Ericoid Fungi Research Articles

Acquisition of nitrogen from tannin protein complexes in ectomycorrhizal pine seedlings

Ectomycorrhizal and ericoid fungi are increasingly recognized for their capacity to break down soil organic matter and getting access to organic nitrogen (N). In many forest ecosystems proteins complexed by plant-produced tannins constitute a substantial amount of organic N. Yet, it is currently unknown to what extent these N sources are accessible to ectomycorrhizae and their associated plants. In a pot experiment, we provided ectomycorrhizal pine (Pinus pinea) seedlings with exactly the same amount of N either in mineral form, as protein, or as two different tannin-protein complexes, formed with commercially available tannins or tannins isolated from pine leaf litter. Over a period of 18 months, pine seedlings grew at least two times bigger in all N-treatments. However, growth and N acquisition were roughly two and three times larger, respectively, with mineral N or protein supply compared to tannin-protein complexes as the sole N source (no difference between the two different complexes). With tannin-protein complexes, pine seedlings allocated relatively more biomass into fine roots. In addition, the decrease in tissue N concentration in the tannin-protein complex treatments was lower in fine roots (30%) than in needles (53%). Our results showed that tannins strongly influence N nutrition in ectomycorrhizal pine seedlings. Tannin-protein complexes are an accessible N source for ectomycorrhizal pine seedlings although they grew better with easier accessible N. The respective contributions of ectomycorrhizal fungi and other free or root-associated microorganisms in the breakdown of tannin protein complexes recquires further exploration. Tannin-protein complexes may be an important N source in ecosystems where organic nitrogen dominates, but the respective contributions of ectomycorrhizal fungi and other free or root-associated microorganisms in the breakdown of tannin protein complexes recquires further exploration.

Host ancestry and morphology differentially influence bacterial and fungal community structure of Rhododendron leaves, roots, and soil

Rhododendron are popular ornamental plants that are well-known for forming mycorrhizal associations with ericoid fungi, but little is known about how host traits influence their microbiome more broadly. This study investigated leaf, root, rhizosphere soil, and bulk soil bacterial and fungal community structure for 12 Rhododendron species, representing four taxonomic clades with different leaf habits. Samples were collected when ephemeral hair roots colonized by ericoid mycorrhizae were absent, and microbial community structure was compared to leaf and root morphology for the same plants. Root morphology and the fungal communities of roots and rhizosphere soil were primarily structured by host ancestry. Leaf bacterial and fungal communities were even more distinct across clades than for roots or rhizosphere, and microbial communities of leaves and bulk soil were similarly structured by clade-wise differences in leaf morphology, suggesting a role for Rhododendron leaf litter in belowground microbial community structure. This work sheds new light on host traits influencing microbial community structure of ericaceous plants, showing a strong influence of ancestry, but also that different host traits drive bacterial and fungal communities across different plant compartments, suggesting future work on factors that drive similarity among close relatives in the non-ericoid microbes associating with Rhododendron.

Endophytic fungi in blueberry cultivars, in three production areas of Argentina

Blueberries develop a shallow and fibrous root system, with sparse root hairs, normally colonized by mycorrhizal fungi. The presence of endophytic fungi in blueberry roots has been studied mainly in the area of origin of each species. The aims of the present study were to determine the occurrence of endophytic fungi in the roots of southern highbush blueberry (SHB) cultivars, in the three most important blueberry production areas of Argentina, and identify them. Soil samples with blueberry rootlets were obtained and endophytic fungi were isolated from them. Some of them by classical taxonomy identification, and, when this was not possible, PCR amplified material were sequenced (Macrogen laboratory), DNA fragments were analyzed with the Basic Local Alignment Search Tool (BLAST) and identified, through GenBank. Blueberry roots were found to be colonized by a large number of fungal genera, which varied greatly among locations and cultivars. Some of the endophytic fungi identified have pathogenic function, others are only plant hosts, and some of them have mycorrhizal function as is the case of genus Oidiodendron where we found O. maius and O. echinulatum. We may conclude that SHB is associated with local ericoid fungi, some of which are mycorrhizal and some dark septate endophytes, which, in most cases, do not match with those found in production regions of their native area, but same of them are important to promote blueberry growth.

