A novel plant-fungal mutualism associated with fire

Fire shapes fungal guild diversity and composition through direct and indirect pathways

Fire has shaped global ecosystems for millennia by directly killing organisms and indirectly altering habitats and resources. All terrestrial ecosystems, including fire-prone ecosystems, rely on soil-inhabiting fungi, where they play vital roles in ecological processes. Yet our understanding of how fire regimes influence soil fungi remains limited and our knowledge of these interactions in semiarid landscapes is virtually absent. We collected soil samples and vegetation measurements from sites across a gradient in time-since-fire ages (0-75 years-since-fire) and fire frequency (burnt 0-5 times during the recent 29-year period) in a semiarid heathland of south-eastern Australia. We characterized fungal communities using ITS amplicon-sequencing and assigned fungi taxonomically to trophic guilds. We used structural equation models to examine direct, indirect and total effects of time-since-fire and fire frequency on total fungal, ectomycorrhizal, saprotrophic and pathogenic richness. We used multivariate analyses to investigate how total fungal, ectomycorrhizal, saprotrophic and pathogenic species composition differed between post-fire successional stages and fire frequency classes. Time-since-fire was an important driver of saprotrophic richness; directly, saprotrophic richness increased with time-since-fire, and indirectly, saprotrophic richness declined with time-since-fire (resulting in a positive total effect), mediated through the impact of fire on substrates. Frequently burnt sites had lower numbers of saprotrophic and pathogenic species. Post-fire successional stages and fire frequency classes were characterized by distinct fungal communities, with large differences in ectomycorrhizal species composition. Understanding the complex responses of fungal communities to fire can be improved by exploring how the effects of fire flow through ecosystems. Diverse fire histories may be important for maintaining the functional diversity of fungi in semiarid regions.

Safe Production Strategies for Soil-Covered Cultivation of Morel in Heavy Metal-Contaminated Soils

Morel is a popular edible mushroom with considerable medicinal and economic value which has garnered global popularity. However, the increasing heavy metal (HM) pollution in the soil presents a significant challenge to morels cultivation. Given the susceptibility of morels to HM accumulation, the quality and output of morels are at risk, posing a serious food safety concern that hinders the development of the morel industry. Nonetheless, research on the mechanism of HM enrichment and mitigation strategies in morel remains scarce. The morel, being cultivated in soil, shows a positive correlation between HM content in its fruiting body and the HM content in the soil. Therefore, soil remediation emerges as the most practical and effective approach to tackle HM pollution. Compared to physical and chemical remediation, bioremediation is a low-cost and eco-friendly approach that poses minimal threats to soil composition and structure. HMs easily enriched during morels cultivation were examined, including Cd, Cu, Hg, and Pb, and we assessed soil passivation technology, microbial remediation, strain screening and cultivation, and agronomic measures as potential approaches for HM pollution prevention. The current review underscores the importance of establishing a comprehensive system for preventing HM pollution in morels.

Soil biogeochemistry and microbial community dynamics in Pinus pinaster Ait. forests subjected to increased fire frequency

Fire frequency might increase in many fire-dominated ecosystems of the world due to the combined effects of global warming, land-use change and increased human pressures. Understanding how changes in fire frequency can affect the main soil biogeochemical dynamics, as well as the microbial community, in the long term is utmost important. Here we determined the effect of changes in fire frequency and other fire history characteristics on soil C and N dynamics and the main microbial groups (using soil fatty acid profiles), in Pinus pinaster forests from central Spain. Stands were chosen to differ in the number of fires (1 to 3) occurred between 1976 and 2018, in the time elapsed since the last fire and the interval undergone between the last two consecutive fires. We found that, in general, most of the studied biogeochemical and microbial variables showed clear differences between unburned and burned stands. The time elapsed since the last fire was the most important fire history covariable and governed the main soil nutrient dynamics and microbial groups. Recovery to pre-fire values took 30-40 years. Increased wildfire frequency only modified total C and nitrification rate, but results were not consistent between stands burned twice and thrice. The time interval (years) between the last two fires was not a significant covariable. The fact that some stands burnt up to thrice in a period of 43 years supports the strong capacity of this ecosystem to recover, even under an increased fire frequency.

Symbiosis and host responses to heating

Virtually all organisms are colonized by microbes. Average temperatures are rising because of global climate change - accompanied by increases in extreme climatic events and heat shock - and symbioses with microbes may determine species persistence in the 21st century. Although parasite infection typically reduces host upper thermal limits, interactions with beneficial microbes can facilitate host adaptation to warming. The effects of warming on the ecology and evolution of the microbial symbionts remain understudied but are important for understanding how climate change might affect host health and disease. We present a framework for untangling the contributions of symbiosis to predictions of host persistence in the face of global change.

