Spatial structure and the effects of host and soil environments on communities of ectomycorrhizal fungi in wooded savannas and rain forests of Continental Africa and Madagascar

Mycorrhizal fungi play a key role in mineral nutrition of terrestrial plants, but the factors affecting natural distribution, diversity and community composition of particularly tropical fungi remain poorly understood. This study addresses shifts in community structure and species frequency of ectomycorrhizal (EcM) fungi in relation to host taxa, soil depth and spatial structure in four contrasting African ecosystems. We used the rDNA and plastid trnL intron sequence analysis for identification of fungi and host plants, respectively. By partitioning out spatial autocorrelation in plant and fungal distribution, we suggest that African EcM fungal communities are little structured by soil horizon and host at the plant species and family levels. These findings contrast with patterns of vegetation in these forests and EcM fungal communities in other tropical and temperate ecosystems. The low level of host preference indirectly supports an earlier hypothesis that pioneer Phyllanthaceae may facilitate the establishment of late successional Fabaceae and potentially other EcM host trees by providing compatible fungal inoculum in deforested and naturally disturbed ecosystems of tropical Africa.     

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 ectotnycorrhizal 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.     

Forest microsite effects on community composition of ectomycorrhizal fungi on seedlings of Picea abies and Betula pendula

Niche differentiation in soil horizons, host species and natural nutrient gradients contribute to the high diversity of ectomycorrhizal fungi in boreal forests. This study aims at documenting the diversity and community composition of ectomycorrhizal fungi of Norway spruce ( Picea abies ) and silver birch ( Betula pendula ) seedlings in five most abundant microsites in three Estonian old-growth forests. Undisturbed forest floor, windthrow mounds and pits harboured more species than brown- and white-rotted wood. Several species of ectomycorrhizal fungi were differentially represented on either hosts, microsites and sites. Generally, the most frequent species in dead wood were also common in forest floor soil. Ordination analyses suggested that decay type determined the composition of EcM fungal community in dead wood. Root connections with in-growing mature tree roots from below affected the occurrence of certain fungal species on seedling roots systems in dead wood. This study demonstrates that ectomycorrhizal fungi differentially establish in certain forest microsites that is attributable to their dispersal and competitive abilities. Elevated microsites, especially decayed wood, act as seed beds for both ectomycorrhizal forest trees and fungi, thus affecting the succession of boreal forest ecosystems.     

Diversity and community structure of ectomycorrhizal fungi in <Emphasis Type="Italic">Pinus thunbergii</Emphasis> coastal forests in the eastern region of Korea

We investigated the diversity and community structure of ectomycorrhizal (EcM) fungi in Pinus thunbergii stands on the eastern coast of Korea. We established two 10 × 10-m plots in six forest stands and sampled soil blocks containing rootlets of mature P. thunbergii trees. EcM roots were classified into morphological groups, and the fungal taxa associated with each morphotype were identified by sequencing the nuclear rDNA internal transcribed spacer region. Cenococcum geophilum and the Atheliales, Clavulinaceae, Russulaceae and Thelephoraceae species were the main members of the EcM fungal community, which included a total of 68 observed fungal taxa. As a whole, the community consisted of a few dominant fungal taxa, such as C. geophilum (28.6% relative abundance), and a large number of rare fungal taxa that showed low abundances and local distributions. Colonization patterns at the local site scale and at the scale of the study plots greatly differed among the EcM fungal taxa; C. geophilum was distributed extensively and was dominant in several study sites, whereas a certain Lactarius sp. was distributed locally but dominated in a given study site. We conclude with a discussion of the relationship between colonization patterns of EcM fungi and soil and environmental conditions.     

