317 research outputs found

    Differential effects of elevated <scp> <i>p</i> CO <sub>2</sub> </scp> and warming on marine phytoplankton stoichiometry

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    Phytoplankton stand at the base of the marine food-web, and play a major role in global carbon cycling. Rising CO2 levels and temperatures are expected to enhance growth and alter carbon:nutrient stoichiometry of marine phytoplankton, with possible consequences for the functioning of marine food-webs and the oceanic carbon pump. To date, however, the consistency of phytoplankton stoichiometric responses remains unclear. We therefore performed a meta-analysis on data from experimental studies on stoichiometric responses of marine phytoplankton to elevated pCO2 and 3–5° warming under nutrient replete and limited conditions. Our results demonstrate that elevated pCO2 increased overall phytoplankton C:N (by 4%) and C:P (by 9%) molar ratios under nutrient replete conditions, as well as phytoplankton growth rates (by 6%). Nutrient limitation amplified the CO2 effect on C:N and C:P ratios, with increases to 27% and 17%, respectively. In contrast to elevated pCO2, warming did not consistently alter phytoplankton elemental composition. This could be attributed to species- and study-specific increases and decreases in stoichiometry in response to warming. While our observed moderate CO2-driven changes in stoichiometry are not likely to drive marked changes in food web functioning, they are in the same order of magnitude as current and projected estimations of oceanic carbon export. Therefore, our results may indicate a stoichiometric compensation mechanism for reduced oceanic carbon export due to declining primary production in the near future

    Initial Soil Microbiome Composition and Functioning Predetermine Future Plant Health

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    Plant-pathogen interactions are shaped by multiple environmental factors making it difficult to predict disease dynamics even in relatively simple agricultural monocultures. Here we explored how variation in the initial soil microbiome predicts future disease outcomes at the level of individual plants. We found that the composition and functioning of the initial soil microbiome predetermined whether the plants survived or succumbed to disease. Surviving plant microbiomes were associated with specific rare taxa, highly pathogen-suppressing Pseudomonas and Bacillus bacteria and high abundance of genes encoding antimicrobial compounds. Microbiome-mediated plant protection could subsequently be transferred to the next plant generation via soil transplantation. Together, our results suggest that small initial variation in soil microbiome composition and functioning can determine the outcomes of plant-pathogen interactions in natural field conditions

    Facilitation promotes invasions in plant-associated microbial communities

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    While several studies have established a positive correlation between community diversity and invasion resistance, it is less clear how species interactions within resident communities shape this process. Here we experimentally tested how antagonistic and facilitative pairwise interactions within resident model microbial communities predict invasion by the plant-pathogenic bacterium Ralstonia solanacearum. We found that facilitative resident community interactions promoted and antagonistic interactions suppressed invasions both in the lab and in the tomato plant rhizosphere. Crucially, pairwise interactions could reliably explain observed invasions outcomes also in multispecies communities, and mechanistically, this was linked to direct inhibition of the invader by antagonistic communities (antibiosis), and to a lesser degree by resource competition between the members of the resident community and the invader. Together our findings suggest that the type and strength of pairwise interactions can reliably predict the outcome of invasions in more complex multispecies communities

    Variations of Bacterial and Diazotrophic Community Assemblies throughout the Soil Profile in Distinct Paddy Soil Types and Their Contributions to Soil Functionality

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    Soil microbiota plays fundamental roles in maintaining ecosystem functions and services, including biogeochemical processes and plant productivity. Despite the ubiquity of soil microorganisms from the topsoil to deeper layers, their vertical distribution and contribution to element cycling in subsoils remain poorly understood. Here, nine soil profiles (0 to 135 cm) were collected at the local scale (within 300 km) from two canonical paddy soil types (Fe-accumuli and Hapli stagnic anthrosols), representing redoximorphic and oxidative soil types, respectively. Variations with depth in edaphic characteristics and soil bacterial and diazotrophic community assemblies and their associations with element cycling were explored. The results revealed that nitrogen and iron status were the most distinguishing edaphic characteristics of the two soil types throughout the soil profile. The acidic Fe-accumuli stagnic anthrosols were characterized by lower concentrations of free iron oxides and total iron in topsoil and ammonia in deeper layers compared with the Hapli stagnic anthrosols. The bacterial and diazotrophic community assemblies were mainly shaped by soil depth, followed by soil type. Random forest analysis revealed that nitrogen and iron cycling were strongly correlated in Fe-accumuli stagnic anthrosol, whereas in Hapli soil, available sulfur was the most important variable predicting both nitrogen and iron cycling. The distinctive biogeochemical processes could be explained by the differences in enrichment of microbial taxa between the two soil types. The main discriminant clades were the iron-oxidizing denitrifier Rhodanobacter, Actinobacteria, and diazotrophic taxa (ironreducing Geobacter, Nitrospirillum, and Burkholderia) in Fe-accumuli stagnic anthrosol and the sulfur-reducing diazotroph Desulfobacca in Hapli stagnic anthrosol