Soil fungal communities in abandoned agricultural land has not yet moved towards the seminatural forest

The increasing trend in the abandonment of agricultural land provides a unique opportunity for the restoration of forests. However, not only vegetation but also belowground microbial communities are vital for the development of stable forest stands. To assess whether soil fungi can affect the succession of abandoned agricultural lands, we analyzed soil fungal communities, including total and arbuscular mycorrhizal (AM) fungi in agricultural lands (AG), short- and long-term abandoned agricultural lands (SA and LA), and short- and long-term regenerating seminatural forests (SR and LR). Vegetation analysis showed that the abandoned lands were gradually converting to seminatural forests. However, significantly lower soil pH values and higher C and N concentrations were found in the LR forests than in the other land use types. Although there were no significant differences observed in the total and AM fungal diversity among land use types, the species compositions of seminatural forests (LR and SR), abandoned lands (SA and LA), and agricultural land (AG) were clearly differentiated in the ordination analysis. Significant differences were observed between AG and other land use types and between LR and abandoned land in the case of total fungal communities. The ECM fungi associated with Alnus occurred on the LA plots, whereas the LR plots were characterized by different ECM fungi (Russula, Lactifluus) and a high abundance of ericoid fungi along with hygrocyboid and clavarioid taxa. These results indicate that fungal succession is not as straightforward as vegetation changes. AM fungi will probably not constrain the abandoned land succession towards seminatural forests, but total fungal communities could be hindered by soil properties and absence of host trees.

Phosphate solubilizing and PGR activities of ericaceous shrubs microorganisms isolated from Mediterranean forest soil

Abstract Many soil microorganisms are able to transform insoluble forms of phosphorus into an accessible soluble form, thus contributing to plant nutrition through exhibiting other beneficial traits such as production of organic acids, siderophore indole acetic acid (IAA) and production of hydrogen cyanide (HCN). Achieving this purpose, ericoid fungi and actinobacteria were isolated from roots and rhizospheric soil of Calluna vulgaris L., belonging to the ericaceous family. All isolates were shown to be able to solubilize insoluble phosphate in liquid cultures and to produce transparent halos of solubilization on PVK solid medium. The actinobacteria isolate AH6 was the most efficient compared to others, producing 145.5 mg/L of phosphate and 141 μg/L of IAA. However, fungi isolate S2 and S3 had high solubilization capacity and produced a high concentration of IAA in comparison with S1, which was a good siderophore producer. We applied a sequencing approach by amplifying the ITS region for fungi and 16S for actinobacteria. Most of the actinobacteria isolates belong to the Streptomyces genus while fungi were identified as related to ericoid mycorrhizal fungi. To evaluate the effectiveness of selected rhizobacteria and symbiotic fungi isolates and to confirm their role as biofertilizers, inoculation experimentations on plants are required.

Time- and age-related effects of experimentally simulated nitrogen deposition on the functioning of montane heathland ecosystems

Ecosystems adapted to low nitrogen (N) conditions such as Calluna-heathlands are especially sensitive to enhanced atmospheric N deposition that affects many aspects of ecosystem functioning like nutrient cycling, soil properties and plant-microbial-enzyme relationships. We investigated the effects of five levels of experimentally-simulated N deposition rates (i.e., N fertilization treatments: 0, 10, 20 and 50kgNha−1yr−1 for 3years, and 56kgNha−1yr−1 for 10years) on: plant, litter, microbial biomass and soil nutrient contents, soil extracellular enzymatic activities, and plant root ericoid mycorrhizal colonization. The study was conducted in marginal montane Calluna-heathlands at different developmental stages resulting from management (young/building-phase and mature-phase). Our findings revealed that many soil properties did not show a statistically significant response to the experimental addition of N, including: total N, organic carbon (C), C:N ratio, extractable N-NO3−, available phosphorus (P), urease and β-glucosidase enzyme activities, and microbial biomass C and N. Our results also evidenced a considerable positive impact of chronic (10-year) high-N loading on soil extractable N-NH4+, acid phosphatase enzyme activity, Calluna root mycorrhizal colonization by ericoid fungi, Calluna shoot N and P contents, and litter N content and N:P ratio. The age of heathland vegetation influenced the effects of N addition on ericoid mycorrhizal colonization, resulting in higher colonized roots in young heathlands at the control, low and medium N-input rates; and in mature ones at the high and chronically high N rates. Also, young heathlands exhibited greater soil extractable N-NO3−, available P, microbial biomass N, Calluna shoot N and P contents, and litter N content, compared to mature ones. Our results highlighted that accounting for the N-input load and duration, as well as the developmental stage of the vegetation, is important for assessing the effects of added N, particularly at the heathlands' southern distribution limit.

