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Differences between arbuscular (AM) and ectomycorrhizal (EcM) trees strongly influence forest ecosystem processes, in part through their impact on saprotrophic fungal communities. Ericoid mycorrhizal (ErM) shrubs likely also impact saprotrophic communities given that they can shape nutrient cycling by slowing decomposition rates and intensifying nitrogen limitation. We investigated the depth distributions of saprotrophic and EcM fungal communities in paired subplots with and without a common understory ErM shrub, mountain laurel (Kalmia latifolia L.), across an AM to EcM tree dominance gradient in a temperate forest by analyzing soils from the organic, upper mineral (0–10 cm), and lower mineral (cumulative depth of 30 cm) horizons. The presence of K. latifolia was strongly associated with the taxonomic and functional composition of saprotrophic and EcM communities. Saprotrophic richness was consistently lower in the Oa horizon when this ErM shrub species was present. However, in AM tree-dominated plots, the presence of the ErM shrub was associated with a higher relative abundance of saprotrophs. Given that EcM trees suppress both the diversity and relative abundance of saprotrophic communities, our results suggest that separate consideration of ErM shrubs and EcM trees may be necessary when assessing the impacts of plant mycorrhizal associations on belowground communities. [ABSTRACT FROM AUTHOR]

Ectomycorrhizal fungi are among the most prevalent fungal partners of plants and can constitute up to one-third of forest microbial biomass. As mutualistic partners that supply nutrients, water, and pathogen defense, these fungi impact host plant health and biogeochemical cycling. Ectomycorrhizal fungi are also extremely diverse, and the community of fungal partners on a single plant host can consist of dozens of individuals. However, the factors that govern competition and coexistence within these communities are still poorly understood. In this study, we used in vitro competitive assays between five ectomycorrhizal fungal strains to examine how competition and pH affect fungal growth. We also tested the ability of evolutionary history to predict the outcomes of fungal competition. We found that the effects of pH and competition on fungal performance varied extensively, with changes in growth media pH sometimes reversing competitive outcomes. Furthermore, when comparing the use of phylogenetic distance and growth rate in predicting competitive outcomes, we found that both methods worked equally well. Our study further highlights the complexity of ectomycorrhizal fungal competition and the importance of considering phylogenetic distance, ecologically relevant traits, and environmental conditions in predicting the outcomes of these interactions. [ABSTRACT FROM AUTHOR]

Despite growing interest in fungal necromass decomposition due to its importance in soil carbon retention, whether a consistent group of microorganisms is associated with decomposing necromass remains unresolved. Here, we synthesize knowledge on the composition of the bacterial and fungal communities present on decomposing fungal necromass from a variety of fungal species, geographic locations, habitats, and incubation times. We found that there is a core group of both bacterial and fungal genera (i.e. a core fungal necrobiome), although the specific size of the core depended on definition. Based on a metric that included both microbial frequency and abundance, we demonstrate that the core is taxonomically and functionally diverse, including bacterial copiotrophs and oligotrophs as well as fungal saprotrophs, ectomycorrhizal fungi, and both fungal and animal parasites. We also show that the composition of the core necrobiome is notably dynamic over time, with many core bacterial and fungal genera having specific associations with the early, middle, or late stages of necromass decomposition. While this study establishes the existence of a core fungal necrobiome, we advocate that profiling the composition of fungal necromass decomposer communities in tropical environments and other terrestrial biomes beyond forests is needed to fill key knowledge gaps regarding the global nature of the fungal necrobiome. [ABSTRACT FROM AUTHOR]

Bark beetle disturbances are a critical event in the life cycle of Norway spruce forests. However, our knowledge of their effects on ectomycorrhizal fungi (EMF), which play a key role in forest productivity and nutrient cycling, is still incomplete. Special attention has been paid to the dynamics and diversity of EMF communities in managed forests, but studies dealing with disturbed natural stands are underrepresented. We conducted a study in an unmanaged natural spruce forest in the Bohemian Forest (Czech Republic), which suffered severe forest dieback caused by bark beetle. Approximately a decade after the disturbance, the character of the forest structure in the study area (∼60 ha, 41 study plots) ranged from sites with open canopy and sparse tree cover to areas with dense spruce regeneration to patches of closed-canopy forest. We found that relative EMF abundance in soils was positively related to surviving tree and regeneration density. The number of surviving trees also positively affected species EMF richness and tended to support preservation of late-successional EMF species. Our results suggest that trees that survive bark beetle disturbance are key for the fate of the EMF community in natural forests. [ABSTRACT FROM AUTHOR]

Truffle growers devote great efforts to improve black truffle productivity, developing agronomic practices such as 'truffle nests' (peat amendments that are supplemented with truffle spore inoculum). It has been hypothesized that improved fruiting associated with nests is linked to stimulation of truffle mycelia previously established in soil or to changes generated in soil fungal community. To assess this, we used real-time PCR to quantify black truffle extraradical mycelium during 2 years after nests installation. We also characterized the fungal community via high-throughput amplicon sequencing of the ITS region of rRNA genes. We found that neither the abundance of truffle mycelium in nests nor in the soil—nest interphase was higher than in the bulk soil, which indicates that nests do not improve mycelial growth. The fungal community in nests showed lower richness and Shannon index and was compositionally different from that of soil, which suggests that nests may act as an open niche for fungal colonization that facilitates truffle fruiting. The ectomycorrhizal fungal community showed lower richness in nests. However, no negative relationships between amount of truffle mycelium and reads of other ectomycorrhizal fungi were found, thus countering the hypothesis that ectomycorrhizal competition plays a role in the nest effect. [ABSTRACT FROM AUTHOR]

A large part of ecosystem function in woodland systems depends on soil fungal communities. However, global climate change has the potential to fundamentally alter these communities as fungal species are filtered with changing environmental conditions. In this study, we examined the potential effects of climate on host-associated (i.e. tree-associated) soil fungal communities at climatically distinct sites in the Tehachapi Mountains in California, where more arid conditions represent likely regional climate futures. We found that soil fungal community composition changes strongly across sites, with species richness and diversity being highest at the most arid site. However, host association may buffer the effects of climate on community composition, as host-associated fungal communities are more similar to each other across climatically distinct sites than the whole fungal community. Lastly, an examination of functional traits for ectomycorrhizal fungi, a well-studied guild of fungal mutualist species, showed that stress-tolerant traits were more abundant at arid sites than mesic sites, providing a mechanistic understanding of these community patterns. Taken together, our results indicate that fungal community composition will likely shift with future climate change but that host association may buffer these effects, with shifts in functional traits having implications for future ecosystem function. [ABSTRACT FROM AUTHOR]

The response to global change by soil microbes is set to affect important ecosystem processes. These impacts could be most immediate in transitional zones, such as the temperate-boreal forest ecotone, yet previous work in these forests has primarily focused on specific subsets of microbial taxa. Here, we examined how bacterial and fungal communities respond to simulated above- and below-ground warming under realistic field conditions in closed and open canopy treatments in Minnesota, USA. Our results show that warming and canopy disturbance shifted bacterial and fungal community structure as dominant bacterial and fungal groups differed in the direction and intensity of their responses. Ectomycorrhizal and saprotrophic fungal communities with greater connectivity (higher prevalence of strongly interconnected taxa based on pairwise co-occurrence relationships) were more resistant to compositional change. Warming effects on soil enzymes involved in the hydrolytic and oxidative liberation of carbon from plant cell walls and nutrients from organic matter were most strongly linked to fungal community responses, although community structure–function relationships differed between fungal guilds. Collectively, these findings indicate that warming and disturbance will influence the composition and function of microbial communities in the temperate-boreal ecotone, and fungal responses are particularly important to understand for predicting future ecosystem functioning. [ABSTRACT FROM AUTHOR]

