Mycorrhizal Anatomy Research Articles

Tomentella brunneoincrustata, the first described species of the Pisonieae-associated Neotropical Tomentella clade, and phylogenetic analysis of the genus in Mexico

The /tomentella-thelephora lineage is one of the most highly dominant clades among ectomycorrhizal communities worldwide. Despite its importance as a root symbiont, its fruit bodies are inconspicuous and rarely found. Knowledge regarding the diversity of Tomentella in the Neotropics is scarce, and is based largely on environmental samples. Here, we describe a new species, Tomentella brunneoincrustata, including its basidiocarp morphology, mycorrhizal anatomy, and ecology. Because knowledge of Tomentella in Mexico is scarce, we provide the first phylogenetic analysis of this genus in the country. We sequenced the nrITS region of the fungal samples, and sequenced the rbcL and trnL regions to identify the host plant. The phylogenetic analyses were conducted by Bayesian inference. The Bayesian analysis showed that several paraphyletic clades within the lineage /tomentella-thelephora are associated with Pisonieae present across tropical regions of the world. However, the ectomycorrhizae sequences from Puerto Rico, Florida, Dominica, and Mexico constituted a well-supported monophyletic clade that we denote as the “Pisonieae-associated Neotropical Tomentella clade”. Within this clade, T. brunneoincrustata was characterized as follows: a thin crustose, strongly attached to the substrate basidiome; concolorous subiculum, undifferentiated and sterile margin; two types of subiculum hyphae; and small (<8 μm) globose to ellipsoid spores. This species develops in tropical dry forests, where it associates with hosts in the Pisonieae tribe within the Nyctaginaceae. The remaining Tomentella fruit body vouchers collected in temperate forests of Mexico belonged to clades related to T. atramentaria, T. pilosa, T. muricata, T. fuscocinerea, T. stuposa, T. punicea, T. atroarenicolor, T. bryophila, and T. lateritia. Five fruit body vouchers had unique sequences forming independent and unknown clades of Tomentella.

Specificity of plant-microbe interactions in the tree mycorrhizosphere biome and consequences for soil C cycling.

Mycorrhizal associations are ubiquitous and form a substantial component of the microbial biomass in forest ecosystems and fluxes of C to these belowground organisms account for a substantial portion of carbon assimilated by forest vegetation. Climate change has been predicted to alter belowground plant-allocated C which may cause compositional shifts in soil microbial communities, and it has been hypothesized that this community change will influence C mitigation in forest ecosystems. Some 10,000 species of ectomycorrhizal fungi are currently recognized, some of which are host specific and will only associate with a single tree species, for example, Suillus grevillei with larch. Mycorrhizae are a strong sink for plant C, differences in mycorrhizal anatomy, particularly the presence and extent of emanating hyphae, can affect the amount of plant C allocated to these assemblages. Mycorrhizal morphology affects not only spatial distribution of C in forests, but also differences in the longevity of these diverse structures may have important consequences for C sequestration in soil. Mycorrhizal growth form has been used to group fungi into distinctive functional groups that vary qualitatively and spatially in their foraging and nutrient acquiring potential. Through new genomic techniques we are beginning to understand the mechanisms involved in the specificity and selection of ectomycorrhizal associations though much less is known about arbuscular mycorrhizal associations. In this review we examine evidence for tree species- mycorrhizal specificity, and the mechanisms involved (e.g., signal compounds). We also explore what is known about the effects of these associations and interactions with other soil organisms on the quality and quantity of C flow into the mycorrhizosphere (the area under the influence of mycorrhizal root tips), including spatial and seasonal variations. The enormity of the mycorrhizosphere biome in forests and its potential to sequester substantial C belowground highlights the vital importance of increasing our knowledge of the dynamics of the different mycorrhizal functional groups in diverse forests.

Fungal associates of Pyrola rotundifolia, a mixotrophic Ericaceae, from two Estonian boreal forests

Pyrola rotundifolia (Ericaceae, Pyroleae tribe) is an understorey subshrub that was recently demonstrated to receive considerable amount of carbon from its fungal mycorrhizal associates. So far, little is known of the identity of these fungi and the mycorrhizal anatomy in the Pyroleae. Using 140 mycorrhizal root fragments collected from two Estonian boreal forests already studied in the context of mixotrophic Ericaceae in sequence analysis of the ribosomal DNA internal transcribed spacer region, we recovered 71 sequences that corresponded to 45 putative species in 19 fungal genera. The identified fungi were mainly ectomycorrhizal basidiomycetes, including Tomentella, Cortinarius, Russula, Hebeloma, as well as some ectomycorrhizal and/or endophytic ascomycetes. The P. rotundifolia fungal communities of the two forests did not differ significantly in terms of species richness, diversity and nutritional mode. The relatively high diversity retrieved suggests that P. rotundifolia does not have a strict preference for any fungal taxa. Anatomical analyses showed typical arbutoid mycorrhizae, with variable mantle structures, uniseriate Hartig nets and intracellular hyphal coils in the large epidermal cells. Whenever compared, fungal ultrastructure was congruent with the molecular identification. Similarly to other mixotrophic and autotrophic pyroloids in the same forests, P. rotundifolia shares its mycorrhizal fungal associates with surrounding trees that are likely a carbon source for pyroloids.

