Disproportionate abundance between ectomycorrhizal root tips and their associated mycelia

Three New Species of Laccaria (Hydnangiaceae) from India (Darjeeling Hills) Based on Molecular and Morphological Evidence

Three new species of Laccaria infundibuliformis, L. pallidus, and L. darjeelingensis, collected from Darjeeling, India, are described based on morphological and molecular evidence. Laccaria infundibuliformis is characterized by its small infundibuliform basidiocarps, and echinulate basidiospores with spines up to 1.36 µm long. Laccaria pallidus is characterized by medium-sized greyish-red basidiocarps, and echinulate basidiospores with spines up to 1.9 µm long. Laccaria darjeelingensis is characterized by dull red basidiocarps, and echinulate basidiospores with spines up to 1.27 µm long. Altogether, the study shows that these three Laccaria species are previously unknown to science.

Morphology and Molecular Phylogeny Reveal Five New Species of Laccaria (Hydnangiaceae, Agaricales) from Southern China

The genus Laccaria is a type of cosmopolitan and ecologically important fungal group. Members can form ectomycorrhizal associations with numerous trees, and some species are common edible fungi in local markets. Although some new species from China are recently published, the species diversity of Laccaria is still unclear in China. In this study, some samples of Laccaria were collected from southern China, and morphological characteristics and phylogenetic analyses based on the multilocus dataset of ITS-LSU-tef1-rpb2 confirmed five new species. Laccaria miniata, L. nanlingensis and L. neovinaceoavellanea were collected from subtropical broad-leaved forests, and L. rufobrunnea and L. umbilicata were collected from subtropical mixed forests of southwest China. Full descriptions, illustrations, comparisons with similar species and phylogenetic analysis are provided.

An improved method for extraction of soil fungal mycelium

Fungal mycelium is a major component of the soil microbiome. The soil hyphosphere represents a complex and dynamic niche for specific microorganisms, where multitrophic interactions occur, affecting ecosystem processes. However, extracting fungal mycelium from the soil to enable its taxonomical, chemical, and structural characterisation is challenging in the absence of a fast, efficient, and low-cost procedure. In this study, an old method (Bingle and Paul 1985), based on successive soil wet filtrations and density gradient centrifugation, was improved and tested in three different soil types (silty clay, silty clay loam, and loamy sand). The improved method reduced the number of filtrations by about five times and the centrifugation time from 40 min to 1 min. It avoided using any chemical substance which may impair further chemical analyses or DNA isolation and amplification. The method efficiency was about 50 % in the clay and 23 % in the sandy soils. However, a pre-step consisting of removing the fine-root fragments and other debris under the stereomicroscope may increase the method efficiency to more than 65 %, independent of the soil type.•A simple, efficient, and low-cost method suitable for extracting soil mycelium from a large number of samples.•The protocol includes successive soil wet filtrations and sucrose gradient centrifugation.•The method efficiency increases if the fine-root fragments and other debris are previously removed from the soil.

Bacillus thuringiensis CHGP12 uses a multifaceted approach for the suppression of Fusarium oxysporum f. sp. ciceris and to enhance the biomass of chickpea plants

BACKGROUND

Bacillus species synthesize antifungal lipopeptides (LPs) making them a sustainable and eco-friendly management option to combat Fusarium wilt of chickpea.

RESULTS

In this study, 18 endophytic Bacillus strains were assessed for their antifungal activity against Fusarium oxysporum f. sp. ciceris (FOC) associated with Fusarium wilt of chickpea. Among them, 13 strains produced significant inhibition zones in a direct antifungal assay while five strains failed to produce the inhibition of FOC. Bacillus thuringiensis CHGP12 exhibited the highest inhibition 3.45 cm of FOC. The LPs extracted from CHGP12 showed significant inhibition of the pathogen. Liquid chromatography-mass spectrometry (LC-MS) analysis confirmed that CHGP12 possessed the ability to produce fengycin, surfactin, iturin, bacillaene, bacillibactin, plantazolicin, and bacilysin. In an in vitro qualitative assay CHGP12 exhibited the ability to produce lipase, amylase, cellulase, protease, siderophores, and indole 3-acetic acid (IAA). IAA and gibberellic acid (GA) were quantified using ultra-performance liquid chromatography (UPLC) with 370 and 770 ng mL^-1 concentrations of IAA and GA respectively. Furthermore, the disease severity showed a 40% decrease over control in CHGP12 treated plants compared to the control in a glasshouse experiment. Moreover, CHGP12 also exhibited a significant increase in total biomass of the plants namely, root and shoot growth parameters, stomatal conductance, and photosynthesis rate.

CONCLUSION

In conclusion, our findings suggest that B. thuringiensis CHGP12 is a promising strain with high antagonistic and growth-promoting potential against Fusarium wilt of chickpea. © 2022 Society of Chemical Industry.

Do ectomycorrhizal exploration types reflect mycelial foraging strategies?

Ectomycorrhizal exploration types are commonly assumed to denote spatial foraging patterns and resource-related niches of extraradical mycelia. However, empirical evidence of the consistency of foraging strategies within exploration types is lacking. Here, we analysed ectomycorrhizal foraging patterns by incubating root-excluding ingrowth mesh bags filled with six different substrates in mature Picea abies forests. High-throughput sequencing was used to characterise ectomycorrhizal fungal communities in the mesh bags and on adjacent fine roots after one growing season. Contrary to expectations, many ectomycorrhizal genera of exploration types that are thought to produce little extraradical mycelium colonised ingrowth bags extensively, whereas genera commonly associated with ample mycelial production occurred sparsely in ingrowth bags relative to their abundance on roots. Previous assumptions about soil foraging patterns of exploration types do not seem to hold. Instead, we propose that variation in the proliferation of extraradical mycelium is related to intergeneric differences in mycelial longevity and the mobility of targeted resources.

Host genotype interacts with aerial spore communities and influences the needle mycobiome of Norway spruce

The factors shaping the composition of the tree mycobiome are still under investigation. We tested the effects of host genotype, site, host phenotypic traits, and air fungal spore communities on the assembly of the fungi inhabiting Norway spruce needles. We used Norway spruce clones and spore traps within the collection sites and characterized both needle and air mycobiome communities by high‐throughput sequencing of the ITS2 region. The composition of the needle mycobiome differed between Norway spruce clones, and clones with high genetic similarity had a more similar mycobiome. The needle mycobiome also varied across sites and was associated with the composition of the local air mycobiome and climate. Phenotypic traits such as diameter at breast height or crown health influenced the needle mycobiome to a lesser extent than host genotype and air mycobiome. Altogether, our results suggest that the needle mycobiome is mainly driven by the host genotype in combination with the composition of the local air spore communities. Our work highlights the role of host intraspecific variation in shaping the mycobiome of trees and provides new insights on the ecological processes structuring fungal communities inhabiting woody plants.