Despite the extensive, ongoing conversion of tropical forests to rubber plantation, the effects of this land-use change on soil fungal community diversity and composition are still poorly known. We compared a network of sites of tropical forest in southern Yunnan, China, with a network of rubber plantation sites originally derived from this forest. Soil DNA was amplified for ITS2 and sequenced using Illumina MiSeq. We found that there was a major shift in community composition across all phyla, including a large reduction in ectomycorrhizal fungi likely related to the absence of hosts. Conversion from forest to rubber plantation had no effect on total fungal α-diversity, but rubber plantation had lower β-diversity, resulting in lower overall gamma diversity. Networks based on co-occurrence of operational taxonomic unit in each land-use type showed that network complexity decreased with land-use change from forest to rubber plantation. Further investigation of soil functionality is needed to investigate whether this lower network complexity is related to reduced soil ecosystem resilience. [ABSTRACT FROM AUTHOR]

Ectomycorrhizal (ECM) fungi establish symbiosis with roots of most trees of boreal and temperate ecosystems and are major drivers of nutrient fluxes between trees and the soil. ECM fungi constantly interact with bacteria all along their life cycle and the extended networks of hyphae provide a habitat for complex bacterial communities. Despite the important effects these bacteria can have on the growth and activities of ECM fungi, little is known about the mechanisms by which these microorganisms interact. Here we investigated the ability of bacteria to form biofilm on the hyphae of the ECM fungus Laccaria bicolor. We showed that the ability to form biofilms on the hyphae of the ECM fungus is widely shared among soil bacteria. Conversely, some fungi, belonging to the Ascomycete class, did not allow for the formation of bacterial biofilms on their surfaces. The formation of biofilms was also modulated by the presence of tree roots and ectomycorrhizae, suggesting that biofilm formation does not occur randomly in soil but that it is regulated by several biotic factors. In addition, our study demonstrated that the formation of bacterial biofilm on fungal hyphae relies on the production of networks of filaments made of extracellular DNA. [ABSTRACT FROM AUTHOR]

Fennoscandian forestry has in the past decades changed from natural regeneration of forests towards replantation of clear-cuts, which negatively impacts ectomycorrhizal fungal (EMF) diversity. Retention of trees during harvesting enables EMF survival, and we therefore expected EMF communities to be more similar to those in old natural stands after forest regeneration using seed trees compared to full clear-cutting and replanting. We sequenced fungal internal transcribed spacer 2 (ITS2) amplicons to assess EMF communities in 10- to 60-year-old Scots pine stands regenerated either using seed trees or through replanting of clear-cuts with old natural stands as reference. We also investigated local EMF communities around retained old trees. We found that retention of seed trees failed to mitigate the impact of harvesting on EMF community composition and diversity. With increasing stand age, EMF communities became increasingly similar to those in old natural stands and permanently retained trees maintained EMF locally. From our observations, we conclude that EMF communities, at least common species, post-harvest are more influenced by environmental filtering, resulting from environmental changes induced by harvest, than by the continuity of trees. These results suggest that retention of intact forest patches is a more efficient way to conserve EMF diversity than retaining dispersed single trees. [ABSTRACT FROM AUTHOR]

Fungal communities are important for carbon (C) transformations in boreal forests that are one of the largest C pools in terrestrial ecosystems, warranting thus further investigation of fungal community dynamics in time and space. We investigated fungal diversity and community composition seasonally and across defined soil horizons in boreal Scots pine forest in Finland using 454 pyrosequencing. We collected a total of 120 samples from five vertical soil horizons monthly from March to October; in March, under snow. Boreal forest soil generally harbored diverse fungal communities across soil horizons. The communities shifted drastically and rapidly over time. In late winter, saprotrophs dominated the community and were replaced by ectomycorrhizal fungi during the growing season. Our studies are among the first to dissect the spatial and temporal dynamics in boreal forest ecosystems and highlights the ecological importance of vertically distinct communities and their rapid seasonal dynamics. As climate change is predicted to result in warmer and longer snow-free winter seasons, as well as increase the rooting depth of trees in boreal forest, the seasonal and vertical distribution of fungal communities may change. These changes are likely to affect the organic matter decomposition by the soil-inhabiting fungi and thus alter organic C pools. [ABSTRACT FROM AUTHOR]

Ectomycorrhizal fungi (EMF) are highly diversified and dominant in a number of forest ecosystems. Nevertheless, their scales of spatial distribution and the underlying ecological processes remain poorly understood. Although most EMF are considered to be generalists regarding host identity, a preference toward functional strategies of host trees has never been tested. Here, the EMF community was characterised by DNA sequencing in a 10-ha tropical dry season forest--referred to as miombo--an understudied ecosystem from a mycorrhizal perspective. We used 36 soil parameters and 21 host functional traits (FTs) as candidate explanatory variables in spatial constrained ordinations for explaining the EMF community assemblage. Results highlighted that the community variability was explained by host FTs related to the 'leaf economics spectrum' (adjusted R² = 11%; SLA, leaf area, foliar Mg content), and by soil parameters (adjusted R² = 17%), notably total forms of micronutrients or correlated available elements (Al, N, K, P). Both FTs and soil generated patterns in the community at scales ranging from 75 to 375 m. Our results indicate that soil is more important than previously thought for EMF in miombo woodlands, and show that FTs of host species can be better predictors of symbiont distribution than taxonomical identity. [ABSTRACT FROM AUTHOR]

Root systems are simultaneously colonized by multiple individuals of mycorrhizal fungi. Intraspecific competitive interactions between fungal isolates are likely to affect both fungal and plant performance and be influenced by abiotic factors. Here, we assessed the impact of intraspecific competition between three Pisolithus microcarpus isolates on the establishment of, and benefit derived from, symbioses with Eucalyptus grandis seedlings. We investigated the outcomes of competition under ambient and elevated temperature and CO2 concentration ([CO2]) in a factorial design. We observed a reduction in mycelium growth, mycorrhiza formation and seedling mass when two P. microcarpus isolates were co-inoculated on a single E. grandis seedling. Isolates invested more in mycelium than in mycorrhizas in the presence of a competitor. All isolates responded negatively to elevated [CO2] and positively to elevated temperature, which led to no changes on the outcomes of the interactions with changing conditions. However, the presence of a competitor hindered the positive response of P. microcarpus isolates to warming, which resulted in larger negative effects of competition under elevated temperature than under ambient conditions. Our study highlights the need to consider how competition affects individual fungal responses as well as plant performance when trying to predict the impacts of climate change. [ABSTRACT FROM AUTHOR]

