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Abstract

Many ectomycorrhizal fungi (EMF) are generalists, but most plant genera that form ectomycorrhizas have at least some fungal partners that are specific to that host genus. Because shared mycorrhizal fungi mediate plant community interactions, host preference has implications for plant succession and competition. We studied the EMF of oaks (Quercus spp.) and pines (Pinus spp.) in a forest in northern Florida, USA, focusing on symbionts shared with longleaf pine (Pinus palustris Mill.). Longleaf pine is an important species in the southeastern USA, both for timber plantations and for restoring savanna and woodland habitat. However, we found no research on the composition of naturally occurring EMF on longleaf pine roots. A lower proportion of EMF operational taxonomic units (OTUs) were found colonizing both oaks and pines than expected, providing evidence of host preference within the community. Although most EMF were detected only on either oaks or pines, the OTUs found on both tended to be frequently occurring and abundant. Cenococcum OTUs were found to be significantly associated with oaks, an unexpected finding as this genus is widespread, with a broad host range. These results suggest that host preference of EMF may structure EMF communities and therefore influence ecosystem effects of mycorrhizal networks.

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... We conclude that this species is ectomycorrhizal from the placement of GenBank sequence MF946050 which was obtained from an American ectomycorrhizal root tip of Quercus section Lobatae and identified as S. scabrosus in Rasmussen et al. (2018). From field observations we infer that H. fagiscabrosum is a mycorrhizal partner of Fagus sylvatica, Quercus spp. ...
... The true extent of its European distribution is currently unknown due to its former inclusion within the circumscription of S. scabrosus, but we have produced molecular evidence for its presence in Norway, Sweden, UK and Italy and therefore suspect it is a very widespread, albeit relatively uncommon, member of the European Fagaceae-associated stipitate hydnoid community. Placement of GenBank sequences in Fig. 3 demonstrate that H. fagiscabrosum is also present in the southeastern USA in Florida, North Carolina and Tennessee where it has been assigned to S. scabrosus (Hughes et al. 2009, Baird et al. 2013, Rasmussen et al. 2018 Notes: Historically, our species has been included in a broad concept of Sarcodon scabrosus which has an inferred association with both Fagaceae and Pinaceae, at least in Europe. However, based on its protologue, the discussion in Maas Geesteranus & Nannfeldt (1969) and the clustering of a sequence derived from its neotype with several sequences derived from coniferassociated basidiomata and mycorrhizal root samples (see Fig. 3), Hydnellum scabrosum sensu stricto was revealed to be an ectomycorrhizal partner of Pinaceae only. ...
Article
Four new Hydnellum species are described. Hydnellum roseoviolaceum sp. nov. grows in dry pine heaths on acidic, sandy soil. It is close to H. fuligineoviolaceum , another pine-associated species, but differs by smaller spores, an initially rose-coloured instead of violet flesh in fresh basidiomata and a mild taste. Hydnellum scabrosellum sp. nov. grows in coniferous forests on calcareous soil. It shares a general morphology with H. scabrosum , which also is its closest relative. It differs by having smaller and slenderer basidiomata and by the yellowish ochraceous colour of flesh and spines in dried specimens compared to the whitish or reddish brown colour seen in H. scabrosum . Hydnellum fagiscabrosum sp. nov. is another species with morphological and phylogenetic affinities to H. scabrosum . However, it is associated with trees from Fagales whereas H. scabrosum is associated with Pinaceae . Hydnellum nemorosum sp. nov. is yet another species that associates with broadleaved trees. It seems to be a rare species, morphologically reminiscent of H. fuligineoviolaceum , H. ioeides and H. scabrosum , but it is phylogenetically close to H. fennicum . Sequences from the type specimens of H. glaucopus , H. lepidum , H. scabrosum , Sarcodon illudens and S. regalis are included in the analyses. Specimens given the provisional name “ Sarcodon pseudoglaucopus ” in Sweden are now shown to be referable to S. illudens . The analyses further showed that S. illudens is close to H. lepidum . The new combination Hydnellum illudens is proposed. Sarcodon regalis and H. lepidum are shown to be conspecific and, although their basionyms were simultaneously published, the name S. regalis was only validated in a later publication. Hydnellum lepidum therefore takes priority and S. regalis becomes a synonym.
... The lower abundance of Russulaceae taxa in the savanna is notable, as the greater proportion of Pinus would lead us to presume it would be more abundant there as pines favor ectomycorrhiza. However, others have noted, specifically Rasmussen, Busby, & Hoeksema (2018), there are many oak hosts with which Russulaceae pairs. Indeed, ectomycorrhiza are not conifer obligates and their presence in the closed-forest portions of SWMA are not unusual. ...
Article
Due to anthropogenic pressures, by the 1990s longleaf pine forests were at 3% its peak area. Restoration is difficult as vegetation communities constitute a mosaic across the longleaf range. Hence, vegetation description is important wherever longleaf pine communities exist. Vegetation strongly associates with specific soil fungi operational taxonomic units (OTUs) and description of longleaf pine ecosystems are incomplete without description of microbial taxa. My goals were to begin describing soil fungal communities of the longleaf pine at Sheffield Wildlife Management Area (SWMA) and describe changes to the fungal community after the removal of dominant plants in a longleaf savanna. I hypothesized the closed-forest would differ in fungal community composition compared to the savanna restoration area and removal of the dominant plant understory species will result in changes to the relative abundance of fungi communities. I used previous fungi and tree community data, determined ground-cover species dominance, and set up six randomized blocks within the savanna at SWMA. I extracted DNA from soil samples and a third-party lab used ITS gene sequencing to identify fungal taxa. Fungi relative abundance was compared using Kruskal-Wallis tests. Ordinal regression, analysis of variance between ranks, and Tukey HSD post hoc compared fungal taxa of interest. This work indicates fungal communities are resilient and fungi representing the family Russulaceae play a large role in these assemblages. Outside of findings that support a difference in closed-forested areas versus savanna areas with respect to unclassified fungal families, I was unable to reject the null for my other hypotheses.
