Ectomycorrhizal root tips harbor distinctive fungal associates along a soil nitrogen gradient

A diverse range of fungi associate with ectomycorrhizal (EcM) root tips, however, their identity and the biotic and abiotic filters structuring these communities remain unknown. We employed a metabarcoding approach to characterize fungal communities associating with the EcM root tips of Quercus rubra along a natural soil nitrogen gradient. EcM communities and ectomycorrhizal associated fungi (EcAF) were tightly linked across the breadth of the soil gradient. Notably, EcAF communities were primarily shaped by the morphological attributes of EcM communities, particularly the relative abundance of EcM taxa forming rhizomorphic hyphae. Edaphic properties (soil C:N and net N mineralization) exerted minimal influence, suggesting a strong role of biotic interactions in EcAF community assembly. The presence of plants forming ericoid mycorrhizal associations also shapes the prevalence of ericoid mycorrhizal fungi associating with EcM root tips. Overall, EcAF communities were dominated by helotialean fungi, ericoid mycorrhizal fungi, dark septate endophytes, and the white-rot fungi Mycena.     

Pine microsatellite markers allow roots and ectomycorrhizas to be linked to individual trees

Linking roots and ectomycorrhizas (EcM) to individual host trees in the field is required to test whether individual trees support different ectomycorrhizal communities. Here we describe a method that identifies the source of EcM roots by PCR of polymorphic pine nuclear microsatellite loci using fluorescently labelled primers and high-throughput fragment analysis. ITS-PCR can also be performed on the same EcM DNA extract for fungal identification. The method was tested on five neighbouring Scots pine (Pinus sylvestris var scotica) trees in native woodland. Successful host tree identification from DNA extracts of EcM root tips was achieved for 93% of all root fragments recovered from soil cores. It was estimated that each individual mature pine sampled was colonised by between 15 and 19 EcM fungi. The most abundant fungal species were found on all five trees, and within the constraints of the sampling scheme, no differences between trees in EcM fungal community structure or composition were detected.     

Proportion of mycorrhiza-associated trees mediates community assemblages of soil fungi but not of bacteria

Recent studies have shown that mycorrhizal trees can greatly influence soil microbial communities, which in turn play important roles in the function offorest ecosystems. However, there is lack of understanding how the composition of trees with different mycorrhizal types affects soil microbial communities. Here, we collected 1606 soil samples from a 25-ha subtropical forest plot to investigate how the proportion of arbuscular mycorrhizal (AM) versus ectomycorrhizal (EcM) trees mediated soil microbial assemblages. Results showed the alpha diversities of both soil fungal and bacterial communities were significantly positively correlated with the ratio of AM/EcM trees. The AM/EcM tree ratio was important to the fungal community assembly, whereas soil pH was key to the bacterial communities. The increase in the AM/EcM tree ratio decreased the importance of stochastic forces in assembling fungal communities, while it had no significant effect on the bacterial communities. The differential importance of the AM/EcM tree ratio to fungal and bacterial communities highlights the role of mycorrhiza-associated tree composition in regulating soil microbial communities. This finding suggests that forests with different AM/EcM tree ratios would have different soil microbial communities, potentially leading to differences in soil nutrient cycling and in return different tree diversity and forest productivity.     

Mycorrhizal Response to Experimental pH and P Manipulation in Acidic Hardwood Forests

