Ectomycorrhizal Fungal Diversity Research Articles

Fungal diversity in ectomycorrhizal communities: sampling effort and species detection

A number of recent review articles on ectomycorrhizal (ECM) fungal community diversity have highlighted the unprecedented increase in the number of publications on this ecologically important but neglected area. The general features of these species-rich, highly dynamic and complex communities have been comprehensively covered but one aspect crucial to our assessment of diversity, namely the sampling of ECM communities has received less attention. This is a complex issue with two principal components, the physical sampling strategy employed and the life cycle traits of the ECM fungi being examined. Combined, these two components provide the image that we perceive as ECM diversity. This contribution will focus primarily on the former of these components using a recent study from a pine forest in central Sweden to highlight some sampling problems and also to discuss some features common to ECM communities. The two commonly used elements of diversity, species richness and community evenness, present rather different problems in the assessment of ECM diversity. The applicability of using current measures of abundance (number or percentage of root tips colonised) to determine community evenness is discussed in relation to our lack of knowledge on the size of individual genets of ECM fungi. The inherent structure of most ECM communities, with a few common species and a large number of rare species, severely limits our ability to accurately assess species richness. A discussion of theoretical detection limits is included that demonstrates the importance of the sampling effort (no. of samples or tips) involved in assessing species richness. Species area abundance plots are also discussed in this context. It is suggested that sampling strategy (bulk samples versus multiple collections of single tips) may have important consequences when sampling from communities where root tip densities differ. Finally, the need for studies of the spatial distribution of ECM on roots in relation to small-scale soil heterogeneity and of the temporal aspects of ECM community dynamics is raised.

BELOWGROUND ECTOMYCORRHIZAL FUNGAL COMMUNITY CHANGE OVER A NITROGEN DEPOSITION GRADIENT IN ALASKA

Nitrogen availability may be a major factor structuring ectomycorrhizal fungal communities. Atmospheric nitrogen (N) deposition has been implicated in the decline of ectomycorrhizal fungal (EMF) sporocarp diversity. We previously characterized the pattern of decreased sporocarp species richness over an anthropogenic N deposition gradient in Alaska (USA). To determine whether this change in sporocarp community structure was paralleled below ground, we used molecular and morphological techniques to characterize the ectomycorrhizal community of white spruce (Picea glauca) over this gradient. We then related patterns of richness and relative abundance of taxa to various N-affected environmental parameters. Species richness of EMF declined dramatically with increasing N inputs. Over 30 taxa were identified at the low-N sites, compared with nine at the high-N sites. Low-N site dominants (Piloderma spp., Amphinema byssoides, Cortinarius spp., and various dark-mantled Tomentella spp.) disappeared completely at th...

Ectomycorrhizal diversity alters growth and nutrient acquisition of grey birch (Betula populifolia) seedlings in host–symbiont culture conditions

• The influence of ectomycorrhizal fungal diversity on plant performance was investigated by establishing a gradient of ectomycorrhizal diversity on Betula populifolia (grey birch) seedlings. • We measured growth, as well as N and P uptake, of individual B. populifolia seedlings inoculated with replicate one, two and four species 'communities' of ectomycorrhizal fungi simultaneously and without mycorrhizas in axenic culture. • Colonization of B. populifolia by individual species of ectomycorrhizal fungi decreased with increasing fungal diversity although total colonization increased. Shoot biomass decreased with increasing ectomycorrhizal diversity and mycorrhizal root biomass increased. Plant biomass did not differ with individual mycorrhizal species or composition. Shoot N concentration showed a small increase with increasing ectomycorrhizal diversity. Whole plant P content and concentration increased across the ectomycorrhizal diversity gradient. Despite higher mycorrhizal colonization rates with increasing fungal diversity, plant growth and nutrient responses were best explained by changes in ectomycorrhizal diversity. • Greater ectomycorrhizal diversity per se, rather than colonization or composition, increased mycorrhizal root biomass at the expense of shoot biomass and increased P uptake of B. populifolia seedlings.