Large-scale commercial cultivation of morels: current state and perspectives

Since morels were first successfully cultivated commercially in Sichuan in 2012, morel cultivation has expanded to more than 20 provinces in China. The highest yield currently reaches 15,000 kg/ha. Morel cultivation is characterized by its environmental friendliness, short cycle length, and high profit. However, the yield obtained is unstable which makes morel cultivation a high-risk industry. Although 10 production cycles have passed, there is still a gap between morel cultivation practice and our basic knowledge of morel biology. This mini-review concentrates on the development needs of morel cultivation. We illustrate the key techniques used in the large-scale commercial cultivation of morels and their relevant studies, including nutritional requirements, mechanisms of nutrient bag, soil type, vegetative and reproductive growth conditions, and disease control. This review will be a useful practical reference for the commercial artificial cultivation of morels and promoting the vital technologies required. KEY POINTS: •Unstable yield still exists after commercial cultivation of morels realized. •There is a gap between cultivation practice and our knowledge of morel biology. •Key techniques are illustrated for morel cultivation practice.

Fire as a driver of fungal diversity - A synthesis of current knowledge

Fires occur in most terrestrial ecosystems where they drive changes in the traits, composition, and diversity of fungal communities. Fires range from rare, stand-replacing wildfires to frequent, prescribed fires used to mimic natural fire regimes. Fire regime factors, including burn severity, fire intensity, and timing, vary widely and likely determine how fungi respond to fires. Despite the importance of fungi to post-fire plant communities and ecosystem functioning, attempts to identify common fungal responses and their major drivers are lacking. This synthesis addresses this knowledge gap and ranges from fire adaptations of specific fungi to succession and assembly fungal communities as they respond to spatially heterogenous burning within the landscape. Fires impact fungi directly and indirectly through their effects on fungal survival, substrate and habitat modifications, changes in environmental conditions, and/or physiological responses of the hosts with which fungi interact. Some specific pyrophilous, or "fire-loving," fungi often appear after fire. Our synthesis explores whether such taxa can be considered cosmopolitan, and whether they are truly fire-adapted or simply opportunists adapted to rapidly occupy substrates and habitats made available by fires. We also discuss the possible inoculum sources of post-fire fungi and explore existing conceptual models and ecological frameworks that may be useful in generalizing fungal fire responses. We conclude with identifying research gaps and areas that may best transform the current knowledge and understanding of fungal responses to fire.

Taxonomic Description of Stenodiplosis tectori n. sp. (Diptera: Cecidomyiidae), a Seed Parasite of Cheatgrass, Anisantha tectorum, Based on Morphological and Mitochondrial DNA Data

Cheatgrass is an annual grass species from Eurasia that has become invasive in much of western North America. It has been implicated in recent increases in the frequency, size, and intensity of wildfires, contributing to severe economic, environmental, and social destruction. In order to reduce this damage, the USDA-ARS established a classical biological control program against cheatgrass. In 2018 and 2019, adult gall midges were collected emerging from cheatgrass seed heads collected at several sites in Bulgaria and Greece; this is the first gall midge ever recorded from cheatgrass. Morphological comparisons with related midge species recorded from other plant hosts revealed that this midge from cheatgrass is a new species, described here as Stenodiplosis tectori n. sp. This status was supported by sequence comparisons of a barcode region of the gene encoding the mitochondrial cytochrome c subunit I (CO1) protein in Stenodiplosis tectori n. sp. and three congeners. The present study is the first to report MT-CO1 data in the genus Stenodiplosis. The ingroup Stenodiplosis tectori n. sp. collected in the Balkans grouped in one phylogenetic supported clade, with an average K2P-distance from its closest related congener, S. sorghicola, of 7.73% (SD = 1.10). The findings indicated relatively high year-to-year within-population diversity. Implications for this gall midge's utility as a biological control agent of cheatgrass are discussed.