Deep sequencing across multiple host species tests pine-endophyte specificity

PREMISE

Foliar fungal endophytes vary in their distributions across landscapes or plant host taxa, indicative of specialized ecologies and host specific adaptations. Accounts of specialization, however, depend on the taxonomic breadth and geographic range of the host plants included in each study. A broad region-scale study or deep sampling of diverse potential host species still remains relatively rare but is becoming increasingly possible with high-throughput sequencing.

METHODS

Amplicon sequencing was used to rapidly identify the fungal endophytic community among six pine (Pinus, Pinaceae) species co-occurring across northeastern United States and to test for site and host specialization. We focused on the endophytic genus Lophodermium (Rhytismataceae), whose species members are thought to specialize on different pine species, to test if amplicon sequencing could rapidly verify previously implied or discover new patterns of host specificity.

RESULTS

While amplicon sequencing could analyze more samples at greater depths and recover greater numbers of unique Lophodermium taxa than when endophyte communities were surveyed with traditional culturing methods, patterns of specialization were not better supported. This may be because amplicon sequencing can indiscriminately capture non-host specific organisms found incidentally from plant tissues or because we have overestimated host-specificity in the past with biased culturing techniques.

CONCLUSIONS

Amplicon sequencing can quickly identify patterns of host specificity by allowing large-scale surveys but has limitations in quantifying the level of intimacy of these relationships.

Fungal biodiversity and conservation mycology in light of new technology, big data, and changing attitudes

Fungi have successfully established themselves across seemingly every possible niche, substrate, and biome. They are fundamental to biogeochemical cycling, interspecies interactions, food production, and drug bioprocessing, as well as playing less heroic roles as difficult to treat human infections and devastating plant pathogens. Despite community efforts to estimate and catalog fungal diversity, we have only named and described a minute fraction of the fungal world. The identification, characterization, and conservation of fungal diversity is paramount to preserving fungal bioresources, and to understanding and predicting ecosystem cycling and the evolution and epidemiology of fungal disease. Although species and ecosystem conservation are necessarily the foundation of preserving this diversity, there is value in expanding our definition of conservation to include the protection of biological collections, ecological metadata, genetic and genomic data, and the methods and code used for our analyses. These definitions of conservation are interdependent. For example, we need metadata on host specificity and biogeography to understand rarity and set priorities for conservation. To aid in these efforts, we need to draw expertise from diverse fields to tie traditional taxonomic knowledge to data obtained from modern -omics-based approaches, and support the advancement of diverse research perspectives. We also need new tools, including an updated framework for describing and tracking species known only from DNA, and the continued integration of functional predictions to link genetic diversity to functional and ecological diversity. Here, we review the state of fungal diversity research as shaped by recent technological advancements, and how changing viewpoints in taxonomy, -omics, and systematics can be integrated to advance mycological research and preserve fungal biodiversity.

A fresh outlook on the smooth-spored species of Inocybe: type studies and 18 new species

On the basis of detailed morphological and molecular investigation, eighteen new species of Inocybe (I. alberichiana, I. beatifica, I. bellidiana, I. clandestina, I. drenthensis, I. dryadiana, I. gaiana, I. ghibliana, I. grusiana, I. knautiana, I. lampetiana, I. oetziana, I. orionis, I. plurabellae, I. rivierana, I. scolopacis, I. sitibunda and I. tiburtina) are described. All of them are smooth-spored, and most of them are pruinose only in the apical part of the stipe. The new species are compared to 40 type specimens, all of which are described here and for several of which (partial) ITS sequences have been generated. For eight species, epi-, lecto- or neotypes were selected, among these are I. geophylla, I. glabripes and I. tigrina. Based on these studies, we suggest twelve synonymies, i.e. that I. clarkii is synonymous with I. sindonia, I. conformata with I. cincinnata, I. elegans with I. griseolilacina, I. fuscidula with I. glabripes, I. griseotarda with I. psammobrunnea, I. obscurella with I. obscuroides, I. obscuromellea with I. semifulva, I. patibilis and I. tigrinella with I. tigrina, I. petroselinolens with I. tenuicystidiata and I. rubidofracta with I. pseudorubens and I. subporospora is synonymized with I. tjallingiorum. All of the new species are supported by phylogenetic analyses. Among the previously described species accepted here, sixteen are represented by types in the phylogenetic analyses and ten by own collections morphologically corresponding to the type. In summary, we here verify or provide morphological concepts associated with molecular data for 44 smooth-spored species of Inocybe.

Soil fungal networks moderate density-dependent survival and growth of seedlings

Pathogenic and mutualistic fungi have contrasting effects on seedling establishment, but it remains unclear whether density-dependent survival and growth are regulated by access to different types of mycorrhizal fungal networks supported by neighbouring adult trees. Here, we conducted an extensive field survey to test how mycorrhizal and pathogenic fungal colonization of arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) seedlings in a subtropical forest respond to density of neighbouring adult trees. In addition, we undertook a hyphal exclusion experiment to explicitly test the role of soil fungal networks in driving density-dependent effects on seedling growth and survival. Conspecific adult density was a strong predictor for the relative abundance of putative pathogens, which was greater in roots of AM than of ECM seedlings, while mycorrhizal fungal abundance and colonization were not consistently affected by conspecific adult density. Both ECM and AM fungal networks counteracted conspecific density-dependent mortality, but ECM fungi were more effective at weakening the negative effects of high seedling density than AM fungi. Our findings reveal a critical role of common fungal networks in mitigating negative density-dependent effects of pathogenic fungi on seedling establishment, which provides mechanistic insights into how soil fungal diversity shapes plant community structure in subtropical forests.

