Soil fungi associated with plant roots, notably ectomycorrhizal (EcM) fungi, are central in above- and below-ground interactions in Mediterranean forests. They are a key component in soil nutrient ...cycling and plant productivity. Yet, major disturbances of Mediterranean forests, particularly in the Southern Mediterranean basin, are observed due to the greater human pressures and climate changes. These disturbances highly impact forest cover, soil properties and consequently the root-associated fungal communities. The implementation of efficient conservation strategies of Mediterranean forests is thus closely tied to our understanding of root-associated fungal biodiversity and environmental rules driving its diversity and structure. In our study, the root-associated fungal community of Q. suber was analyzed using high-throughput sequencing across three major Moroccan cork oak habitats. Significant differences in root-associated fungal community structures of Q. suber were observed among Moroccan cork oak habitats (Maâmora, Benslimane, Chefchaoun) subjected to different human disturbance levels (high to low disturbances, respectively). The fungal community structure changes correlated with a wide range of soil properties, notably with pH, C:N ratio (P = 0.0002), and available phosphorus levels (P = 0.0001). More than 90 below-ground fungal indicators (P < 0.01)-either of a type of habitat and/or a soil property-were revealed. The results shed light on the ecological significance of ubiquitous ectomycorrhiza (Tomentella, Russula, Cenococcum), and putative sclerotia-associated/ericoid mycorrhizal fungal taxa (Cladophialophora, Oidiodendron) in the Moroccan cork oak forest, and their intraspecific variability regarding their response to land use and soil characteristics.
Cropping systems based on carefully designed species mixtures reveal many potential advantages in terms of enhancing crop productivity, reducing pest and diseases, and enhancing ecological services. ...Associating cereals and legume production either through intercropping or rotations might be a relevant strategy of producing both type of culture, while benefiting from combined nitrogen fixed by the legume through its symbiotic association with nitrogen-fixing bacteria, and from a better use of P and water through mycorrhizal associations. These practices also participate to the diversification of agricultural productions, enabling to secure the regularity of income returns across the seasonal and climatic uncertainties. In this context, we designed a field experiment aiming to estimate the 2 years impact of these practices on wheat yield and on soil microbial activities as estimated through Substrate Induced Respiration method and mycorrhizal soil infectivity (MSI) measurement. It is expected that understanding soil microbial functionalities in response to these agricultural practices might allows to target the best type of combination, in regard to crop productivity. We found that the tested cropping systems largely impacted soil microbial functionalities and MSI. Intercropping gave better results in terms of crop productivity than the rotation practice after two cropping seasons. Benefits resulting from intercrop should be highly linked with changes recorded on soil microbial functionalities.
Mediterranean forests are found in the Mediterranean basin, California, the South African Cape Province, South and southwestern Australia and parts of Central Chile. They represent 1.8 % of the world ...forest areas of which the vast majority is found in the Mediterranean basin, where historical and paleogeographic episodes, long-term human influence and geographical and climatic contrasts have created ecosystemic diversity and heterogeneity. Even if evergreen is dominant, deciduous trees are also represented, with different forest types including dense stands with a closed canopy (forests sensu stricto) and pre-forestal or pre-steppic structures with lower trees density and height. The Mediterranean basin is also a hot spot of forest species and genetic diversity, with 290 woody species versus only 135 for non-Mediterranean Europe. However, the characteristics of the Mediterranean area (long-standing anthropogenic pressure, significant current human activity and broad biodiversity) make it one of the world’s regions most threatened by current changes. Four examples of Mediterranean forest types, present in south and north of the Mediterranean basin and more or less threatened, are developed in order to show that linking “hard sciences” and humanities and social sciences is necessary to understand these complex ecosystems. We show also that these forests, in spite of specific climatic constraints, can also be healthy and productive and play a major ecological and social role. Furthermore, even if the current human activity and global change constitute a risk for these exceptional ecosystems, Mediterranean forests represent a great asset and opportunities for the future of the Mediterranean basin.
Aim
Phylogeography of fruit trees is challenging due to recurrent exchanges between domesticated and wild populations. Here we tested the eastern refugium hypothesis (ERH) for the carob tree, ...Ceratonia siliqua, which supports its natural and domestication origins in the eastern Mediterranean and a feral origin in the west.
Location
Mediterranean basin.
Taxon
Ceratonia siliqua L., Leguminosae.