Context dependent effects of ectomycorrhizal species richness on tree seedling productivity

While there has been much recent interest about the relationships between plant diversity and plant productivity, much remains unknown about how the diversity of mycorrhizal fungi affects plant productivity. We investigated the effects of ectomycorrhizal fungal community composition and diversity on the productivity and growth characteristics of seedlings of two tree species (Pinus sylvetris and Betula pendula) as well as their interactions with each other. This involved setting up a mycorrhizal fungal diversity gradient from one to eight species using a design previously demonstrated to be able to separate diversity effects from compositional effects. We found that the eight mycorrhizal fungal species differed in their effects on seedling productivity and that the nature of effects was determined by the fertility of the substrate. Fungal species richness effects were also important in affecting seedling productivity over and above what could be explained by “sampling effect” but only in some situations. For B. pendula in a low fertility substrate there were clear positive causative effects between fungal species richness and productivity with the eight species treatment having over double the productivity of any of the eight monoculture treatments; no diversity effects were, however, detected in a high fertility substrate. For P. sylvestris in a high fertility substrate there were significant negative effects of fungal diversity on productivity while in a low fertility substrate no effects were apparent. The possible mechanistic bases for these results are discussed. The growth of P. sylvestris relative to that of B. pendula when grown in combination was unaffected by mycorrhizal treatments. Our results provide clear evidence that effects of mycorrhizal fungal diversity on productivity are context dependent and may be positive, negative or neutral depending on the situation considered.

Post-fire legacy of ectomycorrhizal fungal communities in the Swedish boreal forest in relation to fire severity and logging intensity

Swedish foresters are placing increasing reliance in burning of forestland and green tree retention, in order to enhance biodiversity in the Swedish boreal forests. However, much remains to be learned about how to optimise nature conservation goals by different logging and burning procedures. We monitored the survival of ectomycorrhizal (EM) fungi as mycorrhizas, at a clear-cut, a seed tree stand and an uncut stand of Scots pine in central Sweden, with and without burning at two levels of fire severity. The abundance of mycorrhizas and the EM fungal diversity declined with increased logging intensity and with increased depth of burn. Deep burning fires in combination with logging or fire-caused tree mortality can kill much of the existing EM community. Logging intensity, fire intensity and fire severity are all factors that can be manipulated, thus changing the effects on EM fungi and other soil biota.

Community structure of ectomycorrhizal fungi across an alpine/subalpine ecotone

In order to assess changes in the community structure of ectomycorrhizal fungi across the tree line, data on distributions of fungi and their host plants, as well as on edaphic factors and stand age, were collected at two montane sites in the Front Range of the Canadian Rockies. Canonical correspondence analysis (CCA) was used to explore relationships between fungal species composition and environmental factors. Richness and diversity of ectomycorrhizal fungi decreased with elevation, in spite of the fact that host plant diversity was highest at the ecotone between the subalpine forest and the alpine zone. Both host plant distribution and edaphic factors were important in explaining the observed changes in fungal species diversity and composition. The majority of ectomycorrhizal fungi found in the subalpine forest and at the ecotone were conifer associates, while a large proportion of those in the alpine zone were non‐host specific and able to form mycorrhizae with both angiosperms and gymnosperms. The abundance of non‐host specific fungi in the alpine zone is expected to provide a favorable environment for the establishment of conifer seedlings above the present tree line.

The impacts of broadcast burning after clear-cutting on the diversity of ectomycorrhizal fungi associated with hybrid spruce seedlings in central British Columbia