... van der Linde [50] also reported that only approximately 10% of EMF are host-specific. However, this is in contrast to our main hypothesis that is based on the theory of the fungi's evolutionary history and previous findings, where AMF are commonly assumed to be generalists, whereas EMF are host-specific [48,51]. Generalistic AMF were also confirmed by Weißbecker et al. [6], who used the same measure of species specialisation, but analysed soil from the root zone. ...
Article
Plant diversity and plant-related ecosystem functions have been important in biodiversity-ecosystem functioning studies. However, biotic interactions with mycorrhizal fungi have been understudied although they are crucial for plant-resource acquisition. Here, we investigated the effects of tree species richness and tree mycorrhizal type on arbuscular (AMF) and ectomycorrhizal fungal (EMF) communities. We aimed to understand how dissimilarities in taxa composition and beta-diversity are related to target trees and neighbours of the same or different mycorrhizal type. We sampled a tree diversity experiment with saplings (~7 years old), where tree species richness (monocultures, 2-species, and 4-species mixtures) and mycorrhizal type were manipulated. AMF and EMF richness significantly increased with increasing tree species richness. AMF richness of mixture plots resembled that of the sum of the respective monocultures, whereas EMF richness of mixture plots was lower compared to the sum of the respective monocultures. Specialisation scores revealed significantly more specialised AMF than EMF suggesting that, in contrast to previous studies, AMF were more specialised, whereas EMF were not. We further found that AMF communities were little driven by the surrounding trees, whereas EMF communities were. Our study revealed drivers of mycorrhizal fungal communities and further highlights the distinct strategies of AMF and EMF.
... These two oak species are more phylogenetically distinct from the pine than one another, though blue oaks are deciduous and belong to the white oak group while coast live oaks are evergreen and belong to the red oak group (Plumb and Gomez, 1983). Previous studies have described distinct differences in the ectomycorrhizal (but not saprotrophic) communities associated with such phylogenetically diverged oaks (Morris et al., 2008), as well as between oaks and cooccurring pine species (Smith et al., 2009;Suz et al., 2017;Rasmussen et al., 2018). ...
Article
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Host and symbiont diversity are inextricably linked across partnerships and ecosystems, with degree of partner reliance governing the strength of this correlation. In many forest soils, symbiotic ectomycorrhizal fungi coexist and compete with free-living saprotrophic fungi, with the outcomes of these interactions shaping resource availability and competitive outcomes for the trees aboveground. Traditional approaches to characterizing these communities rely on DNA sequencing of a ribosomal precursor RNA gene (the internal transcribed spacer region), but directly sequencing the precursor rRNA may provide a more functionally relevant perspective on the potentially active fungal communities. Here, we map ectomycorrhizal and saprotrophic soil fungal communities through a mixed hardwood-conifer forest to assess how above- and belowground diversity linkages compare across these differently adapted guilds. Using highly spatially resolved transects (sampled every 2 m) and well-mapped stands of varying host tree diversity, we sought to understand the relative influence of symbiosis versus environment in predicting fungal diversity measures. Canopy species in this forest included two oaks (Quercus agrifolia and Quercus douglasii) and one pine (Pinus sabiniana). At the scale of our study, spatial turnover in rRNA-based communities was much more predictable from measurable environmental attributes than DNA-based communities. And while turnover of ectomycorrhizal fungi and saprotrophs were predictable by the presence and abundance of different canopy species, they both responded strongly to soil nutrient characteristics, namely pH and nitrogen availability, highlighting the niche overlap of these coexisting guilds and the strong influence of aboveground plants on belowground fungal communities.
... In such cases, "host preference" is more appropriate, meaning that the fungus prefers one host over another [5]. For mycorrhizal fungi, strong host preference was apparent for many species [6,7], but the contrary is also true for many other species [8,9]. ...
Article
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Host preference of root endophytes of the three European tree species of Norway spruce (Picea abies), common ash (Fraxinus excelsior), and sycamore maple (Acer pseudoplatanus) were investigated in two forest stands near Zurich, Switzerland. The focus was placed on members of the Phialocephala fortinii s.l. (sensu lato)—Acephala applanata species complex (PAC), as well as other dark septate endopyhtes (DSE). PAC species were identified based on 13 microsatellite loci. Eleven PAC species were found, with Phialocephala helvetica, P. europaea being the most frequent. All but cryptic species 12 (CSP12) preferred Norway spruce as a host. Though very rare in general, CSP12 was most frequently isolated from maple roots. Regarding the abundant PAC species, P. helvetica and P. europaea, the preference of spruce as a host was least pronounced in P. europaea, as it was also often isolated from ash and maple. It is the first record of PAC found on common ash (Fraxinus excelsior). Cadophora orchidicola, a close relative of PAC, has frequently been isolated from ash. Various species of the Nectriaceae (Cylindrocarpon spp.) have often been isolated, particularly from maple roots. By comparison, Pezicula spp. (Cryptosporiopsis spp.) was found to be abundant on all three hosts. Phomopsis phaseoli exhibits a clear preference for spruce.
... Differences in the symbiont preferences of locally abundant ectomycorrhizal host species (i.e. Douglas-firs and oaks) between the two systems likely affect community assembly of these fungal guilds (Rasmussen et al., 2017) and such differences in plant community could also indirectly affect soil microbial community assembly more broadly by altering soil chemistry (Waring et al., 2015). Additionally, differences in fire frequency between these two ecosystem types (Van Wagtendonk et al., 2018) could contribute to the development of different belowground communities as well as aboveground. ...
Article
Wildfire affects our planet's biogeochemistry both by burning biomass and by driving changes in ecological communities and landcover. Some plants and ecosystem types are threatened by increasing fire pressure while others respond positively to fire, growing in local and regional abundance when it occurs regularly. However, quantifying total ecosystem response to fire demands consideration of impacts not only on aboveground vegetation, but also on soil microbes like fungi, which influence decomposition and nutrient mineralization. If fire‐resistant soil fungal communities co‐occur with similarly adapted plants, these above‐ and belowground ecosystem components should shift and recover in relative synchrony after burning. If not, fire might decouple ecosystem processes governed by these different communities, affecting total functioning. Here, we use a natural experiment to test whether fire‐dependent ecosystems host unique, fire‐resistant fungal communities. We surveyed burned and unburned areas across two California ecosystem types with differing fire ecologies in the immediate aftermath of a wildfire, finding that the soil fungal communities of fire‐dependent oak woodlands differ from those of neighbouring mixed evergreen forests. We discovered furthermore that the latter are more strongly altered compositionally by fire than the former, suggesting that differences in fungal community structure support divergent community responses to fire across ecosystems. Our results thus indicate that fire‐dependent ecosystems may host fire‐resistant fungal communities.