Methods
A phylogenetic reconstruction based on two nuclear and one plastid sequences was performed to estimate the divergence time between the carob tree and its sister species, Ceratonia oreothauma. Variation from four plastid regions and 17 nuclear microsatellite loci were used to decipher genetic structure in the carob tree and to test coalescent‐based models by an Approximate Bayesian computation (ABC) approach. We assessed our hypotheses by examining palaeobotanical records and hindcasting the past distribution of the carob tree at Mid‐Holocene, Last Glacial Maximum (LGM) and Last Interglacial (LIG) using species distribution modelling.
Results
The split between C. oreothauma and C. siliqua was estimated at 6.4 Ma, and a first divergence within C. siliqua at 1.3 Ma. After a continuous presence since the Oligocene, Ceratonia was rarely found in the fossil record during the Pleistocene but present in the western and the eastern Mediterranean. Plastid and nuclear markers, characterized by low allelic richness, revealed a strong west‐east genetic structuring. ABC analyses rejected the ERH.
Main conclusions
Our study supports a severe population decline during LIG. The strong west–east divergence and the occurrence of four lineages within C. siliqua provided support for a new hypothesis of multiple domestications of the carob tree from native populations throughout the Mediterranean basin.
Summary
The Honghe Hani rice terraces system (HHRTS) is a traditional rice cultivation system where Hani people cultivate remarkably diverse rice varieties. Recent introductions of modern rice ...varieties to the HHRTS have significantly increased the severity of rice diseases within the terraces. Here, we determine the impacts of these recent introductions on the composition of the rice‐associated microbial communities. We confirm that the HHRTS contains a range of both traditional HHRTS landraces and introduced modern rice varieties and find differences between the microbial communities of these two groups. However, this introduction of modern rice varieties has not strongly impacted the overall diversity of the HHRTS rice microbial community. Furthermore, we find that the rice varieties (i.e. groups of closely related genotypes) have significantly structured the rice microbial community composition (accounting for 15%–22% of the variance) and that the core microbial community of HHRTS rice plants represents less than 3.3% of all the microbial taxa identified. Collectively, our study suggests a highly diverse HHRTS rice holobiont (host with its associated microbes) where the diversity of rice hosts mirrors the diversity of their microbial communities. Further studies will be needed to better determine how such changes might impact the sustainability of the HHRTS.
Cooperation involving Plant Growth-Promoting Rhizobacteria results in improvements of plant growth and health. While pathogenic and symbiotic interactions are known to induce transcriptional changes ...for genes related to plant defense and development, little is known about the impact of phytostimulating rhizobacteria on plant gene expression. This study aims at identifying genes significantly regulated in rice roots upon Azospirillum inoculation, considering possible favored interaction between a strain and its original host cultivar. Genome-wide analyzes of Oryza sativa japonica cultivars Cigalon and Nipponbare were performed, by using microarrays, seven days post-inoculation with Azospirillum lipoferum 4B (isolated from Cigalon) or Azospirillum sp. B510 (isolated from Nipponbare) and compared to the respective non-inoculated condition. A total of 7384 genes were significantly regulated, which represent about 16% of total rice genes. A set of 34 genes is regulated by both Azospirillum strains in both cultivars, including a gene orthologous to PR10 of Brachypodium, and these could represent plant markers of Azospirillum-rice interactions. The results highlight a strain-dependent response of rice, with 83% of the differentially expressed genes being classified as combination-specific. Whatever the combination, most of the differentially expressed genes are involved in primary metabolism, transport, regulation of transcription and protein fate. When considering genes involved in response to stress and plant defense, it appears that strain B510, a strain displaying endophytic properties, leads to the repression of a wider set of genes than strain 4B. Individual genotypic variations could be the most important driving force of rice roots gene expression upon Azospirillum inoculation. Strain-dependent transcriptional changes observed for genes related to auxin and ethylene signaling highlight the complexity of hormone signaling networks in the Azospirillum-rice cooperation.
Despite the strong ecological importance of ectomycorrhizal (ECM) fungi, their vertical distribution remains poorly understood. To our knowledge, ECM structures associated with trees have never been ...reported in depths below 2 meters. In this study, fine roots and ECM root tips were sampled down to 4-m depth during the digging of two independent pits differing by their water availability. A meta-barcoding approach based on Illumina sequencing of internal transcribed spacers (ITS1 and ITS2) was carried out on DNA extracted from root samples (fine roots and ECM root tips separately). ECM fungi dominated the root-associated fungal community, with more than 90% of sequences assigned to the genus
Pisolithus
. The morphological and barcoding results demonstrated, for the first time, the presence of ECM symbiosis down to 4-m. The molecular diversity of
Pisolithus
spp. was strongly dependent on depth, with soil pH and soil water content as primary drivers of the
Pisolithus
spp. structure. Altogether, our results highlight the importance to consider the ECM symbiosis in deep soil layers to improve our understanding of fine roots functioning in tropical soils.