Species diversity of fungal endophytes across a stress gradient for plants

Foliar fungal endophytes are one of the most diverse guilds of symbiotic fungi found in the photosynthetic tissues of every plant lineage, but it is unclear how plant environments and leaf resource availability shape their diversity. We explored correlations between leaf nutrient availability and endophyte diversity among Pinus muricata and Vaccinium ovatum plants growing across a soil nutrient gradient spanning a series of coastal terraces in Mendocino, California. Endophyte richness decreased in plants with higher leaf nitrogen-to-phosphorus ratios for both host species, but increased with sodium, which may be toxic to fungi at high concentrations. Isolation frequency, a proxy of fungal biomass, was not significantly predicted by any of the same leaf constituents in the two plant species. We propose that stressed plants can exhibit both low foliar nutrients or high levels of toxic compounds, and that both of these stress responses predict endophyte species richness. Stressful conditions that limit growth of fungi may increase their diversity due to the suppression of otherwise dominating species. Differences between the host species in their endophyte communities may be explained by host specificity, leaf phenology, or microclimates.

Production of Fungal Mycelia in a Temperate Coniferous Forest Shows Distinct Seasonal Patterns

In temperate forests, climate seasonality restricts the photosynthetic activity of primary producers to the warm season from spring to autumn, while the cold season with temperatures below the freezing point represents a period of strongly reduced plant activity. Although soil microorganisms are active all-year-round, their expressions show seasonal patterns. This is especially visible on the ectomycorrhizal fungi, the most abundant guild of fungi in coniferous forests. We quantified the production of fungal mycelia using ingrowth sandbags in the organic layer of soil in temperate coniferous forest and analysed the composition of fungal communities in four consecutive seasons. We show that fungal biomass production is as low as 0.029 µg g-1 of sand in December-March, while it reaches 0.122 µg g-1 in June-September. The majority of fungi show distinct patterns of seasonal mycelial production, with most ectomycorrhizal fungi colonising ingrowth bags in the spring or summer, while the autumn and winter colonisation was mostly due to moulds. Our results indicate that fungal taxa differ in their seasonal patterns of mycelial production. Although fungal biomass turnover appears all-year-round, its rates are much faster in the period of plant activity than in the cold season.

Alien ectomycorrhizal plants differ in their ability to interact with co-introduced and native ectomycorrhizal fungi in novel sites

Alien plants represent a potential threat to environment and society. Understanding the process of alien plants naturalization is therefore of primary importance. In alien plants, successful establishment can be constrained by the absence of suitable fungal partners. Here, we used 42 independent datasets of ectomycorrhizal fungal (EcMF) communities associated with alien Pinaceae and Eucalyptus spp., as the most commonly introduced tree species worldwide, to explore the strategies these plant groups utilize to establish symbioses with EcMF in the areas of introduction. We have also determined the differences in composition of EcMF communities associated with alien ectomycorrhizal plants in different regions. While alien Pinaceae introduced to new regions rely upon association with co-introduced EcMF, alien Eucalyptus often form novel interactions with EcMF species native to the region where the plant was introduced. The region of origin primarily determines species composition of EcMF communities associated with alien Pinaceae in new areas, which may largely affect invasion potential of the alien plants. Our study shows that alien ectomycorrhizal plants largely differ in their ability to interact with co-introduced and native ectomycorrhizal fungi in sites of introduction, which may potentially affect their invasive potential.

Significant host- and environment-dependent differentiation among highly sporadic fungal endophyte communities in cereal crops-related wild grasses

Endophytic fungi compose a significant part of plant microbiomes. However, while a small number of fungal taxa have proven beneficial impact, the vast majority of fungal endophytes remain uncharacterized, and the drivers of fungal endophyte community (FEC) assembly are not well understood. Here, we analysed FECs in three cereal crops-related wild grasses - Avena sterilis, Hordeum spontaneum and Aegilops peregrina - that grow in mixed populations in natural habitats. Taxa in Ascomycota class Dothideomycetes, particularly the genera Alternaria and Cladosporium, were the most abundant and prevalent across all populations, but there was also high incidence of basidiomyceteous yeasts of the class Tremellomycetes. The fungal community was shaped to large extent by stochastic processes, as indicated by high level of variation even between individuals from local populations of the same plant species, and confirmed by the neutral community model and Raup-Crick index. Nevertheless, we still found strong determinism in FEC assembly with both incidence and abundance data sets. Substantial differences in community composition across host species and locations were revealed. Our research demonstrated that assembly of FECs is affected by stochastic as well as deterministic processes and suggests strong effects of environment heterogeneity and plant species on community composition. In addition, a small number of taxa had high incidence and abundance in all of the 15 populations. These taxa represent an important part of the core FEC and might be of general functional importance.

Fine-scale diversity patterns in belowground microbial communities are consistent across kingdoms

The belowground environment is heterogeneous and complex at fine spatial scales. Physical structures, biotic components and abiotic conditions create a patchwork mosaic of potential niches for microbes. Questions remain about mechanisms and patterns of community assembly belowground, including: Do fungal and bacterial communities assemble differently? How do microbes reach the roots of host plants? Within a 4 m2 plot in alpine vegetation, high throughput sequencing of the 16S (bacteria) and ITS1 (fungal) ribosomal RNA genes was used to characterise microbial community composition in roots and adjacent soil of a viviparous host plant (Bistorta vivipara). At fine spatial scales, beta-diversity patterns in belowground bacterial and fungal communities were consistent, although compositional change was greater in bacteria than fungi. Spatial structure and distance-decay relationships were also similar for bacteria and fungi, with significant spatial structure detected at <50 cm among root- but not soil-associated microbes. Recruitment of root microbes from the soil community appeared limited at this sampling and sequencing depth. Possible explanations for this include recruitment from low-abundance populations of soil microbes, active recruitment from neighbouring plants and/or vertical transmission of symbionts to new clones, suggesting varied methods of microbial community assembly for viviparous plants. Our results suggest that even at relatively small spatial scales, deterministic processes play a significant role in belowground microbial community structure and assembly.

Apple endophyte community is shaped by tissue type, cultivar and site and has members with biocontrol potential against Neonectria ditissima

AIMS

This research aimed to identify factors influencing endophyte community structure in apple shoots and the bioactivity of cultured representatives against the fungal pathogen Neonectria ditissima.

METHODS AND RESULTS

The endophyte community in leaves and stems of the apple cultivars 'Royal Gala' and 'Braeburn' were analysed by a cultivation-independent method (PCR-DGGE) which showed that tissue type, cultivar and site were determinant factors, with the endophyte taxa in 'Royal Gala' more variable than that in 'Braeburn', with leaf endophyte communities typically differing from stems in both cultivars. Seasonal (spring vs autumn) and regional (Nelson vs Hawke's Bay) variations were not obvious in woody stems. A collection of 783 bacterial and 87 fungal endophytes were recovered from leaves and stems of 'Royal Gala', 'Braeburn', 'Scilate' and/or 'Scifresh' from Nelson (nine sites) and Hawke's Bay (five sites) in spring and from Nelson (three sites) in autumn. A dual culture plating assay was used to test their ability to inhibit the mycelial growth of N. ditissima. Thirteen bacterial (mean of percent inhibition ≥20%) and 17 fungal isolates were antagonistic towards N. ditissima. These isolates belonged to the bacterial genera Bacillus and Pseudomonas, and fungal genera Chaetomium, Epicoccum, Biscogniauxia, Penicillium, Diaporthe, Phlyctema and two unidentified fungal isolates.

