Quantitation of endorhizal fungi in High Arctic tundra ecosystems through space and time: The value of herbarium archives
Abstract and Figures
Mycorrhizal fungi are widespread in temperate and tropical regions, but generally are thought to be relatively depauperate at high latitudes. The potential impact of global warming on the polar ecosystems has renewed interest in research into tundra soil microbiota. Although logistical impediments limit field access, herbarium accessions are a potential resource for surveying mycorrhizal distribution. We present: (i) a method for examining fungi in roots of herbarium specimens that provides morphological preservation comparable to formalin fixation; and (ii) a multiple quantitation method to assess diverse morphotypes. Arbuscular mycorrhizae, fine endophytes, and septate endophytes were widespread in Asteraceae roots from Axel Heiberg and Ellesmere islands, Arctic Canada, during 2004. Roots from the same species collected from this region since 1982, stored in our herbarium, consistently contained abundant endorhizal fungi. Although 2004 was one of the coolest growing seasons in the survey, mycorrhizal abundance was highest in that year. Endorhizal fungi are likely to be important for plant survival and soil-forming processes in High Arctic tundra environments, and may be sensitive to climate variation.
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... colonised) have been recorded in the roots of six of seven Asteraceae species in the Geodetic Hills on Axel Heiberg Island at 80°N (Allen et al. 2006). Frequent AM colonisation (8-85% root lengths colonised) has been found in the roots of Erigeron and Taraxacum species from Ellesmere Island at 82°N (Ormsby et al. 2007), and AM endophytes have also been found to be commonplace (37-85% root lengths colonised) in the roots of Arnica, Erigeron and Potentilla species sampled from Banks Island at 73°N (Olsson et al. 2004). ...
... This observation is counterintuitive: although situated in the High Arctic at c. 77-80°N, Spitsbergen has a mild climate for its latitude, with the West Spitsbergen Current bringing warm water to the island's western shores all year round, and with approximate mean annual and summer air temperatures (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015) of −3.3 and 4.8°C, respectively (Isaksen et al. 2016). Given that the abundance of AM fungal structures in roots in polar ecosystems is positively associated with seasonal air temperatures (Upson et al. 2008), and that AM endophytes colonise roots in the colder Canadian High Arctic (Olsson et al. 2004;Allen et al. 2006;Ormsby et al. 2007), it seems plausible that the AM symbiosis is present on Spitsbergen. In support of this, a recent study used the polymerase chain reaction (PCR) to amplify AM fungal DNA from the roots of one Saxifraga oppositifolia and three Ranunculus sulphureus plants sampled from two locations in Longyearbyen on the island (Öpik et al. 2013). ...
... from the roots of plants in Longyearbyen (Öpik et al. 2013), our observations indicate that the symbiosis occurs more widely on the island, and that significant lengths of root can be occupied by AM structures in colonised plants. In common with observations at other locations in the High Arctic (Olsson et al. 2004;Allen et al. 2006;Ormsby et al. 2007), the occurrence in roots of arbuscules, the point at which P and other elements are transferred from the fungal symbiont to plant tissues (Smith and Read 2008), suggests that AM symbioses have the capacity to influence plant nutrient acquisition on Spitsbergen. ...
A previous study of 76 plant species on Spitsbergen in the High Arctic concluded that structures resembling arbuscular mycorrhizas were absent from roots. Here, we report a survey examining the roots of 13 grass and forb species collected from 12 sites on the island for arbuscular mycorrhizal (AM) colonisation. Of the 102 individuals collected, we recorded AM endophytes in the roots of 41 plants of 11 species (Alopecurus ovatus, Deschampsia alpina, Festuca rubra ssp. richardsonii, putative viviparous hybrids of Poa arctica and Poa pratensis, Poa arctica ssp. arctica, Trisetum spicatum, Coptidium spitsbergense, Ranunculus nivalis, Ranunculus
pygmaeus, Ranunculus sulphureus and Taraxacum arcticum) sampled from 10 sites. Both coarse AM endophyte, with hyphae of 5–10 μm width, vesicles and occasional arbuscules, and fine endophyte, consisting of hyphae of 1–3 μm width and sparse arbuscules, were recorded in roots. Coarse AM hyphae, vesicles, arbuscules and fine endophyte hyphae occupied 1.0–30.7, 0.8–18.3, 0.7–11.9 and 0.7–12.8% of the root lengths of colonised plants, respectively. Principal component analysis indicated no associations between the abundances of AM structures in roots and edaphic factors. We conclude that the AM symbiosis is present in grass and forb roots on Spitsbergen.