Improved endoglucanase production and mycelial biomass of some ericoid fungi

Fungal species associated with ericaceous plant roots produce a number of enzymes and other bio-active metabolites in order to enhance survival of their host plants in natural environments. This study focussed on endoglucanase production from root associated ericoid mycorrhizal and dark septate endophytic fungal isolates. Out of the five fungal isolates screened, Leohumicola sp. (ChemRU330/PPRI 13195) had the highest relative enzyme activity and was tested along with isolates belonging to Hyloscyphaceae (EdRU083/PPRI 17284) and Leotiomycetes (EdRU002/PPRI 17261) for endoglucanase production under different pH and nutritional conditions that included: carbon sources, nitrogen sources and metal ions, at an optimum temperature of 28 °C. An optimal of pH 5.0 produced enzyme activity of 3.99, 2.18 and 4.31 (U/mg protein) for isolates EdRU083, EdRU002 and Leohumicola sp. respectively. Increased enzyme activities and improved mycelial biomass production were obtained in the presence of supplements such as potassium, sodium, glucose, maltose, cellobiose, tryptone and peptone. While NaFe-EDTA and Co2+ inhibited enzyme activity. The potential role of these fungi as a source of novel enzymes is an ongoing objective of this study.

Influence of biological products on the growth and development of large-fruited cranberry under greenhouse conditions

Abstract The aim of this study was to determine the influence of various biological fertilizers on the growth and development of plants of the large-fruited cranberry and the degree of mycorrhizal association in their roots under controlled conditions. Plants of the ‘Pilgrim’, ‘Stevens’ and ‘Ben Lear’ cranberry cultivars were planted in rhizoboxes filled with soils collected from the areas of Krojczyn and Motoga. The following experimental treatments with fertilizers were applied: control plants, plants fertilized with NPK, a bacterial-mycorrhizal consortium, Vinassa, lignite + Vinassa, Florovit Natura and the fertilizer Crop-UP. The study has shown that there was a tendency to stimulate the vegetative growth and development of cranberry plants through the use of bio-fertilizers and beneficial fungi obtained from the rhizosphere of these plants. There was a tendency for the fresh and dry weight of cranberry shoots to increase, especially in ‘Ben Lear’, under the influence of the bio-fertilizer Florovit Natura when compared with the control plants fertilized with NPK. Compared with the NPK control, all of the bio-fertilizers significantly increased mycorrhizal frequency in the roots of the tested plants of the large-fruited cranberry, with the exception of Crop-UP and lignite compost used in conjunction with Vinassa in ‘Stevens’. No statistically significant differences were obtained for plant size and root colonisation by ericoid fungi in the plants grown in the soil from the areas of Motoga and Krojczyn.

Screening Commercial Peat and Peat-based Products for the Presence of Ericoid Mycorrhizae

Abstract Pieris floribunda (Pursh) Benth. & Hook., a known host of ericoid fungi, was used as a model plant to investigate the presence of ericoid mycorrhizal fungi in select peat and peat-based products. After growing in each medium for 75 days, roots of seedlings were examined and average percent colonization was determined for each sample. Results indicate that these fungi are present in the majority of peat and peat-based media tested. Seedlings grown in some of the selected media had a greater percentage of root cells colonized by ericoid mycorrhizae than others in the study.