CONCLUSIONS

Endophyte communities in apple shoots were determined by tissue type, cultivar and site. Endophytic bacterial and fungal isolates inhibiting N. ditissima growth in vitro were found.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results provided new evidence of factors influencing apple endophyte community in New Zealand. Endophytes with potential to reduce N. ditissima infection were identified, with the potential to be developed into a biocontrol strategy for European canker.

Fungal diversity in canopy soil of silver beech, Nothofagus menziesii (Nothofagaceae)

Adventitious roots in canopy soils associated with silver beech (Nothofagus menziesii Hook.f. (Nothofagaceae)) form ectomycorrhizal associations. We investigated the extent to which canopy ectomycorrhizal communities contribute to overall diversity of ectomycorrhizal fungi associated with silver beech. Hyphal ingrowth bags were buried for 12 months in canopy and terrestrial soils of five trees at one site. We used amplicon sequencing of the nuclear ribosomal internal transcribed spacer 2 region (ITS2) to assess diversity of both ectomycorrhizal and non-ectomycorrhizal OTUs in hyphal ingrowth bags. There was a significant difference in ectomycorrhizal fungal community diversity between the terrestrial and canopy hyphal ingrowth bag communities. Ectomycorrhizal community composition of the terrestrial and canopy environments was also significantly different. Some ectomycorrhizal taxa were significantly differentially represented in either the terrestrial or canopy environment. The hyphal ingrowth bags also accumulated non-ectomycorrhizal species. The non-ectomycorrhizal fungi also had significantly different diversity and community composition between the canopy and terrestrial environments. Like the ectomycorrhizal community, some non-ectomycorrhizal taxa were significantly differentially represented in either the terrestrial or canopy environment. The canopy soil microhabitat provides a novel environment for growth of ectomycorrhizal adventitious roots and enables the spatial partitioning of ectomycorrhizal and non-ectomycorrhizal fungal diversity in the forest.

Fungal community assembly in drought-stressed sorghum shows stochasticity, selection, and universal ecological dynamics

Community assembly of crop-associated fungi is thought to be strongly influenced by deterministic selection exerted by the plant host, rather than stochastic processes. Here we use a simple, sorghum system with abundant sampling to show that stochastic forces (drift or stochastic dispersal) act on fungal community assembly in leaves and roots early in host development and when sorghum is drought stressed, conditions when mycobiomes are small. Unexpectedly, we find no signal for stochasticity when drought stress is relieved, likely due to renewed selection by the host. In our experimental system, the host compartment exerts the strongest effects on mycobiome assembly, followed by the timing of plant development and lastly by plant genotype. Using a dissimilarity-overlap approach, we find a universality in the forces of community assembly of the mycobiomes of the different sorghum compartments and in functional guilds of fungi.

Fungal community assembly on crop plants is thought to be driven by deterministic selection exerted by the host. Here Gao et al. use a sorghum system to show that stochastic forces act on fungal community assembly in leaves and roots early in host development and when sorghum is drought stressed.

Genotypic variation in Norway spruce correlates to fungal communities in vegetative buds

The taxonomically diverse phyllosphere fungi inhabit leaves of plants. Thus, apart from the fungi's dispersal capacities and environmental factors, the assembly of the phyllosphere community associated with a given host plant depends on factors encoded by the host's genome. The host genetic factors and their influence on the assembly of phyllosphere communities under natural conditions are poorly understood, especially in trees. Recent work indicates that Norway spruce (Picea abies) vegetative buds harbour active fungal communities, but these are hitherto largely uncharacterized. This study combines internal transcribed spacer sequencing of the fungal communities associated with dormant vegetative buds with a genome-wide association study (GWAS) in 478 unrelated Norway spruce trees. The aim was to detect host loci associated with variation in the fungal communities across the population, and to identify loci correlating with the presence of specific, latent, pathogens. The fungal communities were dominated by known Norway spruce phyllosphere endophytes and pathogens. We identified six quantitative trait loci (QTLs) associated with the relative abundance of the dominating taxa (i.e., top 1% most abundant taxa). Three additional QTLs associated with colonization by the spruce needle cast pathogen Lirula macrospora or the cherry spruce rust (Thekopsora areolata) in asymptomatic tissues were detected. The identification of the nine QTLs shows that the genetic variation in Norway spruce influences the fungal community in dormant buds and that mechanisms underlying the assembly of the communities and the colonization of latent pathogens in trees may be uncovered by combining molecular identification of fungi with GWAS.

Fungal functional ecology: bringing a trait-based approach to plant-associated fungi

Fungi play many essential roles in ecosystems. They facilitate plant access to nutrients and water, serve as decay agents that cycle carbon and nutrients through the soil, water and atmosphere, and are major regulators of macro-organismal populations. Although technological advances are improving the detection and identification of fungi, there still exist key gaps in our ecological knowledge of this kingdom, especially related to function. Trait-based approaches have been instrumental in strengthening our understanding of plant functional ecology and, as such, provide excellent models for deepening our understanding of fungal functional ecology in ways that complement insights gained from traditional and -omics-based techniques. In this review, we synthesize current knowledge of fungal functional ecology, taxonomy and systematics and introduce a novel database of fungal functional traits (Fun^Fun ). Fun^Fun is built to interface with other databases to explore and predict how fungal functional diversity varies by taxonomy, guild, and other evolutionary or ecological grouping variables. To highlight how a quantitative trait-based approach can provide new insights, we describe multiple targeted examples and end by suggesting next steps in the rapidly growing field of fungal functional ecology.