... low temperature) and the reports of high colonization by FRE and high FRE colonization ratios were mostly from the Arctic (e.g. Olsson et al. 2004;Ormsby et al. 2007;Hodson et al. 2009;Walker et al. 2010). Even so, the limited data for less extreme environments from the same region showed that the level of colonization by FRE in Equisetaceae in the Canadian prairies did not differ from that of Equisetaceae in the Canadian Arctic (Hodson et al. 2009; BExtreme environments^section). ...
... Within the Canadian Arctic, relatively high colonization by FRE and clear dominance of FRE relative to AMF was reported in the Ranunculaceae and, to a lesser extent, the Equisetaceae and Poaceae (this trend was reversed in natural-moderate environments-data not shown). For all three families, there was a much broader range of colonization levels for FRE than for AMF ( Fig. 9; Olsson et al. 2004;Ormsby et al. 2007;Hodson et al. 2009;Walker et al. 2010). In contrast, colonization levels by FRE and AMF were similar for the Asteraceae. ...
... In summary, colonization by FRE can be high in some extreme environments, particularly in low temperatures, and in these environments, FRE may dominate over AMF in some host plants. It is unknown whether high colonization by FRE results from the environmental extreme favoring their growth Fig. 8 The percentage root length colonized (mean + standard error) by fine root endophytes (dark green) and arbuscular mycorrhizal fungi (AMF) (grey) for various plants sampled in New Zealand from a natural environment (data reproduced from Crush 1973bfrom Crush , 1975) Fig. 9 The percentage root length colonised by fine root endophytes (FRE) and arbuscular mycorrhizal fungi (AMF) from low-temperature environments in the Canadian Arctic (Olsson et al. 2004;Ormsby et al. 2007;Hodson et al. 2009;Walker et al. 2010) from Asteraceae, Equisetaceae, Poaceae, Ranunculaceae and Rosaceae (n = 24,14,4,14 and 2,respectively). The boxes show the median, 90th percentiles and outliers (black dots) of the reported data or a competitive release from AMF, or other edaphic factors such as nutrient availability. ...
Fine root endophytes (FRE) are arbuscule-forming fungi presently considered as a single species-Glomus tenue in the Glomeromycota (Glomeromycotina)-but probably belong within the Mucoromycotina. Thus, FRE are the only known arbuscule-forming fungi not within the arbuscular mycorrhizal fungi (AMF; Glomeromycotina) as currently understood. Phylogenetic differences between FRE and AMF could reflect ecological differences. To synthesize current ecological knowledge, we reviewed the literature on FRE and identified 108 papers that noted the presence of FRE and, in some, the colonization levels for FRE or AMF (or both). We categorized these records by geographic region, host-plant family and environment (agriculture, moderate-natural, low-temperature, high-altitude and other) and determined their influence on the percentage of root length colonized by FRE in a meta-analysis. We found that FRE are globally distributed, with many observations from Poaceae, perhaps due to grasses being widely distributed. In agricultural environments, colonization by FRE often equalled or exceeded that of AMF, particularly in Australasia. In moderate-natural and high-altitude environments, average colonization by FRE (~10%) was lower than that of AMF (~35%), whereas in low-temperature environments, colonization was similar (~20%). Several studies suggested that FRE can enhance host-plant phosphorus uptake and growth, and may be more resilient than AMF to environmental stress in some host plants. Further research is required on the functioning of FRE in relation to the environment, host plant and co-occurring AMF and, in particular, to examine whether FRE are important for plant growth in stressful environments. Targeted molecular primers are urgently needed for further research on FRE.