Plant species richness and productivity determine the diversity of soil fungal guilds in temperate coniferous forest and bog habitats

Fungi have important roles as decomposers, mycorrhizal root symbionts and pathogens in forest ecosystems, but there is limited information about their diversity and composition at the landscape scale. This work aimed to disentangle the factors underlying fungal richness and composition along the landscape‐scale moisture, organic matter and productivity gradients. Using high‐throughput sequencing, we identified soil fungi from 54 low‐productivity Pinus sylvestris‐dominated plots across three study areas in Estonia and determined the main predictors of fungal richness based on edaphic, floristic and spatial variables. Fungal richness displayed unimodal relationship with organic matter and deduced soil moisture. Plant richness and productivity constituted the key predictors for taxonomic richness of functional guilds. Composition of fungi and the main ectomycorrhizal fungal lineages and hyphal exploration types was segregated by moisture availability and soil nitrogen. We conclude that plant productivity and diversity determine the richness and proportion of most functional groups of soil fungi in low‐productive pine forests on a landscape scale. Adjacent stands of pine forest may differ greatly in the dominance of functional guilds that have marked effects on soil carbon and nitrogen cycling in these forest ecosystems.     

Fruiting body and soil rDNA sampling detects complementary assemblage of Agaricomycotina (Basidiomycota, Fungi) in a hemlock-dominated forest plot in southern Ontario

This is the first study to assess the diversity and community structure of the Agaricomycotina in an ectotrophic forest using above-ground fruiting body surveys as well as soil rDNA sampling. We recovered 132 molecular operational taxonomic units, or 'species', from fruiting bodies and 66 from soil, with little overlap. Fruiting body sampling primarily recovered fungi from the Agaricales, Russulales, Boletales and Cantharellales. Many of these species are ectomycorrhizal and form large fruiting bodies. Soil rDNA sampling recovered fungi from these groups in addition to taxa overlooked during the fruiting body survey from the Atheliales, Trechisporales and Sebacinales. Species from these groups form inconspicuous, resupinate and corticioid fruiting bodies. Soil sampling also detected fungi from the Hysterangiales that form fruiting bodies underground. Generally, fruiting body and soil rDNA samples recover a largely different assemblage of fungi at the species level; however, both methods identify the same dominant fungi at the genus-order level and ectomycorrhizal fungi as the prevailing type. Richness, abundance, and phylogenetic diversity (PD) identify the Agaricales as the dominant fungal group above- and below-ground; however, we find that molecularly highly divergent lineages may account for a greater proportion of total diversity using the PD measure compared with richness and abundance. Unless an exhaustive inventory is required, the rapidity and versatility of DNA-based sampling may be sufficient for a first assessment of the dominant taxonomic and ecological groups of fungi in forest soil.     

Towards global patterns in the diversity and community structure of ectomycorrhizal fungi

Global species richness patterns of soil micro-organisms remain poorly understood compared to macro-organisms. We use a global analysis to disentangle the global determinants of diversity and community composition for ectomycorrhizal (EcM) fungi-microbial symbionts that play key roles in plant nutrition in most temperate and many tropical forest ecosystems. Host plant family has the strongest effect on the phylogenetic community composition of fungi, whereas temperature and precipitation mostly affect EcM fungal richness that peaks in the temperate and boreal forest biomes, contrasting with latitudinal patterns of macro-organisms. Tropical ecosystems experience rapid turnover of organic material and have weak soil stratification, suggesting that poor habitat conditions may contribute to the relatively low richness of EcM fungi, and perhaps other soil biota, in most tropical ecosystems. For EcM fungi, greater evolutionary age and larger total area of EcM host vegetation may also contribute to the higher diversity in temperate ecosystems. Our results provide useful biogeographic and ecological hypotheses for explaining the distribution of fungi that remain to be tested by involving next-generation sequencing techniques and relevant soil metadata.     

Lack of host specificity leads to independent assortment of dipterocarps and ectomycorrhizal fungi across a soil fertility gradient

Plants interact with a diversity of microorganisms, and there is often concordance in their community structures. Because most community‐level studies are observational, it is unclear if such concordance arises because of host specificity, in which microorganisms or plants limit each other's occurrence. Using a reciprocal transplant experiment, we tested the hypothesis that host specificity between trees and ectomycorrhizal fungi determines patterns of tree and fungal soil specialisation. Seedlings of 13 dipterocarp species with contrasting soil specialisations were seeded into plots crossing soil type and canopy openness. Ectomycorrhizal colonists were identified by DNA sequencing. After 2.5 years, we found no evidence of host specificity. Rather, soil environment was the primary determinant of ectomycorrhizal diversity and composition on seedlings. Despite their close symbiosis, our results show that ectomycorrhizal fungi and tree communities in this Bornean rain forest assemble independently of host‐specific interactions, raising questions about how mutualism shapes the realised niche.     