... These studies have generally focused on the water utilize strategy of P. sylvestris plantations and have recognized deficiently soil moisture as T improving trees under stress (Twieg et al., 2007;Oliveira et al., 2012;Sousa et al., 2012;Policelli et al., 2019). And a huge extent of EMF have significant host specificity with pine (Rasmussen et al., 2017). ...
Article
Pinus sylvestris var. mongolica is an important afforestation species in northern China. However, P. sylvestris plantations have severely declined in most areas where they have been introduced. Ectomycorrhizal fungi (EMF) are closely related to host plant growth and have important roles in the forest ecosystem, especially in Pinus forests. Hence, EMF may additionally furnish perception toward decline of P. sylvestris plantations. To date, the community composition of EMF associated with P. sylvestris stay vague. Therefore, to characterize the ectomycorrhizal (EM) fungal community, soil-root samples were analyzed from P. sylvestris plantations with three stand ages in the Horqin Sandy Land. (1) EMF associated with P. sylvestris plantations belonged to 2 phyla, 4 classes, 10 orders, 14 families, and 17 genera in the Horqin Sandy Land. The dominant fungal genus was Wilcoxina. (2) The diversity and community composition of EMF differed with stand age (P < 0.01), and the EMF community composition was most similar between half-mature and nearly-mature plantations. (3) The soil porosity, soil particle composition, pH, soil organic carbon and total phosphorus content had been the predominant determinants of the EMF community structure. This improved information indicated that the EM fungal community associated with P. sylvestris changed with soil environment ensuring from stand ageing in the Horqin Sandy Land. It contributes to the variations in EM fungal communities with the forest development, and affords a firm premise for the higher grasp of the degradation of the P. sylvestris plantations in northern China.
... Across the three soil inoculation sources (MS, AL, GA), four morpho- types of fungi were identified as the most dominant root tip coloniz- ers, Rhizopogon, Cenococcum, Wilcoxina, and Thelephora. These are common colonizers of Pinus and frequently found on pines in the field (e.g., Hoeksema, Hernandez, Rogers, Mendoza, & Thompson, 2012;Izzo, Nguyen, & Bruns, 2006;Rasmussen, Busby, & Hoeksema, 2018). These results are also consistent with other studies of pines F I G U R E 4 Relative growth rate (RGR) of the four pathogen resistance categories (FRt, fusiform rust tolerant; FRs, fusiform rust susceptible; PDt, pine decline tolerant; PDs, pine decline susceptible), in different soil types (MS, Mississippi; AL, Alabama; and GA, Georgia). ...
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Selection on genetically correlated traits within species can create indirect effects on one trait by selection on another. The consequences of these trait correlations are of interest because they may influence how suites of traits within species evolve under differing selection pressures, both natural and artificial. By utilizing genetic families of loblolly pine either tolerant (t) or susceptible (s) to two different suites of pathogenic fungi responsible for causing either pine decline or fusiform rust disease, we investigated trait variation and trait correlations within loblolly pine (Pinus taeda L.) by determining how ectomycorrhizal (EM) colonization relates to pathogen susceptibility. We detected interactions between susceptibility to pathogenic fungi and soil inoculation source on loblolly pine compatibility with the EM fungi Thelephora, and on relative growth rate of loblolly pine. Additionally, we detected spatial variation in the loblolly pine–EM fungi interaction, and found that variation in colonization rates by some members of the EM community is not dictated by genetic variation in the host plant but rather soil inoculation source alone. The work presented here illustrates the potential for indirect selection on compatibility with symbiotic EM fungi as a result of selection for resistance to fungal pathogens. Additionally, we present evidence that the host plant does not have a single “mycorrhizal trait” governing interactions with all EM fungi, but rather that it can interact with different fungal taxa independently. Synthesis. An understanding of the genetic architecture of essential traits in focal species is crucial if we are to anticipate and manage the results of natural and artificial selection. As demonstrated here, an essential but often overlooked symbiosis (that between plants and mycorrhizal fungi) may be indirectly influenced by directed selection on the host plant.
... In this sense, the association of plant species harboring a distinct MF community can increase the diversity of MF in the shared rhizosphere, enhancing plant coexistence (Montesinos-Navarro et al., 2012a). The two processes are not mutually exclusive, as interacting plants could harbor both CMN and non-shared MF (Rasmussen et al., 2018). Thus, contrasting effects might emerge from the combinations of the two processes. ...
Article
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Mycorrhizal symbiosis has important implications for the diversity and productivity of plant communities. However, our mechanistic understanding of its influence on the outcome of plant-plant interactions is still expanding. In this review we propose a framework that might be useful to efficiently approach the effects of mycorrhizal fungi (MF) on plant-plant interactions. We propose several scenarios that can theoretically result in different outcomes of plant-plant interactions based on the combination of two processes: the diversity of resources provided by MF taxa to their host (resource dissimilarity) and contrasting ways of distributing those resources (resource distribution). Then, we illustrate our arguments with different ecological contexts where certain combinations of these two processes are prone to occur. The proposed framework suggests testable hypotheses that can contribute to elucidate relevant processes underlying the effects of mycorrhizal symbiosis on plant-plant interactions.