... From the perspective of an Arctic plant, the costs for sustaining an AM fungal partner may then outweigh the benefits. With regards to AM fungal colonization of roots, several studies from the Arctic nonetheless have found colonization levels ranging from 11-36% root length colonized (Allen et al., 2006), through 27-51% root length colonized (Ormsby et al., 2007), to 37-85% root length colonized (Olsson et al., 2004). Newsham et al. (2017) studied 102 plants from 11 plant species, and found structures resembling AM fungi in 41 of the plant individuals. ...
... Overall, although studies suggest that the presence of AM fungal symbiosis is low in the Arctic at the level of both plant species (Allen et al., 2006;Newsham et al., 2017) and individuals (Newsham et al., 2017), cases of high root colonization by AM fungal structures have still been reported (Olsson et al., 2004;Ormsby et al., 2007), as have several species of AM fungi (Greipsson et al., 2002;€ Opik et al., 2013). It thus appears that there is still much to learn about AM fungal diversity in the Arctic and how it relates to plant species identity. ...
Knowledge about the distribution and local diversity patterns of arbuscular mycorrhizal (AM) fungi are limited for extreme environments such as the Arctic, where most studies have focused on spore morphology or root colonization. We here studied the joint effects of plant species identity and elevation on AM fungal distribution and diversity.
We sampled roots of 19 plant species in 18 locations in Northeast Greenland, using next generation sequencing to identify AM fungi. We studied the joint effect of plant species, elevation and selected abiotic conditions on AM fungal presence, richness and composition.
We identified 29 AM fungal virtual taxa (VT), of which six represent putatively new VT. Arbuscular mycorrhizal fungal presence increased with elevation, and as vegetation cover and the active soil layer decreased. Arbuscular mycorrhizal fungal composition was shaped jointly by elevation and plant species identity.
We demonstrate that the Arctic harbours a relatively species‐rich and nonrandomly distributed diversity of AM fungi. Given the high diversity and general lack of knowledge exposed herein, we encourage further research into the diversity, drivers and functional role of AM fungi in the Arctic. Such insight is urgently needed for an area with some of the globally highest rates of climate change.
... Research in Antarctica has also shown that fungi such as Cadophora that caused degradation in the historic huts built by polar explorers to the South Pole were also prevalent in soils that were sampled near the huts and even in soils located at great distances away from them [14,26]. Genera such as Cadophora, Coniochaeta, Mollisia, Phialocephala, and Phoma also have been found to have endophytic relationships with plants [43][44][45][46][47]. These dark septate endophytes are commonly associated with plant roots in Polar Regions and appear to be widespread [48]. ...
Historic wooden structures in Polar Regions are being adversely affected by decay fungi and a warming climate will likely accelerate degradation. Fort Conger and the Peary Huts at Lady Franklin Bay in northern Ellesmere Island are important international heritage sites associated with early exploration in the High Arctic. Fort Conger, built by Adolphus Greely and expedition members during the First International Polar Year in 1881, was dismantled and used by Robert Peary and his expedition crew in the early 1900’s to build several smaller shelters. These historic structures remain at the site but are deteriorating. This investigation examines the fungi associated with wood decay in the historic woods. Soft rot was observed in all 125 wood samples obtained from the site. The major taxa found associated with the decayed wood were Coniochaeta (18%), Phoma (13%) Cadophora (12%), Graphium (9%), and Penicillium (9%) as well as many other Ascomycota that are known to cause soft rot in wood. Micromorphological observations using scanning electron microscopy of historic wooden timbers that were in ground contact revealed advanced stages of type I soft rot. No wood destroying Basidiomycota were found. Identification of the fungi associated with decay in these historic woods is a first step to better understand the unusual decomposition processes underway in this extreme environment and will aid future research to help control decay and preserve this important cultural heritage.
... Previous studies have hypothesised that FRE are adapted to colder, wetter, and more acidic environments than AMF [19,36,40,42,53]. We found that root colonization by FRE was higher in wetter environments, while soil acidity also had a positive effect on richness of FRE. ...
