Afforestation of abandoned farmland with conifer seedlings inoculated with three ectomycorrhizal fungi - impact on plant performance and ectomycorrhizal community

Optimizing conditions of mycelial inoculum immobilized in Ca-alginate beads: a case study in ectomycorrhizal fungus Astraeus odoratus

Ectomycorrhizal inoculum has emerged as a critical tool for forest restoration, especially under challenging climate change conditions. The inoculation of selective ectomycorrhizal fungi can enhance seedling survival and subsequent growth in the field. This study optimized the liquid media for mycelial growth of Astraeus odoratus strain K1 and the sodium alginate solution composition for enhanced mycelial viability after entrapment. Using Modified Melin-Norkrans as the optimal media for mycelial cultivation and 2% sodium alginate supplemented with Czapek medium, 0.25% activated charcoal, 5% sucrose, and 5% sorbitol in the alginate solution yielded the highest viability of A. odoratus mycelia. Preservation in distilled water and 10% glycerol at 25 °C for 60 days proved to be the most effective storage condition for the alginate beads. Both fresh and preserved alginate beads were tested for colonizing on Hopea odorata Roxb. seedlings, showing successful colonization and ectomycorrhizal root formation, with over 49% colonization. This study fills a crucial gap in biotechnology and ectomycorrhizal inoculum, paving the way for more effective and sustainable forest restoration practices.

Ectomycorrhizal Community Shifts at a Former Uranium Mining Site

Ectomycorrhizal communities at young oak, pine, and birch stands in a former uranium mining site showed a low diversity of morphotypes with a preference for contact and short-distance exploration strategies formed by the fungi Russulaceae, Inocybaceae, Cortinariaceae, Thelephoraceae, Rhizopogonaceae, Tricholomataceae, as well as abundant Meliniomyces bicolor. In order to have better control over abiotic conditions, we established pot experiments with re-potted trees taken from the sites of direct investigation. This more standardized cultivation resulted in a lower diversity and decreased prominence of M. bicolor. In addition, the exploration strategies shifted to include long-distance exploration types. To mimic secondary succession with a high prevalence of fungal propagules present in the soil, inoculation of re-potted trees observed under standardized conditions for two years was used. The super-inoculation increased the effect of lower abundance and diversity of morphotypes. The contact morphotypes correlated with high Al, Cu, Fe, Sr, and U soil contents, the dark-colored short-distance exploration type did not show a specific preference for soil characteristics, and the medium fringe type with rhizomorphs on oaks correlated with total nitrogen. Thus, we could demonstrate that field trees, in a species-dependent manner, selected for ectomycorrhizal fungi with exploration types are likely to improve the plant's tolerance to specific abiotic conditions.

The role of internal transcribed spacer 2 secondary structures in classifying mycoparasitic Ampelomyces

Many fungi require specific growth conditions before they can be identified. Direct environmental DNA sequencing is advantageous, although for some taxa, specific primers need to be used for successful amplification of molecular markers. The internal transcribed spacer region is the preferred DNA barcode for fungi. However, inter- and intra-specific distances in ITS sequences highly vary among some fungal groups; consequently, it is not a solely reliable tool for species delineation. Ampelomyces, mycoparasites of the fungal phytopathogen order Erysiphales, can have ITS genetic differences up to 15%; this may lead to misidentification with other closely related unknown fungi. Indeed, Ampelomyces were initially misidentified as other pycnidial mycoparasites, but subsequent research showed that they differ in pycnidia morphology and culture characteristics. We investigated whether the ITS2 nucleotide content and secondary structure was different between Ampelomyces ITS2 sequences and those unrelated to this genus. To this end, we retrieved all ITS sequences referred to as Ampelomyces from the GenBank database. This analysis revealed that fungal ITS environmental DNA sequences are still being deposited in the database under the name Ampelomyces, but they do not belong to this genus. We also detected variations in the conserved hybridization model of the ITS2 proximal 5.8S and 28S stem from two Ampelomyces strains. Moreover, we suggested for the first time that pseudogenes form in the ITS region of this mycoparasite. A phylogenetic analysis based on ITS2 sequences-structures grouped the environmental sequences of putative Ampelomyces into a different clade from the Ampelomyces-containing clades. Indeed, when conducting ITS2 analysis, resolution of genetic distances between Ampelomyces and those putative Ampelomyces improved. Each clade represented a distinct consensus ITS2 S2, which suggested that different pre-ribosomal RNA (pre-rRNA) processes occur across different lineages. This study recommends the use of ITS2 S2s as an important tool to analyse environmental sequencing and unveiling the underlying evolutionary processes.