Morphological and molecular (polymerase chain reaction – restriction fragment length polymorphism) methods were used to assess ectomycorrhiza (ECM) diversity in naturally regenerating and planted Picea engelmannii Parry ex Engelm. × Picea glauca (Moench) Voss seedlings in two recently clear-cut sites, two clear-cut and broadcast burned sites, and two mature forests (>100 years) in central British Columbia. Based on 24 characterized ECM, burning did not affect overall diversity (Shannon, Simpson, Shannon evenness, and Margalef indices). However, the occurrence and relative abundance of some ECM morphotypes varied significantly. Hebeloma and a Russulaceae type 1 were more abundant and Cenococcum was less abundant in planted seedlings from cut-burned sites compared with those from clear-cut sites. E-strain, MRA, and Amphinema were more abundant in planted seedlings from both cut-burned and clear-cut sites compared with naturally regenerating seedlings from mature sites. ECM diversity of regenerating seedlings was significantly greater in mature forests compared with clear-cut sites and was greater in planted seedlings than naturally regenerating seedlings in clear-cut sites. Molecular analysis of the internal transcribed spacer region of the nuclear-encoded ribosomal RNA gene repeat showed no significant differences among treatments or seedling type. Twenty-two genotypes were identified from eight common morphotypes: Cenococcum (one), Thelephora (two), E-strain, Tuber, Hebeloma, and Russulaceae type 1 (three each), MRA (four), and Amphinema (six). Hebeloma genotypes matched three for Amphinema; genotypes from unidentified lightly colonized tips matched those for E-strain, MRA, and Amphinema-Hebeloma.

The impacts of broadcast burning after clear-cutting on the diversity of ectomycorrhizal fungi associated with hybrid spruce seedlings in central British Columbia

The impacts of broadcast burning after clear-cutting on the diversity of ectomycorrhizal fungi associated with hybrid spruce seedlings in central British Columbia

The influence of clear-cutting on ectomycorrhizal fungus diversity in a lodgepole pine (Pinus contorta) stand, Yellowstone National Park, Wyoming, and Gallatin National Forest, Montana

Effects of clear-cutting on the ectomycorrhizal (EM) fungus community in a Pinus contorta Dougl. ex Loud. forest near Yellowstone National Park, Wyoming, U.S.A., were assessed using molecular techniques. Samples were taken by soil core in both undisturbed and clear-cut sites by randomized block design. Species overlap was compared between clear-cut and undisturbed sites and ascomycete-basidiomycete ratio was determined, using PCR-RFLP methods. Fifty species of EM fungi were detected in the clear-cut sites, the most common being Cenococcum geophilum Fr., Suillus sp., a member of the suilloid group, a Russulaceae species, and a Thelephoraceae species. Sixty-six species were detected in the undisturbed sites, which were dominated by a Suilloid species, a Tricholomataceae species, Cortinarius sp., and Cenococcum geophilum. Species composition in the clear-cut sites differed significantly from that in the undisturbed sites (P = 0.0001). However, 9 of the 14 species most commonly found in the clear-cut sites were also found in the undisturbed sites, but in much lower abundance, while species rank curves of both stand types mirrored each other. There were no significant differences in species richness, root-tip abundance, or ascomycete-basidiomycete ratio between the clear-cut and undisturbed sites. However, species richness was lower in the clear-cut sites than in the undisturbed sites. An overall loss of species richness after clear-cutting and significant changes in species composition indicate that clear-cutting can negatively alter the EM fungal community, and this may have profound effects on ecosystem function.Key words: ectomycorrhizae, community structure, clear-cutting, molecular techniques.

The influence of clear-cutting on ectomycorrhizal fungus diversity in a lodgepole pine (<i>Pinus contorta</i>) stand, Yellowstone National Park, Wyoming, and Gallatin National Forest, Montana

Effects of clear-cutting on the ectomycorrhizal (EM) fungus community in a Pinus contorta Dougl. ex Loud. forest near Yellowstone National Park, Wyoming, U.S.A., were assessed using molecular techn...