Topography-specific emergence of fungal fruiting bodies in warm temperate evergreen broad-leaved forests on Yakushima Island,Japan

We conducted line route censuses of fungal fruiting bodies from August to September in 2005 and 2006 along ridges and valleys and compared the differences in the encounter rates of fungal fruiting bodies (= fruiting bodies seen per census kilometer) between types of topography and between fungal functional groups (i.e., ectomycorrhizal and saprobic fungi) in warm temperate evergreen broad-leaved forests on Yakushima Island, Japan. We found 251 fungal fruiting bodies (26 families, 50 genera, and 65 species) in total, including 51 bodies from Tricholomataceae, 41 from Russulaceae, 25 from Boletaceae, and 19 from Amanitaceae. The encounter rate of ectomycorrhizal fungi was greater at the ridge route (26.7 unit/km) than at the valley route (8.7 unit/km) and that of saprobic fungi was greater at the valley route (25.0 unit/km) than at the ridge route (12.5 unit/km). In addition, we conducted 7-year intermittent sampling and identified 40 families, 96 genera, and 142 species. The topography-specific emergence pattern of the intermittent sampling method was similar to that of the line census method. The fungal species composition in this study was possibly affected by a topographic gradient for both fungal functional groups through soil moisture, nutrient availability, and host tree distribution.     

Spatial Ecology of the Fungal Genus Xylaria in a Tropical Cloud Forest

Fungal symbioses with plants are ubiquitous, ancient, and vital to both ecosystem function and plant health. However, benefits to fungal symbionts are not well explored, especially in non‐mycorrhizal fungi. The Foraging Ascomycete hypothesis proposes that some wood‐decomposing fungi may shift life‐history strategies to endophytism to bridge gaps in time and space between suitable substrates. To test this hypothesis we examine spatial relationships of Xylaria endophytic fungi in the forest canopy with Xylaria decomposer fungi on the forest floor. We sampled for fungi of the genus Xylaria using a spatially explicit sampling scheme in a remote Ecuadorian cloud forest, and concurrently carried out an extensive culture‐based sampling of fungal foliar endophytes. We found 36 species of Xylaria in our 0.5 ha plot, 31 of which were found to only occur as fruiting bodies. All five species of Xylaria found as endophytes were also found as fruiting bodies. We also tested the relationships of both stages of these fungi to environmental variables. Decomposer fungi were differentiated by species‐specific habitat preferences, with three species being found closer to water than expected by chance. In contrast, endophytes displayed no sensitivity to environmental conditions, such as host, moisture, or canopy cover. We found evidence of spatial linkage between life stages in two species. We also demonstrate that direct transmission of endophytes from leaves to woody substrates is possible. These results indicate that endophytism may represent one way for decomposer fungi to escape moisture limitation, and that endophytic fungi may act as sources of dispersal for decomposer fungi consistent with predictions of the Foraging Ascomycete hypothesis.     

Wildfire severity reduces richness and alters composition of soil fungal communities in boreal forests of western Canada