Morphological and molecular comparison of white truffle ectomycorrhizae

In the present study, white truffle ectomycorrhizae (EM) collected in deciduous forests (Populus, Quercus, and Fagus) from Hungary were characterized by morphological-anatomical and molecular methods. Our investigations suggest that the EM of white truffles (e.g., Tuber rapaeodorum, Tuber puberulum, Tuber rufum) are common and abundant members of the forest communities in the area. The ITS sequences of 14 EM specimens and 46 additional fruitbody sequences from the GenBank were clustered into four main groups in phylogenetic analyses. In the ITS-1 region, a characteristic indel pattern was found, which supports the clades. Although our analyses indicate definite genetic distance between the groups of the phylogenetic tree, these clades do not correspond to the traditional taxons identified by fruitbody characteristics. Comparison of the ectomycorrhizae shows that neither is mycorrhizal anatomy a good tool to separate the groups, because the characters (like the epidermoid or angular mantle structure, cell wall thickness, the sape and size of cystidia) are too variable and overlap between the clades. The interspecific similarity, observed both in ectomycorrhizal and fruitbody characters, strengthen the sensu lato morpho-species concept of this group. Our study, which combines comprehensive molecular and anatomical approach to characterize and identify ectomycorrhizae of white truffles from natural samples, stress out the need of the taxonomical revision of this group.

Mycorrhiza of the host-specific Lactarius deterrimus on the roots of Picea abies and Arctostaphylos uva-ursi

The ectomycorrhizal basidiomycete species Lactarius deterrimus Gröger is considered to be a strictly host-specific mycobiont of Picea abies (L.) Karst. However, we identified arbutoid mycorrhiza formed by this fungus on the roots of Arctostaphylos uva-ursi (L.) Spreng. in a mixed stand at the alpine timberline; typical ectomycorrhiza of P. abies were found in close relation. A. uva-ursi is known as an extremely unspecific phytobiont. The mycorrhizae of both associations are described and compared morphologically. The mycorrhiza formed by L. deterrimus on both A. uva-ursi and P. abies show typical ectomycorrhizal features such as a hyphal mantle and a Hartig net. The main difference between the mycorrhizal symbioses with the different phytobionts is the occurrence of intracellular hyphae in the epidermal cells of A. uva-ursi. This emphasizes the importance of the plant partner for mycorrhizal anatomy. This is the first report of a previously considered host-specific ectomycorrhizal fungus in association with A. uva-ursi under natural conditions. The advantages of this loose specificity between the fungus and plant species is discussed.

Molecular kinship analyses of the agaricoid Russulaceae: Correspondence with mycorrhizal anatomy and sporocarp features in the genus Russula

A data set of LSU DNA sequences of mainly European Russula and Lactarius species was subjected to molecular phylogenetic analysis. Species could be allocated to six clades, with an unresolved phylogeny. One of these clades represents the genus Lactarius. The only analysed species of the section Archaeinae (Russula) was placed basal to both genera. Thus Lactarius appears to be derived from Russula. Russula was divided into four clusters, corresponding to the sections Plorantinae and Nigricantinae, subgenus Heterophyllidia including the section Foetentinae, and a cluster representing the remaining subgenera of the “Genuinae”. Even though the resulting groups can be considered as valid classificatory groups, species associations resulting from molecular analyses neither support the division of Russula into the subgenus Compacta (including the sections Nigricantinae, Plorantinae, and Archaeinae) and the “Genuinae” (including all remaining taxa), nor do they support previously proposed evolutionary lineages within the “Genuinae”. Ribosomal ITS DNA sequences of Russula species were analysed to achieve better infrageneric resolution. The results are discussed in relation to current classification systems and to what is known about the mycorrhizae formed by Russula species. While the systematic value attached to many macroscopic and microscopic sporocarp features was not supported by sequence data, mycorrhizal anatomy is in good correspondence with many of the results from the phylogenetic analysis.

Cultivation of mushrooms of edible ectomycorrhizal fungi associated with Pinus densiflora by in vitro mycorrhizal synthesis

The morphology and anatomy of ectomycorrhizas of edible mushroom fungi in association with Pinus densiflora seedlings are described. These include species of Lyophyllum, Tricholoma, Suillus, Rhizopogon, and Lactarius. Almost all mycorrhizas synthesized in vitro could be acclimatized in open-pot soil conditions after 8–9 months. Although mycorrhizal anatomy was almost identical under in vitro and open-pot culture conditions, external morphology, such as the development of rhizomorphs and hydrophobic aerial hyphae, differed between the two conditions in some fungal species. Fully developed, mature mycorrhizas of different fungal species could be distinguished as ectomycorrhizal morphotypes, which could also be distinguished by PCR-RFLP analysis of their rDNA.

Variation in Mycorrhizal and Spore Morphology of Glomus Occultum and Glomus Diaphanum as Influenced by Plant Host and Soil Environment

Spore and mycorrhizal morphology were examined among isolates of Glomus occultum and Glomus diaphanum collected from soils with dissimilar physical and chemieal properties and maintained in pot culture on five plant species. Spore size, color, and structure were not influenced significantly by host or soil environmental interactions. Spore wall structure consistently separated G. occultum and G. diaphanum. Intraspecific variation in overlapping taxonomic characteristics such as spore size did not obscure significant differences between species. These results provide further evidence that spore morphological characteristics are valid criteria for identifying and classifying VA mycorrhizal fungi. However, mycorrhizal morphology also differentiated the two endophyte species. Intraradical structures formed by G. occultum stained weakly within two weeks after initial penetration of roots and disappeared thereafter. Glomus diaphanum produced arbuscules, vesicles, and spores in stained roots. Mycorrhizal morphology and ontogeny of each endophyte were similar in all hosts. Significant variation was expressed in the rate and degree of mycorrhizal development. Disparate, yet consistent, mycorrhizae formed by G. occultum and G. diaphanum indicate that mycorrhizal anatomy also may be important in the classification of VA mycorrhizal fungi.