Article
Pine invasions lead to losses of native biodiversity and ecosystem function, but pine invasion success is often linked to co‐invading non‐native ectomycorrhizal (EM) fungi. How the community composition, traits, and distributions of these fungi vary over the landscape and how this in‐turn affects pine success is understudied. A greenhouse bioassay experiment was performed to test the effects of changes in EM fungal community structure from a pine plantation, to an invasion front to currently pine‐free areas on percent root colonization and seedling biomass. Soils were also analyzed by qPCR to determine changes in inoculum and spore density over distance for a common co‐invading EM fungus, Suillus pungens. Percent colonization increased with distance from the plantation, which corresponded with an increase in seedling biomass and stark changes in EM fungal community membership where Suillus spp. dominated currently pine‐free areas. However, there was a negative relationship between S. pungens inoculum potential versus root colonization over distance. We conclude that the success of pine invasions is facilitated by specific traits of Suillus spp., but that the success of Suillus is contingent on a lack of competition with other ectomycorrhizal fungi.
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We induced basidioma formation of a fungus belonging to the Thelephoraceae that was isolated from the orchid Cephalanthera falcata. The mycobiont was isolated from root, cultured on modified Melin-Norkrans medium, and then inoculated onto fine roots of a Quercus serrata (Fagaceae) seedling. After observation of ectomycorrhiza formation, the Q. serrata seedling was grown in a pot. Thirty-six mo after ectomycorrhiza formation, basidioma formation was confirmed at the bottom of the pot. From comparisons in morphological characteristics between the mycobiont and known related Thelephoraceae species, and sequence similarities of internal transcribed spacer region in ribosomal DNA, we identified the mycobiont as Thelephora ellisii sensu lato in Thelephoraceae (Basidiomycota). Phylogenetic analysis indicated that the related sequences came from ectomycorrhizae of trees of the Salicaceae, Pinaceae, and Fagaceae distributed in East Asia, the USA, central Africa, and Europe.
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In natural forests, hundreds of fungal species colonize plant roots. The preference or specificity for partners in these symbiotic relationships is a key to understanding how the community structures of root-associated fungi and their host plants influence each other. In an oak-dominated forest in Japan, we investigated the root-associated fungal community based on a pyrosequencing analysis of the roots of 33 plant species. Of the 387 fungal taxa observed, 153 (39.5%) were identified on at least two plant species. Although many mycorrhizal and root-endophytic fungi are shared between the plant species, the five most common plant species in the community had specificity in their association with fungal taxa. Likewise, fungi displayed remarkable variation in their association specificity for plants even within the same phylogenetic or ecological groups. For example, some fungi in the ectomycorrhizal family Russulaceae were detected almost exclusively on specific oak (Quercus) species, whereas other Russulaceae fungi were found even on "non-ectomycorrhizal" plants (e.g., Lyonia and Ilex). Putatively endophytic ascomycetes in the orders Helotiales and Chaetothyriales also displayed variation in their association specificity and many of them were shared among plant species as major symbionts. These results suggest that the entire structure of belowground plant-fungal associations is described neither by the random sharing of hosts/symbionts nor by complete compartmentalization by mycorrhizal type. Rather, the colonization of multiple types of mycorrhizal fungi on the same plant species and the prevalence of diverse root-endophytic fungi may be important features of belowground linkage between plant and fungal communities.
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Mycorrhizal networks, defined as a common mycorrhizal mycelium linking the roots of at least two plants, occur in all major terrestrial ecosystems. This review discusses the recent progress and challenges in our understanding of the characteristics, functions, ecology and models of mycorrhizal networks, with the goal of encouraging future research to improve our understanding of their ecology, adaptability and evolution. We focus on four themes in the recent literature: (1) the physical, physiological and molecular evidence for the existence of mycorrhizal networks, as well as the genetic characteristics and topology of networks in natural ecosystems; (2) the types, amounts and mechanisms of interplant material transfer (including carbon, nutrients, water, defence signals and allelochemicals) in autotrophic, mycoheterotrophic or partial mycoheterotrophic plants, with particular focus on carbon transfer; (3) the influence of mycorrhizal networks on plant establishment, survival and growth, and the implications for community diversity or stability in response to environmental stress; and (4) insights into emerging methods for modelling the spatial configuration and temporal dynamics of mycorrhizal networks, including the inclusion of mycorrhizal networks in conceptual models of complex adaptive systems. We suggest that mycorrhizal networks are fundamental agents of complex adaptive systems (ecosystems) because they provide avenues for feedbacks and cross-scale interactions that lead to self-organization and emergent properties in ecosystems. We have found that research in the genetics of mycorrhizal networks has accelerated rapidly in the past 5 y with increasing resolution and throughput of molecular tools, but there still remains a large gap between understanding genes and understanding the physiology, ecology and evolution of mycorrhizal networks in our changing environment. There is now enormous and exciting potential for mycorrhizal researchers to address these higher level questions and thus inform ecosystem and evolutionary research more broadly.
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Some evidence suggests that longleaf pine might be more tolerant of high winds than either slash pine (Pinus elliotii Englem.) or loblolly pine (Pinus taeda L.). We studied wind damage to these three pine species in a common garden experiment in southeast Mississippi following Hurricane Katrina, a very large, Category 3 hurricane that directly affected the stand in August 2005. The experiment, a factorial arrangement of silvicultural treatments established in 1960, included 120 plots of 100 trees each, covering about 22 ha. Following the hurricane, dbh was measured on all trees, and each tree was rated with respect to mortality from wind damage. Longleaf pine suffered less mortality (7%) than the other two species (slash pine, 14%; loblolly pine, 26%), although the differences in mortality were statistically significant only between longleaf pine and loblolly pine. Longleaf pine lost significantly fewer stems per hectare and less basal area than the two other species. Differences in mortality among species were not a function of mean plot tree height or plot density. Our analyses indicate that longleaf pine is more resistant to wind damage than loblolly pine.