Many temperate forests of the Northeastern United States and Europe have received significant anthropogenic acid and nitrogen (N) deposition over the last century. Although temperate hardwood forests are generally thought to be N-limited, anthropogenic deposition increases the possibility of phosphorus (P) limiting productivity in these forest ecosystems. Moreover, inorganic P availability is largely controlled by soil pH and biogeochemical theory suggests that forests with acidic soils (i.e., <pH 5) are particularly vulnerable to P limitation. Results from previous studies in these systems are mixed with evidence both for and against P limitation. We hypothesized that shifts in mycorrhizal colonization and community structure help temperate forest ecosystems overcome an underlying P limitation by accessing mineral and organic P sources that are otherwise unavailable for direct plant uptake. We examined arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) communities and soil microbial activity in an ecosystem-level experiment where soil pH and P availability were manipulated in mixed deciduous forests across eastern Ohio, USA. One year after treatment initiation, AM root biomass was positively correlated with the most available P pool, resin P, while AM colonization was negatively correlated. In total, 15,876 EcM root tips were identified and assigned to 26 genera and 219 operational taxonomic units (97% similarity). Ectomycorrhizal richness and root tip abundance were negatively correlated with the moderately available P pools, while the relative percent of tips colonized by Ascomycetes was positively correlated with soil pH. Canonical correspondence analysis revealed regional, but not treatment, differences in AM communities, while EcM communities had both treatment and regional differences. Our findings highlight the complex interactions between mycorrhizae and the soil environment and further underscore the fact that mycorrhizal communities do not merely reflect the host plant community.     

Effects of long-term temperature and nutrient manipulation on Norway spruce fine roots and mycelia production

Aims and methods

The effects of changing climate on ectomycorrhizal (EcM) fine roots were studied in northern Sweden by manipulating soil temperature for 14 years and/or by fertilizing for 22 years. Fine root biomass, necromass, EcM root tip biomass, morphology and number as well as mycelia production were determined from soil cores and mesh bags.

Results and conclusions

The fine root biomass and necromass were highest in the fertilized plots, following similar trends in the above-ground biomass, whereas the EcM root tip biomass per basal area decreased by 22 % in the fertilized plots compared to the control. Warming increased the fine root biomass, live/dead-ratio and the number of EcM root tips in the mineral soil and tended to increase the production of EcM mycelia. Greater fine root biomass meant more EcM root tips, although the tip frequency was not affected by fertilization or warming. Significantly higher specific root length of EcM root tips indicated an increased need for nutrients in warmed and in unfertilized plots. Better nutrient supply and warmer soil temperature provide a potential to increase the flow of carbon into the soil via increased fine root biomass, but the carbon balance also depends on root turnover.     

DNA-based fungal diversity in Madagascar and arrival of the ectomycorrhizal fungi to the island

Madagascar is known for its high diversity and endemism of fauna and flora. Fungi, however, have been largely overlooked in diversity and evolution studies on the island, and whether fungi exhibit the same patterns as animals and plants has yet to be further examined. We collected fungal sporocarps and ectomycorrhizal (EcM) roots during three opportunistic surveys in five forests in Madagascar and generated a dataset of fungal Internal Transcribed Spacer (ITS) DNA sequences. We analyzed them together with all publicly available fungal ITS DNA sequences and identified 620 Operational Taxonomic Units (OTUs) from Madagascar, 10% of which contained only sequences from our surveys. Two hundred and ninety-two OTUs belonged to EcM species with /russula-lactarius, /boletus, /tomentella-telephora, /cortinarius, and /amanita being the most abundant EcM lineages. Overall, 60% of all fungi and 81% of the EcM species from Madagascar appear to be endemic. We conducted a phylogenetic analysis using all the OTUs in Amanitaceae, Boletaceae, and Russulaceae families to elucidate their relative timing of arrival in Madagascar. We found that most EcM species from Madagascar in the three families diverged less than 22 million years ago (mya), long after the separation of India and Madagascar (88 mya), which is consistent with a dispersal mediated process of arrival to the island. Our study provides the first comprehensive view of the overall DNA-based fungal diversity in Madagascar and the current state of knowledge of EcM fungi based on DNA sequences, useful for further ecological and evolutionary studies. Abstract in Malagasy is available with online material.     

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.     