Diversity and host specificity of ectomycorrhizal fungi retrieved from three adjacent forest sites by five host species

Seedlings of Abies grandis (Dougl.) Lindl. (grand fir), Lithocarpus densiflora (Hook. & Arn.) Rehd. (tanoak), Pinus ponderosa Dougl. ex Laws. (ponderosa pine), Pseudotsuga menziesii (Mirb.) Franco (Douglas-fir), and Arbutus menziesii Pursh (madrone) were planted in mixture and monoculture in soil collected from three adjacent forest sites in southwestern Oregon (a clearcut area, a 25-year-old Douglas-fir plantation, and a mature 90- to 160-year-old Douglas-fir - pine forest) to determine the effect of host tree diversity on retrieval of ectomycorrhizal morphotypes. In this greenhouse bioassay, 18 morphotypes of mycorrhizae were recognized overall from all soils with a total of 55 host-fungus combinations: 14 types with ponderosa pine, 14 with Douglas-fir, 10 with tanoak, 10 with grand fir, and 7 for madrone. Four genus-specific morphotypes were retrieved (three on ponderosa pine and one on Douglas-fir), even in mixture situations, demonstrating selectivity of some fungal propagules by their respective host. Five types were detected on all hosts, but not necessarily in soils from all sites. The remaining nine types were associated with two, three, or four hosts, which indicates a wide potential for interspecific hyphal linkages between trees. More morphotypes were retrieved from the monoculture treatments compared with the mixture treatments, although the differences were not significant. Several examples of acropetal replacement of one fungus by another (interpreted as succession) were recorded on all hosts during the course of the experiment. These results illustrate the importance of different host species in maintaining ectomycorrhizal fungus diversity, especially fungi with restricted host range, and the strong potential for fungal linkages between trees in forest ecosystems.Key words: fungal succession, fungal communities, compatibility, Arbutus menziesii, Pseudotsuga menziesii, Pinus ponderosa, Abies grandis, Lithocarpus densiflora.

Produção de compostos fenólicos durante a infecção ectomicorrízica por dois isolados de Pisolithus tinctorius em Eucalyptus urophylla in vitro

Physiological and structural diversity of ectomycorrhizal fungi can lead to differences in their behaviour during root infection and colonization. In incompatible interactions, the plant reacts against infection with structural and biochemical defenses, including production of antifungal compounds like phenolics. This study investigated the initial stages of ectomycorrhizal infection in interactions between P. tinctorius and E. urophylla to determine the plant reaction. E. urophylla seedlings were inoculated with a compatible (1604) or an incompatible (185) isolate of P. tinctorius. Extration of phenolic compounds was carried out at 0, 12, 24, 72, 96 and 120 hours after inoculation. At the same time, root samples were collected, processed and embedded in glycol methacrylate resin. Sections were studied under ligth microscopy. Ectomycorrhiza was formed on eucalyptus roots by 96 hours after inoculation with isolate 185 and by 24 hours in plants inoculated with isolate 1604. Structural reactions were not observed by light microscopy. On the other hand, a higher concentration of phenolic compounds in roots inoculated with the isolate 185 was observed 96 hours after inoculation. Although only plants inoculated with isolate 185 showed significant differences in phenolic concentration at the various infection stages, phenol accumulation could not be associated with delay in infection.

Ectomycorrhizal fungal communities in late‐successional Swedish boreal forests, and their composition following wildfire

This study was conducted to evaluate the effects of wildfires on ectomycorrhizal (EM) fungal communities in Scots pine (Pinus sylvestris) stands. Below‐ and above‐ground communities were analysed in terms of species richness and evenness by examining mycorrhizas and sporocarps in a chronosequence of burned stands in comparison with adjacent unburned late‐successional stands. The internal transcribed spacer (ITS)‐region (rDNA) of mycobionts from single mycorrhizas was digested with three restriction enzymes and compared with an ITS–restriction fragment length polymorphism (RFLP) reference database of EM sporocarps. Spatial variation seemed to be more prominent than the effects of fire on the EM fungal species composition. Most of the common species tended to be found in all sites, suggesting that EM fungal communities show a high degree of continuity following low‐intensity wildfires. Species richness was not affected by fire, whereas the evenness of species distributions of mycorrhizas was lower in the burned stands. The diversity of EM fungi was relatively high considering that there were only three EM tree species present in the stands. In total, 135 EM taxa were identified on the basis of their RFLP patterns; 66 species were recorded as sporocarps, but only 11 of these were also recorded as mycorrhizas. The species composition of the below‐ground community of EM fungi did not reflect that of the sporocarps produced. EM fungal species present in our ITS–RFLP reference database accounted for 54–99% of the total sporocarp production in the stands, but only 0–32% of the mycorrhizal abundance.