Microorganisms can be versatile in their interactions with each other, being variously beneficial, neutral or antagonistic in their effect. Although this versatility has been observed among many microorganisms and in many environments, little is known regarding the mechanisms leading to these changes in behavior. In the present work, we analyzed the mechanism by which the soil bacterium Pseudomonas fluorescens BBc6R8 shifts from stimulating the growth of the ectomycorrhizal fungus Laccaria bicolor S238N to killing the fungus. We show that among the three secondary metabolites produced by the bacterial strain--the siderophores enantio-pyochelin and pyoverdine, and the biosurfactant viscosin--the siderophores are mainly responsible for the antagonistic activity of the bacterium under iron-limited conditions. While the bacterial strain continues to produce beneficial factors, their effects are overridden by the action of their siderophores. This antagonistic activity of the strain P. fluorescens BBC6R8 in iron-depleted environments is not restricted to its influence on L. bicolor, since it was also seen to inhibit the growth of the actinomycete Streptomyces ambofaciens ATCC23877. We show that the strain P. fluorescens BBc6R8 uses different strategies to acquire iron, depending on certain biotic and abiotic factors. [ABSTRACT FROM AUTHOR]

Community compositions of ectomycorrhizal (ECM) fungi are known to show spatial distance decay of similarity, which arises from both deterministic niche-based processes and stochastic spatial-based processes (e.g. dispersal limitation). Recent studies have highlighted the importance of incorporating the spatial-based processes in the study of community ecology of ECM fungi. However, few studies have investigated the temporal distance decay of similarity of ECM fungal communities. More specifically, the role of stochastic temporal-based processes, which could drive the temporal distance decay of similarity independently of niche-based processes, in the temporal variation of the communities remains unclear. Here we investigated ECM fungi associated with roots of Castanopsis sieboldii at 3-month intervals over a 2-year period. We found that dissimilarity of the ECM fungal community composition was significantly correlated with temporal distance but not with environmental distance among sampling dates. Both climatic and temporal variables significantly explained the temporal variation of the community composition. These results suggest that temporal variations of ECM fungi can be affected not only by niche-based processes but also by temporal-based processes. Our findings imply that priority effects may play important roles in the temporal turnover of ECM fungal community at the site. [ABSTRACT FROM AUTHOR]

Recent studies have shown that changes in community compositions of ectomycorrhizal (ECM) fungi along elevation gradients are mainly affected by changes in host tree communities and/or in abiotic environments. However, few studies have taken the effects of processes related to fungal dispersal (i.e. spatial processes) into account and distinguished the effects of host community, abiotic environment and spatial processes on community composition along elevation gradients. This has left unclear the relative importance of these factors in structuring the ECM community assemblages. To address this, we investigated the community composition of ECM fungi along an elevation gradient in northern Japan with 454 meta-barcoding. We found that the community composition of ECM fungi changed along the elevation and that all three factors jointly affected the compositional changes. We separated the magnitude of importance of the three factors in structuring ECM fungal communities and found that most of the spatial variation in ECM fungal community was explained by host communities and abiotic environments. Our results suggest that while biotic and/or abiotic environments can be important factors in determining the ECM fungal community composition along an elevation gradient, spatial processes may also be a primary determinant. [ABSTRACT FROM AUTHOR]

Different distance-based threshold selection approaches were used to assess and compare use of the internal transcribed spacer (ITS) region to distinguish among 901 Cortinarius species represented by >3000 collections. Sources of error associated with genetic markers and selection approaches were explored and evaluated using MOTUs from genus and lineage based-alignments. Our study indicates that 1%-2% more species can be distinguished by using the full-length ITS barcode as compared to either the ITS1 or ITS2 regions alone. Optimal threshold values for different picking approaches and genetic marker lengths inferred from a subset of species containing major lineages ranged from 97.0% to 99.5% sequence similarity using clustering optimization and UNITE SH, and from 1% to 2% sequence dissimilarity with CROP. Errors for the optimal cutoff ranged from 0% to 70%, and these can be reduced to a maximum of 22% when excluding species lacking a barcode gap. A threshold value of 99% is suitable for distinguishing species in the majority of lineages in the genus using the entire ITS region but only 90% of the species could be identified using just the ITS1 or ITS2 region. Prior identification of species, lacking barcode gaps and their subsequent separate analyses, maximized the accuracy of threshold approaches. [ABSTRACT FROM AUTHOR]

Many forests are affected by chronic acid deposition, which can lower soil pH and limit the availability of nutrients such as phosphorus (P), but the response of mycorrhizal fungi to changes in soil pH and P availability and how this affects tree acquisition of nutrients is not well understood. Here, we describe an ecosystem-level manipulation in 72 plots, which increased pH and/or P availability across six forests in Ohio, USA. Two years after treatment initiation, mycorrhizal fungi on roots were examined with molecular techniques, including 454-pyrosequencing. Elevating pH significantly increased arbuscular mycorrhizal (AM) fungal colonization and total fungal biomass, and affected community structure of AM and ectomycorrhizal (EcM) fungi, suggesting that raising soil pH altered both mycorrhizal fungal communities and fungal growth. AM fungal taxa were generally negatively correlated with recalcitrant P pools and soil enzyme activity, whereas EcM fungal taxa displayed variable responses, suggesting that these groups respond differently to P availability. Additionally, the production of extracellular phosphatase enzymes in soil decreased under elevated pH, suggesting a shift in functional activity of soil microbes with pH alteration. Thus, our findings suggest that elevating pH increased soil P availability, which may partly underlie the mycorrhizal fungal responses we observed. [ABSTRACT FROM AUTHOR]

Influences of soil environment and willow host species on ectomycorrhizal fungi communities was studied across an hydrologic gradient in temperate North America. Soil moisture, organic matter and pH strongly predicted changes in fungal community composition. In contrast, increased fungal richness strongly correlated with higher plant-available phosphorus. The 93 willow trees sampled for ectomycorrhizal fungi included seven willow species. Host identity did not influence fungal richness or community composition, nor was there strong evidence of willow host preference for fungal species. Network analysis suggests that these mutualist interaction networks are not significantly nested or modular. Across a strong environmental gradient, fungal abiotic niche determined the fungal species available to associate with host plants within a habitat. [ABSTRACT FROM AUTHOR]

The asexual ectomycorrhizal fungus Cenococcum geophilum has a wide geographic range in diverse forest ecosystems. Although its genetic diversity has been documented at a stand or regional scale, knowledge of spatial genetic structure is limited. We studied the genetic diversity and spatial structure of C. geophilum in eight Japanese coastal pine forests with a maximum geographic range of 1364 km. A total of 225 samples were subjected to phylogenetic analysis based on the glyceraldehyde 3-phosphate dehydrogenase gene (GAPDH) followed by microsatellite analysis with five loci. The phylogenetic analysis based on GAPDH resolved three groups with most isolates falling into one dominant lineage. Microsatellite analyses generated 104 multilocus genotypes in the overall populations. We detected significant genetic variation within populations and genetic clusters indicating that high genetic diversity may be maintained by possible recombination processes at a stand scale. Although no spatial autocorrelation was detected at a stand scale, the relationship between genetic and geographic distances among the populations was significant, suggesting a pattern of isolation by distance. These results indicate that cryptic recombination events at a local scale and unknown migration events at both stand and regional scales influence spatial distribution and genetic structure of C. geophilum in coastal pine forests of Japan. [ABSTRACT FROM AUTHOR]