    Neighbourhood species richness and drought-tolerance traits modulate tree growth and δ13C responses to drought

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    Mixed-species forests are promoted as a forest management strategy for climate change mitigation and adaptation because they are more productive and can be more resistant and resilient than monospecific forests under drought stress. However, the trait-based mechanisms driving these properties remain elusive, making it difficult to predict which functional identities of species best improve tree growth and decrease tree physiological water stress under drought. We investigated tree growth and physiological stress responses (i.e. increase in wood carbon isotopic ratio; δ13C) to changes in climate-induced water availability (wet-to-dry years) along gradients in neighbourhood tree species richness and drought-tolerance traits. Using tree cores from a large-scale biodiversity experiment, we tested the overarching hypothesis that neighbourhood species richness increases growth and decreases δ13C. We further hypothesized that the abiotic (i.e. climatic conditions) and the biotic context modulate these biodiversity-ecosystem functioning relationships. We characterized the biotic context using drought-tolerance traits of focal trees and their neighbours. These traits are related to cavitation resistance vs. resource acquisition and stomatal control. We found that tree growth increased with neighbourhood species richness. However, we did not observe a universal relief of water stress in species-rich neighbourhoods, nor an increase in the strength of the relationship between richness and growth and between richness and δ13C from wet-to-dry years. Instead, these relationships depended on both the traits of the focal trees and their neighbours. At either end of each drought-tolerance gradient, species responded in opposing directions during drought and non-drought years. Synthesis. We report that the biotic context can determine the strength and nature of biodiversity-ecosystem functioning relationships in experimental tree communities. We derive two key conclusions: (1) drought-tolerance traits of focal trees and their neighbours can explain divergent tree responses to drought and diversity, and (2) contrasting, trait-driven responses of tree species to wet vs dry climatic conditions can promote forest community stability. Mixing tree species with a range of drought-tolerance traits may therefore increase forest productivity and stability

    Toward more sustainable tropical agriculture with cover crops: Soil microbiome responses to nitrogen management

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    Cover crops are a potential pathway for ecological cultivation in agricultural systems. In tropical no-till agricultural systems, the maintenance of residues on the soil surface and the addition of nitrogen (N) benefit the growth and grain yield of cash crops as well as the chemical and physical properties of the soil. However, the effects of these management practices on the soil microbiota are largely unknown. Here, we evaluated the effects of the timing of N application as a pulse disturbance and the growth of different cover crop species before maize in rotation on soil properties, maize productivity, and soil bacterial and fungal community diversity and composition. N fertilizer was applied either on live cover crops (palisade grass or ruzigrass), on cover crop straw just before maize seeding or in the maize V4 growth stage. Soils previously cultivated with palisade grass established similar microbial communities regardless of N application timing, with increases in total bacteria, total archaea, nutrients, and the C:N ratio. The soil microbial alpha diversity in treatments with palisade grass did not vary with N application timing, whereas the bacterial and fungal diversities in the treatments with ruzigrass decreased when N was applied to live ruzigrass or maize in the V4 growth stage. We conclude that palisade grass is a more suitable cover crop than ruzigrass, as palisade grass enhanced soil microbial diversity and maize productivity regardless of N application timing. Ruzigrass could be used as an alternative to palisade grass when N is applied during the straw phase. However, considering the entire agricultural system (soil–plant–microbe), ruzigrass is not as efficient as palisade grass in tropical no-till cover crop–maize rotation systems. Palisade grass is a suitable cover crop alternative for enhancing maize productivity, soil chemical properties and nutrient cycling, regardless of the timing of N application. Additionally, this study demonstrates that a holistic approach is valuable for evaluating soil diversity and crop productivity in agricultural systems

    Species richness and asynchrony maintain the stability of primary productivity against seasonal climatic variability

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    The stability of grassland communities informs us about the ability of grasslands to provide reliable services despite environmental fluctuations. There is large evidence that higher plant diversity and asynchrony among species stabilizes grassland primary productivity against interannual climate variability. Whether biodiversity and asynchrony among species and functional groups stabilize grassland productivity against seasonal climate variability remains unknown. Here, using 29-year monitoring of a temperate grassland, we found lower community temporal stability with higher seasonal climate variability (temperature and precipitation). This was due to a combination of processes including related species richness, species asynchrony, functional group asynchrony and dominant species stability. Among those processes, functional group asynchrony had the strongest contribution to community compensatory dynamics and community stability. Based on a long-term study spanning 29 years, our results indicate that biodiversity and compensatory dynamics a key for the stable provision of grassland function against increasing seasonal climate variability