Facultative symbiosis with a saprotrophic soil fungus promotes potassium uptake in American sweetgum trees

Several species of soil free-living saprotrophs can sometimes establish biotrophic symbiosis with plants, but the basic biology of this association remains largely unknown. Here, we investigate the symbiotic interaction between a common soil saprotroph, Clitopilus hobsonii (Agaricomycetes), and the American sweetgum (Liquidambar styraciflua). The colonized root cortical cells were found to contain numerous microsclerotia-like structures. Fungal colonization led to increased plant growth and facilitated potassium uptake, particularly under potassium limitation (0.05 mM K⁺ ). The expression of plant genes related to potassium uptake was not altered by the symbiosis, but colonized roots contained the transcripts of three fungal genes with homology to K⁺ transporters (ACU and HAK) and channel (SKC). Heterologously expressed ChACU and ChSKC restored the growth of a yeast K⁺ -uptake-defective mutant. Upregulation of ChACU transcript under low K⁺ conditions (0 and 0.05 mM K⁺ ) compared to control (5 mM K⁺ ) was demonstrated in planta and in vitro. Colonized plants displayed a larger accumulation of soluble sugars under 0.05 mM K⁺ than non-colonized plants. The present study suggests reciprocal benefits of this novel tree-fungus symbiosis under potassium limitation mainly through an exchange of additional carbon and potassium between both partners.

Disruption of Traditional Grazing and Fire Regimes Shape the Fungal Endophyte Assemblages of the Tall-Grass Brachypodium rupestre

The plant microbiome is likely to play a key role in the resilience of communities to the global climate change. This research analyses the culturable fungal mycobiota of Brachypodium rupestre across a sharp gradient of disturbance caused by an intense, anthropogenic fire regime. This factor has dramatic consequences for the community composition and diversity of high-altitude grasslands in the Pyrenees. Plants were sampled at six sites, and the fungal assemblages of shoots, rhizomes, and roots were characterized by culture-dependent techniques. Compared to other co-occurring grasses, B. rupestre hosted a poorer mycobiome which consisted of many rare species and a few core species that differed between aerial and belowground tissues. Recurrent burnings did not affect the diversity of the endophyte assemblages, but the percentages of infection of two core species -Omnidemptus graminis and Lachnum sp. -increased significantly. The patterns observed might be explained by (1) the capacity to survive in belowground tissues during winter and rapidly spread to the shoots when the grass starts its spring growth (O. graminis), and (2) the location in belowground tissues and its resistance to stress (Lachnum sp.). Future work should address whether the enhanced taxa have a role in the expansive success of B. rupestre in these anthropized environments.

In Vitro Observations of the Interactions between Pholiota carbonaria and Polytrichum commune and Its Potential Environmental Relevance

Wildfires play a critical role in maintaining biodiversity and shaping ecosystem structure in fire-prone regions, and successional patterns involving numerous plant and fungal species in post-fire events have been elucidated. Evidence is growing to support the idea that some post-fire fungi can form endophytic/endolichenic relationships with plants and lichens. However, no direct observations of fire-associated fungal-moss interactions have been visualized to date. Therefore, physical interactions between a post-fire fungus, Pholiota carbonaria, and a moss, Polytrichum commune, were visually examined under laboratory conditions. Fungal appressoria were visualized on germinating spores and living protonemata within two weeks of inoculation in most growth chambers. Appressoria were pigmented, reddish gold to braun, and with a penetration peg. Pigmented, reddish gold to braun fungal hyphae were associated with living tissue, and numerous mature rhizoids contained fungal hyphae at six months. Inter-rhizoidal hyphae were pigmented and reddish gold to braun, but no structures were visualized on mature gametophyte leaf or stem tissues. Based on our visual evidence and previous work, we provide additional support for P. carbonaria having multiple strategies in how it obtains nutrients from the environment, and provide the first visual documentation of these structures in vitro.

Extended phylogeography of the ancestral Morchella anatolica supports preglacial presence in Europe and Mediterranean origin of morels

Over 80 species are recognized in the commercially important genus Morchella, many of them endemic to specific regions or continents. Among them, M. anatolica and M. rufobrunnea are the earliest diverging lineages and are key in decoding the evolutionary history, global biogeography, and ecological trends within this iconic genus. Early ancestral area reconstruction (AAR) tests postulated a western North American origin of morels but had not included in the analyses M. anatolica, whose phylogenetic identity remained at the time unresolved. Following new collections of M. anatolica and M. rufobrunnea from the Mediterranean islands of Cyprus, Kefalonia, Lesvos, Malta, and Zakynthos, we performed revised AAR tests to update the historical biogeography of the genus. Our results, inferred from multilocus analysis of an expanded data set of 79 phylospecies, challenge previous reconstructions and designate the Mediterranean basin as the most likely place of origin for morels. Detailed morphoanatomical analyses demonstrate that ascocarp rufescence, the nondarkening apothecial ridges, the absence of a sinus, and the stipe pruinescence are all stable synapomorphic features of sect. Rufobrunnea, which could be interpreted as ancestral for the genus. The saprotrophic mode of nutrition, suggested by the prolific in vitro growth of M. anatolica, might also be an ancestral trait. Emended descriptions, including extensive imagery and scanning electron microscopy, are provided, and a new evolutionary hypothesis of the genus is proposed.