The diversity of ectomycorrhizal fungi associated with introduced Pinus spp. in the Southern Hemisphere, with particular reference to Western Australia

Although pines have been established in plantations in Western Australia for over 100 years, knowledge of the ectomycorrhizal fungal flora is incomplete, or lies in unpublished reports. A survey of ectomycorrhizal fungi associated with Pinus spp. was conducted throughout south-western Australia. Compared with other regions in the Southern Hemisphere where pines have been introduced, the ectomycorrhizal flora of pines in Western Australia is particularly depauperate, with only nine species of fungi identified from sporocarps and a further two taxa identified from mycorrhizas. Species identified from sporocarps (Hebeloma crustuliniforme, Lactarius deliciosus, Paxillus involutus, Rhizopogon luteolus, R. roseolus, R. vulgaris, Suillus luteus, S. granulatus, Thelephora terrestris) and Cenococcum geophilum are a subset of a larger pine mycorrhizal flora found in eastern Australia, and 8 of the 10 identified species are common to all regions in the Southern Hemisphere where pines have been introduced. These fungi are typically associated with trees, including pines, in the Northern Hemisphere and, apart from Cenococcum geophilum and T. terrestris, are not associated with indigenous vegetation in Western Australia. The mycorrhizal flora colonising roots in a plantation of Pinus radiata D. Don was also investigated, and compared with species identified as present by above-ground sporocarp production. Potential reasons for the limited ectomycorrhizal flora of pines in Western Australia are discussed.

Diversity of ectomycorrhizal fungi in Britain: a test of the species–area relationship, and the role of host specificity

The host range of ectomycorrhizal (ECM) fungi in Britain was examined by compilation of a data matrix from published literature sources, based primarily on accounts of sporocarp associations with particular host genera. Information was gathered for 577 species of ECM fungi belonging to 51 genera, and 25 genera of host trees, representing the majority of ECM fungal species and host genera recorded in Britain.Pronounced variation was recorded in the number of ECM fungal species associated with different host genera, with over 200 species recorded with Betula, Fagus, Pinus and Quercus. There was a positive linear relationship (r2=0·47, P=0·007) between the number of species of ECM fungi associated with different host genera and the total area occupied by each tree genus in Britain (both values log‐transformed). There was also variation in the number of species of ECM fungi which were apparently specific to particular host genera, values ranging from zero (in 15 genera) to >40 in the case of Betula and Fagus. In total, 233 fungal species appeared to be specific to a single host genus (i.e. 40% of those surveyed). Comparison of the ECM mycota associated with different host genera by PCA accounted for 17% of the total variation, with genera belonging to the Fagaceae (Quercus, Fagus and Castanea) tending to cluster together, indicating a degree of overlap in their ECM associates. Exotic conifer species, which displayed a lower ECM diversity than would be expected from their distributional areas, were characterized by a high degree of overlap with the ECM associates of Pinus and Betula.These results indicate that the abundance of different genera of host trees and variation in host specificity could provide a basis for understanding patterns of diversity in ECM fungi within Britain.

Effects of soil trenching on occurrence of ectomycorrhizas on Pseudotsuga menziesii seedlings grown in mature forests of Betula papyrifera and Pseudotsuga menziesii