Wildfire is the dominant disturbance in boreal forests and fire activity is increasing in these regions. Soil fungal communities are important for plant growth and nutrient cycling postfire but there is little understanding of how fires impact fungal communities across landscapes, fire severity gradients, and stand types in boreal forests. Understanding relationships between fungal community composition, particularly mycorrhizas, and understory plant composition is therefore important in predicting how future fire regimes may affect vegetation. We used an extreme wildfire event in boreal forests of Canada's Northwest Territories to test drivers of fungal communities and assess relationships with plant communities. We sampled soils from 39 plots 1 year after fire and 8 unburned plots. High‐throughput sequencing (MiSeq, ITS) revealed 2,034 fungal operational taxonomic units. We found soil pH and fire severity (proportion soil organic layer combusted), and interactions between these drivers were important for fungal community structure (composition, richness, diversity, functional groups). Where fire severity was low, samples with low pH had higher total fungal, mycorrhizal, and saprotroph richness compared to where severity was high. Increased fire severity caused declines in richness of total fungi, mycorrhizas, and saprotrophs, and declines in diversity of total fungi and mycorrhizas. The importance of stand age (a surrogate for fire return interval) for fungal composition suggests we could detect long‐term successional patterns even after fire. Mycorrhizal and plant community composition, richness, and diversity were weakly but significantly correlated. These weak relationships and the distribution of fungi across plots suggest that the underlying driver of fungal community structure is pH, which is modified by fire severity. This study shows the importance of edaphic factors in determining fungal community structure at large scales, but suggests these patterns are mediated by interactions between fire and forest stand composition.     

Comparison of root-associated communities of native and non-native ectomycorrhizal hosts in an urban landscape

Non-native tree species are often used as ornamentals in urban landscapes. However, their root-associated fungal communities remain yet to be examined in detail. Here, we compared richness, diversity and community composition of ectomycorrhizosphere fungi in general and ectomycorrhizal (EcM) fungi in particular between a non-native Pinus nigra and a native Quercus macrocarpa across a growing season in urban parks using 454-pyrosequencing. Our data show that, while the ectomycorrhizosphere community richness and diversity did not differ between the two host, the EcM communities associated with the native host were often more species rich and included more exclusive members than those of the non-native hosts. In contrast, the ectomycorrhizosphere communities of the two hosts were compositionally clearly distinct in nonmetric multidimensional ordination analyses, whereas the EcM communities were only marginally so. Taken together, our data suggest EcM communities with broad host compatibilities and with a limited numbers of taxa with preference to the non-native host. Furthermore, many common fungi in the non-native Pinus were not EcM taxa, suggesting that the fungal communities of the non-native host may be enriched in non-mycorrhizal fungi at the cost of the EcM taxa. Finally, while our colonization estimates did not suggest a shortage in EcM inoculum for either host in urban parks, the differences in the fungi associated with the two hosts emphasize the importance of using native hosts in urban environments as a tool to conserve endemic fungal diversity and richness in man-made systems.     

Assembly processes of trophic guilds in the root mycobiome of temperate forests

Root‐associated mycobiomes (RAMs) link plant and soil ecological processes, thereby supporting ecosystem functions. Understanding the forces that govern the assembly of RAMs is key to sustainable ecosystem management. Here, we dissected RAMs according to functional guilds and combined phylogenetic and multivariate analyses to distinguish and quantify the forces driving RAM assembly processes. Across large biogeographic scales (>1,000 km) in temperate forests (>100 plots), RAMs were taxonomically highly distinct but composed of a stable trophic structure encompassing symbiotrophic, ectomycorrhizal (55%), saprotrophic (7%), endotrophic (3%) and pathotrophic fungi (<1%). Taxonomic community composition of RAMs is explained by abiotic factors, forest management intensity, dominant tree family (Fagaceae, Pinaceae) and root resource traits. Local RAM assemblies are phylogenetically clustered, indicating stronger habitat filtering on roots in dry, acid soils and in conifer stands than in other forest types. The local assembly of ectomycorrhizal communities is driven by forest management intensity. At larger scales, root resource traits and soil pH shift the assembly process of ectomycorrhizal fungi from deterministic to neutral. Neutral or weak deterministic assembly processes are prevalent in saprotrophic and endophytic guilds. The remarkable consistency of the trophic composition of the RAMs suggests that temperate forests attract fungal assemblages that afford functional resilience under the current range of climatic and edaphic conditions. At local scales, the filtering processes that structure symbiotrophic assemblies can be influenced by forest management and tree selection, but at larger scales, environmental cues and host resource traits are the most prevalent forces.     