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Summary1. Ecological specialization is one of the main concepts in ecology and conservation. However, this concept has become highly context-dependent and is now obscured by the great variability of existing definitions and methods used to characterize ecological specialization.2. In this study, we clarify this concept by reviewing the strengths and limitations of different approaches commonly used to define and measure ecological specialization. We first show that ecological specialization can either be considered as reflecting species’ requirements or species’ impacts. We then explain how specialization depends on species-specific characteristics and on local and contingent environmental constraints. We further show why and how ecological specialization should be scaled across spatial and temporal scales, and from individuals to communities.3. We then illustrate how this review can be used as a practical toolbox to classify widely used metrics of ecological specialization in applied ecology, depending on the question being addressed, the method used, and the data available.4. Synthesis and applications. Clarifying ecological specialization is useful to make explicit connections between several fields of ecology using the niche concept. Defining this concept and its practical metrics is also a crucial step to better formulate predictions of scientific interest in ecology and conservation. Finally, understanding the different facets of ecological specialization should facilitate to investigate the causes and consequences of biotic homogenization and to derive relevant indicators of biodiversity responses to land-use changes.
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Molecular tools have now been applied for the past 5 years to dissect ectomycorrhizal (EM) community structure, and they have propelled a resurgence in interest in the field. Results from these studies have revealed that: (i) EM communities are impressively diverse and are patchily distributed at a fine scale below ground; (ii) there is a poor correspondence between fungi that appear dominant as sporocarps vs. those that appear dominant on roots; (iii) members of Russulaceae, Thelephoraceae, and/or non-thelephoroid resupinates are among the most abundant EM taxa in ecosystems sampled to date; (iv) dissimilar plants are associated with many of the same EM species when their roots intermingle — this occurs on a small enough spatial scale that fungal individuals are likely to be shared by dissimilar plants; and (v) mycoheterotrophic plants have highly specific fungal associations. Although, these results have been impressive, they have been tempered by sampling difficulties and limited by the taxonomic resolution of restriction fragment length polymorphism methods. Minor modifications of the sampling schemes, and more use of direct sequencing, has the potential to solve these problems. Use of additional methods, such as in situ hybridization to ribosomal RNA or hybridization coupled to microarrays, are necessary to open up the analysis of the mycelial component of community structure.
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Classic ectomycorrhizal symbioses are mutualisms that involve the exchange of fixed carbon for mineral nutrients between plant roots and fungi. They are unique in the way they contain features of both intimate and diffuse symbioses. The degree of host specificity varies, particularly among the fungi. Here we examine two exceptional cases of specificity to see what they tell us about the advantages of specificity, how it is initiated, and the potential role that it plays in complex ecosystems. The first case involves non-photosynthetic epiparasitic plants, which contrary to virtually all other plants, exhibit high levels of specificity toward their fungal hosts. The second case involves suilloid fungi; this is the largest monophyletic group of ectomycorrhizal fungi that is essentially restricted to associations with a single plant family. In both cases, new symbioses are initiated by dormant propagules that are stimulated to germinate by chemical cues from the host. This reduces the cost of wasting propagules on non-hosts. The advantages of specificity remain unclear in both cases, but we argue that increased benefit to the specialist may result from specialized physiological adaptations. We reexamine the idea that specialist fungi may help their hosts compete in complex ecosystems by reducing facultative epiparasitism by other plants, and suggest an alternative hypothesis for the observed pattern.
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Chloroplast DNA sequences are a primary source of data for plant molecular systematic studies. A few key papers have provided the molecular systematics community with universal primer pairs for noncoding regions that have dominated the field, namely trnL-trnF and trnK/matK. These two regions have provided adequate information to resolve species relationships in some taxa, but often provide little resolution at low taxonomic levels. To obtain better phylogenetic resolution, sequence data from these regions are often coupled with other sequence data. Choosing an appropriate cpDNA region for phylogenetic investigation is difficult because of the scarcity of information about the tempo of evolutionary rates among different noncoding cpDNA regions. The focus of this investigation was to determine whether there is any predictable rate heterogeneity among 21 noncoding cpDNA regions identified as phylogenetically useful at low levels. To test for rate heterogeneity among the different cpDNA regions, we used three species from each of 10 groups representing eight major phylogenetic lineages of phanerogams. The results of this study clearly show that a survey using as few as three representative taxa can be predictive of the amount of phylogenetic information offered by a cpDNA region and that rate heterogeneity exists among noncoding cpDNA regions.
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Predominant frameworks for understanding plant ecology have an aboveground bias that neglects soil micro-organisms. This is inconsistent with recent work illustrating the importance of soil microbes in terrestrial ecology. Microbial effects have been incorporated into plant community dynamics using ideas of niche modification and plant-soil community feedbacks. Here, we expand and integrate qualitative conceptual models of plant niche and feedback to explore implications of microbial interactions for understanding plant community ecology. At the same time we review the empirical evidence for these processes. We also consider common mycorrhizal networks, and propose that these are best interpreted within the feedback framework. Finally, we apply our integrated model of niche and feedback to understanding plant coexistence, monodominance and invasion ecology.
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SUMMARY: Coevolution can be a potent force in maintaining and generating biological diversity. Although coevolution is likely to have played a key role in the early development of mycorrhizal interactions, it is unclear how important coevolutionary processes are for ongoing trait evolution in those interactions. Empirical studies have shown that candidate coevolving traits, such as mycorrhizal colonization intensity, exhibit substantial heritable genetic variation within plant and fungal species and are influenced by plant genotype x fungal genotype interactions, suggesting the potential for ongoing coevolutionary selection. Selective source analysis (SSA) could be employed to build on these results, testing explicitly for ongoing coevolutionary selection and analyzing the influence of community context on local coevolutionary selection. Recent empirical studies suggest the potential for coevolution to drive adaptive differentiation among populations of plants and fungi, but further studies, especially using SSA in the context of field reciprocal transplant experiments, are needed to determine the importance of coevolutionary selection compared with nonreciprocal selection on species traits.
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Six primers for the amplification of three non-coding regions of chloroplast DNA via the polymerase chain reaction (PCR) have been designed. In order to find out whether these primers were universal, we used them in an attempt to amplify DNA from various plant species. The primers worked for most species tested including algae, bryophytes, pteridophytes, gymnosperms and angiosperms. The fact that they amplify chloroplast DNA non-coding regions over a wide taxonomic range means that these primers may be used to study the population biology (in supplying markers) and evolution (inter- and probably intraspecific phylogenies) of plants.