    Trichoderma-amended biofertilizer stimulates soil resident Aspergillus population for joint plant growth promotion

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    Application of plant growth-promoting microbes (PGPMs) can contribute to sustainable agricultural ecosystems. From a three-year field experiment, we already found that the addition of Trichoderma bio-organic fertilizer (BF) significantly improved crop growth and yield compared to the application of organic fertilizer (OF). Here, we tracked the responses of soil bacterial and fungal communities to these treatments to find the key soil microbial taxa that contribute to the crop yield enhancement. We also examined if bacterial and fungal suspensions from resulting soils could improve plant growth upon inoculation into sterilized soil. Lastly, we isolated a number of fungal strains related to populations affected by treatments to examine their role in plant growth promotion. Results showed that consecutive application of BF impacted soil fungal communities, and the biological nature of plant growth promotion was confirmed via pot experiments using Îł-sterilized versus none-sterilized soils collected from the field. Soil slurry experiments suggested that fungal, but not bacterial communities, played an important role in plant growth promotion, consistent with the results of our field experimental data. Fungal community analysis of both field and slurry experimental soils revealed increases in specific resident Aspergillus spp. Interestingly, Aspergillus tamarii showed no plant growth promotion by itself, but strongly increased the growth promotion activity of the Trichoderma amendment strain upon their co-inoculation. The effectiveness of the fungal amendment appears to stem not only from its own action, but also from synergetic interactions with resident fungal populations activated upon biofertilizer application

    Effect of strigolactones on recruitment of the rice root-associated microbiome

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    Strigolactones are endogenous plant hormones regulating plant development and are exuded into the rhizosphere when plants experience nutrient deficiency. There, they promote the mutualistic association of plants with arbuscular mycorrhizal fungi that help the plant with the uptake of nutrients from the soil. This shows that plants actively establish - through the exudation of strigolactones - mutualistic interactions with microbes to overcome inadequate nutrition. The signaling function of strigolactones could possibly extend to other microbial partners, but the effect of strigolactones on the global root and rhizosphere microbiome remains poorly understood. Therefore, we analyzed the bacterial and fungal microbial communities of 16 rice genotypes differing in their root strigolactone exudation. Using multivariate analyses, distinctive differences in the microbiome composition were uncovered depending on strigolactone exudation. Moreover, the results of regression modeling showed that structural differences in the exuded strigolactones affected different sets of microbes. In particular, orobanchol was linked to the relative abundance of Burkholderia-Caballeronia-Paraburkholderia and Acidobacteria that potentially solubilize phosphate, while 4-deoxyorobanchol was associated with the genera Dyella and Umbelopsis. With this research, we provide new insight into the role of strigolactones in the interplay between plants and microbes in the rhizosphere

    Shared Core Microbiome and Functionality of Key Taxa Suppressive to Banana Fusarium Wilt

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    Microbial contributions to natural soil suppressiveness have been reported for a range of plant pathogens and cropping systems. To disentangle the mechanisms underlying suppression of banana Panama disease caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc4), we used amplicon sequencing to analyze the composition of the soil microbiome from six separate locations, each comprised of paired orchards, one potentially suppressive and one conducive to the disease. Functional potentials of the microbiomes from one site were further examined by shotgun metagenomic sequencing after soil suppressiveness was confirmed by greenhouse experiments. Potential key antagonists involved in disease suppression were also isolated, and their activities were validated by a combination of microcosm and pot experiments. We found that potentially suppressive soils shared a common core community with relatively low levels of F. oxysporum and relatively high proportions of Myxococcales, Pseudomonadales, and Xanthomonadales, with five genera, Anaeromyxobacter, Kofleria, Plesiocystis, Pseudomonas, and Rhodanobacter being significantly enriched. Further, Pseudomonas was identified as a potential key taxon linked to pathogen suppression. Metagenomic analysis showed that, compared to the conducive soil, the microbiome in the disease suppressive soil displayed a significantly greater incidence of genes related to quorum sensing, biofilm formation, and synthesis of antimicrobial compounds potentially active against Foc4. We also recovered a higher frequency of antagonistic Pseudomonas isolates from disease suppressive experimental field sites, and their protective effects against banana Fusarium wilt disease were demonstrated under greenhouse conditions. Despite differences in location and soil conditions, separately located suppressive soils shared common characteristics, including enrichment of Myxococcales, Pseudomonadales, and Xanthomonadales, and enrichment of specific Pseudomonas populations with antagonistic activity against the pathogen. Moreover, changes in functional capacity toward an increase in quorum sensing, biofilm formation, and antimicrobial compound synthesizing involve in disease suppression
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