Leaf Endophytes of Populus trichocarpa Act as Pathogens of Neighboring Plant Species

The conventional definition of endophytes is that they do not cause disease, whereas pathogens do. Complicating this convention, however, is the poorly explored phenomenon that some microbes are endophytes in some plants but pathogens in others. Black cottonwood or poplar (Populus trichocarpa) and wheat (Triticum aestivum) are common wild and crop plants, respectively, in the Pacific Northwest USA. The former anchors wild, riparian communities, whereas the latter is an introduced domesticate of commercial importance in the region. We isolated Fusarium culmorum – a well-known pathogen of wheat causing both blight and rot – from the leaf of a black cottonwood tree in western Washington. The pathogenicity of this cottonwood isolate and of a wheat isolate of F. culmorum were compared by inoculating both cottonwood and wheat in a greenhouse experiment. We found that both the cottonwood and wheat isolates of F. culmorum significantly reduced the growth of wheat, whereas they had no impact on cottonwood growth. Our results demonstrate that the cottonwood isolate of F. culmorum is endophytic in one plant species but pathogenic in another. Using sequence-based methods, we found an additional 56 taxa in the foliar microbiome of cottonwood that matched the sequences of pathogens of other plants of the region. These sequence-based findings suggest, though they do not prove, that P. trichocarpa may host many additional pathogens of other plants.

Pyrophilous fungi detected after wildfires in the Great Smoky Mountains National Park expand known species ranges and biodiversity estimates

Following a late fall wildfire in 2016 in the Great Smoky Mountains National Park, pyrophilous fungi in burn zones were documented over a 2-y period with respect to burn severity and phenology. Nuc rDNA internal transcribed spacer (ITS1-5.8S-ITS2 = ITS) barcodes were obtained to confirm morphological evaluations. Forty-one taxa of Ascomycota and Basidiomycota were identified from burn sites and categorized as fruiting only in response to fire or fruiting enhanced by fire. Twenty-two species of Pezizales (Ascomycota) were among the earliest to form ascomata in severe burn zones, only one of which had previously been documented in the Great Smoky Mountains National Park. Nineteen species of Basidiomycota, primarily Agaricales, were also documented. Among these, only five species (Coprinellus angulatus, Gymnopilus decipiens, Lyophyllum anthracophilum, Pholiota carbonicola, and Psathyrella pennata) were considered to be obligate pyrophilous taxa, but fruiting of two additional taxa (Hygrocybe conica and Mycena galericulata) was clearly enhanced by fire. Laccaria trichodermophora was an early colonizer of severe burn sites and persisted through the winter of 2017 and into spring and summer of 2018, often appearing in close association with Pinus pungens seedlings. Fruiting of pyrophilous fungi peaked 4-6 mo post fire then diminished, but some continued to fruit up to 2.5 y after the fire. In all, a total of 27 previously unrecorded taxa were added to the All Taxa Biodiversity Inventory (ATBI) database (~0.9%). Most pyrophilous fungi identified in this study are either cosmopolitan or have a Northern Hemisphere distribution, but cryptic endemic lineages were detected in Anthracobia and Sphaerosporella. One new combination, Hygrocybe spadicea var. spadicea f. odora, is proposed.

Promotion of maize growth by a yellow morel, Morchella crassipes

Fungal species of morel (genus Morchella) have recently been found to form a symbiotic relationship with grasses. Our previous study documented that M. crassipes from Shaanxi, northwest China, increased growth of sweet corn Zea mays var. saccharata and suppressed Fusarium infections. In the present study, we examined the effect of M. crassipes inoculation on dent corn, Zea mays var. indentata cv. Plant growth response indexes and variables and soil variables were used to demonstrate how M. crassipes inoculation stimulates maize growth. Three suspensions of M. crassipes mycelium (50, 100, 150 mL) were inoculated into Zea may var. indentata. The results showed that M. crassipes inoculation significantly affected growth of all the inoculated maize plants and influenced some variables and indexes that are related to tissue specificity and dose dependence. Soil moisture, available K and P accumulation by M. crassipes were affected in inoculated plants and resulted in growth enhancements that were equal to that of the plants treated with urea. Our findings reveal that inoculation with M. crassipes had a positive effect on maize yield, making the crop system more sustainable. Thus M. crassipes has the potential to become a supplement or an alternative to urea fertilizers.