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In diverse mutualisms, it is common for potential partners to vary in the quality of benefits they provide. When weakly beneficial mutualists and parasites have a competitive advantage over strongly beneficial mutualists, it is not clear how strongly beneficial mutualists persist. If mutualism is destabilized by competitive superiority of weakly beneficial mutualists or cheaters, then mechanisms providing for stable coexistence among competing species may also provide for the persistence of mutualism. We analyze coexistence of species within a mutualist guild using a simple spatial model of patch occupancy to suggest hypotheses about the ecological persistence of mutualism in the interaction between plants and ectomycorrhizal fungi. We suggest that plants could facilitate the persistence of mutualistic mycorrhizal fungi by enhancing the mortality of root tips colonized by competitively superior and less mutualistic fungi. We also discuss previous empirical studies and present original data from field observations in plant-ectomycorrhizal systems to address our predictions and to suggest profitable avenues for further work.
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Pine decline is an emerging forest health issue in the southeastern United States. Observations suggest pine decline is caused by environmental stress arising from competition, weather, insects and fungi, anthropogenic disturbances, and previous management. The problem is most severe for loblolly pine on sites that historically supported longleaf pine, are highly eroded, or are not managed. The purposes of this technical note are (1) to describe the symptomology and extent of pine decline in the southeastern United States; (2) to describe its connection with root disease, resource stress, and silviculture; and (3) to summarize the consensus opinion of scientists and land managers during a workshop sponsored by the US Army Strategic Environmental Research and Development Program regarding the scope of this syndrome and the best research avenues to counter its potential effect on the sustainability of southern pine forests.
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One percent of Hobcaw Forest, a 3077 ha tract in South Carolina's lower coastal plain, was inventoried with fixed area plots within four months after the eye of Hurricane Hugo passed 97 km south of the forest. Results of this sampling confirmed our hypotheses that the amount and nature of hurricane wind damage differed among the tree species sampled. Approximately 73 percent of the 16,870 trees inventoried were either not damaged or had light crown damage. Longleaf pine (Pinus palustris) was less damaged than loblolly pine (Pinus taeda) or pond pine (Pinus serotina). Bald cypress (Taxodium distichum) suffered light crown damage. Upland oaks were more heavily damaged than the pine species. Live oak (Quercus virginiana) was less damaged than laurel oak (Quercus laurifolia) and water oak (Quercus nigra). Those tree species commonly found in the lower coastal plain (longleaf pine, bald cypress, and live oak) suffered less damage than species with larger natural ranges.
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DNA barcoding, a species identification system based on sequences from a short, standardized DNA region, has emerged recently as a new tool for taxonomists. We investigated the discriminatory power of a subset of highly variable proposed plant barcoding loci (matK, trnH-psbA, ITS2) in Quercus, a taxonomically complex tree genus of global importance. The research included all currently recognized species and some major variants of the Mediterranean region and Europe (32 taxa) and 17 East Asian and North American species used for comparison. Based on sequence character state, we assigned unique plastid haplotypes to 40.8% of the investigated species; ITS2 increased the resolution up to 87.8% of total taxa. Nevertheless, unsuccessful genetic distance-based discrimination questioned the potential efficiency of correct species identification for future studies. Most species appeared to be nonmonophyletic in parallel phylogenetic tests. Three subgeneric groups were outlined, with different rates of within-group variability and geographical differentiation. Members of one of these groups (corresponding to the Eurasian Group Ilex) were paraphyletic to Group Quercus from the New and Old World and the Eurasian Group Cerris. The data gathered indicate that barcoding markers may help to identify closely related species clusters and contribute to the inference of major diversification and evolutionary patterns in oaks, but the methodology per se appears to be of limited efficacy in defining species limits, unless we make a profound revision of traditional Quercus taxonomic categories.
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summaryLongleaf pine (Pinus palustris Mill.) seedlings were exposed to two concentrations of atmospheric CO2 (365 or 720 μmol mol−1) and two levels of N (0.02 or 0.20 mg N g−1 soil yr−1) within open-top chambers for 20 months. Seedlings were adequately watered for 19 wk to ensure seedling establishment, after which two water-stress treatments (target values −0·5 or −1·5 MPa xylem pressure potential) were implemented. Fine-root samples were collected in July and November 1993, and in March and November 1994. Ectomycorrhizal and non-mycorrhizal short roots per unit length of fine root were quantified. The percentage of ectomycorrhizal short roots and numbers of ectomycorrhizas per unit root length were higher for seedlings grown with elevated CO2, low N and adequate water. Interactions among main treatment variables demonstrated higher percentages of ectomycorrhizal short roots, fine root length per seedling, and total numbers of ectomycorrhizas per seedling for plants grown with high CO2 (compared with ambient) or adequate water (compared with water stress) only under high N conditions. Increased fine-root length and ectomycorrhizal colonization under elevated CO2 resulted in higher (almost double) numbers of ectomycorrhizas per seedling at each sampling.
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Publisher Summary The chapter discusses mycorrhiza, a symbiotic, non-pathogenic association between a plant root and a fungus. This paper first summarizes evidence that mycorrhizal links between plants that occur. It then reviews evidence on various possible functions of these links, and finally considers if there is any evidence that the links influence the species composition and structure of plant communities, and ecosystem processes such as nutrient cycling. Evidence on almost every aspect of mycorrhizal links and their possible roles is inadequate; any conclusions must therefore be preliminary and tentative. There is evidence that seedlings can become infected by forming mycorrhizal links with established plants, and growth of seedlings of some species is faster under these conditions. Transfer of I4C from one plant to another via mycorrhizal links can occur, but it is not clear that net transfer of organic compounds is ever great enough to increase significantly growth or survival of the receiver plant. There is no clear evidence that mycorrhizal links prevent these relationships from occurring or introduce fundamentally new interactions between plants. The evidence so far available suggests that mycorrhizal links can alter the relationships between plants, but that they do so by modifying competition and nutrient cycling rather than replacing them.
