: Understanding the present and future distribution of soil-borne plant pathogens is critical to supporting food and fibre production in a warmer world. Using data from a global field survey and a nine-year field experiment, we show that warmer temperatures increase the relative abundance of soil-borne potential fungal plant pathogens. Moreover, we provide a global atlas of these organisms along with future distribution projections under different climate change and land-use scenarios. These projections show an overall increase in the relative abundance of potential plant pathogens worldwide. This work advances our understanding of the global distribution of potential fungal plant pathogens and their sensitivity to ongoing climate and land-use changes, which is fundamental to reduce their incidence and impacts on terrestrial ecosystems globally. Plant pathogens threaten food security and ecosystem health. Projections of potential fungal plant pathogens under different warming and land-use scenarios indicate that warming temperatures under climate change will lead to increases in the relative abundance of such pathogens in most soils worldwide.

The global-scale distributions of soil protists and their contributions to belowground systems

Abstract: Protists are ubiquitous in soil, where they are key contributors to nutrient cycling and energy transfer. However, protists have received far less attention than other components of the soil microbiome. We used amplicon sequencing of soils from 180 locations across six continents to investigate the ecological preferences of protists and their functional contributions to belowground systems. We complemented these analyses with shotgun metagenomic sequencing of 46 soils to validate the identities of the more abundant protist lineages. We found that most soils are dominated by consumers, although parasites and phototrophs are particularly abundant in tropical and arid ecosystems, respectively. The best predictors of protist composition (primarily annual precipitation) are fundamentally distinct from those shaping bacterial and archaeal communities (namely, soil pH). Some protists and bacteria co-occur globally, highlighting the potential importance of these largely undescribed belowground interactions. Together, this study allowed us to identify the most abundant and ubiquitous protists living in soil, with our work providing a cross-ecosystem perspective on the factors structuring soil protist communities and their likely contributions to soil functioning.

Blind spots in global soil biodiversity and ecosystem function research.

Abstract: Soils harbor a substantial fraction of the world's biodiversity, contributing to many crucial ecosystem functions. It is thus essential to identify general macroecological patterns related to the distribution and functioning of soil organisms to support their conservation and consideration by governance. These macroecological analyses need to represent the diversity of environmental conditions that can be found worldwide. Here we identify and characterize existing environmental gaps in soil taxa and ecosystem functioning data across soil macroecological studies and 17,186 sampling sites across the globe. These data gaps include important spatial, environmental, taxonomic, and functional gaps, and an almost complete absence of temporally explicit data. We also identify the limitations of soil macroecological studies to explore general patterns in soil biodiversity-ecosystem functioning relationships, with only 0.3% of all sampling sites having both information about biodiversity and function, although with different taxonomic groups and functions at each site. Based on this information, we provide clear priorities to support and expand soil macroecological research.

Crop microbiome and sustainable agriculture.

Abstract: A global assessment of the structure and function of the crop microbiome is urgently needed for the development of effective and rationally designed microbiome technologies for sustainable agriculture. Such an effort will provide new knowledge on the key ecological and evolutionary interactions between plant species and their microbiomes that can be harnessed for increasing agriculture productivity.

Soil Microbial Biogeography in a Changing World: Recent Advances and Future Perspectives.

Abstract: Soil microbial communities are fundamental to maintaining key soil processes associated with litter decomposition, nutrient cycling, and plant productivity and are thus integral to human well-being. Recent technological advances have exponentially increased our knowledge concerning the global ecological distributions of microbial communities across space and time and have provided evidence for their contribution to ecosystem functions. However, major knowledge gaps in soil biogeography remain to be addressed over the coming years as technology and research questions continue to evolve. In this minireview, we state recent advances and future directions in the study of soil microbial biogeography and discuss the need for a clearer concept of microbial species, projections of soil microbial distributions toward future global change scenarios, and the importance of embracing culture and isolation approaches to determine microbial functional profiles. This knowledge will be critical to better predict ecosystem functions in a changing world.

Effects of Spatial Variability and Relic DNA Removal on the Detection of Temporal Dynamics in Soil Microbial Communities.