Patterns in Ectomycorrhizal Diversity, Community Composition, and Exploration Types in European Beech, Pine, and Spruce Forests

Ectomycorrhizal (EM) fungi are pivotal drivers of ecosystem functioning in temperate and boreal forests. They constitute an important pathway for plant-derived carbon into the soil and facilitate nitrogen and phosphorus acquisition. However, the mechanisms that drive ectomycorrhizal diversity and community composition are still subject to discussion. We investigated patterns in ectomycorrhizal diversity, community composition, and exploration types on root tips in Fagus sylvatica,Picea abies, and Pinus sylvestris stands across Europe. Host tree species is the most important factor shaping the ectomycorrhizal community as well as the distribution of exploration types. Moreover, abiotic factors such as soil properties, N deposition, temperature, and precipitation, were found to significantly influence EM diversity and community composition. A clear differentiation into functional traits by means of exploration types was shown for all ectomycorrhizal communities across the three analyzed tree species. Contact and short-distance exploration types were clearly significantly more abundant than cord- or rhizomorph-forming long-distance exploration types of EM fungi. Medium-distance exploration types were significantly lower in abundance than contact and short-distance types, however they were the most frequent EM taxa and constituted nearly half of the EM community. Furthermore, EM taxa exhibit distinct ecological ranges, and the type of soil exploration seemed to determine whether EM taxa have small or rather big environmental ranges.

Distributions of ectomycorrhizal and foliar endophytic fungal communities associated with Pinus ponderosa along a spatially constrained elevation gradient

PREMISE OF THE STUDY

Understanding distributions of plant-symbiotic fungi is important for projecting responses to environmental change. Many coniferous trees host ectomycorrhizal fungi (EM) in association with roots and foliar endophytic fungi (FE) in leaves. We examined how EM and FE associated with Pinus ponderosa each vary in abundance, diversity, and community structure over a spatially constrained elevation gradient that traverses four plant communities, 4°C in mean annual temperature, and 15 cm in mean annual precipitation.

METHODS

We sampled 63 individuals of Pinus ponderosa in 10 sites along a 635 m elevation gradient that encompassed a geographic distance of 9.8 km. We used standard methods to characterize each fungal group (amplified and sequenced EM from root tips; isolated and sequenced FE from leaves).

KEY RESULTS

Abundance and diversity of EM were similar across sites, but community composition and distributions of the most common EM differed with elevation (i.e., with climate, soil chemistry, and plant communities). Abundance and composition of FE did not differ with elevation, but diversity peaked in mid-to-high elevations.

CONCLUSIONS

Our results suggest relatively tight linkages between EM and climate, soil chemistry, and plant communities. That FE appear less linked with these factors may speak to limitations of a culture-based approach, but more likely reflects the small spatial scale encompassed by our study. Future work should consider comparable methods for characterizing these functional groups, and additional transects to understand relationships of EM and FE to environmental factors that are likely to shift as a function of climate change.

Guild Patterns of Basidiomycetes Community Associated With Quercus mongolica in Mt. Jeombong, Republic of Korea

Depending on the mode of nutrition exploitation, major fungal guilds are distinguished as ectomycorrhizal and saprotrophic fungi. It is generally known that diverse environmental factors influence fungal communities; however, it is unclear how fungal communities respond differently to environment factors depend on fungal guilds. In this study, we investigated basidiomycetes communities associated with Quercus mongolica using 454 pyrosequencing. We attempted to detect guild pattern (ectomycorrhizal or saprotrophic fungal communities) by comparing the influence of geography and source (root and surrounding soil). A total of 515 mOTUs were detected from root (321) and soil (394) of Q. mongolica at three sites of Mt. Jeombong in Inje County. We found that patterns of diversity and community structure were different depending on the guilds. In terms of alpha diversity, only ectomycorrhizal fungi showed significant differences between sources. In terms of community structure, however, geography significantly influenced the ectomycorrhizal community, while source appeared to have a greater influence on the saprotrophic community. Therefore, a guild-based view will help to elucidates novel features of the relationship between environmental factors and fungal communities.

Seasonal dynamics of extraradical mycelium and mycorrhizas in a black truffle (Tuber melanosporum) plantation

Seasonal dynamics of black truffle (Tuber melanosporum) extraradical mycelium as well as the associated mycorrhizal community have been evaluated in a 16-year-old plantation with productive and non-productive trees. Mycelium biomass was seasonally quantified by real-time PCR over two consecutive years and the correlation with environmental variables explored. Extraradical mycelium biomass varied seasonally and between the two consecutive years, being correlated with the precipitation that occurred 1 month before sampling. In addition, productive trees had more mycelium in the brûlé area than non-productive trees did. The ectomycorrhizal community composition inside the burnt areas was seasonally evaluated during a year. Ten mycorrhizal morphotypes were detected; T. melanosporum was the most abundant in productive and non-productive trees. Black truffle mycorrhizas were more abundant (mycorrhizal tips per unit of soil volume) in productive trees, and no seasonal variation was observed. The occurrence of black truffle mycorrhizas was significantly and positively correlated with the biomass of extraradical mycelium. The mycorrhizal community within the brûlé areas was significantly different between productive and non-productive trees, and no variation was detected between seasons. The assessment of the fungal vegetative structures in a mature plantation is of paramount importance to develop trufficulture methods based on the knowledge of the biological cycle of the fungus and its relationships with the associated ectomycorrhizal communities.

Changes in turnover rather than production regulate biomass of ectomycorrhizal fungal mycelium across a Pinus sylvestris chronosequence

In boreal forest soils, ectomycorrhizal fungi are fundamentally important for carbon (C) dynamics and nutrient cycling. Although their extraradical mycelium (ERM) is pivotal for processes such as soil organic matter build-up and nitrogen cycling, very little is known about its dynamics and regulation. In this study, we quantified ERM production and turnover, and examined how these two processes together regulated standing ERM biomass in seven sites forming a chronosequence of 12- to 100-yr-old managed Pinus sylvestris forests. This was done by determining ERM biomass, using ergosterol as a proxy, in sequentially harvested in-growth mesh bags and by applying mathematical models. Although ERM production declined with increasing forest age from 1.2 to 0.5 kg ha^-1  d^-1 , the standing biomass increased from 50 to 112 kg ha^-1 . This was explained by a drastic decline in mycelial turnover from seven times to one time per year with increasing forest age, corresponding to mean residence times from 25 d up to 1 yr. Our results demonstrate that ERM turnover is the main factor regulating biomass across differently aged forest stands. Explicit inclusion of ERM parameters in forest ecosystem C models may significantly improve their capacity to predict responses of mycorrhiza-mediated processes to management and environmental changes.