The role of inoculum dispersal and plant species identity in the assembly of leaf endophytic fungal communities

Because of disturbance and plant species loss at the local level, many arid ecosystems in the western USA benefit from revegetation. There is a growing interest in improving revegetation success by purposefully inoculating revegetation plants with mutualistic endophytic fungi that increase plant stress tolerance. However, inoculant fungi must compete against fungi that indigenous to the habitat, many of which may not be mutualistic. Our overall goal, therefore, is to learn how to efficiently colonize revegetation plants using endophytic fungal inoculum. The goal will be facilitated by understanding the factors that limit colonization of plants by endophytic fungi, including inoculum dispersal and host compatibility. We analyzed endophytic fungal communities in leaves of Bromus tectorum and Elymus elymoides (Poaceae), Chrysothamnus depressus and Artemisia tridentata (Asteraceae), Alyssum alyssoides (Brassicaceae) and Atriplex canescens (Amaranthaceae), each occurring in each of 18 field plots. We found that dispersal limitation was significant for endophytic fungal communities of Atriplex canescens and Bromus tectorum, accounting for 9 and 17%, respectively, of the variation in endophytic fungal community structure, even though the maximum distance between plots was only 350 m. Plant species identity accounted for 33% of the variation in endophytic fungal community structure. These results indicate that the communities of endophytic fungi assembling in these plant species depend significantly on proximity to inoculum source as well as the identity of the plant species. Therefore, if endophytic fungi are to be used to facilitate revegetation by these plant species, land managers may find it profitable to consider both the proximity of inoculum to revegetation plants and the suitability of the inoculum to targeted host plant species.

Structural plasticity in root-fungal symbioses: diverse interactions lead to improved plant fitness

Root-fungal symbioses such as mycorrhizas and endophytes are key components of terrestrial ecosystems. Diverse in trophy habits (obligate, facultative or hemi-biotrophs) and symbiotic relations (from mutualism to parasitism), these associations also show great variability in their root colonization and nutritional strategies. Specialized interface structures such as arbuscules and Hartig nets are formed by certain associations while others are restricted to non-specialized intercellular or intracellular hyphae in roots. In either case, there are documented examples of active nutrient exchange, reinforcing the fact that specialized structures used to define specific mycorrhizal associations are not essential for reciprocal exchange of nutrients and plant growth promotion. In feremycorrhiza (with Austroboletus occidentalis and eucalypts), the fungal partner markedly enhances plant growth and nutrient acquisition without colonizing roots, emphasizing that a conventional focus on structural form of associations may have resulted in important functional components of rhizospheres being overlooked. In support of this viewpoint, mycobiome studies using the state-of-the-art DNA sequencing technologies have unearthed much more complexity in root-fungal relationships than those discovered using the traditional morphology-based approaches. In this review, we explore the existing literature and most recent findings surrounding structure, functioning, and ecology of root-fungal symbiosis, which highlight the fact that plant fitness can be altered by taxonomically/ecologically diverse fungal symbionts regardless of root colonization and interface specialization. Furthermore, transition from saprotrophy to biotrophy seems to be a common event that occurs in diverse fungal lineages (consisting of root endophytes, soil saprotrophs, wood decayers etc.), and which may be accompanied by development of specialized interface structures and/or mycorrhiza-like effects on plant growth and nutrition.

Artificial cultivation of true morels: current state, issues and perspectives

Morels (Morchella, Ascomycota), which are some of the most highly prized edible and medicinal mushrooms, are of great economic and scientific value. Morel cultivation has been a research focus worldwide for more than 100 years, and the outdoor cultivation of morels has succeeded and expanded to a large scale in China in recent years. In this study, we review the progress in recent research regarding the life cycle and reproductive systems in the genus Morchella and the current state of outdoor cultivation. Sclerotia formation and conidia production are two important phases during the life cycle. The morel species cultivated commercially in America is M. rufobrunnea based on molecular phylogenetic analysis. The species currently cultivated in China are black morels, including M. importuna, M. sextalata and M. eximia. The field cultivation of morels expanded in the majority of the provinces in China with a yield of fresh morels of 0-7620 kg per ha. The key techniques include spawn production, land preparation and spawning, the addition of exogenous nutrition, fruiting management and harvesting. The application of exogenous nutrition is the most important breakthrough in the field of morel cultivation, but the mechanism remains unclear. It was estimated that the total amount of field cultivated fresh morels was ∼500 t in 2015-2016. We also discuss the potential issues remaining in the current literature and suggest directions for future studies.