Abstract: Few studies have comprehensively investigated the temporal variability in soil microbial communities despite widespread recognition that the belowground environment is dynamic. In part, this stems from the challenges associated with the high degree of spatial heterogeneity in soil microbial communities and because the presence of relic DNA (DNA from dead cells or secreted extracellular DNA) may dampen temporal signals. Here, we disentangle the relationships among spatial, temporal, and relic DNA effects on prokaryotic and fungal communities in soils collected from contrasting hillslopes in Colorado, USA. We intensively sampled plots on each hillslope over 6 months to discriminate between temporal variability, intraplot spatial heterogeneity, and relic DNA effects on the soil prokaryotic and fungal communities. We show that the intraplot spatial variability in microbial community composition was strong and independent of relic DNA effects and that these spatial patterns persisted throughout the study. When controlling for intraplot spatial variability, we identified significant temporal variability in both plots over the 6-month study. These microbial communities were more dissimilar over time after relic DNA was removed, suggesting that relic DNA hinders the detection of important temporal dynamics in belowground microbial communities. We identified microbial taxa that exhibited shared temporal responses and show that these responses were often predictable from temporal changes in soil conditions. Our findings highlight approaches that can be used to better characterize temporal shifts in soil microbial communities, information that is critical for predicting the environmental preferences of individual soil microbial taxa and identifying linkages between soil microbial community composition and belowground processes.IMPORTANCE Nearly all microbial communities are dynamic in time. Understanding how temporal dynamics in microbial community structure affect soil biogeochemistry and fertility are key to being able to predict the responses of the soil microbiome to environmental perturbations. Here, we explain the effects of soil spatial structure and relic DNA on the determination of microbial community fluctuations over time. We found that intensive spatial sampling was required to identify temporal effects in microbial communities because of the high degree of spatial heterogeneity in soil and that DNA from nonliving sources masks important temporal patterns. We identified groups of microbes with shared temporal responses and show that these patterns were predictable from changes in soil characteristics. These results provide insight into the environmental preferences and temporal relationships between individual microbial taxa and highlight the importance of considering relic DNA when trying to detect temporal dynamics in belowground communities.

Space Is More Important than Season when Shaping Soil Microbial Communities at a Large Spatial Scale.

Abstract: The relative importance of spatial and temporal variability in shaping the distribution of soil microbial communities at a large spatial scale remains poorly understood. Here, we explored the relative importance of space versus time when predicting the distribution of soil bacterial and fungal communities across North China Plain in two contrasting seasons (summer versus winter). Although we found that microbial alpha (number of phylotypes) and beta (changes in community composition) diversities differed significantly between summer and winter, space rather than season explained more of the spatiotemporal variation of soil microbial alpha and beta diversities. Environmental covariates explained some of microbial spatiotemporal variation observed, with fast-changing environmental covariates-climate variables, soil moisture, and available nutrient-likely being the main factors that drove the seasonal variation found in bacterial and fungal beta diversities. Using random forest modeling, we further identified a group of microbial exact sequence variants (ESVs) as indicators of summer and winter seasons and for which relative abundance was associated with fast-changing environmental variables (e.g., soil moisture and dissolved organic nitrogen). Together, our empirical field study's results suggest soil microbial seasonal variation could arise from the changes of fast-changing environmental variables, thus providing integral support to the large emerging body of snapshot studies related to microbial biogeography.IMPORTANCE Both space and time are key factors that regulate microbial community, but microbial temporal variation is often ignored at a large spatial scale. In this study, we compared spatial and seasonal effects on bacterial and fungal diversity variation across an 878-km transect and found direct evidence that space is far more important than season in regulating the soil microbial community. Partitioning the effect of season, space and environmental variables on microbial community, we further found that fast-changing environmental factors contributed to microbial temporal variation.