Host associations and beta diversity of fungal endophyte communities in New Guinea rainforest trees

Processes shaping the distribution of foliar fungal endophyte species remain poorly understood. Despite increasing evidence that these cryptic fungal symbionts of plants mediate interactions with pathogens and herbivores, there remain basic questions regarding the extent to which dispersal limitation and host specificity might shape fungal endophyte community composition in rainforests. To assess the relative importance of spatial pattern and host specificity, we isolated fungi from a sample of mapped trees in lowland Papua New Guinea. Sequences of the internal transcribed spacer (ITS) region were obtained for 2079 fungal endophytes from three sites and clustered into molecular operational taxonomic units (MOTUs) at 95% similarity. Multivariate analyses suggest that host affinity plays a significant role in structuring endophyte community composition whereas there was no evidence of endophyte spatial pattern at the scale of tens to hundreds of metres. Differences in endophyte communities between sampled trees were weakly correlated with variation in foliar traits but not with tree species relatedness. The dominance of relatively few generalist endophytes and the presence of a large number of rare MOTUs was a consistent observation at three sites separated by hundreds of kilometres and regional turnover was low. Host specificity appears to play a relatively weak but more important role than dispersal limitation in shaping the distribution of fungal endophyte communities in New Guinea forests. Our results suggest that in the absence of strong ecological gradients and host turnover, beta diversity of endophyte communities could be low in large areas of contiguous forest.

Soil DNA pyrosequencing and fruitbody surveys reveal contrasting diversity for various fungal ecological guilds in chestnut orchards

Fungal diversity in Mediterranean forest soils is poorly documented, particularly when considering saprobic and pathogenic organisms. Next-generation sequencing (NGS) methods applied to soil fungi provide the opportunity to unveil the most inconspicuous functional guilds (e.g. saprobes) and life forms (e.g. Corticiaceae) of this tremendous diversity. We used fruitbody surveys over 2 years and soil 454 metabarcoding in Castanea sativa orchards to evaluate respectively the reproductive (fruitbodies) and vegetative (mycelia) parts of fungal communities in three 100-year-old stands. Analysis of 839 fruitbodies and 210 291 ITS1 reads revealed high fungal diversity, mainly shown by belowground analysis, with high (dominant) abundance of mycorrhizal fruitbodies and reads. Both methods displayed contrasted composition and structure of fungal communities, with Basidio- and Ascomycetes dominating above- and belowground, respectively. For the two dominant fungal guilds (i.e. ectomycorrhizal and saprobic), diversity above- and belowground overlapped weakly. This study is the first assessment of the complementarity of fruitbody surveys and NGS for analysing fungal diversity in Mediterranean ecosystems and shows that belowground methods still need to be completed by fruiting diversity to provide a comprehensive overview of the different fungal guilds. The results shed light on chestnut soil biodiversity and question the spatial distribution and synergies among fungal guilds.

Solving the ecological puzzle of mycorrhizal associations using data from annotated collections and environmental samples - an example of saddle fungi

The relation between ecological and genetic divergence of Helvella species (saddle fungi) has been perplexing. While a few species have been clearly demonstrated to be ectomycorrhizal fungi, ecological roles of many other species have been controversial, alternately considered as either saprotrophic or mycorrhizal. We applied SATé to build an inclusive deoxyribonucleic acid sequence alignment for the internal transcribed spacers (ITS) of annotated Helvella species and related environmental sequences. Phylogenetic informativeness of ITS and its regions were assessed using PhyDesign. Mycorrhizal lineages present a diversity of ecology, host type and geographic distribution. In two Helvella clades, no Helvella ITS sequences were recovered from root tips. Inclusion of environmental sequences in the ITS phylogeny from these sequences has the potential to link these data and reveal Helvella ecology. This study can serve as a model for revealing the diversity of relationships between unculturable fungi and their potential plant hosts. How non-mycorrhizal life styles within Helvella evolved will require expanded metagenomic investigation of soil and other environmental samples along with study of Helvella genomes.

Local-scale biogeography and spatiotemporal variability in communities of mycorrhizal fungi

Knowledge of spatiotemporal patterns in species distribution is fundamental to understanding the ecological and evolutionary processes shaping communities. The emergence of DNA-based tools has expanded the geographic and taxonomic scope of studies examining spatial and temporal distribution of mycorrhizal fungi. However, the nature of spatiotemporal patterns documented and subsequent interpretation of ecological processes can vary significantly from study to study. In order to look for general patterns we synthesize the available data across different sampling scales and mycorrhizal types. The results of this analysis shed light on the relative importance of space, time and vertical soil structure on community variability across different mycorrhizal types. Although we found no significant trend in spatiotemporal variation amongmycorrhizal types, the vertical community variation was distinctly greater than the spatial and temporal variability in mycorrhizal fungal communities. Both spatial and temporal variability of communities was greater in topsoil compared with lower horizons, suggesting that greater environmental heterogeneity drives community variation on a fine scale. This further emphasizes the importance of both niche differentiation and environmental filtering in maintaining diverse fungal communities.

Genetic variation in horizontally transmitted fungal endophytes of pine needles reveals population structure in cryptic species

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PREMISE OF THE STUDY

Fungal endophytes comprise one of the most ubiquitous groups of plant symbionts, inhabiting healthy leaves and stems of all major lineages of plants. Together, they comprise immense species richness, but little is known about the fundamental processes that generate their diversity. Exploration of their population structure is needed, especially with regard to geographic distributions and host affiliations.•

METHODS

We take a multilocus approach to examine genetic variation within and among populations of Lophodermium australe, an endophytic fungus commonly associated with healthy foliage of pines in the southeastern United States. Sampling focused on two pine species ranging from montane to coastal regions of North Carolina and Virginia.•

KEY RESULTS

Our sampling revealed two genetically distinct groups within Lophodermium australe. Our analysis detected less than one migrant per generation between them, indicating that they are distinct species. The species comprising the majority of isolates (major species) demonstrated a panmictic structure, whereas the species comprising the minority of isolates (cryptic species) demonstrated isolation by distance. Distantly related pine species hosted the same Lophodermium species, and host species did not influence genetic structure.•

CONCLUSIONS

We present the first evidence for isolation by distance in a foliar fungal endophyte that is horizontally transmitted. Cryptic species may be common among microbial symbionts and are important to delimit when exploring their genetic structure and microevolutionary processes. The hyperdiversity of endophytic fungi may be explained in part by cryptic species without apparent ecological and morphological differences as well as genetic diversification within rare fungal species across large spatial scales.