Susceptibility of ectomycorrhizal fungi to soil heating

Ectomycorrhizal (EcM) fungi are an important biotic factor for successful tree recruitment because they enhance plant growth and alleviate drought stress of their hosts. Thus, EcM propagules are expected to be a key factor for forest regeneration after major disturbance events such as stand-replacing forest fires. Yet the susceptibility of soil-borne EcM fungi to heat is unclear. In this study, we investigated the heat tolerance of EcM fungi of Scots pine (Pinus sylvestris L., Pinaceae). Soil samples of three soil depths were heated to the temperature of 45, 60 and 70 °C, respectively, and surviving EcM fungi were assessed by a bioassay using Scots pine as an experimental host plant. EcM species were identified by a combination of morphotyping and sequencing of the ITS region. We found that mean number of species per sample was reduced by the 60 and 70 °C treatment, but not by the 45 °C treatment. Species composition changed due to heat. While some EcM fungi species did not survive heating, the majority of species was also found in the heated samples. The most frequent species in the heat treatment were Rhizopogon roseolus, Cenococcum geophilum and several unidentified species.     

Presence of arbuscular mycorrhizas in typically ectomycorrhizal host species from Cameroon and New Zealand

 Ectomycorrhizas (EcM) and arbuscular mycorrhizas (AM) were screened for in saplings of 14 EcM tree species from the N'Dupé and Korup National Park rainforests, SW Cameroon, belonging to Caesalpiniaceae and Uapacaceae. The pattern of EcM and AM colonisation of a dual mycorrhizal species from this rainforest (Uapaca staudtii, Uapacaceae) was compared with dual EcM/AM colonisation of Leptospermum scoparium (Myrtaceae) from New Zealand. Both species were collected in a range of habitats. EcM and AM colonisation differed among species in the Korup National Park rainforest: 12 species belonging to the Caesalpiniaceae (Amherstieae) were consistently EcM, and AM structures occurred occasionally in six of them; two other species belonging to Caesalpiniaceae (Afzelia bipindensis) and Uapacaceae (U. staudtii) were dual mycorrhizal with variable levels of colonisation by both EcM and AM fungi. EcM and AM dual colonisation varied with both habitat and identity of the partners. The presence of EcM fungi in most of the root samples of U. staudtii and a negative relationship between AM and EcM colonisation within the same root system suggested a greater EcM affinity of this species. In contrast, most root samples of L. scoparium were colonised by AM, but only a few by EcM. Genuine dual EcM/AM associations in root samples of U. staudtii where the two mycorrhizal types co-occurred could be attributed to an AM-EcM succession. However, differences between predicted and observed frequencies of genuine dual EcM/AM associations in several samples of both U. staudtii and L. scoparium indicated that other factors influenced dual EcM/AM associations. The results of this study showed the importance of the identity of the host species in determining the pattern of dual EcM and AM colonisation. Accepted: 18 September 1998     

Host plants and edaphic factors influence the distribution and diversity of ectomycorrhizal fungal fruiting bodies within rainforests from Tshopo,Democratic Republic of the Congo

Ectomycorrhizal fungi constitute an important component of forest ecosystems that enhances plant nutrition and resistance against stresses. Diversity of ectomycorrhizal (EcM) fungi is, however, affected by host plant diversity and soil heterogeneity. This study provides information about the influence of host plants and soil resources on the diversity of ectomycorrhizal fungal fruiting bodies from rainforests of the Democratic Republic of the Congo. Based on the presence of fungal fruiting bodies, significant differences in the number of ectomycorrhizal fungi species existed between forest stand types (p < 0.001). The most ectomycorrhizal species‐rich forest was the Gilbertiodendron dewevrei‐dominated forest (61 species). Of all 93 species of ectomycorrhizal fungi, 19 demonstrated a significant indicator value for particular forest stand types. Of all analysed edaphic factors, the percentage of silt particles was the most important parameter influencing EcM fungi host plant tree distribution. Both host trees and edaphic factors strongly affected the distribution and diversity of EcM fungi. EcM fungi may have developed differently their ability to successfully colonise root systems in relation to the availability of nutrients.     

Assessing ectomycorrhizal fungal spore banks of truffle producing soils with pecan seedling trap-plants

Background and Aims

Recently, the truffle species Tuber lyonii Butters was found to be dominant in ectomycorrhizal (EcM) fungal communities of cultivated pecan (Carya illinoinensis (Wangenh.) K. Koch). Many truffle fungi exhibit the trait of effectively colonizing plant roots via spores. We hypothesized that T. lyonii would be well represented in the spore bank of pecan orchard soils where it is found.