Decoupled diversity patterns in bacteria and fungi across continental forest ecosystems

Abstract: Recent evidence showed that bacteria and fungi appear to have different latitudinal diversity gradients at the global scale. However, the ecological drivers explaining these decoupled ecological and evolutionary patterns remain poorly understood. We identified the ecological predictors of such a decoupled pattern between bacterial and fungal diversity across a 4100 km latitudinal transect, from tropical to temperate forests in eastern China. Bacterial diversity showed a hump-shaped trend with latitude, while the diversity of fungi, and especially fungal saprobes and pathogens decreased with increasing latitude. In addition, our results provided evidence that while temperature and primary productivity, which decreased with increasing latitude, were the best predictors of fungal diversity, soil properties such as pH and N:P ratio were the best predictors for the latitudinal pattern in bacterial diversity. Further statistical results showed that sampling bias should be carefully considered in disentangling the underlying mechanisms of microbial geographical distribution. Our findings suggest that temperature is more likely to associate with fungal diversity than with bacterial diversity in eastern China, with important implications for the prediction of soil biodiversity and functions under climate change scenarios.

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

Abstract: 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.

The influence of soil age on ecosystem structure and function across biomes.

Abstract: The importance of soil age as an ecosystem driver across biomes remains largely unresolved. By combining a cross-biome global field survey, including data for 32 soil, plant, and microbial properties in 16 soil chronosequences, with a global meta-analysis, we show that soil age is a significant ecosystem driver, but only accounts for a relatively small proportion of the cross-biome variation in multiple ecosystem properties. Parent material, climate, vegetation and topography predict, collectively, 24 times more variation in ecosystem properties than soil age alone. Soil age is an important local-scale ecosystem driver; however, environmental context, rather than soil age, determines the rates and trajectories of ecosystem development in structure and function across biomes. Our work provides insights into the natural history of terrestrial ecosystems. We propose that, regardless of soil age, changes in the environmental context, such as those associated with global climatic and land-use changes, will have important long-term impacts on the structure and function of terrestrial ecosystems across biomes.

Surface indicators are correlated with soil multifunctionality in global drylands

Abstract: This work was funded by the European Research Council ERC Grant agreement 242658 (BIOCOM). CYTED funded networking activities (EPES, Accion 407AC0323). D.J.E. acknowledges support from the Australian Research Council (DP150104199) and F.T.M. support from the European Research Council (BIODESERT project, ERC Grant agreement no 647038), from the Spanish Ministerio de Economia y Competitividad (BIOMOD project, ref. CGL2013-44661-R) and from a Humboldt Research Award from the Alexander von Humboldt Foundation. M.D.-B. was supported by REA grant agreement no 702057 from the Marie Sklodowska-Curie Actions of the Horizon 2020 Framework Programme H2020-MSCA-IF-2016), J.R.G. acknowledges support from CONICYT/FONDECYT no 1160026.

Crop production correlates with soil multitrophic communities at the large spatial scale

Abstract: Strong associations exist between microbial communities and soil functions in natural ecosystems at large spatial scales; however, it is unclear whether these linkages are maintained in intensively managed croplands and whether these associations influence plant productivity. We collected bulk and rhizosphere soils from wheat fields –one of the most functionally and economically important crops worldwide –across the North China Plain (~300,000 km2), and examined the relationship between species-level multitrophic taxa, functional genes and wheat productivity. Our work identified significant and positive correlations of wheat productivity to the relative abundance of multitrophic clusters (co-occurring groups of soil biota including bacteria, fungi, arbuscular mycorrhizal fungi, and nematodes), and absolute abundance of functional genes associated with carbon, nitrogen, phosphorus, and sulfur cycles. We observed significant, biologically meaningful correlations between plant productivity and the abundance of specific root-associated microbial taxa and functional genes. These important linkages were robust when considered in combination with spatial, climate, and edaphic variables. Our findings highlight the importance of soil multitrophic communities in regulating soil functional potential and plant productivity, and provide a list of key-stone functional genes, which could be targeted to promote food security and production.