Fine root endophytes (FRE) were traditionally considered a morphotype of arbuscular mycorrhizal fungi (AMF), but recent genetic studies demonstrate that FRE belong within the subphylum Mucoromycotina, rather than in the subphylum Glomeromycotina with the AMF. These findings prompt enquiry into the fundamental ecology of FRE and AMF. We sampled FRE and AMF in roots of Trifolium subterraneum from 58 sites across temperate southern Australia. We investigated the environmental drivers of composition, richness, and root colonization of FRE and AMF by using structural equation modelling and canonical correspondence analyses. Root colonization by FRE increased with increasing temperature and rainfall but decreased with increasing phosphorus (P). Root colonization by AMF increased with increasing soil organic carbon but decreased with increasing P. Richness of FRE decreased with increasing temperature and soil pH. Richness of AMF increased with increasing temperature and rainfall but decreased with increasing soil aluminium (Al) and pH. Aluminium, soil pH, and rainfall were, in decreasing order, the strongest drivers of community composition of FRE; they were also important drivers of community composition of AMF, along with temperature, in decreasing order: rainfall, Al, temperature, and soil pH. Thus, FRE and AMF showed the same responses to some (e.g. soil P, soil pH) and different responses to other (e.g. temperature) key environmental factors. Overall, our data are evidence for niche differentiation among these co-occurring mycorrhizal associates.
... Fine root endophyte has recently been aligned with subphylum Mucoromycotina, rather than the phylum Glomeromycota which contains the AM fungi (Orchard et al. 2017). Storage of samples for greater than two days may have contributed to under-reporting of what could be a second ubiquitous group (Abbott and Robson 1982;Orchard et al. 2016b;Read and Haselwandter 1981;Ormsby et al. 2007) of arbuscule-producing root-colonising fungi. ...
... Numerous ascomyceteous and basidiomycetous fungi form facultative ectomycorrhizal symbiosis with tree roots (Zuccaro et al., 2014). Additionally, several new types of root-fungal mutualistic interactions such as class 2 fungal endophytes (see more details in the following sections) (Rodriguez et al., 2009), dark septate endophytes (DSEs) and fine endophytes (Allen et al., 2006;Kivlin et al., 2013;Ormsby et al., 2007;Postma et al., 2007) have been described. Some early root-fungal intimate cellular interactions have been preserved in fossils, indicating that plants already contained the major fungal lineages (both mycorrhizal and endophytic fungi) when they first invaded swampy land (Blackwell, 2000;Krings et al., 2007). ...
Soil salinization adversely affects plant growth and has become one of the major limiting factors for crop productivity worldwide. The conventional approach, breeding salt-tolerant plant cultivars, has often failed to efficiently alleviate the situation. In contrast, the use of a diverse array of microorganisms harbored by plants has attracted increasing attention because of the remarkable beneficial effects of microorganisms on plants. Multiple advanced '-omics' technologies have enabled us to gain insights into the structure and function of plant-associated microbes. In this review, we first focus on microbe-mediated plant salt tolerance, in particular on the physiological and molecular mechanisms underlying root-microbe symbiosis. Unfortunately, when introducing such microbes as single strains to soils, they are often ineffective in improving plant growth and stress tolerance, largely due to competition with native soil microbial communities and limited colonization efficiency. Rapid progress in rhizosphere microbiome research has revived the belief that plants may benefit more from association with interacting, diverse microbial communities (microbiome) than from individual members in a community. Understanding how a microbiome assembles in the continuous compartments (endosphere, rhizoplane, and rhizosphere) will assist in predicting a subset of core or minimal microbiome and thus facilitate synthetic re-construction of microbial communities and their functional complementarity and synergistic effects. These developments will open a new avenue for capitalizing on the cultivable microbiome to strengthen plant salt tolerance and thus to refine agricultural practices and production under saline conditions.
... Research in Antarctica has also shown that fungi such as Cadophora that caused degradation in the historic huts built by polar explorers to the South Pole were also prevalent in soils that were sampled near the huts and even in soils located at great distances away from them [14,26]. Genera such as Cadophora, Coniochaeta, Mollisia, Phialocephala, and Phoma also have been found to have endophytic relationships with plants [43][44][45][46][47]. These dark septate endophytes are commonly associated with plant roots in Polar Regions and appear to be widespread [48]. ...