Ericoid mycorrhizal fungi: some new perspectives on old acquaintances

Many ericaceous species colonize as pioneer plants substrates ranging from arid sandy soils to moist mor humus, in association with their mycorrhizal fungi. Thanks to the symbiosis with ericoid mycorrhizal fungi, ericaceous plants are also able to grow in highly polluted environments, where metal ions can reach toxic levels in the soil substrate. For a long time this mycorrhizal type has been regarded as an example of a highly specific interaction between plants and fungi. More recent studies have been challenging this view because some ericoid mycorrhizal endophytes seem also able to colonise plants from very distant taxa. A molecular approach has allowed the investigation of genetic diversity and molecular ecology of ericoid mycorrhizal fungi, and has revealed that ericaceous plants can be very promiscuous, with multiple occupancy of their thin roots. The molecular analysis of sterile morphotypes involved in this symbiosis has also led to deeper understanding of the species diversity of ericoid fungi. Genetic polymorphism of ericoid fungi is wider than previously thought, and often increased by the presence of Group I introns in the nuclear small subunit rDNA.

564 Screening Commercial Peat and Peat-based Products for the Presence of Ericoid Mycorrhizae

A study was conducted to investigate the presence of ericoid mycorrhizal fungi in select peat and peat-based products. Vaccinium corymbosum, a known host of ericoid fungi, was used as a model plant. Peat and peat-based products were obtained from all major sources that supply the northeastern United States. Seedling roots were examined and average percent colonization was determined for each sample. Results indicate that these fungi are present in the majority of peat and peat-based media tested. Seedlings grown in some of the selected media exhibited an increased percentage of colonized root cells. Mycorrhizal fungi colonizing roots of test plants were isolated. These fungi exhibited typical ericoid fungal growth characteristics.

Physiology of organic nitrogen acquisition by ectomycorrhizal fungi and ectomycorrhizas.

Ectomycorrhizal fungi are symbiotically associated microorganisms which ecological importance has been repeatedly demonstrated. There has been a considerable amount of research aimed at assessing the ability of ectomycorrhizal fungi and ectomycorrhizas to utilize organic nitrogen sources. The fate of soil proteins, peptides and amino acids has been studied from a number of perspectives. Exocellular hydrolytic enzymes have been detected and characterized in a number of ectomycorrhizal and ericoid fungi. Studies on amino acid transport through the plasma membrane have demonstrated the ability of ectomycorrhizal fungi to take up the products of proteolytic activities. Investigations on intracellular metabolism of amino acids have allowed the identification of the metabolic pathways involved. Possible intracellular compartmentation of amino acids will be examined by immunocytochemistry. Further translocation of amino acids in symbiotic tissues has been established by experiments using isotopic tracers, although the exact nature of the nitrogenous compounds transferred at the symbiotic interface remained unclear. One of the main future challenges in the physiology of organic nitrogen acquisition is to determine the nature, the regulation and the location of N-compound transporters at the soil-fungus and fungus-plant interfaces. The molecular approach which is just emerging in this particular research area will greatly improve our knowledge. Future research should also address the extent of competition between different ectomycorrhizal species and between different microbial populations for organic nitrogen.

Physiology of organic nitrogen acquisition by ectomycorrhizal fungi and ectomycorrhizas

Ectomycorrhizal fungi are symbiotically associated microorganisms which ecological importance has been repeatedly demonstrated. There has been a considerable amount of research aimed at assessing the ability of ectomycorrhizal fungi and ectomycorrhizas to utilize organic nitrogen sources. The fate of soil proteins, peptides and amino acids has been studied from a number of perspectives. Exocellular hydrolytic enzymes have been detected and characterized in a number of ectomycorrhizal and ericoid fungi. Studies on amino acid transport through the plasma membrane have demonstrated the ability of ectomycorrhizal fungi to take up the products of proteolytic activities. Investigations on intracellular metabolism of amino acids have allowed the identification of the metabolic pathways involved. Possible intracellular compartmentation of amino acids will be examined by immunocytochemistry. Further translocation of amino acids in symbiotic tissues has been established by experiments using isotopic tracers, although the exact nature of the nitrogenous compounds transferred at the symbiotic interface remained unclear. One of the main future challenges in the physiology of organic nitrogen acquisition is to determine the nature, the regulation and the location of N-compound transporters at the soil-fungus and fungus-plant interfaces. The molecular approach which is just emerging in this particular research area will greatly improve our knowledge. Future research should also address the extent of competition between different ectomycorrhizal species and between different microbial populations for organic nitrogen.