Grazing Regulates the Spatial Heterogeneity of Soil Microbial Communities Within Ecological Networks

Abstract: Grazing is a major driver of the composition of microbial communities, which play important roles in soil functioning. Mechanisms whereby grazing might regulate the spatial heterogeneity of microbial communities within ecological networks remain largely untested. We used network analysis to identify the impacts of increasing grazing intensity by livestock (cattle, sheep, goats), and native (kangaroos) and wild (rabbits) animals, on the spatial heterogeneity of the relative abundance of eight ecological clusters of co-occurring soil microbial taxa: four from Grasslands and four from Forests. Grazing effects on microbial spatial heterogeneity were strongly nuanced and depended on (1) plant community type, (2) herbivore type and (3) microbial identity. Microbial within-site spatial heterogeneity was greater in Grasslands than in Forests, and most effects of grazing on microbial spatial heterogeneity were in Forests, effecting three of the four Forest clusters, but only one Grassland cluster. The associations between grazing intensity and microbial heterogeneity were driven indirectly by changes in the spatial heterogeneity of litter cover and soil pH. For Grasslands, we also detected a direct effect of grazing intensity on the heterogeneity of particular microbial groups. Our results indicate that increased grazing intensity will advantage some microbial clusters but disadvantage others. Together, our study provides evidence that grazing intensity regulates the abundance and spatial heterogeneity of microbial communities within ecological networks. Knowing the potential effects of herbivores on different microbial clusters can help us predict the likely effects of grazing on soil function. This has important implications for future sustainable management and conservation policies.

Climatic vulnerabilities and ecological preferences of soil invertebrates across biomes.

Abstract: 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.

Links between soil microbial communities, functioning, and plant nutrition under altered rainfall in Australian grassland

Abstract: The size, frequency, and timing of precipitation events are predicted to become more variable worldwide. Despite these predictions, the importance of changes in precipitation in driving multiple above- and belowground ecosystem attributes simultaneously remains largely underexplored. Here, we carried out 3 yr of rainfall manipulations at the DRI-Grass facility, located in a mesic grassland in eastern Australia. Treatments were implemented through automated water reapplication and included +50% and −50% amount, reduced frequency of events, and an extreme summer drought. We evaluated the spatiotemporal responses of multiple ecosystem attributes including microbial biomass, community composition and activity, soil nutrient content and availability, and plant nutritional status to altered rainfall regimes. We found that changing precipitation patterns resulted in multiple direct and indirect changes in microbial communities and soil and plant nutrient content. Main results included greater availability of soil macronutrients and reduced availability of micronutrients under drought, and taxon-specific changes in the composition of soil microbial communities in response to altered rainfall. Moreover, using structural equation modeling, we showed that, in summer 2015, plant macronutrient contents, a widely used ecological indicator of pasture quality, were simultaneously explained by greater soil nutrient availability and the structure of soil microbial communities, and significantly reduced by lower rainfall. Plant micronutrients were also reduced by lower rainfall and explained by changes in microbial attributes. Despite treatment effects on many of the soil, microbial, and plant variables analyzed across the 3 yr of study, many of these ecosystem attributes varied greatly across sampling events. This resulted in many significant interactions between the rainfall treatments and experimental duration, suggesting complex system-level responses to changing rainfall in our grassland, and a high natural buffering capacity of the ecosystem to varying rainfall conditions. Some interactions manifested as changes in the coefficient of variation of ecosystem attributes, particularly in response to changes in the timing of precipitation events and the extreme summer drought. Finally, we posit that a detailed understanding of plant–soil–microbial interactions, and the role of climate in modifying these linkages, will be key for adapting the sustainability of grasslands to a future that will be shaped by climate change.

Successional trajectory of bacterial communities in soil are shaped by plant-driven changes during secondary succession.

Abstract: This study investigated the potential role of a nitrogen-fixing early-coloniser Alnus Nepalensis D. Don (alder) in driving the changes in soil bacterial communities during secondary succession. We found that bacterial diversity was positively associated with alder growth during course of ecosystem development. Alder development elicited multiple changes in bacterial community composition and ecological networks. For example, the initial dominance of actinobacteria within bacterial community transitioned to the dominance of proteobacteria with stand development. Ecological networks approximating species associations tend to stabilize with alder growth. Janthinobacterium lividum, Candidatus Xiphinematobacter and Rhodoplanes were indicator species of different growth stages of alder. While the growth stages of alder has a major independent contribution to the bacterial diversity, its influence on the community composition was explained conjointly by the changes in soil properties with alder. Alder growth increased trace mineral element concentrations in the soil and explained 63% of variance in the Shannon-diversity. We also found positive association of alder with late-successional Quercus leucotrichophora (Oak). Together, the changes in soil bacterial community shaped by early-coloniser alder and its positive association with late-successional oak suggests a crucial role played by alder in ecosystem recovery of degraded habitats.