A morel improved growth and suppressed Fusarium infection in sweet corn

A post-fire morel collected from Populus simonii stands in Mt. Qingling was identified as Morchella crassipes Mes-20 by using nuclear ribosomal DNA internal transcribed spacer phylogeny. It was inoculated into sweet corn to observe colonized roots in purified culture and in greenhouse experiments. The elongation and maturation zones of sweet corn were remarkably colonized at the cortex intercellular and intracellular cells, vessel cells, and around the Casparian strip, forming ectendomycorrhiza-like structures. Colonization was also observed in the zone of cell division proximal to the root cap. Greenhouse assays with sweet corn showed that this morel stimulated the development of the root system and significantly increased the dry root biomass. M. crassipes also significantly reduced the incidence of Fusarium verticillioides in the kernels of mature ears when inoculated into young ears before Fusarium inoculation and prevented Fusarium infection in corn ears compared with that of the control in the greenhouse. When grown under axenic conditions, M. crassipes produced the phytohormones abscisic acid, indole-3-acetic acid, and salicylic acid. The benefits to plants elicited by M. crassipes may result from these phytohormones which may improve the drought resistance, biomass growth and resistance to Fusarium.

Change in abundance of three phytophagous mite species (Acari: Eriophyidae, Tetranychidae) on quackgrass in the presence of choke disease

Phytophagous mites and endophytic fungi may interact when sharing a host plant, potentially influencing one another's growth or population dynamics; however, interactions between them are poorly known and remain largely unexplored. In this study, quantitative associations between three species of phytophagous mites and the endophytic fungus Epichloë bromicola Leuchtm. & Schardl (Clavicipitaceae, Ascomycotina) on quackgrass, Elymus repens (L.) Gould are reported. The mites' abundance was assessed on field-collected grass shoots that were either exhibiting choke disease symptoms or without the fungus. Overall, the abundance of Tetranychus urticae and Aculodes mckenziei was significantly lower on quackgrass plants infected by E. bromicola compared to plants without the fungus. Conversely, populations of Abacarus hystrix were significantly larger on plants colonised by the fungus than on uninfected plants. Thus, the presence of this endophytic fungus may have divergent effects on different phytophagous mite species although the basis of these effects is not yet known.

Fungal endophytes: modifiers of plant disease

Many recent studies have demonstrated that non-pathogenic fungi within plant microbiomes, i.e., endophytes ("endo" = within, "phyte" = plant), can significantly modify the expression of host plant disease. The rapid pace of advancement in endophyte ecology warrants a pause to synthesize our understanding of endophyte disease modification and to discuss future research directions. We reviewed recent literature on fungal endophyte disease modification, and here report on several emergent themes: (1) Fungal endophyte effects on plant disease span the full spectrum from pathogen antagonism to pathogen facilitation, with pathogen antagonism most commonly reported. (2) Agricultural plant pathosystems are the focus of research on endophyte disease modification. (3) A taxonomically diverse group of fungal endophytes can influence plant disease severity. And (4) Fungal endophyte effects on plant disease severity are context-dependent. Our review highlights the importance of fungal endophytes for plant disease across a broad range of plant pathosystems, yet simultaneously reveals that complexity within plant microbiomes presents a significant challenge to disentangling the biotic environmental factors affecting plant disease severity. Manipulative studies integrating eco-evolutionary approaches with emerging molecular tools will be poised to elucidate the functional importance of endophytes in natural plant pathosystems that are fundamental to biodiversity and conservation.

Revisiting the Life Cycle of Dung Fungi, Including Sordaria fimicola

Dung fungi, such as Sordaria fimicola, generally reproduce sexually with ascospores discharged from mammalian dung after passage through herbivores. Their life cycle is thought to be obligate to dung, and thus their ascospores in Quaternary sediments have been interpreted as evidence of past mammalian herbivore activity. Reports of dung fungi as endophytes would seem to challenge the view that they are obligate to dung. However, endophyte status is controversial because surface-sterilization protocols could fail to kill dung fungus ascospores stuck to the plant surface. Thus, we first tested the ability of representative isolates of three common genera of dung fungi to affect plant growth and fecundity given that significant effects on plant fitness could not result from ascospores merely stuck to the plant surface. Isolates of S. fimicola, Preussia sp., and Sporormiella sp. reduced growth and fecundity of two of three populations of Bromus tectorum, the host from which they had been isolated. In further work with S. fimicola we showed that inoculations of roots of B. tectorum led to some colonization of aboveground tissues. The same isolate of S. fimicola reproduced sexually on inoculated host plant tissues as well as in dung after passage through sheep, thus demonstrating a facultative rather than an obligate life cycle. Finally, plants inoculated with S. fimicola were not preferred by sheep; preference had been expected if the fungus were obligate to dung. Overall, these findings make us question the assumption that these fungi are obligate to dung.