Seasonal and interannual variability in temperature, precipitation and chemical resources may regulate fungal community structure in forests but the effect of such variability is still poorly understood. In this study, I examined changes in fungal communities over two years and how these changes were correlated to natural variation in soil conditions. Soil cores were collected every month for three years from permanent plots established in an old-growth hardwood forest, and molecular methods were used to detect fungal species. Species richness and diversity were not consistent between years with richness and diversity significantly affected by season in one year but significantly affected by depth in the other year. These differences were associated with variation in late winter snow cover. Fungal communities significantly varied by plot location, season and depth and differences were consistent between years but fungal species within the community were not consistent in their seasonality or in their preference for certain soil depths. Some fungal species, however, were found to be consistently correlated with soil chemistry across sampled years. These results suggest that fungal community changes reflect the behavior of the individual species within the community pool and how those species respond to local resource availability. [ABSTRACT FROM AUTHOR]

The amounts of carbon allocated to the fungal partner in ectomycorrhizal associations can vary substantially depending on the plant growth and the soil nutrient conditions, and the fungus may frequently be confronted with limitations in carbon. We used chemical analysis and transcriptome profiling to examine the physiological response of the ectomycorrhizal fungus Paxillus involutus to carbon starvation during axenic cultivation. Carbon starvation induced a decrease in the biomass. Concomitantly, ammonium, cell wall material (chitin) and proteolytic enzymes were released into the medium, which suggest autolysis. Compared with the transcriptome of actively growing hyphae, about 45% of the transcripts analyzed were differentially regulated during C-starvation. Induced during starvation were transcripts encoding extracellular enzymes such as peptidases, chitinases and laccases. In parallel, transcripts of N-transporters were upregulated, which suggest that some of the released nitrogen compounds were re-assimilated by the mycelium. The observed changes suggest that the carbon starvation response in P. involutus is associated with complex cellular changes that involves autolysis, recycling of intracellular compounds by autophagy and reabsorption of the extracellular released material. The study provides molecular markers that can be used to examine the role of autolysis for the turnover and survival of the ectomycorrhizal mycelium in soils. [ABSTRACT FROM AUTHOR]

The ectomycorrhizal fungus Cenococcum geophilum ( Ascomycota, Dothideomycetes) forms black, round to irregular sclerotia in forest soils. Fungi that colonize the sclerotia appear to affect sclerotia viability and may play an important role in the life history of Cenococcum. Some of the fungi could also affect nutrient cycling by decomposing Cenococcum sclerotia, which are melanized and recalcitrant to decay. We used a culture-based method to document the fungal communities growing inside surface-sterilized sclerotia that were collected from forest soils. Cenococcum was successfully isolated from 297 of 971 sclerotia whereas 427 sclerotia hosted fungi other than Cenococcum. DNA barcoding of the internal transcribed spacer rDNA followed by grouping at 97% sequence similarity yielded 85 operational taxonomic units (OTUs) that consisted primarily of Ascomycota (e.g. Chaetothyriales, Eurotiales, Helotiales, Pleosporales) and a few Basidiomycota and Mucoromycotina. Although most fungal OTUs were infrequently cultured, several OTUs such as members of Asterostroma, Cladophialophora, Oidiodendron, and Pleosporales were common and found across many sites. Our results suggest that Cenococcum sclerotia act as a substrate for diverse fungi. The occurrence of several OTUs in sclerotia across many sites suggests that these fungi may be active parasites of Cenococcum sclerotia or may preferentially use sclerotia as a nutrient source. [ABSTRACT FROM AUTHOR]

Multispecies mutualisms, such as the association between trees and ectomycorrhizal fungi, are often shaped by environmental context. Here, we explored the functional mechanisms underlying this environmental filtering. Using a single population of Pinus muricata ( Bishop pine) growing along a strong edaphic gradient, we examined how environmental stress affected ectomycorrhizal fungi. The gradient spans c. 400 000 years of soil age, and reduced nutrient availability and increased water stress dwarf trees on older sites. Fungal community composition shifted with nutrient and water availability and with the stature of the P. muricata host trees. Not only did pygmy trees host a taxonomically different fungal subset as compared to nonpygmy trees, but associated fungal communities also differed in life history strategies: trees in more stressful conditions hosted fungi with more carbon-intensive foraging strategies. Our results indicate a link between environmental controls of host nutritional status and turnover in the ectomycorrhizal fungal community. The transition to more energy-intensive strategies under nutrient stress may allow for close recycling of recalcitrant nutrient pools within the root zone and facilitate transport of nutrients and water over long distances. These results highlight the value of life history data to understanding the mechanistic underpinnings of species distributions. [ABSTRACT FROM AUTHOR]

Soil microbial processes have a central role in global fluxes of the key biogenic greenhouse gases and are likely to respond rapidly to climate change. Whether climate change effects on microbial processes lead to a positive or negative feedback for terrestrial ecosystem resilience is unclear. In this study, we investigated the interactive effects of [ CO2] and temperature on soil fungi associated with faster-growing Eucalyptus saligna and slower-growing Eucalyptus sideroxylon, and fungi that colonised hyphal in-growth bags. Plants were grown in native soil under controlled soil moisture conditions, while subjecting the above-ground compartment to defined atmospheric conditions differing in CO2 concentrations (290, 400, 650 μL L−1) and temperature (26 and 30 °C). Terminal restriction fragment length polymorphism and sequencing methods were used to examine effects on the structure of the soil fungal communities. There was no significant effect of host plant or [ CO2]/temperature treatment on fungal species richness (α diversity); however, there was a significant effect on soil fungal community composition (β diversity) which was strongly influenced by eucalypt species. Interestingly, β diversity of soil fungi associated with both eucalypt species was significantly influenced by the elevated [ CO2]/high temperature treatment, suggesting that the combination of future predicted levels of atmospheric [ CO2] and projected increases in global temperature will significantly alter soil fungal community composition in eucalypt forest ecosystems, independent of eucalypt species composition. These changes may arise through direct effects of changes in [ CO2] and temperature on soil fungi or through indirect effects, which is likely the case in this study given the plant-dependent nature of our observations. This study highlights the role of plant species in moderating below-ground responses to future predicted changes to [ CO2] and temperature and the importance of considering integrated plant-soil system responses. [ABSTRACT FROM AUTHOR]

Truffles are hypogeous ectomycorrhizal ( EM) fungi belonging to the genus Tuber. Although outplanting of truffle-inoculated host plants has enabled the realization of productive orchards, truffle cultivation is not yet standardized. Therefore, monitoring the distribution of fungal species in different truffle fields may help us to elucidate the factors that shape microbial communities and influence the propagation and fruiting of Tuber spp. In this study, we compared the fungal biodiversity in cultivated and natural Tuber melanosporum truffle fields located in Central Italy. To this end, ectomycorrhizas ( ECM) and soil samples were molecularly analyzed, and an inventory of the fungi associated with Quercus pubescens plants colonized by T. melanosporum, Tuber aestivum or Tuber brumale was compiled. T. melanosporum and T. aestivum were dominant on the cultivated plants, and the number of EM species was markedly lower in the cultivated sites than in the natural sites. However, in the same site, EM biodiversity was higher in T. brumale-colonized plants than in T. melanosporum-colonized plants. These results suggest that different Tuber spp. may have different competitive effects on the other mycobionts. Additionally, in keeping with our previous findings, we found that the number of T. melanosporum genotypes recovered from the soil samples was higher than that of the underlying ECM. [ABSTRACT FROM AUTHOR]