The annual invasive plant Impatiens glandulifera reduces hyphal biomass of soil fungi in deciduous forests

Soil fungi play a crucial role in ecosystem functioning and there is increasing evidence that exotic plants invading forests can affect soil fungal communities. We examined potential effects of the invasive plant Impatiens glandulifera on hyphal biomass of ectomycorrhizal fungi, their genetic diversity and the diversity of other soil fungi in deciduous forests in Switzerland. We compared invaded patches with patches where I. glandulifera had been removed, by establishing pairs of 3-m long transect lines at the edge of seven areas of either type. Along the transects we assessed the length of ectomycorrhizal fungal hyphae using the ‘ingrowth mesh bag method’, and used terminal restriction fragment length polymorphism (T-RFLP) analysis to examine fungal genetic diversity. The invasive plant reduced fungal hyphal biomass by 30–80%: the reduction was largest in the centre of the patch. I. glandulifera did not alter fungal richness, but affected the composition of fungal communities. This is probably the result of a decrease of mycorrhizal fungi, coupled with an increase of saprotrophic fungi. Our findings demonstrate the adverse impacts of an annual invasive plant species on both fungal hyphal biomass and the composition of soil fungal communities. This may negatively affect forest nutrient and carbon cycling, soil stability and the functionality of the fungal community, with major consequences for forest ecosystem functioning.     

Ectomycorrhizal fungal response to warming is linked to poor host performance at the boreal‐temperate ecotone

Rising temperatures associated with climate change have been shown to negatively affect the photosynthetic rates of boreal forest tree saplings at their southern range limits. To quantify the responses of ectomycorrhizal (EM) fungal communities associated with poorly performing hosts, we sampled the roots of Betula papyrifera and Abies balsamea saplings growing in the B4Warmed (Boreal Forest Warming at an Ecotone in Danger) experiment. EM fungi on the root systems of both hosts were compared from ambient and +3.4 °C air and soil warmed plots at two sites in northern Minnesota. EM fungal communities were assessed with high‐throughput sequencing along with measures of plant photosynthesis, soil temperature, moisture, and nitrogen. Warming selectively altered EM fungal community composition at both the phylum and genus levels, but had no significant effect on EM fungal operational taxonomic unit (OTU) diversity. Notably, warming strongly favored EM Ascomycetes and EM fungi with short‐contact hyphal exploration types. Declining host photosynthetic rates were also significantly inversely correlated with EM Ascomycete and EM short‐contact exploration type abundance, which may reflect a shift to less carbon demanding fungi due to lower photosynthetic capacity. Given the variation in EM host responses to warming, both within and between ecosystems, better understanding the link between host performance and EM fungal community structure will to clarify how climate change effects cascade belowground.     

连续三年夜间增温和施氮对云杉外生菌根及菌根真菌多样性的影响

以西南亚高山针叶林建群种粗枝云杉(Picea asperata)为研究对象,采用红外加热模拟增温结合外施氮肥(NH₄NO₃ 25 g N m^-2 a^-1)的方法,研究连续3a夜间增温和施肥对云杉幼苗外生菌根侵染率、土壤外生菌根真菌生物量及其群落多样性的影响。结果表明:夜间增温对云杉外生菌根侵染率的影响具有季节性及根级差异。夜间增温对春季(2011年5月)云杉1级根,夏季(2011年7月)和秋季(2010年10月)云杉2级根侵染率影响显著。除2011年7月1级根外,施氮对云杉1、2级根侵染率无显著影响。夜间增温对土壤中外生菌根真菌的生物量和群落多样性无显著影响,施氮及增温与施氮联合处理使土壤中外生菌根真菌生物量显著降低,但却提高了外生菌根真菌群落的多样性。这说明云杉幼苗外生菌根侵染率对温度较敏感,土壤外生菌根真菌生物量及其群落多样性对施氮较敏感。这为进一步研究该区域亚高山针叶林地下过程对全球气候变化的响应机制提供了科学依据。     

