Symbioses with fungi are important and ubiquitous on dry land but underexplored in the sea. As yet only one seagrass has been shown to form a specific root-fungus symbiosis that resembles those occurring in terrestrial plants, namely the dominant long-lived Mediterranean species Posidonia oceanica (Alismatales: Posidoniaceae) forming a dark septate (DS) endophytic association with the ascomycete Posidoniomyces atricolor (Pleosporales: Aigialaceae). Using stereomicroscopy, light and scanning electron microscopy, and DNA cloning, here we describe a novel root-fungus symbiosis in the Indo-Pacific seagrass Thalassodendron ciliatum (Alismatales: Cymodoceaceae) from a site in the Gulf of Aqaba in the Red Sea. Similarly to P. oceanica, the mycobiont of T. ciliatum occurs more frequently in thinner roots that engage in nutrient uptake from the seabed and forms extensive hyphal mantles composed of DS hyphae on the root surface. Contrary to P. oceanica, the mycobiont occurs on the roots with root hairs and does not colonize its host intraradically. While the cloning revealed a relatively rich spectrum of fungi, they were mostly parasites or saprobes of uncertain origin and the identity of the mycobiont thus remains unknown. Symbioses of seagrasses with fungi are probably more frequent than previously thought, but their functioning and significance are unknown. Melanin present in DS hyphae slows down their decomposition and so is true for the colonized roots. DS fungi may in this way conserve organic detritus in the seagrasses' rhizosphere, thus contributing to blue carbon sequestration in seagrass meadows.

• Keywords
• Blue carbon sequestration, Dark septate endophytes, Epiphytism, Marine fungi, Necromass decomposition, Nutrient uptake, Root-fungus symbioses, Seagrasses,
• MeSH
• Alismatales * microbiology   physiology   MeSH
• Ascomycota physiology   MeSH
• Plant Roots * microbiology   MeSH
• Symbiosis * MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• Indian Ocean MeSH

Despite decades of intensive research (especially from 1970s to 1990s), the ericoid mycorrhizal (ErM) hair root is still largely terra incognita and this simplified guide is intended to revive and promote the study of its mycobiota. Basic theoretical knowledge on the ErM symbiosis is summarized, followed by practical advices on Ericaceae root sample collection and handling, microscopic observations and photo-documentation of root fungal colonization, mycobiont isolation, maintenance and identification and resynthesis experiments with ericoid plants. The necessity of a proper selection of the root material and its surface sterilization prior to mycobiont isolation is stressed, together with the need of including suitable control treatments in inoculation experiments. The culture-dependent approach employing plating of single short (~ 2 mm) hair root segments on nutrient media is substantiated as a useful tool for characterization of Ericaceae root-associated fungal communities; it targets living mycelium and provides metabolically active cultures that can be used in physiological experiments and taxonomic studies, thus providing essential reference material for culture-independent approaches. On the other hand, it is stressed that not every mycobiont isolated from an ericoid hair root necessarily represent an ErM fungus. Likewise, not every intracellular hyphal coil formed in the Ericaceae rhizodermis necessarily represents the ErM symbiosis. Taxonomy of the most important ericoid mycobionts is updated, mutualism in the ErM symbiosis is briefly discussed from the mycobiont perspective, and some interesting lines of possible future research are highlighted.

• Keywords
• Culture-dependent approach, Ericaceae, Ericoid mycorrhizal fungal diversity, In vitro resynthesis, Isolate identification, Microscopy, Mycobiont isolation, Plating of surface-sterilized root segments,
• MeSH
• Ericaceae * MeSH
• Plant Roots MeSH
• Mycorrhizae * MeSH
• Plants MeSH
• Symbiosis MeSH
• Publication type
• Journal Article MeSH
• Review MeSH