Very little is known about fungal diversity in Antarctica as compared to other biomes and how these important organisms function in this unusual ecosystem. Perhaps one of the most unusual ecosystem is that of Deception Island; an active volcanic island part of the South Shetland Islands of the Antarctic Peninsula. Here we describe the fungal diversity associated with historic wood from structures on the island, which reveals a diverse fungal assemblage of known wood decay fungi as well as the discovery of undescribed species. The major group of wood decay fungi identified were species of Cadophora and as shown in previous studies in other geographic regions of Antarctica, they caused a soft-rot type of decay in the introduced woods. Additionally, unlike other areas of Antarctica that have been studied, filamentous basidiomycetes (Hypochniciellum spp. and Pholiota spp.) were also identified that have different modes of degradation including brown and white rot. Matches of fungal sequences to known species in temperate regions likely introduced on building materials indicates human influences and volcanic activity have greatly impacted fungal diversity. Lahars (mudslides from volcanic activity) have partially buried many of the structures and the buried environment as well as the moist, warm soils provided conditions conducive for fungal growth that are not found in other regions of Antarctica. The diverse assemblage of decay fungi and many different forms of aggressive wood decomposition add to the difficulty of conserving wooden structures at these important polar heritage sites.
Mining sites are harsh environments and establishment of root associated symbiotic fungi may be crucial for plant establishment and long term community development. Diamond mining in the Northwest Territories produces large amounts of processed kimberlite, and in some cases lake bed sediment and reclamation is needed for re-establishment of ecosystem function. This study investigated early fungal colonization with arbuscular mycorrhizae and dark septate endophytes on common reclamation substrates of different ages, relative to native tundra. Natural colonization of vegetation free sites with mycorrhizal spores on a trajectory associated with substrate age and type was very low. Fungal spore quantity and diversity was significantly accelerated by establishment of vegetation. Dark septate endophytes dominated native site Cyperaceae whereas reclamation site grasses were dominated by arbuscular mycorrhizae. Topsoil amendment was most effective for fungal colonization on reclamation substrates suggesting that a single application of topsoil can have a long term effect on the soil fungal community.
The occurrence of arbuscular mycorrhizal (AM) fungi was surveyed along a latitudinal gradient in Arctic Canada including Banks Island (73°N), Devon Island (74°N), Ellesmere Island (76°N), and the Magnetic North Pole at Ellef Ringnes Island (78°N). At Banks Island, AM fungi were present and colonized at a high intensity in all specimens of Potentilla hookeriana Lehm. – Potentilla pulchella R.Br., Arnica angustifolia Vahl, and Erigeron uniflorus L. ssp. eriocephalus (Vahl ex Hornen.) Cronq. sampled. The soil collected under these plants showed a high inoculum potential when tested at greenhouse conditions using Plantago lanceolata L. as a bait plant. Occasional occurrence of AM fungi was recorded in Festuca hyperborea Holmen ex Frederiksen, Trisetum spicatum (L.) Richt., and Potentilla hookeriana – Potentilla pulchella at Devon Island. Despite the fact that potential AM plants are present, no AM was found at the two most northern sites, Ellesmere Island and Ellef Ringnes Island. There seems to be climatic or dispersal limitations to AM colonization at these northern sites. Fine endophytic fungi, formerly named Glomus tenue (Grenall) I.R. Hall, were recorded at all four sites, but most frequently at Banks Island. We thereby provide further evidence that fine endophytes are more frequent in harsh climatic conditions than AM fungi. There was a relatively high proportion of nonmycorrhizal plant species at all sites, and this proportion increased towards the north.Key words: arctic, arbuscular mycorrhiza, fine endophytes, dark septate fungi.