DNA-Metabarcoding of Belowground Fungal Communities in Bare-Root Forest Nurseries: Focus on Different Tree Species

The production of tree seedlings in forest nurseries and their use in the replanting of clear-cut forest sites is a common practice in the temperate and boreal forests of Europe. Although conifers dominate on replanted sites, in recent years, deciduous tree species have received more attention due to their often-higher resilience to abiotic and biotic stress factors. The aim of the present study was to assess the belowground fungal communities of bare-root cultivated seedlings of Alnus glutinosa , Betula pendula, Pinus sylvestris, Picea abies and Quercus robur in order to gain a better understanding of the associated fungi and oomycetes, and their potential effects on the seedling performance in forest nurseries and after outplanting. The study sites were at the seven largest bare-root forest nurseries in Lithuania. The sampling included the roots and adjacent soil of 2-3 year old healthy-looking seedlings. Following the isolation of the DNA from the individual root and soil samples, these were amplified using ITS rRNA as a marker, and subjected to high-throughput PacBio sequencing. The results showed the presence of 161,302 high-quality sequences, representing 2003 fungal and oomycete taxa. The most common fungi were Malassezia restricta (6.7% of all of the high-quality sequences), Wilcoxina mikolae (5.0%), Pustularia sp. 3993_4 (4.6%), and Fusarium oxysporum (3.5%). The most common oomycetes were Pythium ultimum var. ultimum (0.6%), Pythium heterothallicum (0.3%), Pythium spiculum (0.3%), and Pythium sylvaticum (0.2%). The coniferous tree species (P. abies and P. sylvestris) generally showed a higher richness of fungal taxa and a rather distinct fungal community composition compared to the deciduous tree species (A. glutinosa, B. pendula , and Q. robur). The results demonstrated that the seedling roots and the rhizosphere soil in forest nurseries support a high richness of fungal taxa. The seedling roots were primarily inhabited by saprotrophic and mycorrhizal fungi, while fungal pathogens and oomycetes were less abundant, showing that the cultivation practices used in forest nurseries secured both the production of high-quality planting stock and disease control.

Chestnuts bred for blight resistance depart nursery with distinct fungal rhizobiomes

Restoration of the American chestnut (Castanea dentata) is underway using backcross breeding that confers chestnut blight disease resistance from Asian chestnuts (most often Castanea mollissima) to the susceptible host. Successful restoration will depend on blight resistance and performance of hybrid seedlings, which can be impacted by below-ground fungal communities. We compared fungal communities in roots and rhizospheres (rhizobiomes) of nursery-grown, 1-year-old chestnut seedlings from different genetic families of American chestnut, Chinese chestnut, and hybrids from backcross breeding generations as well as those present in the nursery soil. We specifically focused on the ectomycorrhizal (EcM) fungi that may facilitate host performance in the nursery and aid in seedling establishment after outplanting. Seedling rhizobiomes and nursery soil communities were distinct and seedlings recruited heterogeneous communities from shared nursery soil. The rhizobiomes included EcM fungi as well as endophytes, putative pathogens, and likely saprobes, but their relative proportions varied widely within and among the chestnut families. Notably, hybrid seedlings that hosted few EcM fungi hosted a large proportion of potential pathogens and endophytes, with possible consequences in outplanting success. Our data show that chestnut seedlings recruit divergent rhizobiomes and depart nurseries with communities that may facilitate or compromise the seedling performance in the field.