Ectomycorrhizal identification in environmental samples of tree roots by Fourier-transform infrared (FTIR) spectroscopy

Roots of forest trees are associated with various ectomycorrhizal (ECM) fungal species that are involved in nutrient exchange between host plant and the soil compartment. The identification of ECM fungi in small environmental samples is difficult. The present study tested the feasibility of attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy followed by hierarchical cluster analysis (HCA) to discriminate in situ collected ECM fungal species. Root tips colonized by distinct ECM fungal species, i.e., Amanita rubescens, Cenococcum geophilum, Lactarius subdulcis, Russula ochroleuca, and Xerocomus pruinatus were collected in mono-specific beech (Fagus sylvatica) and mixed deciduous forests in different geographic areas to investigate the environmental variability of the ECM FTIR signatures. A clear HCA discrimination was obtained for ECM fungal species independent of individual provenance. Environmental variability neither limited the discrimination between fungal species nor provided sufficient resolution to discern species sub-clusters for different sites. However, the de-convoluted FTIR spectra contained site-related spectral information for fungi with wide nutrient ranges, but not for Lactarius subdulcis, a fungus residing only in the litter layer. Specific markers for distinct ECM were identified in spectral regions associated with carbohydrates (i.e., mannans), lipids, and secondary protein structures. The present results support that FTIR spectroscopy coupled with multivariate analysis is a reliable and fast method to identify ECM fungal species in minute environmental samples. Moreover, our data suggest that the FTIR spectral signatures contain information on physiological and functional traits of ECM fungi.

Ectomycorrhizal fungi contribute to soil organic matter cycling in sub-boreal forests

Soils of northern temperate and boreal forests represent a large terrestrial carbon (C) sink. The fate of this C under elevated atmospheric CO2 and climate change is still uncertain. A fundamental knowledge gap is the extent to which ectomycorrhizal fungi (EMF) and saprotrophic fungi contribute to C cycling in the systems by soil organic matter (SOM) decomposition. In this study, we used a novel approach to generate and compare enzymatically active EMF hyphae-dominated and saprotrophic hyphae-enriched communities under field conditions. Fermentation-humus (FH)-filled mesh bags, surrounded by a sand barrier, effectively trapped EMF hyphae with a community structure comparable to that found in the surrounding FH layer, at both trophic and taxonomic levels. In contrast, over half the sequences from mesh bags with no sand barrier were identified as belonging to saprotrophic fungi. The EMF hyphae-dominated systems exhibited levels of hydrolytic and oxidative enzyme activities that were comparable to or higher than saprotroph-enriched systems. The enzymes assayed included those associated with both labile and recalcitrant SOM degradation. Our study shows that EMF hyphae are likely important contributors to current SOM turnover in sub-boreal systems. Our results also suggest that any increased EMF biomass that might result from higher below-ground C allocation by trees would not suppress C fluxes from sub-boreal soils.

Seasonal dynamics of Boletus edulis and Lactarius deliciosus extraradical mycelium in pine forests of central Spain

The annual belowground dynamics of extraradical soil mycelium and sporocarp production of two ectomycorrhizal fungi, Boletus edulis and Lactarius deliciosus, have been studied in two different pine forests (Pinar Grande and Pinares Llanos, respectively) in Soria (central Spain). Soil samples (five per plot) were taken monthly (from September 2009 to August 2010 in Pinar Grande and from September 2010 to September 2011 in Pinares Llanos) in eight permanent plots (four for each site). B. edulis and L. deliciosus extraradical soil mycelium was quantified by real-time polymerase chain reaction, with DNA extracted from soil samples, using specific primers and TaqMan® probes. The quantities of B. edulis soil mycelium did not differ significantly between plots, but there was a significant difference over time with a maximum in February (0.1576 mg mycelium/g soil) and a minimum in October (0.0170 mg mycelium/g soil). For L. deliciosus, significant differences were detected between plots and over time. The highest amount of mycelium was found in December (1.84 mg mycelium/g soil) and the minimum in February (0.0332 mg mycelium/g soil). B. edulis mycelium quantities were positively correlated with precipitation of the current month and negatively correlated with the mean temperature of the previous month. Mycelium biomass of L. deliciosus was positively correlated with relative humidity and negatively correlated with mean temperature and radiation. No significant correlation between productivity of the plots with the soil mycelium biomass was observed for any of the two species. No correlations were found between B. edulis sporocarp production and weather parameters. Sporocarp production of L. deliciosus was positively correlated with precipitation and relative humidity and negatively correlated with maximum and minimum temperatures. Both species have similar distribution over time, presenting an annual dynamics characterized by a seasonal variability, with a clear increase on the amounts of biomass during the coldest months of the year. Soil mycelial dynamics of both species are strongly dependent on the weather.

Long-term effect of apatite on ectomycorrhizal growth and community structure

Ectomycorrhizal (ECM) fungi are efficient at taking up phosphorus (P) from mineral sources, such as apatite, which are not easily available to the host trees. Since ECM fungal species differ in P uptake rates, it can be expected that the composition of the ECM fungal community will change upon exposure to apatite, provided that the P transfer is rewarded by more carbon being transferred to the fungal symbiont. Control and apatite-amended mesh bags were buried in pairs in the humus layer of a P-poor Norway spruce forest. The ECM fungal community that colonized these bags was analyzed by DNA extraction, PCR amplification of the internal transcribed spacer (ITS) region, cloning, and random sequencing. Fungal biomass was estimated by ergosterol analysis. No change in the ECM fungal community structure was seen after 5 years of apatite exposure, although the fungal biomass increased threefold upon apatite amendment. Our results indicate that host trees enhance carbon allocation to ECM fungi colonizing P sources in P-poor forests but the lack of change in the composition of the ECM fungal community suggests that P transfer rates were similar among the species. Alternatively, higher P transfer among certain species was not rewarded with higher carbon transfer from the host.

Structural and functional interactions between extraradical mycelia of ectomycorrhizal Pisolithus isolates

Extraradical mycelia from different ectomycorrhizal (ECM) roots coexist and interact under the forest floor. We investigated structural connections of conspecific mycelia and translocation of carbon and phosphorus between the same or different genets. Paired ECM Pinus thunbergii seedlings colonized by the same or different Pisolithus isolates were grown side by side in a rhizobox as their mycelia contacted each other. (14)CO(2) or (33)P-phosphoric acid was fed to leaves or a spot on the mycelium in one of the paired seedlings. Time-course distributions of (14)C and (33)P were visualized using a digital autoradiographic technique with imaging plates. Hyphal connections were observed between mycelia of the same Pisolithus isolate near the contact site, but hyphae did not connect between different isolates. (14)C and (33)P were translocated between mycelia of the same isolate. In (33)P-fed mycelia, accumulation of (33)P from the feeding spot toward the host ECM roots was observed. No (14)C and (33)P translocation occurred between mycelia of different isolates. These results provide direct evidence that contact and hyphal connection between mycelia of the same ECM isolate can cause nutrient translocation. The ecological significance of contact between extraradical mycelia is discussed.