Decaying wood plays an important role in forest biodiversity, nutrient cycling and carbon balance. Community structure of wood-inhabiting fungi changes with mass loss of wood, but the relationship between substrate quality and decomposers is poorly understood. This limits the extent to which these ecosystem services can be effectively managed. We studied the fungal community and physico-chemical quality (stage of decay, dimensions, density, moisture, C : N ratio, lignin and water or ethanol extractives) of 543 Norway spruce logs in five unmanaged boreal forest sites of southern Finland. Fungi were identified using denaturing gradient gel electrophoresis and sequencing of DNA extracted directly from wood samples. Macroscopic fruiting bodies were also recorded. Results showed a fungal community succession with decreasing wood density and C : N ratio, and increasing moisture and lignin content. Fungal diversity peaked in the most decayed substrates. Ascomycetes typically colonized recently fallen wood. Brown-rot fungi preferred the intermediate decay stages. White-rot fungi represented approximately one-fifth of sequenced species in all decay phases excluding the final phase, where ectomycorrhizal ( ECM) fungi became dominant. Lignin content of logs with white-rot fungi was low, and ECM fungi were associated with substrates containing abundant nitrogen. Macroscopic fruiting bodies were observed for only a small number of species detected with molecular techniques. [ABSTRACT FROM AUTHOR]

Mexico is a center of diversity for pines, but few studies have examined the ectomycorrhizal ( ECM) fungal communities associated with pines in this country. We investigated the ECM communities associated with Pinus montezumae seedlings and mature trees in neotropical forests of central Mexico and compared their structure and species composition. Root tips were sampled on both planted seedlings and naturally occurring adult trees. A total of 42 ECM operational taxonomic units ( OTUs) was found on P. montezumae. Diversity and similarity indices showed that community structure was similar for both plant growth stages, but phylogenetic diversity and Chao-estimated richness were higher for seedlings. Species composition differed between communities. The dominant OTUs belonged to the families Atheliaceae, Cortinariaceae, and Sebacinaceae, although different taxa appeared to colonize seedlings and adults. Only 12 OTUs were shared between seedlings and adults, which suggests that ECM fungi which colonize seedlings are still not fully incorporated into mycelial networks and that ECM taxa colonizing young individuals of P. montezumae are likely to come from fungal propagules. Intra-generic diversity could be an insurance mechanism to maintain forest productivity under stressed conditions. This is the first report describing the abundance of Atheliaceae in tree roots in neotropical ecosystems. [ABSTRACT FROM AUTHOR]

Ectomycorrhizal fungi (EMF) provide nutrients to their hosts by means of hyphae that extend beyond nutrient-depleted rhizosphere soil. Soil bacteria may compete with EMF for nutrients or may act synergistically to enhance nutrient supply to hosts. To assess the interactions between hyphae and bacteria, two types of small, sand-filled mesh bags were incubated in a Pseudotsuga menziesii/ Betula papyrifera forest. The bags allowed ingrowth by EMF (35-μm mesh) or excluded hyphae (0.5-μm mesh), while allowing migration of soil bacteria. After incubation, bacteria were isolated from bags using a method to enrich for Gram-positive bacteria. Isolates were assayed for phosphatase and N-acetyl glucosaminidase (NAGase) activities to assess the potential to access organic phosphorus and nitrogen. The average phosphatase activities were higher in exclusion than ingrowth bags, while NAGase activities did not differ. Streptomyces isolates, which are expected to be strong competitors and antagonists of EMF, were more prevalent in ingrowth bags and yet had lower phosphatase activities. Furthermore, there were no indications of antagonism between fungi and Streptomyces, as there were no increases in NAGase activities in ingrowth bags. We conclude that fungal hyphae can structure components of the soil bacterial community for decreased extracellular enzyme production. [ABSTRACT FROM AUTHOR]

Truffles ( Tuber spp.) and other ectomycorrhizal species form species-rich assemblages in the wild as well as in cultivated ecosystems. We aimed to investigate the ectomycorrhizal communities of hazels and hornbeams that are growing in a 24-year-old Tuber aestivum orchard. We demonstrated that the ectomycorrhizal communities included numerous species and were phylogenetically diverse. Twenty-nine ectomycorrhizal taxa were identified. Tuber aestivum ectomycorrhizae were abundant (9.3%), only those of Tricholoma scalpturatum were more so (21.4%), and were detected in both plant symbionts with a variation in distribution and abundance between the two different hosts. The Thelephoraceae family was the most diverse, being represented by 12 taxa. The overall observed diversity represented 85% of the potential one as determined by a jackknife estimation of richness and was significantly higher in hazel than in hornbeam. The ectomycorrhizal communities of hornbeam trees were closely related phylogenetically, whereas no clear distribution pattern was observed for the communities in hazel. Uniform site characteristics indicated that ectomycorrhizal relationships were host mediated, but not host specific. Despite the fact that different plant species hosted diverse ectomycorrhizal communities and that the abundance of T. aestivum differed among sites, no difference was detected in the production of fruiting bodies. [ABSTRACT FROM AUTHOR]

Ectomycorrhizal fungi may improve the phosphate nutrition of their host plants by secreting, into the soil solution, acid phosphatases (AcPases) able to release orthophosphate (Pi) from soil organic phosphorus (Po). Using cation-exchange chromatography, we separated four fractions with AcPase activity secreted by the ectomycorrhizal fungus Hebeloma cylindrosporum grown in a pure culture under P-starved conditions. Each AcPase active fraction displayed strong ability in vitro to hydrolyse a wide range of phosphate monoesters, but none of them efficiently hydrolysed phytate. Their efficiency to release Pi from soil NaHCO3-extractable Po was studied in a sandy podzol used intact or autoclaved. Soils were collected in a 15-year-old Pinus pinaster stand, receiving regular fertilization or not. Autoclaving increased the NaHCO3-extractable Po concentrations by 55% in unfertilized and by 32–43% in fertilized soils. The efficiency of each AcPase fraction was affected significantly by the soil fertilization regime and the soil treatment (intact vs. autoclaved). The proportion of labile Po enzyme ranged from 0% to 11% and 14% to 48% after 1 h of incubation in bicarbonate solutions extracted from intact and autoclaved soils, respectively. This work suggests that AcPases secreted from H. cylindrosporum could be efficient in recycling Po pools from soil microorganisms that may be delivered by soil autoclaving. [ABSTRACT FROM AUTHOR]

Root and mycelial exudation contributes significantly to soil carbon (C) fluxes, and is likely to be altered by an elevated atmospheric carbon dioxide (CO2) concentration and nitrogen (N) deposition. We quantified soluble, low-molecular-weight (LMW) organic compounds exuded by ectomycorrhizal plants grown under ambient (360 p.p.m.) or elevated (710 p.p.m.) CO2 concentrations and with different N sources. Scots pine seedlings, colonized by one of five different ectomycorrhizal or nonmycorrhizal fungi, received 70 μM N, either as NH4Cl or as alanine, in a liquid growth medium. Exudation of LMW organic acids (LMWOAs), dissolved monosaccharides and total dissolved organic carbon were determined. Both N and CO2 had a significant impact on exudation, especially of LMWOAs. Exudation of LMWOAs was negatively affected by inorganic N and decreased by 30–85% compared with the organic N treatment, irrespective of the CO2 treatment. Elevated CO2 had a clear impact on the production of individual LMWOAs, although with very contrasting effects depending on which N source was supplied. [ABSTRACT FROM AUTHOR]