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Longleaf (Pinus palustris) and loblolly pine (P. taeda) nursery beds were treated with either vegetative inoculum of Pisolithus tinctorius (Pt) or allowed to become inoculated with natural ectomycorrhizae (NI) from 1987 to 1991. The resulting Pt and NI seedlings were outplanted on 2 sites per year (1988-1992) for a total of 10 demonstration plantings on the Savannah River Site (SRS), South Carolina. After 4 yr (5 yr for Site 5) the presence of Pt on bareroot longleaf pine at the time of planting did not improve seedling diameter or height growth. Longleaf pine survival was increased with the presence of Pt only on one site, while NI seedlings had greater survival on five sites and greater growth on two sites. The presence of Pt on the containerized longleaf pine had no effect on survival or diameter growth after 4 yr. Inoculation of bareroot loblolly pine with Pt resulted in larger diameter seedlings at the time of planting for four of eight sites. However, these differences in diameter were not maintained in three of the sites after 4 yr. The use of Pt as an artificial inoculant of bareroot longleaf and loblolly pine seedlings does not increase survival or growth response of reforestation plantings on the sandhills of South Carolina after 4 (5) yr. South. J. Appl. For. 23(1):46-52.
Article
Benomyl applied to roots of longleaf pine (Pinus palustris Mill.) seedlings at planting significantly reduced brown-spot disease and increased survival, root collar diameter, and early height growth on two sites in Mississippi. Seedlings with half or more of all ectomycorrhizae formed by Pisolithus tinctorius (Pers.) Coker and Couch in the nursery had significantly better survival and growth; Pisolithus ectomycorrhizae did not appreciably affect brown-spot disease. The benefits of benomyl and Pisolithus ectomycorrhizae were most obvious when combined. More than 75 percent of seedlings treated with benomyl and with more than half of all ectomycorrhizae formed by Pisolithus initiated height growth after 3 years. Forty-seven percent of seedlings with only Thelephora terrestris ectomycorrhizae and without benomyl exhibited height growth. The combined use of benomyl to control brown-spot disease and Pisolithus ectomycorrhizae to stimulate early height growth may overcome the major handicaps that have limited artificial regeneration of longleaf pine in the South.
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Species of the ectomycorrhizal genus Leccinum are generally considered to be host specialists. We determined the phylogenetic relationships between species of Leccinum from Europe and North America based on second internal transcribed spacer (ITS2) and glyceraldehyde 3-phosphate dehydrogenase (Gapdh). We plotted host associations onto the phylogenies using maximum likelihood and parsimony approaches. Resolution of the phylogeny was greater with Gapdh vs ITS2, plus the Gapdh and ITS phylogenies were highly incongruent. In Leccinum the coding region of Gapdh evolved clocklike, allowing the application of a molecular clock for the reconstruction of host specificity. Almost all species of Leccinum are highly host tree specific, except Leccinum aurantiacum, which associates with a broad range of host trees. Maximum likelihood reconstructions of the ancestral host associations show that this taxon evolved from a specialist. Our results indicate episodes of rapid speciation coinciding with or immediately following host switches. We propose a model where host niche contraction through geographic isolation and host niche expansion through ecologically equivalent hosts drive cycles of speciation. The role of host race formation and incipient speciation is discussed.
Article
1 The patterns of ectomycorrhizal (ECM) host specificity between understorey and canopy trees were investigated in three mixed evergreen forest stands in northern coastal California. ECM root tips from the dominant canopy (Pseudotsuga menziesii) and understorey (Lithocarpus densiflora) trees were sampled from 18 soil cores (six per stand) and identified using molecular techniques (PCR, RFLP, and DNA sequencing of the rDNA ITS region). 2 We found 56 ECM taxa; 17 on both hosts, 27 solely on Pseudotsuga and 12 on Lithocarpus. There were no significant differences in ECM taxon richness or diversity across stands, although ECM taxon richness was significantly higher on Pseudotsuga than Lithocarpus. ECM taxa similarity across stands was low. 3 Multiple-host ECM taxa had significantly higher abundance than single-host ECM taxa and 13 of the 17 multiple-host ECM taxa were present on both hosts within at least one core. Twelve of the 14 cores had at least one ECM taxon that was present on both hosts, although the specific taxon varied between cores and stands. In addition, shared ECM taxa often had unequal relative abundances on the two hosts. 4 Taken together, our results suggest that there is high potential for common mycorrhizal networks to form between Lithocarpus understories and Pseudotsuga canopies in mixed evergreen forests.
Article
We have designed two taxon-selective primers for the internal transcribed spacer (ITS) region in the nuclear ribosomal repeat unit. These primers, ITS1-F and ITS4-B, were intended to be specific to fungi and basidiomycetes, respectively. We have tested the specificity of these primers against 13 species of ascomycetes, 14 of basidiomycetes, and 15 of plants. Our results showed that ITS4-B, when paired with either a ‘universal’ primer ITS1 or the fungal-specific primer ITS1-F, efficiently amplified DNA from all basidiomycetes and discriminated against ascomycete DNAs. The results with plants were not as clearcut. The ITS1-F/ITS4-B primer pair produced a small amount of PCR product for certain plant species, but the quantity was in most cases less than that produced by the ‘universal’ ITS primers. However, under conditions where both plant and fungal DNAs were present, the fungal DNA was amplified to the apparent exclusion of plant DNA. ITS1-F/ITS4-B preferential amplification was shown to be particularly useful for detection and analysis of the basidiomycete component in ectomycorrhizae and in rust-infected tissues. These primers can be used to study the structure of ectomycorrhizal communities or the distribution of rusts on alternate hosts.
Article
SummaryA growing body of empirical work suggests that soil organisms can exert a strong role in plant community dynamics and may contribute to the coexistence of plant species. Some of this evidence comes from examining the feedback on plant growth through changes in the composition of the soil community. Host specific changes in soil community composition can generate feedback on plant growth and this feedback can be positive or negative. Previous work has demonstrated that negative soil community feedback can contribute to the coexistence of equivalent competitors. In this paper, I show that negative soil community feedback can also contribute to the coexistence of strong competitors, maintaining plant species that would not coexist in the absence of soil community dynamics. I review the evidence for soil community feedback and find accumulating evidence that soil community feedback can be common, strongly negative, and generated by a variety of complementary soil microbial mechanisms, including host-specific changes in the composition of the rhizosphere bacteria, nematodes, pathogenic fungi, and mycorrhizal fungi. Finally, I suggest topics needing further examination.