Ectomycorrhizal fungal diversity and community structure associated with cork oak in different landscapes

Cork oak (Quercus suber L.) forests play an important ecological and economic role. Ectomycorrhizal fungi (ECMF) are key components for the sustainability and functioning of these ecosystems. The community structure and composition of ECMF associated with Q. suber in different landscapes of distinct Mediterranean bioclimate regions have not previously been compared. In this work, soil samples from cork oak forests residing in different bioclimates (arid, semi-arid, sub-humid, and humid) were collected and surveyed for ectomycorrhizal (ECM) root tips. A global analysis performed on 3565 ECM root tips revealed that the ECMF community is highly enriched in Russula, Tomentella, and Cenoccocum, which correspond to the ECMF genera that mainly contribute to community differences. The ECMF communities from the rainiest and the driest cork oak forests were distinct, with soils from the rainiest climates being more heterogeneous than those from the driest climates. The analyses of several abiotic factors on the ECMF communities revealed that bioclimate, precipitation, soil texture, and forest management strongly influenced ECMF structure. Shifts in ECMF with different hyphal exploration types were also detected among forests, with precipitation, forest system, and soil texture being the main drivers controlling their composition. Understanding the effects of environmental factors on the structuring of ECM communities could be the first step for promoting the sustainability of this threatened ecosystem.

Effect of Simulated Climate Warming on the Ectomycorrhizal Fungal Community of Boreal and Temperate Host Species Growing Near Their Shared Ecotonal Range Limits

Ectomycorrhizal (ECM) fungi can influence the establishment and performance of host species by increasing nutrient and water absorption. Therefore, understanding the response of ECM fungi to expected changes in the global climate is crucial for predicting potential changes in the composition and productivity of forests. While anthropogenic activity has, and will continue to, cause global temperature increases, few studies have investigated how increases in temperature will affect the community composition of ectomycorrhizal fungi. The effects of global warming are expected to be particularly strong at biome boundaries and in the northern latitudes. In the present study, we analyzed the effects of experimental manipulations of temperature and canopy structure (open vs. closed) on ectomycorrhizal fungi identified from roots of host seedlings through 454 pyrosequencing. The ecotonal boundary site selected for the study was between the southern boreal and temperate forests in northern Minnesota, USA, which is the southern limit range for Picea glauca and Betula papyrifera and the northern one for Pinus strobus and Quercus rubra. Manipulations that increased air and soil temperature by 1.7 and 3.4 °C above ambient temperatures, respectively, did not change ECM richness but did alter the composition of the ECM community in a manner dependent on host and canopy structure. The prediction that colonization of boreal tree species with ECM symbionts characteristic of temperate species would occur was not substantiated. Overall, only a small proportion of the ECM community appears to be strongly sensitive to warming.

Impact of Heterobasidion root-rot on fine root morphology and associated fungi in Picea abies stands on peat soils

We examined differences in fine root morphology, mycorrhizal colonisation and root-inhabiting fungal communities between Picea abies individuals infected by Heterobasidion root-rot compared with healthy individuals in four stands on peat soils in Latvia. We hypothesised that decreased tree vitality and alteration in supply of photosynthates belowground due to root-rot infection might lead to changes in fungal communities of tree roots. Plots were established in places where trees were infected and in places where they were healthy. Within each stand, five replicate soil cores with roots were taken to 20 cm depth in each root-rot infected and uninfected plot. Root morphological parameters, mycorrhizal colonisation and associated fungal communities, and soil chemical properties were analysed. In three stands root morphological parameters and in all stands root mycorrhizal colonisation were similar between root-rot infected and uninfected plots. In one stand, there were significant differences in root morphological parameters between root-rot infected versus uninfected plots, but these were likely due to significant differences in soil chemical properties between the plots. Sequencing of the internal transcribed spacer of fungal nuclear rDNA from ectomycorrhizal (ECM) root morphotypes of P. abies revealed the presence of 42 fungal species, among which ECM basidiomycetes Tylospora asterophora (24.6 % of fine roots examined), Amphinema byssoides (14.5 %) and Russula sapinea (9.7 %) were most common. Within each stand, the richness of fungal species and the composition of fungal communities in root-rot infected versus uninfected plots were similar. In conclusion, Heterobasidion root-rot had little or no effect on fine root morphology, mycorrhizal colonisation and composition of fungal communities in fine roots of P. abies growing on peat soils.