Truffles are hypogeous ectomycorrhizal fungi. They belong to the genus Tuber and are currently considered a hot spot in fungal biology due to their ecological and economic relevance. Among all the species, Tuber magnatum is the most appreciated because of its special taste and aroma. The aim of this work was to set up a protocol to detect T. magnatum in soil and to assess its distribution in a natural truffle-ground. We used the β-tubulin gene as a marker to identify T. magnatum in the soil. This gene allowed us to trace the distribution of the fungus over the entire truffle-ground. Tuber magnatum was found, in one case, 100 m from the productive host plant. This study highlights that T. magnatum mycelium is more widespread than can be inferred from the distribution of truffles and ectomycorrhizas. Interestingly, a new haplotype – never described from fruiting body material – was identified. The specific detection of T. magnatum in the soil will allow to unravel the ecology of this fungus, following its mycelial network. Moreover, this new tool may have practical importance in projects aimed to increase large-scale truffle production, checking for T. magnatum persistence in plantations. [ABSTRACT FROM AUTHOR]

The introduction of photosynthates through plant roots is a major source of carbon (C) for soil microbial biota and shapes the composition of fungal and bacterial communities in the rhizosphere. Although the importance of this process, especially to ectomycorrhizal fungi, has been known for some time, the extent to which plant belowground C allocation controls the composition of the wider soil community is not understood. A tree-girdling experiment enabled studies of the relationship between plant C allocation and microbial community composition. Girdling involves cutting the phloem of trees to prevent photosynthates from entering the soil. Four years after girdling, fungal and bacterial communities were characterized using DNA-based profiles and cloning and sequencing. Data showed that girdling significantly altered fungal and bacterial communities compared with the control. The ratio of ectomycorrhizal to saprobic fungal sequences significantly decreased in girdled treatments, and this decline was found to correlate with the fungal phospholipid fatty acid biomarker 18:2ω6,9. Bacterial communities also varied in the abundance of the two dominant phyla Acidobacteria and Alphaproteobacteria. Concomitant changes in fungal and bacterial communities suggest linkages between these two groups and point toward plant belowground C allocation as a key determinant of microbial community composition. [ABSTRACT FROM AUTHOR]

Interest in stipitate hydnoid fungi of the genera Bankera, Hydnellum, Phellodon and Sarcodon has increased due to the decline in numbers of sporocarps in Europe. Conservation of these fungi is hindered by a lack of understanding of their basic ecology. In particular, a better understanding of their belowground ecology is required. Real-time PCR in conjunction with spatially explicit sampling was used to quantify the relationship between sporocarps and mycelium of Hydnellum peckii and Phellodon tomentosus. Species-specific DNA of the target species was quantified in 100 soil samples collected on a 360 × 360 cm grid at five locations where sporocarps were present. All sporocarps within the grid and up to 2 m around the grid were mapped. Sporocarp production did not occur over the whole extent of the belowground mycelium of these two species, and mycelium extended up to 330 cm away from the immediate site of sporocarp production. Spatial analyses using Kernel-smoothing and Moran's I correlograms showed that, with a single exception, there was no quantitative relationship between sporocarp distribution and the belowground abundance of mycelium. These findings have important implications for the conservation of this rare group of fungi. [ABSTRACT FROM AUTHOR]

Interactions between host tree species and ectomycorrhizal fungi are important in structuring ectomycorrhizal communities, but there are only a few studies on host influence of congeneric trees. We investigated ectomycorrhizal community assemblages on roots of deciduous Quercus crassifolia and evergreen Quercus laurina in a tropical montane cloud forest, one of the most endangered tropical forest ecosystems. Ectomycorrhizal fungi were identified by sequencing internal transcribed spacer and partial 28S rRNA gene. We sampled 80 soil cores and documented high ectomycorrhizal diversity with a total of 154 taxa. Canonical correspondence analysis indicated that oak host was significant in explaining some of the variation in ectomycorrhizal communities, despite the fact that the two Quercus species belong to the same red oak lineage (section Lobatae). A Tuber species, found in 23% of the soil cores, was the most frequent taxon. Similar to oak-dominated ectomycorrhizal communities in temperate forests, Thelephoraceae, Russulaceae and Sebacinales were diverse and dominant. [ABSTRACT FROM AUTHOR]

We studied the effect of ectomycorrhizal fungi on bacterial communities colonizing roots of Douglas fir ( Pseudotsuga menziesii). Mycorrhizal tips were cleaned of soil and separated based on gross morphological characteristics. Sequencing of the internal transcribed spacers of the nuclear rRNA gene cluster indicated that the majority of the tips were colonized by fungi in the Russulaceae, with the genera Russula and Lactarius comprising 70% of the tips. Because coamplification of organellar 16S rRNA genes can interfere with bacterial community analysis of root tips, we developed and tested a new primer pair that permits amplification of bacterial 16S rRNA genes but discriminates more effectively against organellar sequences than commonly used bacterial primer sets. We then used terminal restriction fragment length polymorphism (T-RFLP) and sequence analysis of the 16S rRNA gene to examine differences in bacterial communities associated with the mycorrhizal tips. Cluster analysis of T-RFLP profiles indicated that there were different bacterial communities among the root tips; however, the communities did not seem to be affected by the taxonomic identity of the ectomycorrhizal fungi. Terminal restriction fragment profiling and sequencing of cloned partial 16S rRNA genes indicated that most bacteria on the ectomycorrhizal tips were related to the Alphaproteobacteria and the Bacteroidetes group. [ABSTRACT FROM AUTHOR]

Carbon (C) availability to ectomycorrhizal fungi is likely to increase at elevated atmospheric CO2. To determine whether there are any broad patterns in species' responses that relate to their ecology, we compared growth, respiration, N uptake and C exudation of 17 fungal isolates in liquid culture. As a surrogate for increased C availability we used three different C:N ratios (10:1, 20:1 and 40:1), moving from conditions of C limitation to conditions of N limitation. Responses were species-specific, and suilloid fungi were the most responsive in terms of growth and respiration. In contrast, a group of eight isolates showed no growth increase above C:N 20:1. This inability to respond was not due to N limitation, although there were marked differences in N uptake between isolates. At higher C availability isolates generally became more efficient in converting C into biomass. Six isolates showed net release of exudates into the culture medium (up to 40% of the C in biomass and respiration). We conclude that the findings were in agreement with field observations, and suggest that pure culture observations can yield ecologically relevant information on how ectomycorrhizal fungi may respond under conditions of elevated CO2. [ABSTRACT FROM AUTHOR]

Extensive knowledge of various ectomycorrhizal fungal communities has been obtained over the past 10 years based on molecular identification of the fungi colonizing fine roots. In contrast, only limited information exists about the species composition of ectomycorrhizal hyphae in soil. This study compared the ectomycorrhizal external mycelial community with the adjacent root-tip community in a Danish beech forest. Sand-filled in-growth mesh bags were used to trap external mycelia by incubating the mesh bags in the soil for 70 days. The adjacent ectomycorrhizal root-tip communities were recorded at the times of insertion and retrieval of the mesh bags. Ectomycorrhizal fungi were identified by sequencing the internal transcribed spacer region. In total, 20, 31 and 24 ectomycorrhizal species were recorded from the two root-tip harvests and from the mesh bags, respectively. Boletoid species were significantly more frequent as mycelia than as root tips, while russuloid and Cortinarius species appeared to be less dominant as mycelia than as root tips. Tomentella species were equally frequent as root tips and as mycelia. These discrepancies between the root-tip and the mycelial view of the ectomycorrhizal fungal community are discussed within the framework of ectomycorrrhizal exploration types. [ABSTRACT FROM AUTHOR]