Production of pectin-degrading enzymes by ericoid mycorrhizal fungi.

Production of enzymes which degrade plant cell wall macromoleculea has been studied in relatively few ericoid fungal isolates, although these polymers arc a major component of the organic litter and an important source of nutrients for these fungi. Our aims were to investigate whether the ability to degrade the wall pectic component, only reported for one isolate, is a general feature of ericoid fungi. Of about 35 isolates from different geographic regions, all were capable of growing on pectin as the sole carbon source. Polygalacturonase (PG) activity was detected to a different degree in the culture filtrates and independently of the fungal growth rate. Solid and liquid isoelectric focusing allowed separation and identification of several polygalacturonase isoforms. Among the fungal isolates investigated, those from the northern hemisphere produced mostly acidic isoforms, whereas isolates from South Africa secreted more abundantly basic isoforms. However, purification and biochemical characterization of several PG isoforms from the different isolates revealed an optimal activity in the acidic pH range for all the PG enzymes tested. Polygalacturonase enzymes seem to be an important component of the enzymatic arsenal secreted by ericoid fungi during their saprotrophic life. In addition, they could also play a role during root colonization, since penetration across the plant cell wall is a prerequisite for the establishment of endomycorrhizal symbiosis.

Ericoid mycorrhizal fungi: cellular and molecular bases of their interactions with the host plant

A number of soil-borne fungi are able to form typical ericoid mycorrhizae with plants belonging to Ericales. Together with Hymenoscyphus ericae, the first isolate from roots of ericaceous plants, other fungal species belonging to the genus Oidiodendron and many sterile mycelia have been recognized as mycorrhizal by several authors. A high genetic diversity was even found when a population of ericoid mycorrhizal fungi isolated from a single plant of Calluna vulgaris was analysed with morphological and molecular techniques. Ericoid fungi have a relevant saprotrophic potential, as they can degrade several organic polymers present in the soil matrices. Different cell wall degrading enzymes, which are part of this arsenal and are produced in vitro by several ericoid fungi, have been investigated biochemically. Immunocytochemical studies on the production of pectin degrading enzymes during the infection process of host and non-host plants suggest that regulation mechanisms for the production of cell wall degrading enzymes in vivo may be a crucial step for the establishment of successful mycorrhiza with host plants. Key words: ericoid mycorrhizae, cell wall degrading enzymes, polygalacturonase, DNA-RAPD techniques.

Ericoid endophytes of Western Australian heaths (Epacridaceae)

summaryThe presence of ericoid endophytes was Confirmed in hair roots of 14 species of Epacridaceae native to the mediterranean south‐west of Western Australia. The phenology of infection was followed in 2‐yr‐old seedlings of Astroloma xerophyllum D.C. (Sond.) and showed increasing infection up to a peak (40% of hair roots infected) in late winter and a decline to zero infection during summer (December February). Over 400 isolates of root‐inhabiting fungi of 14 species from seven genera of native Epacridaceae were obtained. All isolates were dark‐coloured, sterile and slow growing tin potato dextrose agar. Based on morphological characteristics, eight isolates were selected for further investigation. Detailed analysis of morphological and cultural features was used to create three groups, two of which were infective with cuttings of the common Epacridaceae species. Lysinema ciliatum. The groupings based on rnorphological characteristics were reflected in the pectic zymogram patterns of the isolates. Pectic zymogram analysis of ericoid fungi revealed that none of the Australian isolates matched fungi known to be infective with Ericaceae [Hymenoscyphus ericae (Read) Korf. & Kernen and Oidiodendron spp.] even though all isolates appeared morphologically similar with similar growth rates.

Chitin as a nitrogen source for mycorrhizal fungi

Three ericoid and two ectomycorrhizal fungi were tested for their abilities to utilize chitin as a sole source of nitrogen. All of the ericoid fungi readily degraded chitin. The ecto-fungi, in contrast, used it only sparingly. The results extend the range of polymeric N sources known to be utilized by mycorrhizal fungi and imply that some mycorrhizal fungi may be involved in recycling of N from this structural component of hyphal walls in soil. The possible role of chitinase activity in influencing fungal interactions in heathland ecosystems is discu