Multiple trade-offs regulate the effects of woody plant removal on biodiversity and ecosystem functions in global rangelands.

Abstract: Woody plant encroachment is a major land management issue. Woody removal often aims to restore the original grassy ecosystem, but few studies have assessed the role of woody removal on ecosystem functions and biodiversity at global scales. We collected data from 140 global studies and evaluated how different woody plant removal methods affected biodiversity (plant and animal diversity) and ecosystem functions (plant production, hydrological function, soil carbon) across global rangelands. Our results indicate that the impact of removal is strongly context dependent, varying with the specific response variable, removal method, and traits of the target species. Over all treatments, woody plant removal increased grass biomass and total groundstorey diversity. Physical and chemical removal methods increased grass biomass and total groundstorey biomass (i.e., non-woody plants, including grass biomass), but burning reduced animal diversity. The impact of different treatment methods declined with time since removal, particularly for total groundstorey biomass. Removing pyramid-shaped woody plants increased total groundstorey biomass and hydrological function but reduced total groundstorey diversity. Environmental context (e.g., aridity and soil texture) indirectly controlled the effect of removal on biomass and biodiversity by influencing plant traits such as plant shape, allelopathic, or roots types. Our study demonstrates that a one-size-fits-all approach to woody plant removal is not appropriate, and that consideration of woody plant identity, removal method, and environmental context is critical for optimizing removal outcomes. Applying this knowledge is fundamental for maintaining diverse and functional rangeland ecosystems as we move toward a drier and more variable climate.

Contrasting environmental preferences of photosynthetic and non-photosynthetic soil cyanobacteria across the globe

Abstract: M.D.-B. is supported by a Ramon y Cajal grant from the Spanish Ministry of Science and Innovation (RYC2018-025483-I), and by the BES grant agreement No LRB17\1019 (MUSGONET). The work of C.C.-D. and F.T.M. and the global drylands database were supported by the European Research Council [ERC Grant Agreements 242658 (BIOCOM) and 647038 (BIODESERT)] and by the Spanish Ministry of Economy and Competitiveness (BIOMOD project, ref. CGL2013-44661-R). F.T.M. acknowledges support from Generalitat Valenciana (BIOMORES project, ref. CIDEGENT/2018/041). Research on biodiversity by B.K.S. is supported by the Australian Research Council (DP170104634). R.D.B. was supported by the U.K. Department of Environment, Food and Rural Affairs (DEFRA) project no. BD5003 and a Biotechnology and Biological Sciences Research Council (BBSRC) International Exchange Grant (BB/L026406/1).

Phosphorus addition regulates the responses of soil multifunctionality to nitrogen over-fertilization in a temperate grassland

Abstract: Nitrogen (N) and phosphorus (P) are two major limiting factors in terrestrial ecosystems. Excessive N applications alter ecosystem functions by causing nutrient imbalances with P. Yet, little is known about why and how the balance between N and P regulates soil multifunctionality –the simultaneous provision of multiple soil functions–. We explored how P additions regulated the responses of soil multifunctionality to different levels of N fertilization (10, 20, 40 g N m−2 yr−1) using a mesocosm experiment in a temperate grassland in China. Nitrogen alone and P addition increased multifunctionality at rate of ≤10 and 20 g N m−2 yr−1, respectively. However, the magnitude of positive effects decreased with N additions over this level. P additions increased multifunctionality resistance to N at low rate of ≤10 g m−2 yr−1 compared to higher N levels. Soil N:P stoichiometry and plant diversity played dominant roles in regulating soil multifunctionality. We found that a balanced combination of N and P additions (20:10) can help maintain the highest multifunctionality in this temperate grassland. The results provide new insights that through P addition, we could better manage soil multifunctionality and increase its resistance to expected fertilization scenarios (≤ 10 g m−2 yr−1).

