Diversity of putative ericoid mycorrhizal fungi increases with soil age and progressive phosphorus limitation across a 4.1-million-year chronosequence

A cryptic root isolate belonging to Geoglossales from potted Rhododendron: its molecular phylogeny and ability to colonize an ericoid mycorrhizal host in vitro

Although the lifestyle of Geoglossales remains largely unknown, recent advancements have established a hypothesis regarding the ericoid mycorrhizal lifestyle of geoglossoid fungi. In this study, we focused on one isolate of Geoglossales sp. obtained from surface-sterilized roots of potted Rhododendron transiens. We aimed to reveal the phylogenetic position and in vitro colonizing ability of this species in the hair roots of ericoid mycorrhizal plants. Based on our multigene phylogenetic tree, this species is a sister of the genus Sarcoleotia which has not been reported from either other studies or field environment. Its ascocarps could not be obtained, and conspecific sequences were not found in the databases and repositories examined. The Geoglossales sp. colonized the vital rhizodermal cells of blueberries in vitro with hyphal coils. There were relatively large morphological variations of coils consistent with extraradical hyphae; however, overall, the colonization morphologically resembled those by Sarcoleotia globosa and representative ericoid mycorrhizal fungi. The taxonomy and ecological significance of the species remain to be resolved; nevertheless, our results suggest that the ericoid mycorrhizal lifestyle may be widespread within Geoglossales.

Exploring structural and molecular diversity of Ericaceae hair root mycobionts: a comparison between Northern Bohemia and Argentine Patagonia

Core Ericaceae produce delicate hair roots with inflated rhizodermal cells that host plethora of fungal symbionts. These poorly known mycobionts include various endophytes, parasites, saprobes, and the ericoid mycorrhizal (ErM) fungi (ErMF) that form the ErM symbiosis crucial for the fitness of their hosts. Using microscopy and high-throughput sequencing, we investigated their structural and molecular diversity in 14 different host × site combinations in Northern Bohemia (Central Europe) and Argentine Patagonia (South America). While we found typical ericoid mycorrhiza in all combinations, we did not detect ectomycorrhiza and arbuscular mycorrhiza. Superficial mantles of various thickness formed by non-clamped hyphae were observed in all combinations except Calluna vulgaris from N. Bohemia. Some samples contained frequent intercellular hyphae while others possessed previously unreported intracellular haustoria-like structures linked with intracellular hyphal coils. The 711 detected fungal OTU were dominated by Ascomycota (563) and Basidiomycota (119), followed by four other phyla. Ascomycetes comprised Helotiales (255), Pleosporales (53), Chaetothyriales (42), and other 19 orders, while basidiomycetes Sebacinales (42), Agaricales (28), Auriculariales (7), and other 14 orders. While many dominant OTU from both hemispheres lacked close relatives in reference databases, many were very similar to identical to unnamed sequences from around the world. On the other hand, several significant ericaceous mycobionts were absent in our dataset, incl. Cairneyella, Gamarada, Kurtia, Lachnum, and Leohumicola. Most of the detected OTU could not be reliably linked to a particular trophic mode, and only two could be reliably assigned to the archetypal ErMF Hyaloscypha hepaticicola. Probable ErMF comprised Hyaloscypha variabilis and Oidiodendron maius, both detected only in N. Bohemia. Possible ErMF comprised sebacinoid fungi and several unnamed members of Hyaloscypha s. str. While H. hepaticicola was dominant only in C. vulgaris, this model ErM host lacked O. maius and sebacinoid mycobionts. Hyaloscypha hepaticicola was absent in two and very rare in six combinations from Patagonia. Nine OTU represented dark septate endophytes from the Phialocephala fortinii s. lat.-Acephala applanata species complex, including the most abundant OTU (the only detected in all combinations). Statistical analyses revealed marked differences between N. Bohemia and Patagonia, but also within Patagonia, due to the unique community detected in a Valdivian temperate rainforest. Our results show that the ericaceous hair roots may host diverse mycobionts with mostly unknown functions and indicate that many novel ErMF lineages await discovery. Transhemispheric differences (thousands of km) in their communities may be evenly matched by local differences (scales of km, m, and less).

Role of mycorrhizas and root exudates in plant uptake of soil nutrients (calcium, iron, magnesium, and potassium): has the puzzle been completely solved?