The hypothesis of the present study was that the termite mounds of Macrotermes subhyalinus (MS) (a litter–forager termite) were inhabited by a specific microflora that could enhance with the ectomycorrhizal fungal development. We tested the effect of this feeding group mound material on (i) the ectomycorrhization symbiosis between Acacia holosericea (an Australian Acacia introduced in the sahelian areas) and two ectomycorrhizal fungal isolates of Scleroderma dictyosporum (IR408 and IR412) in greenhouse conditions, (ii) the functional diversity of soil microflora and (iii) the diversity of fluorescent pseudomonads. The results showed that the termite mound amendment significantly increased the ectomycorrhizal expansion. MS mound amendment and ectomycorrhizal inoculation induced strong modifications of the soil functional microbial diversity by promoting the multiplication of carboxylic acid catabolizing microorganisms. The phylogenetic analysis showed that fluorescent pseudomonads mostly belong to the Pseudomonads monteillii species. One of these, P. monteillii isolate KR9, increased the ectomycorrhizal development between S. dictyosporum IR412 and A. holosericea. The occurrence of MS termite mounds could be involved in the expansion of ectomycorrhizal symbiosis and could be implicated in nutrient flow and local diversity. [ABSTRACT FROM AUTHOR]

Mycorrhization helper bacteria, Paenibacillus sp. EJP73 and Burkholderia sp. EJP67, were used to study the importance of bacterial inoculum dose and bacterial derived soluble and volatile metabolites localization for enhancing mycorrhiza formation in the Pinus sylvestris- Lactarius rufus symbiosis, using a laboratory based microcosm. EJP73 and EJP67 produced different responses in relation to the inoculum dose; EJP73 significantly enhanced mycorrhiza formation to the same degree at all doses tested (105, 107, 109 and 1010 CFU mL−1), whereas, EJP67 only stimulated mycorrhiza formation within a narrow range of inoculum densities (107 and 109 CFU mL−1). The importance of soluble bacterial metabolites was assessed by applying spent broth derived from exponential and stationary phase bacterial cultures to microcosms. No spent broth enhanced mycorrhiza formation over the control. As EJP73 produced the helper effect over a wide range of inoculum doses, this bacterium was chosen for further study. Physical separation of EJP73 from the fungal and plant symbiosis partners was carried out, in order to determine the contribution of constitutively produced bacterial volatile metabolites to the mycorrhization helper bacteria effect. When EJP73 was physically separated from the symbiosis, it had a significant negative effect on mycorrhiza formation. These results suggest that close proximity, or indeed cell contact, is required for the helper effect. Therefore, fluorescent in situ hybridization in conjunction with cryosectioning was used to determine the localization of EJP73 in mycorrhizal tissue. The cells were found to occur as rows or clusters (∼10 cells) within the mycorrhizal mantle, both at the root tip and along the length of the mycorrhizal short roots. [ABSTRACT FROM AUTHOR]

The diversity of cultivable endobacteria associated with four different ectomycorrhizal morphotypes ( Suillus flavidus, Suillus variegatus, Russula paludosa and Russula sp.) of Scots pine ( Pinus sylvestris) was analysed by restriction fragment length polymorphism profiling of PCR-amplified rDNA intergenic spacer regions and by sequence analyses of 16S rRNA genes. Ectomycorrhizal root tip surface-sterilization methods were developed and assessed for their efficiencies. Bacterial communities from surface-sterilized ectomycorrhizal root tips were different from those of ectomycorrhizal root tips without surface-sterilization for all the morphotypes studied. Endobacteria belonging to the genera Pseudomonas, Burkholderia and Bacillus were isolated from more than one ectomycorrhizal morphotype, whereas species of Rahnella, Janthinobacterium and Rhodococcus were only isolated from the single morphotypes of S. variegatus, R. paludosa and Russula sp., respectively. Some of the isolated endobacteria utilized fungal sugars more readily than typical plant sugars in carbon utilization assays. [ABSTRACT FROM AUTHOR]

Survival of the ectomycorrhizal fungal strain Suillus collinitus Sc-32 on Pinus halepensis after inoculation and outplanting was monitored in a Mediterranean plantation. Three molecular fingerprints were developed: RFLP of the internal transcribed spacer ribosomal DNA, intersimple sequence repeat, and a specific sequence-characterized amplified region marker. The inoculant was demonstrated to survive on inoculated seedlings 4 years after outplanting (56 months after inoculation), although S. collinitus was not fruiting. The designed markers set allows reliable and inexpensive monitoring of inoculated seedlings and suggests that S. collinitus is suitable for inoculation of Mediterranean Pinus. These data are discussed in the framework of suilloid population ecology. [ABSTRACT FROM AUTHOR]

Ectomycorrhizal fungal (EMF) communities are highly diverse at the stand level. To begin to understand what might lead to such diversity, and to improve sampling designs, we investigated the spatial structure of these communities. We used EMF community data from a number of studies carried out in seven mature and one recently fire-initiated forest stand. We applied various measures of spatial pattern to characterize distributions at EMF community and species levels: Mantel tests, Mantel correlograms, variance/mean and standardized variograms. Mantel tests indicated that in four of eight sites community similarity decreased with distance, whereas Mantel correlograms also found spatial autocorrelation in those four plus two additional sites. In all but one of these sites elevated similarity was evident only at relatively small spatial scales (<2.6 m), whereas one exhibited a larger scale pattern (∼25 m). Evenness of biomass distribution among cores varied widely among taxa. Standardized variograms indicated that most of the dominant taxa showed patchiness at a scale of less than 3 m, with a range from 0 to ⩾17 m. These results have implications for both sampling scale and intensity to achieve maximum efficiency of community sampling. In the systems we examined, cores should be at least 3 m apart to achieve the greatest sampling efficiency for stand-level community analysis. In some cases even this spacing may result in reduced sampling efficiency arising from patterns of spatial autocorrelation. Interpretation of the causes and significance of these patterns requires information on the genetic identity of individuals in the communities. [Copyright &y& Elsevier]

The aim of this work was to investigate the quantitative relationships between the rates of fungal soil exploration and their effects on plant growth and phosphorus (P) nutrition in soil with varying P availability. Ectomycorrhizal associations were established between Pinus pinaster and the basidiomycete Hebeloma cylindrosporum. Plants were grown for 4 and 6 months in mini-rhizoboxes filled with a 0.5 mm soil layer with two contrasting P levels (−P and +P soils), containing 3 or 50 mg of bicarbonate extractable P per kg of dry soil, respectively. Surface areas of the soil layers colonised by the roots and the hyphae were estimated using image analysis.High P availability decreased the rates of fungal soil colonisation, calculated as 0.92 ± 0.19 cm2 day−1 plant−1 in the −P soil and 0.42 ± 0.1 cm2 day−1 plant−1 in the +P soil over the 4–6 months period. Four-month old mycorrhizal plants accumulated lower amounts of biomass and total P than non-mycorrhizal plants, regardless the level of P availability. By contrast, 6-month old mycorrhizal plants were larger and contained more P than non-mycorrhizal plants, especially in the +P soil. However, mycorrhizal plants were always different from non-mycorrhizal P-deficient plants, which had an increased root surface and root P allocation. To explain these contradictory results, we propose that P accumulation by mycorrhizal plants derives mainly from fungal P uptake. The net P transfer from the fungus to the plant was estimated as 0.36 and 0.66 μmol of P per cm2 of mycelium in −P and +P soil, respectively. Our data demonstrated that, despite the inhibitory effect of the high soil P availability on the rates of fungal soil colonisation, the ectomycorrhizal symbiosis was more efficient to improve host plant P nutrition in these conditions. [Copyright &y& Elsevier]