SUMMARYSeedlings of Pseudotsuga menziesii (Mirb.) Franco were grown for six‐16 months in untrenched and trenched treatments in three 90–120‐yr‐old mixed forests dominated by Betula papyrifera Marsh, and P. menziesii in the southern interior of British Columbia. Each forest was characterized by mesic conditions and low light intensity (PAR < 200 μmol m−2 s−1) in the understorey. The objective of the study was to evaluate the influence of overstorey tree roots on (i) ectomycorrhizal fungal composition, richness and diversity, and (ii) photosynthesis and growth of understorey P. menziesii seedlings. Seventeen ectomycorrhizal morphotypes were recognized on seedlings in the untrenched treatment, and nine in the trenched treatment over the three sites. Six types occurred in both treatments, of which on average Rhizopogon vinicolor Smith type was 20 times more abundant and Thelephora type six times less abundant in the untrenched as in the trenched treatment. Of types that formed strands or rhizomorphs, eight occurred in the untrenched treatment, where they occupied on average 23% of root tips, and only four occurred in the trenched treatment over 4% of the root tips. Mean richness, diversity, and evenness of ectomycorrhizal associates per seedling were approx. twice as great in the untrenched as in the trenched treatment.Net photosynthetic rate of P. menziesii seedlings was greater in the untrenched than in the trenched treatment in July and August, but not in September 1994. Height, diameter and biomass of seedlings did not differ between treatments, but height: diameter ratio was greater in the untrenched treatment at time of harvest. The effect of trenching on seedling performance was attributed mainly to differences in ectomycorrhizal colonization patterns because trenching had no significant effect on soil nutrient concentrations (total C, total N, NH4‐N, available N, exchangeable Ca, exchangeable Mg, exchangeable K), C:N ratio, soil pH or light availability. Nor was there a significant difference in soil water in August, when seedlings in untrenched plots had higher net photosynthetic rates than those in trenched plots. Results suggest that influence of overstorey trees and pattern of ectomycorrhizal formation are important to P. menziesii seedling performance in deeply shaded forest environments.

The ectomycorrhizal flora of primary and secondary stands of Pinus sylvestris in relation to soil conditions and ectomycorrhizal succession

Abstract. Ectomycorrhizal species composition and sporocarp abundance in two 15–20‐yr old primary stands of Pinus sylvestris in the central part of the Netherlands was compared with those in two 16‐ and 27‐yr old secondary stands of P. sylvestris in the Northeast of the country. The trees of the primary stands were spontaneously seeded in a drifting sand area. Only thin litter and humus layers were present. The trees of the 16‐yr old secondary stand were planted on podzolic sandy soil and those of the 27‐yr old stand on non‐podzolic sandy soil. In both secondary stands thick litter and humus layers had developed. The litter and humus partly originated from former stands at the same sites and partly from the present stands. In the secondary stands the thick litter and humus layers and herb vegetation were removed (‘sod‐cutting’) in order to simulate the thin litter and humus layers in the primary stands. Control treatments were present. Surveys in 1991, 1992 and 1993 showed that sod‐cutting enhanced both abundance and diversity of ectomycorrhizal fungi. However, species richness and diversity were higher in the primary stands than in the secondary ones, also even in the sod‐cut plots. High species richness and diversity were associated with low concentrations of nitrogen and relatively high pH in the litter and humus layers, and in the mineral soil.

Thoughts on the processes that maintain local species diversity of ectomycorrhizal fungi

Thoughts on the processes that maintain local species diversity of ectomycorrhizal fungi

Keys to the British species of russula

Fungi dominate the microbial biomass of temperate forest soils and are a key driver of ecosystem nutrient cycling. Chronic nitrogen (N) amendments frequently cause the accumulation of soil organic matter within soils, suggesting that elevated N disrupts decomposition by altering fungal communities. To link previously observed increases in soil organic matter with potential changes in the fungal community, we assessed the effects of soil N amendment on fungal community structure at a long-term N addition experiment at Harvard Forest (Petersham, MA, USA). A decline in the relative abundance of ectomycorrhizal fungi following long-term N addition was offset by an increase in the relative abundance of saprotrophs. Species richness and diversity of ectomycorrhizal fungi declined, while ascomycetes and saprotrophs responded positively to N enrichment. However, nitrophilic species included ectomycorrhizal as well as saprotrophic fungi, especially the ectomycorrhizal Russula vinacea, whose relative abundance increased from 10 to 37% of the entire community across N treatments. Two decades of soil N enrichment appears to have fundamentally altered the soil fungal community of this temperate forest.