Increases in aridity lead to drastic shifts in the assembly of dryland complex microbial networks

Abstract: We have little information on how and why soil microbial community assembly will respond to predicted increases in aridity by the end of this century. Here, we used correlation networks and structural equation modeling to assess the changes in the abundance of the ecological clusters including potential winner and loser microbial taxa associated with predicted increases in aridity. To do this, we conducted a field survey in an environmental gradient from eastern Australia and obtained information on bacterial and fungal community composition for 120 soil samples and multiple abiotic and biotic factors. Overall, our structural equation model explained 83% of the variance in the two mesic modules. Increases in aridity led to marked shifts in the abundance of the two major microbial modules found in our network, which accounted for >99% of all phylotypes. In particular, the relative abundance of one of these modules, the Mesic Module #1, which was positively related to multiple soil properties and plant productivity, declined strongly with aridity. Conversely, the relative abundance of a second dominant module (Xeric Module #2) was positively correlated with increases in aridity. Our study provides evidence that network analysis is a useful tool to identify microbial taxa that are either winners or losers under increasing aridity and therefore potentially under changing climates. Our work further suggests that climate change, and associated land degradation, could potentially lead to extensive microbial phylotypes exchange and local extinctions, as demonstrated by the reductions of up to 97% in the relative abundance of microbial taxa within Mesic Module #1.

The effects of mowing and multi-level N fertilization on soil bacterial and fungal communities in a semiarid grassland are year-dependent

Abstract: The diversity and structure of plant and soil microbial communities are influenced by temporal variability in environmental conditions (e.g., precipitation); however, it is unclear whether the responses of these biotic communities to land use practices (e.g., N fertilization and mowing) also vary over time. Here we investigated how harvesting hay by mowing and applications of N fertilization at different rates (0, 2.5, 5, 10, 20, and 40 g N m−2 yr−1) affected plant, bacterial, and fungal communities by exploring data collected from a field experiment in a semiarid grassland in northern China over two consecutive years of 2017 and 2018. The cumulative precipitation during the growing season differed between the two studied years. The sampling year had more effect on the structure of the plant and soil microbial community than N fertilization and mowing, suggesting that the effects of land use practices varied by year, and were difficult to predict over time. The diversity of bacteria and fungi showed a different response to N fertilization and mowing between the two years. For example, in the wet year, the fungal diversity was up to 11% lower in soil that had been treated using the highest N fertilizer application than in untreated soil, but showed little variation in the dry year. The bacterial diversity was higher for all N application rates in the mown than the unmown land during the wet year, but no difference was observed during the dry year. There were more opportunistic and sensitive taxa for the two years (over 36.9% of top 10% relative abundance of bacterial and fungal taxa) than for N fertilization and mowing (below 33.0% of top 10% relative abundance of bacterial and fungal taxa). The relationships between plant and soil microbial communities differed between the two years, and were much stronger in the dry year than the wet year. We conclude that N fertilization and mowing had varying effects on plant and soil microbial communities in the study area over the two-year period. Our results also suggest that precipitation is the main control on land use-related changes in plant and soil microbial communities in semiarid ecosystems.

Biocrusts Modulate Responses of Nitrous Oxide and Methane Soil Fluxes to Simulated Climate Change in a Mediterranean Dryland