Pervasive Effects of Wildfire on Foliar Endophyte Communities in Montane Forest Trees

Plants in all terrestrial ecosystems form symbioses with endophytic fungi that inhabit their healthy tissues. How these foliar endophytes respond to wildfires has not been studied previously, but is important given the increasing frequency and intensity of severe wildfires in many ecosystems, and because endophytes can influence plant growth and responses to stress. The goal of this study was to examine effects of severe wildfires on endophyte communities in forest trees, with a focus on traditionally fire-dominated, montane ecosystems in the southwestern USA. We evaluated the abundance, diversity, and composition of endophytes in foliage of Juniperus deppeana (Cupressaceae) and Quercus spp. (Fagaceae) collected contemporaneously from areas affected by recent wildfire and paired areas not affected by recent fire. Study sites spanned four mountain ranges in central and southern Arizona. Our results revealed significant effects of fires on endophyte communities, including decreases in isolation frequency, increases in diversity, and shifts in community structure and taxonomic composition among endophytes of trees affected by recent fires. Responses to fire were similar in endophytes of each host in these fire-dominated ecosystems and reflect regional fire-return intervals, with endophytes after fire representing subsets of the regional mycoflora. Together, these findings contribute to an emerging perspective on the responses of diverse communities to severe fire, and highlight the importance of considering fire history when estimating endophyte diversity and community structure for focal biomes.

Increased Primary Production from an Exotic Invader Does Not Subsidize Native Rodents

Invasive plants have tremendous potential to enrich native food webs by subsidizing net primary productivity. Here, we explored how a potential food subsidy, seeds produced by the aggressive invader cheatgrass (Bromus tectorum), is utilized by an important guild of native consumers--granivorous small mammals--in the Great Basin Desert, USA. In a series of field experiments we examined 1) how cheatgrass invasion affects the density and biomass of seed rain at the ecosystem-level; 2) how seed resources from cheatgrass numerically affect granivorous small mammals; and 3) how the food preferences of native granivores might mediate the trophic integration of cheatgrass seeds. Relative to native productivity, cheatgrass invasion increased the density and biomass of seed rain by over 2000% (P < 0.01) and 3500% (P < 0.01), respectively. However, granivorous small mammals in native communities showed no positive response in abundance, richness, or diversity to experimental additions of cheatgrass seeds over one year. This lack of response correlated with a distinct preference for seeds from native grasses over seeds from cheatgrass. Our experiments demonstrate that increased primary productivity associated with exotic plant invasions may not necessarily subsidize consumers at higher trophic levels. In this context, cheatgrass invasion could disrupt native food webs by providing less-preferred resources that fail to enrich higher trophic levels.

A review on research advances, issues, and perspectives of morels

Morels, a group of the world's most prized edible and medicinal mushrooms, are of very important economic and scientific value. Here, we review recent research progress in the genus Morchella, and focus on its taxonomy, species diversity and distribution, ecological diversity, phylogeny and biogeography, artificial cultivation, and genome. We also discuss the potential issues remaining in the current research and suggest some future directions for study.

Phylogenetic diversity of true morels (Morchella), the main edible non-timber product from native Patagonian forests of Argentina