Methods

We used axenically-grown pecan seedlings as trap-plants to bait for EcM associates in soils collected beneath truffle-producing pecan trees. EcM fungi on seedlings were characterized through rDNA sequencing and were compared to EcM communities of adult trees in these orchards.

Results

Tuber lyonii mycorrhizas were well formed on seedlings inoculated with truffle spores, but were limited to just a few of the trap-plants grown in field soils. We compared EcM communities of adult pecan orchard trees to those on trap-plants and found distinct communities on each, with a high degree of similarity at the ordinal but not species level.

Conclusions

Although species of Pezizales are abundant in pecan EcM communities and as propagules in their soil spore banks, only a low level of T. lyonii was detected in soil spore banks beneath orchard trees naturally colonized by T. lyonii. Other factors including land-use history or orchard management may better explain this truffle species presence and abundance in pecan EcM communities.

     

High diversity and widespread occurrence of mitotic spore mats in ectomycorrhizal Pezizales

Fungal mitospores may function as dispersal units and/ or spermatia and thus play a role in distribution and/or mating of species that produce them. Mitospore production in ectomycorrhizal (EcM) Pezizales is rarely reported, but here we document mitospore production by a high diversity of EcM Pezizales on three continents, in both hemispheres. We sequenced the internal transcribed spacer (ITS) and partial large subunit (LSU) nuclear rDNA from 292 spore mats (visible mitospore clumps) collected in Argentina, Chile, China, Mexico and the USA between 2009 and 2012. We collated spore mat ITS sequences with 105 fruit body and 47 EcM root sequences to generate operational taxonomic units (OTUs). Phylogenetic inferences were made through analyses of both molecular data sets. A total of 48 OTUs from spore mats represented six independent EcM Pezizales lineages and included truffles and cup fungi. Three clades of seven OTUs have no known meiospore stage. Mitospores failed to germinate on sterile media, or form ectomycorrhizas on Quercus, Pinus and Populus seedlings, consistent with a hypothesized role of spermatia. The broad geographic range, high frequency and phylogenetic diversity of spore mats produced by EcM Pezizales suggests that a mitospore stage is important for many species in this group in terms of mating, reproduction and/or dispersal.     

Ectomycorrhizal fungi of exotic pine plantations in relation to native host trees in Iran: evidence of host range expansion by local symbionts to distantly related host taxa

Introduction of exotic plants change soil microbial communities which may have detrimental ecological consequences for ecosystems. In this study, we examined the community structure and species richness of ectomycorrhizal (EcM) fungi associated with exotic pine plantations in relation to adjacent native ectomycorrhizal trees in Iran to elucidate the symbiont exchange between distantly related hosts, i.e. Fagales (Fagaceae and Betulaceae) and Pinaceae. The combination of morphological and molecular identification approaches revealed that 84.6 % of species with more than one occurrence (at least once on pines) were shared with native trees and only 5.9 % were found exclusively on pine root tips. The community diversity of ectomycorrhizal fungi in the pine plantations adjacent to native EcM trees was comparable to their adjacent native trees, but the isolated plantations hosted relatively a species-poor community. Specific mycobionts of conifers were dominant in the isolated plantation while rarely found in the plantations adjacent to native EcM trees. These data demonstrate the importance of habitat isolation and dispersal limitation of EcM fungi in their potential of host range expansion. The great number of shared and possibly compatible symbiotic species between exotic Pinaceae and local Fagales (Fagaceae and Betulaceae) may reflect their evolutionary adaptations and/or ancestral compatibility with one another.     