The aim of this study was to identify ectomycorrhizal species with a potential to release elements from apatite and wood ash and accumulate them in the mycelia. Fungal rhizomorphs and mycelia were sampled from sand-filled mesh bags with or without amendment of apatite or wood ash. The mesh bags were buried in forest soil in the field for 13 or 24 months. Elemental composition of the samples was analyzed with particle-induced X-ray emission and the fungus was identified by polymerase chain reaction–restriction fragment length polymorphism analysis of the ITS-region of ribosomal DNA. The majority of rhizomorphs and mycelia collected from the mesh bags were of mycorrhizal origin with Paxillus involutus being the most common species (31%). Other identified species were Thelephora terrestris, Suillus granulatus and Tylospora fibillosa. S. granulatus contained 3–15 times more K (3 mg g−1) than the other species and had large calcium-rich crystals deposited on the surface of rhizomorphs when grown in contact with apatite. P. involutus contained the largest amount of Ca (2–7 mg g−1). Wood ash addition increased the amount of Ti, Mn and Pb in the rhizomorphs while apatite addition increased the amount of Ca in the rhizomorphs. The high concentration of K in S. granulatus rhizomorphs suggests that this fungus is a good accumulator of K while P. involutus appeared to accumulate heavy metals originating from wood ash. [Copyright &y& Elsevier]

Plant growth, nutrient uptake, microbial biomass and activity were studied in pot systems containing spruce seedlings colonised with different ectomycorrhizal fungi from an ash-fertilised forest. The seedling root systems were enclosed in mesh bags inside an outer compartment containing crushed, hardened wood ash. Three different species of mycorrhizal fungi and a non-mycorrhizal control were exposed to factorial combinations of ash and N addition. Ash treatment had a highly significant, positive effect on plant growth and on shoot and root concentrations of K, Ca and P, irrespective of mycorrhizal status. Mycorrhizal inoculation had a significant effect on plant growth, which was proportionally greater in the absence of ash. N addition had a significant positive effect on plant biomass in mycorrhizal treatments with ash, but no effect in non-mycorrhizal treatments or most of the mycorrhizal treatments without ash. Piloderma sp. 1, which was earlier found to colonise wood ash granules in field studies, appeared to accumulate Ca from ash in the mycorrhizal roots. 5–6.7% of the total P in the ash was solubilised, with 0.9–1.5% in solution, 3.6–4.6% in the plants and 0.5–1.5% in microbial biomass. Bacterial activity as determined by [3H]-thymidine and [14C]-leucine incorporation was significantly greater in ash treatments than in controls with no ash addition. Principal component analysis (PCA) of phospholipid fatty acids (PLFAs) showed a clear difference in bacterial community structure between samples collected from ash-treated pots and controls without ash. [Copyright &y& Elsevier]

Intensive harvesting of forest residues for energy production may lead to the depletion of organic matter and mineral nutrients in the forest floor. In order to restore nutrient content wood ash has been suggested as a fertiliser. Ectomycorrhizal (EM) fungi are involved in the nutrient uptake of forest trees and this study investigates the influence of intensive harvesting and wood ash fertilisation on the external EM mycelium in forest soil. Nylon mesh bags filled with sand were buried in September 1997 in field plots which had or had not been intensively harvested. The effect of wood ash on the production of external EM mycelium was studied in mesh bags amended with wood ash. Mesh bags were retrieved in May and October 1998. The relative amount of fungal mycelia in the mesh bags was estimated with phospholipid fatty acid analysis. The fungi colonising the mesh bags were mainly (>90%) ectomycorrhizal. Fungal biomass in the mesh bags was low in the spring but high in the autumn. No significant effect on EM fungal biomass was observed in the mesh bags collected from intensively harvested plots compared with those from control plots, but wood ash amendment resulted in 2.4 times more EM fungal biomass (P<0.05). The effect of external EM mycelium on the dissolution of wood ash was studied in mesh bags filled with wood ash, using mesh bags buried in soil isolated from roots as EM-free controls. The external EM mycelium had no effect on the dissolution rate of the wood ash. 80% of the potassium was lost from the wood ash within a month, whereas no phosphorus was lost during the experimental period (up to 13 months). [Copyright &y& Elsevier]

Understanding the post-senescent fate of fungal mycelium is critical to accurately quantifying forest carbon and nutrient cycling, but how this organic matter source decomposes in wood remains poorly studied. In this study, we compared the decomposition of dead fungal biomass (a.k.a. necromass) of two species, Mortierella elongata and Meliniomyces bicolor , in paired wood and soil plots in a boreal forest in northern Minnesota, USA. Mass loss was quantified at four time points over an 8-week incubation and the richness and composition of the fungal communities colonizing fungal necromass were characterized using high-throughput sequencing. We found that the structure of fungal decomposer communities in wood and soil differed, but, in both habitats, there was relatively rapid decay (∼30% remaining after 56 days). Mass loss was significantly faster in soil and for high-quality (i.e. high nitrogen and low melanin) fungal necromass. In both habitats, there was a clear trajectory of early colonization by opportunistic fungal taxa followed by colonization of fungi with greater enzymatic capacities to degrade more recalcitrant compounds, including white-rot and ectomycorrhizal fungi. Collectively, our results indicate that patterns emerging regarding substrate quality effects on fungal necromass decomposition in soil and leaf litter can be largely extended to fungal necromass decomposition in wood. [ABSTRACT FROM AUTHOR]

Boreal forest soils store significant amounts of carbon and are cohabited by saprotrophic and ectomycorrhizal fungi (ECM). The 'Gadgil effect' implies antagonistic interactions between saprotrophic fungi and ECM. Plant photosynthates support the competitive fitness of the ECM, and may also shape the soil bacterial communities. Many 'Gadgil effect' experiments have focused on litter layer (OL) or have litter and root-fragments present, and thus possibly favor the saprotrophs. We compared how the restriction of plant roots and exudates affect soil microbial community structures in organic soil (mixed OF and OH). For this, we established a 3-yr field experiment with 3 different mesh treatments affecting the penetration of plant roots and external fungal hyphae. Exclusion of plant photosynthates induced modest changes in both fungal and bacterial community structures, but not to potential functionality of the microbial community. The microbial community was resilient towards rather short-term disturbances. Contrary to the 'Gadgil effect', mesh treatments restricting the entrance of plant roots and external fungal hyphae did not favor saprotrophs that originally inhabited the soil. Thus, we propose that different substrate preferences (fresh litter vs. fermented or humified soil), rather than antagonism, maintain the spatial separation of saprotrophs and mycorrhizal fungi in boreal forest soils. [ABSTRACT FROM AUTHOR]