Morchella species are edible fungi in high demand and therefore command high prices in world markets. Phenotypic-based identification at the species-level remains inadequate because of their complex life cycles, minor differences and plasticity of morphological characteristics between species, and the lack of agreement between scientific and common names. In Patagonia-Argentina, morels are associated with native forests of Austrocedrus chilensis (Cordilleran or Chilean cypress) and Nothofagus antarctica (ñire) and several exotic conifers that were introduced from western North America. Little is known about their taxonomy and phylogenetic relationships with other species in the genus. This work focused on the identification of collections of Morchella from Patagonia and their phylogenetic relationships with other species from the Northern Hemisphere. The comparison was made by analysis of DNA sequences obtained from four loci: the nuclear ribosomal internal transcribed spacer region (ITS) and the partial RNA polymerase I gene (RPB1) for the complete collection; and ITS, RPB1, RNA polymerase II gene (RPB2), and translation elongation factor (EF1-α) for the species-rich Elata Subclade. Analyses of individual and combined data sets revealed that Patagonian morels belong to the Elata Clade and comprised three strongly supported species-level lineages from both Patagonian native forest, and exotic trees introduced from western North America. One lineage was identified as Morchella frustrata phylogenetic species Mel-2, which is known from the USA and Canada. The second lineage, which appeared to be 'fire-adapted', was identified as Morchella septimelata phylogenetic species (Mel-7), which is also known from the USA. This species was collected from burned native forests mainly composed of A. chilensis and N. antarctica but also Pseudotsuga menziesii (Mirb.) Blanco, which is native to western North America. The phylogenetic analyses suggested that the third species from Patagonia was nested within the species-rich Elata Subclade and represents a new species-level lineage (informally designated Mel-37) within Elata Clade. The present collections from Patagonia constitute the southernmost latitude from which Morchella has been reported to date. The identification of two Argentine morels as North American taxa is therefore a remarkable biogeographic pattern. In view of the hypothesis that the Elata Clade originated in western North America, we speculate that at least two of the lineages colonized South America from North America via long distance dispersal, migration or, more likely, they were introduced with the exotic tree species that they were collected near.

How well do ITS rDNA sequences differentiate species of true morels (Morchella)?

Arguably more mycophiles hunt true morels (Morchella) during their brief fruiting season each spring in the northern hemisphere than any other wild edible fungus. Concerns about overharvesting by individual collectors and commercial enterprises make it essential that science-based management practices and conservation policies are developed to ensure the sustainability of commercial harvests and to protect and preserve morel species diversity. Therefore, the primary objectives of the present study were to: (i) investigate the utility of the ITS rDNA locus for identifying Morchella species, using phylogenetic species previously inferred from multilocus DNA sequence data as a reference; and (ii) clarify insufficiently identified sequences and determine whether the named sequences in GenBank were identified correctly. To this end, we generated 553 Morchella ITS rDNA sequences and downloaded 312 additional ones generated by other researchers from GenBank using emerencia and analyzed them phylogenetically. Three major findings emerged: (i) ITS rDNA sequences were useful in identifying 48/62 (77.4%) of the known phylospecies; however, they failed to identify 12 of the 22 species within the species-rich Elata Subclade and two closely related species in the Esculenta Clade; (ii) at least 66% of the named Morchella sequences in GenBank are misidentified; and (iii) ITS rDNA sequences of up to six putatively novel Morchella species were represented in GenBank. Recognizing the need for a dedicated Web-accessible reference database to facilitate the rapid identification of known and novel species, we constructed Morchella MLST (http://www.cbs.knaw.nl/morchella/), which can be queried with ITS rDNA sequences and those of the four other genes used in our prior multilocus molecular systematic studies of this charismatic genus.

Multilocus phylogenetic analysis of true morels (Morchella) reveals high levels of endemics in Turkey relative to other regions of Europe

The present study was conducted to better understand how the phylogenetic diversity of true morels (Morchella) in Turkey compares with species found in other regions of the world. The current research builds on our recently published surveys of 10 Turkish provinces and the northern hemisphere in which DNA sequence data from 247 and 562 collections respectively were analyzed phylogenetically. Herein we report on phylogenetic analyses of 243 additional collections made in spring 2009 and 2010 from eight additional provinces in the Aegean, Black Sea, central Anatolia, eastern Anatolia and Marmara regions of Turkey. Our analysis revealed that five species within the Esculenta clade (yellow morels) and 15 species within the Elata clade (black morels) were present in Turkey. Our preliminary results also indicate that M. anatolica, recently described from a collection in Muğla province in the Aegean region of Turkey, is a closely related sister of M. rufobrunnea; these two species comprise a separate evolutionary lineage from the Esculenta and Elata clades. Nine species of Morchella currently are known only from Turkey, four species were present in Turkey and other European countries and seven species might have been introduced to Turkey anthropogenically. Three of the putatively exotic species in Turkey appear to be endemic to western North America; they are nested within a clade of fire-adapted morels that dates to the late Oligocene, 25 000 000 y ago. Our results indicate that there are roughly twice as many Morchella species in Turkey compared with the other regions of Europe sampled. Knowledge of Morchella species diversity and their biogeographic distribution are crucial for formulating informed conservation policies directed at preventing species loss and ensuring that annual morel harvests are sustainable and ecologically sound.