Abstract: Little is known about the role of biocrusts in regulating the responses of N2O and CH4 fluxes to climate change in drylands. Here, we aim to help filling this knowledge gap by using an 8-year field experiment in central Spain where temperature and rainfall are being manipulated (~ 1.9°C warming, 33% rainfall reduction and their combination) in areas with and without well-developed biocrust communities. Areas with initial high cover of well-developed biocrusts showed lower N2O emissions, enhanced CH4 uptake and higher abundances of functional genes linked to N2O and CH4 fluxes compared with areas with poorly developed biocrusts. Moreover, biocrusts modulated the responses of gases emissions and related functional genes to warming and rainfall reductions. Specifically, we found under rainfall exclusion and its combination with warming a sharp reduction in N2O fluxes (~ 96% and ~ 197%, respectively) only under well-developed biocrust cover. Warming and its combination with rainfall exclusion reduced CH4 consumption in areas with initial low cover of well-developed biocrust, whereas rainfall exclusion enhanced CH4 uptake only in areas with high initial cover of well-developed biocrusts. Similarly, the combination of warming and rainfall exclusion increased the abundance of the nosZ gene compared to the rainfall exclusion treatment and increased the abundance of the pmoA gene compared to the control, but only in areas with low biocrust cover. Taken together, our results indicate that well-developed biocrust communities could counteract the impact of warming and altered rainfall patterns on soil N2O and CH4 fluxes, highlighting their importance and the need to preserve them to minimize climate change impacts on drylands.

Plant Microbiomes: Do Different Preservation Approaches and Primer Sets Alter Our Capacity to Assess Microbial Diversity and Community Composition?

Abstract: The microbial communities associated with plants (the plant microbiome) play critical roles in regulating plant health and productivity. Because of this, in recent years, there have been significant increase in studies targeting the plant microbiome. Amplicon sequencing is widely used to investigate the plant microbiome and to develop sustainable microbial agricultural tools. However, performing large microbiome surveys at the regional and global scales pose several logistic challenges. One of these challenges is related with the preservation of plant materials for sequencing aiming to maintain the integrity of the original diversity and community composition of the plant microbiome. Another significant challenge involves the existence of multiple primer sets used in amplicon sequencing that, especially for bacterial communities, hampers the comparability of datasets across studies. Here, we aimed to examine the effect of different preservation approaches (snap freezing, fresh and kept on ice, and air drying) on the bacterial and fungal diversity and community composition on plant leaves, stems and roots from seven plant species from contrasting functional groups (e.g. C3, C4, N-Fixers, etc.). Another major challenge comes when comparing plant to soil microbiomes, as different primers sets are often used for plant vs. soil microbiomes. Thus, we also investigated if widely used 16S rRNA primer set (779F/1193R) for plant microbiome studies provides comparable data to those often used for soil microbiomes (341F/805R) using 86 soil samples. We found that the community composition and diversity of bacteria or fungi were robust to contrasting preservation methods. The primer sets often used for plants provided similar results to those often used for soil studies suggesting that simultaneous studies on plant and soil microbiomes are possible. Our findings provide novel evidence that preservation approaches do not significantly impact plant microbiome data interpretation and primer differences do not impact the treatment effect, which has significant implication for future large-scale and global surveys of plant microbiomes.

Diversity-productivity relationships vary in response to increasing land-use intensity

Abstract: Theoretical and experimental evidence, predominantly from temperate grasslands, demonstrates strong support for a positive relationship between biodiversity and ecosystem functioning. This relationship is likely to be affected by land use drivers that remove vegetation, and/or disturb the soil surface. Our study aimed to examine the links between land use intensity and plant richness, and potential effects on productivity and function. We examined the impact of mowing, grazing, and mowing plus grazing, on the relationship between plant diversity, and two measures of function; aboveground biomass and soil carbon. Our focus was on Eurasian grasslands, which support a high diversity of plant species, millions of people and their livelihoods, and where livestock grazing and mowing are predominant land uses. We used structural equation modelling to examine the effects of these land use drivers at 371 sites across 100,000 km2 of northern China. Mown sites supported a greater number of plant species than sites that were either grazed, or grazed and mown. Increasing plant richness was associated with greater aboveground biomass and soil carbon when sites were either mown or grazed, but these relationships disappeared when the two land use drivers were combined. Relationships among plant diversity and two measures of function were maintained when we accounted for the spatial differences between sites. Our results demonstrate that additional land use pressure imposed when mowing and grazing are applied together can decouple the positive associations between plant richness and functions. An understanding of these potential effects is important if we are to adopt strategies, such as destocking or reduced mowing, to maintain diverse grassland ecosystems, and their services and functions.