The production of ectomycorrhizal mycelium in forests: Relation between forest nutrient status and local mineral sources

Due to acid rain and nitrogen deposition, there is growing concern that other mineral nutrients, primarily potassium and phosphorus, might limit forest production in boreal forests. Ectomycorrhizal (EcM) fungi are important for the acquisition of potassium and phosphorus by trees. In a field investigation, the effects of poor potassium and phosphorus status of forest trees on the production of EcM mycelium were examined. The production of EcM mycelium was estimated in mesh bags containing sand, which were buried in the soil of forests of different potassium and phosphorus status. Mesh bags with 2% biotite or 1% apatite in sand were also buried to estimate the effect of local sources of nutrients on the production of EcM mycelium. No clear relation could be found between the production of EcM mycelium and nutrient status of the trees. Apatite stimulated the mycelial production, while biotite had no significant effect. EcM root production at the mesh bag surfaces was stimulated by apatite amendment in a forest with poor phosphorus status. The contribution of EcM fungi to apatite weathering was estimated by using rare earth elements (REE) as marker elements. The concentration of REE was 10 times higher in EcM roots, which had grown in contact with the outer surface of apatite-amended mesh bags than in EcM roots grown in contact with the biotite amended or sand-filled mesh bags. In a laboratory study, it was confirmed that REE accumulated in the roots with very low amounts <1 translocated to the shoots. The short-term effect of EcM mycelium on the elemental composition of biotite and apatite was investigated and compared with biotite- and apatite-amended mesh bags buried in trenched soil plots, which were free from EcM fungi. The mesh bags subjected to EcM fungi showed no difference in chemical composition after 17 months in the field. This study suggests that trees respond to phosphorus limitation by increased exploitation of phosphorus-containing minerals by ectomycorrhiza. However, the potential to ameliorate potassium limitation in a similar way appears to be low.     

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.     

Biotic interactions with mycorrhizal systems as extended nutrient acquisition strategies shaping forest soil communities and functions

Plant nutrient acquisition strategies involving ectomycorrhizal (EcM) and arbuscular mycorrhizal (AM) associations, are key plant functional traits leading to distinct carbon (C) and nutrient dynamics in forests. Yet, little is known about how these strategies influence the structure and functioning of soil communities, and if such mycorrhizal effects may be more or less pronounced depending on the type of forest and various abiotic factors. Here we explore the potential interactions occurring between plant-EcM and plant-AM systems with the diverse soil organisms occurring in forest soils, and in the process draw attention to major issues that are worthy for future research directions. Based on these potential interactions, we suggest that EcM systems, especially those involving gymnosperms in colder climates, may select for a soil community with a narrow set of functions. These EcM systems may exhibit low functional redundancy, dominated by symbiotic interactions, where EcM fungi maintain low pH and high C/N conditions in order to tightly control nutrient cycling and maintain the dominance of EcM trees. By contrast, AM systems, particularly those involving deciduous angiosperm trees in mild and warmer climates, may facilitate a functionally more diverse and redundant soil community tending towards the dominance of competitive and antagonistic interactions, but also with a range of symbiotic interactions that together maintain diverse plant communities. We propose that the contrasting belowground interactions in AM and EcM systems act as extended nutrient acquisition traits that contribute greatly to the prevailing nutrient and C dynamics occurring in these systems.     

Ectomycorrhizal fungi diversity in a white sand forest in western Amazonia

The genera Dicymbe and Aldina (Fabaceae) host ectomycorrhizal fungi (EcM) and are common in white sand forests (WSFs), a highly specialized habitat with a high level of plant endemism compared with terra-firme forests. In this study, we visited four times a 1-ha permanent plot established in a small patch of a WSF in the south of Colombia Amazonia. Forty-eight species of EcM fungi were recovered from sporocarps and 15 ITS species-level were detected from root tips. Seventeen species were new reports to Colombia and seven corresponded to undescribed species. These results confirm that this WSF supports a significant EcM fungal diversity. Most of the species found in this study have been previously reported to be associated with other legume and/or dipterocarp species from geographically distant forests. The long-distance occurrence combined with low host specificity, suggest the possibility of gene flow between geographically distant populations of EcM fungi in neotropical lowland rainforests.     

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.