Summary
Bacterial thiopurine methyltransferases (bTPMTs) can favour resistance towards toxic tellurite oxyanions through a pathway leading to the emission of a garlic‐like smell. Gene expression ...profiling completed by genetic, physiological and electron microscopy analyses was performed to identify key bacterial activities contributing to this resistance process. Escherichia coli strain MG1655 expressing the bTPMT was used as a cell model in these experiments. This strain produced a garlic‐like smell which was found to be due to dimethyl telluride, and cell aggregates in culture media supplemented with tellurite. Properties involved in aggregation were correlated with cell attachment to polystyrene, which increased with tellurite concentrations. Gene expression profiling supported a role of adhesins in the resistance process with 14% of the tellurite‐regulated genes involved in cell envelope, flagella and fimbriae biogenesis. Other tellurite‐regulated genes were, at 27%, involved in energy, carbohydrate and amino acid metabolism including the synthesis of antioxidant proteins, and at 12% in the synthesis of transcriptional regulators and signal transduction systems. Escherichia coli mutants impaired in tellurite‐regulated genes showed ubiquinone and adhesins synthesis, oxidative stress response, and efflux to be essential in the bTPMT resistance process. High tellurite resistance required a synergistic expression of these functions and an efficient tellurium volatilization by the bTPMT.
In this study, the physiological responses of two rice cultivars, Oryza sativa cv. Nipponbare and Cigalon, to the inoculation of two Azospirillum PGPR strains, Azospirillum lipoferum 4B that ...colonizes the surface of roots (confocal microscopy image on the left) and the endophytic strain Azospirillum B510 that colonizes both the surface and the inside of roots (confocal microscopy image on the right), were analysed. Higher stimulatory effects of the Azospirillum strains 4B and B510 were observed on the cultivars from which the strains were isolated (i.e. Cigalon and Nipponbare, respectively). Enhanced plant growth effects were combined with major changes of root secondary metabolite profiles. This study demonstrates that plant secondary metabolite profiling is relevant to differentiate the physiological responses of plants to rhizobacteria with distinct root-colonization strategies and ecological relationships with the host plant. Display omitted
► Azospirillum preferentially increases the growth of its cultivar of origin. ► Azospirillum affects rice secondary metabolism in a strain-dependent way. ► Unlike strain 4B, the endophytic strain B510 triggers systemic responses in rice. ► Flavonoids and hydroxycinnamic derivatives are mostly affected by Azospirillum.
Azospirillum is a plant growth-promoting rhizobacterium (PGPR) able to enhance growth and yield of cereals such as rice, maize and wheat. The growth-promoting ability of some Azospirillum strains appears to be highly specific to certain plant species and cultivars. In order to ascertain the specificity of the associative symbiosis between rice and Azospirillum, the physiological response of two rice cultivars, Nipponbare and Cigalon, inoculated with two rice-associated Azospirillum was analyzed at two levels: plant growth response and plant secondary metabolic response. Each strain of Azospirillum (Azospirillum lipoferum 4B isolated from Cigalon and Azospirillum sp. B510 isolated from Nipponbare) preferentially increased growth of the cultivar from which it was isolated. This specific effect is not related to a defect in colonization of host cultivar as each strain colonizes effectively both rice cultivars, either at the rhizoplane (for 4B and B510) and inside the roots (for B510). The metabolic profiling approach showed that, in response to PGPR inoculation, profiles of rice secondary metabolites were modified, with phenolic compounds such as flavonoids and hydroxycinnamic derivatives being the main metabolites affected. Moreover, plant metabolic changes differed according to Azospirillum strain×cultivar combinations; indeed, 4B induced major secondary metabolic profile modifications only on Cigalon roots, while B510, probably due to its endophytic feature, induced metabolic variations on shoots and roots of both cultivars, triggering a systemic response. Plant secondary metabolite profiling thereby evidences the specific interaction between an Azospirillum strain and its original host cultivar.
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