Article
A 35-year-old longleaf pine stand exhibited trees in various stages of decline. A study was conducted to determine root-infecting fungi and other abnormalities associated with varying degrees of crown symptoms. A four-class crown symptom rating system was devised according to ascending symptom severity. Leptographium procerum and L. terebrantis were significantly associated with increasing crown symptom severity. Heterobasidion annosum was also isolated in higher frequency as crown symptoms increased. Also, evidence of insects on roots increased as did amount of resinosis observed. Edaphic and silvicultural factors may interact with these pathogens and insects to pose a pathological limitation on longer-term management objectives. Further research is needed to determine relationships among various edaphic, silvicultural, and biological factors associated with the decline syndrome on this site.
Article
The ectomycorrhizal fungal associations of Douglas fir (Pseudotsuga menziesii D. Don) and bishop pine (Pinus muricata D. Don) were investigated in a mixed forest stand. We identified fungi directly from field-collected ectomycorrhizal (ECM) root tips using PCR-based methods. Sixteen species of fungi were found, of which twelve associated with both hosts. Rhizopogon parksii Smith was specific to Douglas fir. Three other species colonized only one of the hosts, but were too infrequent to draw conclusions about specificity. Seventy-four percent of the biomass of ECM root tips sampled in the stand were colonized by members of the Thelephoraceae and Russulaceae. All 12 species of fungi that associated with both tree species did so within a 10×40 cm soil volume, suggesting that individual fungal genotypes linked the putatively competing tree hosts.
Article
Ectomycorrhizal (ECM) symbiosis is a widespread plant nutrition strategy in Australia, especially in semiarid regions. This study aims to determine the diversity, community structure and host preference of ECM fungi in a Tasmanian wet sclerophyll forest. Ectomycorrhizal fungi were identified based on anatomotyping and rDNA internal transcribed spacer (ITS)-large subunit (LSU) sequence analysis using taxon-specific primers. Host tree roots were identified based on root morphology and length differences of the chloroplast trnL region. A total of 123 species of ECM fungi were recovered from root tips of Eucalyptus regnans (Myrtaceae), Pomaderris apetala (Rhamnaceae) and Nothofagus cunninghamii (Nothofagaceae). The frequency of two thirds of the most common ECM fungi from several lineages was significantly influenced by host species. The lineages of Cortinarius, Tomentella-Thelephora, Russula-Lactarius, Clavulina, Descolea and Laccaria prevailed in the total community and their species richness and relative abundance did not differ by host species. This study demonstrates that strongly host-preferring, though not directly specific, ECM fungi may dominate the below-ground community. Apart from the richness of Descolea, Tulasnella and Helotiales and the lack of Suillus-Rhizopogon and Amphinema-Tylospora, the ECM fungal diversity and phylogenetic community structure is similar to that in the Holarctic realm.
Article
Traditional ecological approaches to species evolution have frequently studied too few species, relatively small areas, and relatively short time spans. In The Coevolutionary Process, John N. Thompson advances a new conceptual approach to the evolution of species interactions—the geographic mosaic theory of coevolution. Thompson demonstrates how an integrated study of life histories, genetics, and the geographic structure of populations yields a broader understanding of coevolution, or the development of reciprocal adaptations and specializations in interdependent species. Using examples of species interactions from an enormous range of taxa, Thompson examines how and when extreme specialization evolves in interdependent species and how geographic differences in specialization, adaptation, and the outcomes of interactions shape coevolution. Through the geographic mosaic theory, Thompson bridges the gap between the study of specialization and coevolution in local communities and the study of broader patterns seen in comparisons of the phylogenies of interacting species.
Article
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 ( approximately 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 < or =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.
Article
* Knowledge of the diversity of arbuscular mycorrhizal fungi (AMF) in natural ecosystems is a major bottleneck in mycorrhizal ecology. Here, we aimed to apply 454 sequencing--providing a new level of descriptive power--to assess the AMF diversity in a boreonemoral forest. * 454 sequencing reads of the small subunit ribosomal RNA (SSU rRNA) gene of Glomeromycota were assigned to sequence groups by blast searches against a custom-made annotated sequence database. * We detected 47 AMF taxa in the roots of 10 plant species in a 10 x 10 m plot, which is almost the same as the number of plant species in the whole studied forest. There was a significant difference between AMF communities in the roots of forest specialist plant species and in the roots of habitat generalist plant species. Forest plant species hosted 22 specialist AMF taxa, and the generalist plants shared all but one AMF taxon with forest plants, including globally distributed generalist fungi. These AMF taxa that have been globally recorded only in forest ecosystems were significantly over-represented in the roots of forest plant species. * Our findings suggest that partner specificity in AM symbiosis may occur at the level of ecological groups, rather than at the species level, of both plant and fungal partners.
Article
We analysed the ectomycorrhizal (ECM) fungal diversity in a Mediterranean old-growth Quercus ilex forest stand from Corsica (France), where Arbutus unedo was the only other ECM host. On a 6400 m2 stand, we investigated whether oak age and host species shaped below-ground ECM diversity. Ectomycorrhizas were collected under Q. ilex individuals of various ages (1 yr seedlings; 3-10 yr saplings; old trees) and A. unedo. They were typed by ITS-RFLP analysis and identified by match to RFLP patterns of fruitbodies, or by sequencing. A diversity of 140 taxa was found among 558 ectomycorrhizas, with many rare taxa. Cenococcum geophilum dominated (35% of ECMs), as well as Russulaceae, Cortinariaceae and Thelephoraceae. Fungal species richness was comparable above and below ground, but the two levels exhibited < 20% overlap in fungal species composition. Quercus ilex age did not strongly shape ECM diversity. The two ECM hosts, A. unedo and Q. ilex, tended to share few ECM species (< 15% of the ECM diversity). Implications for oak forest dynamics are discussed.