Host Specialization among Wood-Decay Polypore Fungi in a Caribbean Mangrove Forest1

Host specialization in highly diverse tropical forests may be limited by the low local abundance of suitable hosts. To address whether or not fungi in a low‐diversity tropical forest were released from this restriction, fruiting bodies of polypore basidiomycete fungi were collected from three species of mangroves (Avicennia germinans, Laguncularia racemosa, and Rhizophora mangle) in a Caribbean mangrove forest in Panama. Unlike other tropical forests, the polypore assemblage in this mangrove forest was strongly dominated by a few host‐specialized species. Three fungal species, each with strong preference for a different mangrove host species, comprised 88 percent of all fungi collected.     

Fine-scale distribution of pine ectomycorrhizas and their extramatrical mycelium

In order to clarify the functional role of individual ectomycorrhizal (EcM) fungal species in the field, we need to relate their abundance and distribution as mycorrhizas to their abundance and distribution as extramatrical mycelium (EMM). We divided each of four 20 cm x 20 cm x 2 cm slices of pine forest soil into 100 cubes of 2 cm x 2 cm. For each cube, ectomycorrhizas were identified and the presence of EMM of the EcM fungi recorded as ectomycorrhizas was determined by terminal restriction fragment length polymorphism (T-RFLP) analysis of ITS rDNA. Ectomycorrhizas and EMM of seven EcM species were mapped. Spatial segregation of mycorrhizas and EMM was evident and some species produced their EMM in different soil layers from their mycorrhizas. The spatial relationship between mycorrhizas and their EMM generally conformed to their reported exploration types, but EMM of smooth types (e.g. Lactarius rufus) was more frequent than expected. Different EcM fungi foraged at different spatial scales.     

Ectomycorrhiza succession patterns in Pinus sylvestris forests after stand-replacing fire in the Central Alps

Fires shape fundamental properties of many forest ecosystems and climate change will increase their relevance in regions where fires occur infrequently today. In ecosystems that are not adapted to fire, post-fire tree recruitment is often sparse, a fact that might be attributed to a transient lack of mycorrhizae. Ectomycorrhizal (EcM) fungi play an important role for recruitment by enhancing nutrient and water uptake of their hosts. The questions arise whether and for how long the EcM community is transformed by fire. We investigated the resistance and resilience of EcM fungal communities on a chronosequence of 12 Pinus sylvestris stands in Valais (Switzerland) and Val d’Aosta (Italy) affected by fire between 1990 and 2006. Soil samples from burnt and non-burnt forests were analyzed with respect to EcM fungi by means of a bioassay. The number of EcM species was significantly lower in samples from recently (2–5 years) burnt sites than non-burnt forest, and increased with time since fire reaching levels of adjacent forests after 15–18 years. Community composition changed after fire but did not converge to that of non-burnt sites over the 18 year period. Only Rhizopogon roseolus and Cenococcum geophilum were abundant in both burnt sites and adjacent forest. Our data indicate fire resistance of some EcM fungal species as well as rapid resilience in terms of species number, but not in species composition. As long as the function of different EcM species for seedling establishment is unknown, the consequences of long-term shifts in EcM community composition for tree recruitment remain unclear.     

Ectomycorrhizas and putative ectomycorrhizal fungi of Shorea leprosula Miq. (Dipterocarpaceae)

 The ectomycorrhizas of Shorea leprosula Miq. are described and their putative fungal associates discussed. Of the 24 ectomycorrhizal types reported from seedlings, wildlings and 20-year-old trees of Shorea leprosula, 20 were associated with the Basidiomycotina, two with the Ascomycotina and two with either members of the Ascomycotina or the Russulaceae. The dominant group of fungi associated with Shorea leprosula ectomycorrhizas were members of the Russulaceae. This was confirmed by collections of fungal fruiting bodies made under adult Shorea leprosula trees in various parts of Peninsular Malaysia over a period of 3 years. Of the 28 species of putative ectomycorrhizal fungi collected, 15 were members of the Russulaceae. Accepted: 26 March 1997