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"Taylor, Andy"
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Soil fungal networks maintain local dominance of ectomycorrhizal trees
The mechanisms regulating community composition and local dominance of trees in species-rich forests are poorly resolved, but the importance of interactions with soil microbes is increasingly acknowledged. Here, we show that tree seedlings that interact via root-associated fungal hyphae with soils beneath neighbouring adult trees grow faster and have greater survival than seedlings that are isolated from external fungal mycelia, but these effects are observed for species possessing ectomycorrhizas (ECM) and not arbuscular mycorrhizal (AM) fungi. Moreover, survival of naturally-regenerating AM seedlings over ten years is negatively related to the density of surrounding conspecific plants, while survival of ECM tree seedlings displays positive density dependence over this interval, and AM seedling roots contain greater abundance of pathogenic fungi than roots of ECM seedlings. Our findings show that neighbourhood interactions mediated by beneficial and pathogenic soil fungi regulate plant demography and community structure in hyperdiverse forests.
Associations with mycorrhizal fungi can affect the outcome of plant competition in complex ways. Here the authors use a decade-long field survey and two hyphal exclusion experiments to reveal a critical role of underground fungal networks in facilitating seedling growth and fitness of ectomycorrhizal plants but not arbuscular mycorrhizal plants.
Journal Article
Strong altitudinal partitioning in the distributions of ectomycorrhizal fungi along a short (300 m) elevation gradient
Changes in species richness and distributions of ectomycorrhizal (ECM) fungal communities along altitudinal gradients have been attributed to changes in both host distributions and abiotic variables. However, few studies have considered altitudinal relationships of ECM fungi associated with a single host to identify the role of abiotic drivers. To address this, ECM fungal communities associated with one host were assessed along five altitudinal transects in Scotland.
Roots of Scots pine (Pinus sylvestris) were collected from sites between 300 and 550–600 m altitude, and ECM fungal communities were identified by 454 pyrosequencing of the fungal internal transcribed spacer (ITS) region. Soil moisture, temperature, pH, carbon : nitrogen (C : N) ratio and organic matter content were measured as potential predictors of fungal species richness and community composition.
Altitude did not affect species richness of ECM fungal communities, but strongly influenced fungal community composition. Shifts in community composition along the altitudinal gradient were most clearly related to changes in soil moisture and temperature.
Our results show that a 300 m altitudinal gradient produced distinct shifts in ECM fungal communities associated with a single host, and that this pattern was strongly related to climatic variables. This finding suggests significant climatic niche partitioning among ECM fungal species.
Journal Article
In vitro evidence of root colonization suggests ecological versatility in the genus Mycena
• The root-associated habit has evolved on numerous occasions in different fungal lineages, suggesting a strong evolutionary pressure for saprotrophic fungi to switch to symbiotic associations with plants. Species within the ubiquitous, saprotrophic genus Mycena are frequently major components in molecular studies of root-associated fungal communities, suggesting that an evaluation of their trophic status is warranted. Here, we report on interactions between a range of Mycena species and the plant Betula pendula.
• In all, 17 Mycena species were inoculated onto B. pendula seedlings. Physical interactions between hyphae and fine roots were examined using differential staining and fluorescence microscopy. Physiological interactions were investigated using 14C and 32P to show potential transfer between symbionts.
• All Mycena species associated closely with fine roots, showing hyphal penetration into the roots, which in some cases were intracellular. Seven species formed mantle-like structures around root tips, but none formed a Hartig net. Mycena pura and Mycena galopus both enhanced seedling growth, with M. pura showing significant transfer of 32P to the seedlings.
• Our results support the view that several Mycena species can associate closely with plant roots and some may potentially occupy a transitional state between saprotrophy and biotrophy.
Journal Article
The nongravitational interactions of dark matter in colliding galaxy clusters
Collisions between galaxy clusters provide a test of the nongravitational forces acting on dark matter. Dark matter's lack of deceleration in the \"bullet cluster\" collision constrained its self-interaction cross section σDM/m < 1.25 square centimenters per gram (cm2μ) [68% confidence limit (CL)] (σDM, self-interaction cross section; m, unit mass of dark matter) for long-ranged forces. Using the Chandra and Hubble Space Telescopes, we have now observed 72 collisions, including both major and minor mergers. Combining these measurements statistically, we detect the existence of dark mass at 7.6σ significance. The position of the dark mass has remained closely aligned within 5.8 ± 8.2 kiloparsecs of associated stars, implying a self-interaction cross section σDM/m < 0.47 cm2/g (95% CL) and disfavoring some proposed extensions to the standard model.
Journal Article
Species composition of an ectomycorrhizal fungal community along a local nutrient gradient in a boreal forest
• Soil abiotic factors are considered to be important in determining the distribution of ectomycorrhizal (ECM) fungal species; however, there are few field data to support this. Here, we relate ECM species distributions to changes in soil chemistry along a short (90-m), natural nutrient gradient. • The ECM community was characterized, using morphological and molecular techniques, in soil samples collected at 10-m intervals. • There were pronounced changes in ECM fungal community structure along the transect, with many taxa showing discrete distributions. Although there was a change of host from Pinus to Picea along the gradient, host-specific fungi did not account for the observed change in community structure. Ordination analyses showed that community structure was strongly correlated with soil characteristics, in particular extractable ammonium and base saturation. However, autocorrelation among soil parameters makes it difficult to isolate the effects of individual parameters. • The distinctive changes in soil and vegetation along the transect used in this study provided an exceptional opportunity to examine the local-scale impact of natural spatial heterogeneity on an ECM fungal community.
Journal Article
Reverse microdialysis of sucrose stimulates soil fungal and bacterial growth at the microscale
Background
The rhizosphere is a critical microenvironment that plays key roles in plant nutrient availability, largely due to root interactions with rhizospheric microbes. However, we lack suitable methods that can elucidate mechanisms determining rhizospheric community structure and function within the context of a dynamic, undisturbed soil. Microdialysis has been used for low intrusive soil nutrient sampling at the scale of a fine root, with small probes that also enable release of defined compounds. We evaluated whether microdialysis could simulate exudation, by the release of sucrose, and stimulate changes in a soil microbial community, allowing us to determine the microbes that responded most to carbon release.
Results
Microdialysis successfully stimulated growth on probe surfaces of fungi and bacteria, which were extracted and sequenced for identification. Microbial growth was also visualized with scanning electron microscopy. The majority of the species stimulated were classified as fast growing or opportunistic, e.g. yeasts, moulds, proteobacteria and actinobacteriota, which are known to respond quickly (within days) to the release of simple sugars as exudates in the rhizosphere.
Conclusions
The study demonstrates the potential of using microdialysis as a tool to investigate interactions between root exudation and soil microbial community composition, initially for individual compounds and in the future for more complex compositions.
Journal Article