Host and geographic structure of endophytic and endolichenic fungi at a continental scale

PREMISE OF THE STUDY

Endophytic and endolichenic fungi occur in healthy tissues of plants and lichens, respectively, playing potentially important roles in the ecology and evolution of their hosts. However, previous sampling has not comprehensively evaluated the biotic, biogeographic, and abiotic factors that structure their communities.

METHODS

Using molecular data we examined the diversity, composition, and distributions of 4154 endophytic and endolichenic Ascomycota cultured from replicate surveys of ca. 20 plant and lichen species in each of five North American sites (Madrean coniferous forest, Arizona; montane semideciduous forest, North Carolina; scrub forest, Florida; Beringian tundra and forest, western Alaska; subalpine tundra, eastern central Alaska).

KEY RESULTS

Endolichenic fungi were more abundant and diverse per host species than endophytes, but communities of endophytes were more diverse overall, reflecting high diversity in mosses and lycophytes. Endophytes of vascular plants were largely distinct from fungal communities that inhabit mosses and lichens. Fungi from closely related hosts from different regions were similar in higher taxonomy, but differed at shallow taxonomic levels. These differences reflected climate factors more strongly than geographic distance alone.

CONCLUSIONS

Our study provides a first evaluation of endophytic and endolichenic fungal associations with their hosts at a continental scale. Both plants and lichens harbor abundant and diverse fungal communities whose incidence, diversity, and composition reflect the interplay of climatic patterns, geographic separation, host type, and host lineage. Although culture-free methods will inform future work, our study sets the stage for empirical assessments of ecological specificity, metabolic capability, and comparative genomics.

Dramatic changes in ectomycorrhizal community composition, root tip abundance and mycelial production along a stand-scale nitrogen deposition gradient

• Nitrogen (N) availability is known to influence ectomycorrhizal fungal components, such as fungal community composition, biomass of root tips and production of mycelia, but effects have never been demonstrated within the same forest. • We measured concurrently the abundance of ectomycorrhizal root tips and the production of external mycelia, and explored the changes in the ectomycorrhizal community composition, across a stand-scale N deposition gradient (from 27 to 43 kg N ha⁻¹ yr⁻¹) at the edge of a spruce forest. The N status was affected along the gradient as shown by a range of N availability indices. • Ectomycorrhizal root tip abundance and mycelial production decreased five and 10-fold, respectively, with increasing N deposition. In addition, the ectomycorrhizal fungal community changed and the species richness decreased. The changes were correlated with the measured indices of N status, in particular N deposition and N leaching. • The relationship between the altered ectomycorrhizal community, root tip abundance and mycelial production is discussed in the context of the N parameters. We suggest that increased N deposition to forests will cause large changes in ectomycorrhizal fungal community structure and functioning, which, in turn, may result in reduced N uptake by roots and fungi, and increased losses of N by leaching.

Quantification of extraradical soil mycelium and ectomycorrhizas of Boletus edulis in a Scots pine forest with variable sporocarp productivity

The availability of most edible ectomycorrhizal mushrooms depends on their natural fructification. Sporocarp formation of these fungi is linked to habitat characteristics and climate conditions, but these data alone do not explain all the trends of fungal fruiting and dynamics. It could be hypothesized that the amount of soil mycelia could also be related to the production of carpophores. Soil samples (five cylinders of 250 cm(3) per plot) were taken monthly, from September to November, in five fenced permanent plots (5 × 5 m) in Pinar Grande (Soria, Spain), a Pinus sylvestris stand situated in the north of the Sistema Ibérico mountain range. Plots were chosen to establish a gradient of Boletus edulis productivity from 0 to 38.5 kg/ha year, according to the mean fresh weight of sporocarps collected during the last 10 years. B. edulis ectomycorrhizal root tips were identified in each soil sample according to its morphology and counted. DNA extractions were performed with the PowerSoil(TM) DNA Isolation Kit and quantification of extraradical soil mycelium by real-time polymerase chain reaction using specific primers and a TaqMan® probe. The concentration of soil mycelium of B. edulis (mg mycelium/g soil) did not differ significantly between plots (p = 0.1397), and sampling time (p = 0.7643) within the fructification period. The number of mycorrhizal short roots per soil volume showed significant differences between the plots (p = 0.0050) and the three sampling times (p < 0.0001). No significant correlation between the number of mycorrhizas and the productivity of the plot (kg of B. edulis/ha year) was detected (p = 0.615). A statistically significant positive correlation (p = 0.0481) was detected between the concentration of mycelia of B. edulis in the soil samples and the presence of short roots mycorrhizal with B. edulis in these samples. The productivity of the plots, in terms of sporocarps produced during the last 10 years, was not correlated either with the concentration of soil mycelium or with the presence or abundance of ectomycorrhizas.

Host preferences and differential contributions of deciduous tree species shape mycorrhizal species richness in a mixed Central European forest

Mycorrhizal species richness and host ranges were investigated in mixed deciduous stands composed of Fagus sylvatica, Tilia spp., Carpinus betulus, Acer spp., and Fraxinus excelsior. Acer and Fraxinus were colonized by arbuscular mycorrhizas and contributed 5% to total stand mycorrhizal fungal species richness. Tilia hosted similar and Carpinus half the number of ectomycorrhizal (EM) fungal taxa compared with Fagus (75 putative taxa). The relative abundance of the host tree the EM fungal richness decreased in the order Fagus > Tilia >> Carpinus. After correction for similar sampling intensities, EM fungal species richness of Carpinus was still about 30-40% lower than that of Fagus and Tilia. About 10% of the mycorrhizal species were shared among the EM forming trees; 29% were associated with two host tree species and 61% with only one of the hosts. The latter group consisted mainly of rare EM fungal species colonizing about 20% of the root tips and included known specialists but also putative non-host associations such as conifer or shrub mycorrhizas. Our data indicate that EM fungal species richness was associated with tree identity and suggest that Fagus secures EM fungal diversity in an ecosystem since it shared more common EM fungi with Tilia and Carpinus than the latter two among each other.