Ericoid mycorrhiza is arguably the least investigated mycorrhizal type, particularly when related to the number of potential hosts and the ecosystems they inhabit. Little is known about the global distribution of ericoid mycorrhizal (ErM) fungi, and this holds true even for the prominent ErM mycobiont Rhizoscyphus ericae. Earlier studies suggested R. ericae might be low in abundance or absent in the roots of Southern Hemisphere's Ericaceae, and our previous investigations in two Argentine Patagonian forests supported this view. Here, we revisited the formerly investigated area, albeit at a higher altitude, and screened fungi inhabiting hair roots of Gaultheria caespitosa and Gaultheria pumila at a treeless alpine site using the same methods as previously. We obtained 234 isolates, most of them belonging to Ascomycota. In contrast to previous findings, however, among 37 detected operational taxonomic units (OTUs), OTU 1 (=R. ericae s. str.) comprised the highest number of isolates (87, ∼37 %). Most of the OTUs and isolates belonged to the Helotiales, and 82.5 % of isolates belonged to OTUs shared between both Gaultheria species. At the alpine site, ericoid mycorrhizal fungi dominated, followed by dark septate endophytes and aquatic hyphomycetes probably acting as root endophytes. Our results suggest that the distribution of R. ericae is influenced, among others, by factors related to altitude such as soil type and presence/absence and type of the neighboring vegetation. Our study is the first report on R. ericae colonizing Ericaceae roots in the Southern Hemisphere and extends the known range of this prominent ErM species to NW Patagonia.

• Keywords
• Ericaceae, Ericoid mycorrhiza, Global distribution, Hymenoscyphus ericae, Pezoloma ericae, Southern Hemisphere,
• MeSH
• Ericaceae microbiology   MeSH
• Phylogeny MeSH
• Glomeromycota classification   genetics   isolation & purification   MeSH
• Plant Roots microbiology   MeSH
• Mycorrhizae physiology   MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• Argentina MeSH

The unresolved ecophysiological significance of Dark Septate Endophytes (DSE) may be in part due to existence of morphologically indistinguishable cryptic species in the most common Phialocephala fortinii s. l.--Acephala applanata species complex (PAC). We inoculated three middle European forest plants (European blueberry, Norway spruce and silver birch) with 16 strains of eight PAC cryptic species and other DSE and ectomycorrhizal/ericoid mycorrhizal fungi and focused on intraradical structures possibly representing interfaces for plant-fungus nutrient transfer and on host growth response. The PAC species Acephala applanata simultaneously formed structures resembling ericoid mycorrhiza (ErM) and DSE microsclerotia in blueberry. A. macrosclerotiorum, a close relative to PAC, formed ectomycorrhizae with spruce but not with birch, and structures resembling ErM in blueberry. Phialocephala glacialis, another close relative to PAC, formed structures resembling ErM in blueberry. In blueberry, six PAC strains significantly decreased dry shoot biomass compared to ErM control. In birch, one A. macrosclerotiorum strain increased root biomass and the other shoot biomass in comparison with non-inoculated control. The dual mycorrhizal ability of A. macrosclerotiorum suggested that it may form mycorrhizal links between Ericaceae and Pinaceae. However, we were unable to detect this species in Ericaceae roots growing in a forest with presence of A. macrosclerotiorum ectomycorrhizae. Nevertheless, the diversity of Ericaceae mycobionts was high (380 OTUs) with individual sites often dominated by hitherto unreported helotialean and chaetothyrialean/verrucarialean species; in contrast, typical ErM fungi were either absent or low in abundance. Some DSE apparently have a potential to form mycorrhizae with typical middle European forest plants. However, except A. applanata, the tested representatives of all hitherto described PAC cryptic species formed typical DSE colonization without specific structures necessary for mycorrhizal nutrient transport. A. macrosclerotiorum forms ectomycorrhiza with conifers but not with broadleaves and probably does not form common mycorrhizal networks between conifers with Ericaceae.

• MeSH
• Endophytes MeSH
• Plant Roots microbiology   MeSH
• Mycorrhizae physiology   MeSH
• Picea microbiology   MeSH
• Symbiosis * MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Europe MeSH