Arbuscular mycorrhizae (AM) are seldom reported from high latitudes. We found that Asteraceae (Arnica, Erigeron, and Taraxacum) at a site on Axel Heiberg Island (approximately 80°N) have abundant AM and fine endophytes (FE). We used standard microscopic methods for examination and quantification, plus high-resolution confocal fluorescence imaging. AM in Arctic Asteraceae were compared with those in congeners from Saskatoon and with those in some other Arctic species. Arctic AM had 6 μm wide aseptate hyphae producing abundant arbuscules, vesicles, and inter- and intra-cellular hyphae. AM colonization exceeded 80% for Arctic Asteraceae, similar to 66%-90% for prairie Taraxacum and Erigeron, the first of this type of comparison. AM/FE abundance in Arctic Ranunculus was 68%. Within Taraxacum roots, hyphal coils predominated near the epidermis and arbuscules near the vascular cylinder. Arctic AM colonization did not vary with soil depth, although permafrost was approximately 15 cm below the surface. FE were abundant in our High Arctic samples, where they may have functional roles comparable with those of AM. Thus, low abundance of AM reported previously at the community level for high-latitude sites may reflect a combination of biotic and abiotic factors. The Axel Heiberg Island thermal oasis is ideal for functional fungal root endophyte studies in the High Arctic.
One of the most cited papers in arbuscular mycorrhizal (AM) research was published by Phillips and Hayman in 1970 describing an easy standard method to stain AM fungi (AMF) in roots. Since then, a number of other methods (destructive–non-destructive; vital–non-vital) on how to visualize AMF in roots have been published. Our review provides an overview on present techniques used to visualize AMF in roots and gives recommendations on their use. We hope that the present review will help the readers to choose an appropriate method to visualize AMF in roots for their specific experimental set-up.
Previously described methods to quantify the proportion of root length colonized by vesicular-arbuscular (VA) mycorrhizal fungi are reviewed. It is argued that these methods give observer-dependent measures of colonization which cannot be used to compare, quantitatively, roots examined by different researchers. A modified method is described here to estimate VA mycorrhizal colonization on an objective scale of measurement, involving inspection of intersections between the microscope eyepiece crosshair and roots at magnification × 200; it is referred to as the magnified intersections method. Whether the vertical eyepiece crosshair crosses one or more arbuscules is noted at each intersection. The estimate of colonization is the proportion of root length containing arbuscules, called the arbuscular colonization (AC). The magnified intersections method also determines the proportion of root length containing vesicles, the vesicular colonization (VC), and the proportion of root length containing hyphae, the hyphal colonization (HC). However, VC and HC should be interpreted with caution because vesicles and hyphae, unlike arbuscules, can be produced in roots by non-mycorrhizal fungi.
The ultrastructural organization and some cytochemical features (protein and polysaccharide distribution) of the mycorrhiza formed by Glomus tenuis in raspberry roots have been investigated. Certain aspects of the fine mycorrhizal endophyte (smaller hyphae, thinner walls, distinct two‐layered wall structure following the PATAg test for polysaccharides, complete absence of septa) distinguish it from the coarse vesicular–arbuscular mycorrhizal fungi. The modifications occurring in the host‐fungus interface during Glomus tenuis mycorrhiza development are however very similar to those that have been described in several mycorrhizae formed by coarse vesicular‐arbuscular endophytes.
Root and soil samples from 13 collecting sites located in the Canadian High Arctic were harvested between July 18 and 29, 1991, and surveyed for root colonization and spore populations of arbuscular mycorrhizal fungi. Grasses of the genus Festuca (Festuca brachyphylla Schult. & Schult., Festuca baffinensis Polunin, and Festuca hyperborea Holmen ex Frederiksen) served as target plants. Of the 197 plant-root systems and soil rhizospheres examined, 28% were associated with arbuscular mycorrhizae. Roots of both F. brachyphylla andF. baffinensis were colonized, while none were detected in F. hyperborea root specimens. Five arbuscular mycorrhizal fungal species were extracted from indigenous soils. The most frequent and abundant species was Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe, which was isolated from 8 of the 13 sites sampled. Other Glomales species in Arctic soils were Glomus macrocarpum Tul & Tul., Glomus fasciculatum (Thaxter sensu Gerd.) Gerd. & Trappe emend. Walker & Koske, and two other unidentified Glomus species. Trap cultures of the indigenous soil with leek (Allium porrum L.) plants confirmed the identity of the species previously identified from original soil and allowed the detection of an additional species, Glomus aggregatum Schenck. & Smith. The novelty of these observations and the relationship between plant mycorrhizal status, fungal species, and soil disturbance are discussed.Key words: mycorrhizae, Arctic, biodiversity, Glomus, Festuca.