Anthropogenic global change is driving an increase in the frequency and intensity of drought and flood events, along with associated imbalances and limitation of several soil nutrients. In the context of an increasing human population, these impacts represent a global-scale challenge for biodiversity conservation and sustainable crop production to ensure food security. Plants have evolved strategies to enhance uptake of soil nutrients under environmental stress conditions; for example, symbioses with fungi (mycorrhization) in the rhizosphere and the release of exudates from roots. Although crop cultivation is managed for the effects of limited availability of nitrogen (N) and phosphorus (P), there is increasing evidence for limitation of plant growth and fitness because of the low availability of other soil nutrients such as the metals potassium (K), calcium (Ca), magnesium (Mg), and iron (Fe), which may become increasingly limiting for plant productivity under global change. The roles of mycorrhizas and plant exudates on N and P uptake have been studied intensively; however, our understanding of the effects on metal nutrients is less clear and still inconsistent. Here, we review the literature on the role of mycorrhizas and root exudates in plant uptake of key nutrients (N, P, K, Ca, Mg, and Fe) in the context of potential nutrient deficiencies in crop and non-crop terrestrial ecosystems, and identify knowledge gaps for future research to improve nutrient-uptake capacity in food crop plants.

Fungi in hair roots of Vaccinium spp. (Ericaceae) growing on decomposing wood: colonization patterns, identity, and in vitro symbiotic potential

Most of our knowledge on the ericoid mycorrhizal (ErM) symbiosis comes from temperate heathlands characterized by acidic peaty soils and many experiments with a few ascomycetous fungi. However, ericaceous plants thrive in many other ecosystems and in temperate coniferous forests, their seedlings often prosper on decomposing wood. While wood is typically exploited by basidiomycetous ectomycorrhizal (EcM) and saprobic fungi, the role of ErM fungi (ErMF) is much less clear. We explored the cultivable mycobiota of surface sterilized hair roots of Vaccinium spp. growing on decomposing wood in two coniferous forests in Mid-Norway (Scandinavia) and Northern Bohemia (Central Europe). Obtained isolates were identified using molecular tools and their symbiotic potential was tested in vitro. While the detected community lacked the archetypal ErMF Hyaloscypha hepaticicola and the incidence of dark septate endophytes and EcM fungi was negligible, it comprised other frequent asexual ascomycetous ErMF, namely H. variabilis and Oidiodendron maius, together with several isolates displaying affinities to sexual saprobic H. daedaleae and H. fuckelii. Ascomycete-suppressing media revealed representatives of the saprobic basidiomycetous genera Coprinellus, Gymnopilus, Mycena (Agaricales), and Hypochnicium (Polyporales). In the resyntheses, the tested basidiomycetes occasionally penetrated the rhizodermal cells of their hosts but never formed ericoid mycorrhizae and in many cases overgrew and killed the inoculated seedlings. In contrast, a representative of the H. daedaleae/H. fuckelii-related isolates repeatedly formed what morphologically appears as the ErM symbiosis and supported host's growth. In conclusion, while basidiomycetous saprobic fungi have a potential to colonize healthy-looking ericaceous hair roots, the mode(-s) of their functioning remain obscure. For the first time, a lineage in Hyaloscypha s. str. (corresponding to the former Hymenoscyphus ericae aggregate) where sexual saprobes are intermingled with root symbionts has been revealed, shedding new light on the ecology and evolution of these prominent ascomycetous ErMF.

Habitat Protection Approaches Facilitate Conservation of Overlooked Fungal Diversity - A Case Study From the Norwegian Coastal Heathland System

European coastal heathlands are distinct ecosystems shaped by land use tradition and they have experienced an 80% area reduction from their historical maximum. These mosaics of mires and wind exposed patches have ericaceous shrub dominated vegetation, and soils within coastal heathlands are characterized by low pH and high levels of recalcitrant debris. Using a culture-based approach with molecular identification of isolates, we characterized root-associated fungal communities of six ericaceous species in eight heathland localities along Norway's western coast. Site-level alpha diversity ranged from 21-38 OTUs, while the total estimated gamma diversity for culturable heathland root fungi was 190-231 OTUs. Most species recovered are previously reported at low abundance in Norway, suggesting the biodiversity in this community is underreported, rather than novel for science. The fungi recovered were primarily Ascomycota, specifically endophytic Phialocephala, and Pezicula, and no host specificity was observed in the communities. The fungal communities exhibited high turnover and low nestedness, both between ericaceous hosts and across heathland sites. We observed no spatial patterns in fungal betadiversity, and this heterogeneity may be a product of the unique historic land use practices at each locality creating a distinct mycofloral "fingerprint". Robust diversity estimates will be key for managing fungal biodiversity in coastal heathlands. Our results indicate that sampling schemes that maximize the number of host plants sampled per site, rather than the number of cultures per plant yield improved alpha diversity estimates. Similarly, gamma diversity estimates are improved by maximizing the total number of localities sampled, rather than increasing the number of plants sampled per locality. We argue that while the current protected status of coastal heathland habitats and restoration efforts have knock-on effects for the conservation of fungal biodiversity, fungi have a vital functional role in the ecosystem and holistic conservation plans that consider fungal biodiversity would be beneficial.