Development of growth media for solid substrate propagation of ectomycorrhizal fungi for inoculation of Norway spruce (Picea abies) seedlings

A silica-based propagation medium was developed for large-scale production of ectomycorrhizal (ECM) fungal inoculum by solid state fermentation. Development of the medium was started by screening for an optimal growth medium among six different semisynthetic agar media traditionally used in cultivation of ECM fungi. The majority (65 %) of the twenty tested ECM fungal strains that typically colonize Norway spruce (Picea abies) seedlings grew best on modified Melin-Norkrans (MMN) medium with reduced sugar content (½MMN). In order to develop a nutritionally similar medium for large-scale cultivation of the ECM fungi, we chose silica to form a solid matrix and light brewery malt extract to provide nutrients. The medium was supplemented with a commercial humic acid product that was shown to boost fungal growth. The optimal concentration of the constituents was screened for in two assays by determining the growth rates of seven potential inoculant ECM fungal strains (Amphinema sp., Cenococcum geophilum, Hebeloma sp., Meliniomyces bicolor, Paxillus involutus, Piloderma byssinum, and Tylospora asterophora). As a result, we composed a silica-based mass propagation medium (pH 5.8) containing 2.5 % brewery malt extract and 0.5 g/l humic acid product Lignohumate AM. This medium is easily produced and supported good growth of even the slowly growing and rarely studied Athelioid ECM strains. Furthermore, root systems of Norway spruce nursery seedlings were colonized by the tested ECM fungi by using solid inoculum formulated from the silica medium.

Diversity and persistence of ectomycorrhizal fungi and their effect on nursery-inoculated Pinus pinaster in a post-fire plantation in Northern Portugal

Ectomycorrhizal fungi (ECMF) play an important role in forest ecosystems, often mitigating stress factors and increasing seedling performance. The aim of this study was to investigate the effects of a nursery inoculation on Pinus pinaster growth and on the fungal communities established when reforesting burned areas. Inoculated P. pinaster saplings showed 1.5-fold higher stem height than the non-inoculated controls after a 5 year growth period, suggesting that fungal inoculation could potentiate tree growth in the field. Ordination analysis revealed the presence of different ECMF communities on both plots. Among the nursery-inoculated fungi, Laccaria sp., Rhizopogon sp., Suillus bovinus and Pisolithus sp. were detected on inoculated Pinus saplings on both sampling periods, indicating that they persisted after field establishment. Other fungi were also detected in the inoculated plants. Phialocephala sp. was found on the first assessment, while Terfezia sp. was detected on both sampling periods. Laccaria sp. and Rhizopogon sp. were identified in the control saplings, belonging however to different species than those found in the inoculated plot. Inocybe sp., Thelephora sp. and Paxillus involutus were present on both sampling periods in the non-inoculated plots. The results suggest that ECMF inoculation at nursery stage can benefit plant growth after transplantation to a post-fire site and that the inoculated fungi can persist in the field. This approach has great potential as a biotechnological tool to aid in the reforestation of burned areas.

Growth of mycorrhizal jack pine (Pinus banksiana) and white spruce (Picea glauca) seedlings planted in oil sands reclaimed areas

The effectiveness of ectomycorrhizal inoculation at the tree nursery seedling production stage on growth and survival was examined in jack pine (Pinus banksiana) and white spruce (Picea glauca) planted in oil sands reclamation sites. The seedlings were inoculated with Hebeloma crustuliniforme strain # UAMH 5247, Suillus tomentosus strain # UAMH 6252, and Laccaria bicolor strain # UAMH 8232, as individual pure cultures and in combinations. These treatments were demonstrated to improve salinity resistance and water uptake in conifer seedlings. The field responses of seedlings to ectomycorrhizal inoculation varied between plant species, inoculation treatments, and measured parameters. Seedling inoculation resulted in higher ectomycorrhizal colonization rates compared with non-inoculated control, which had also a relatively small proportion of roots colonized by the nursery contaminant fungi identified as Amphinema byssoides and Thelephora americana. Seedling inoculation had overall a greater effect on relative height growth rates, dry biomass, and stem volumes in jack pine compared with white spruce. However, when examined after two growing seasons, inoculated white spruce seedlings showed up to 75% higher survival rates than non-inoculated controls. The persistence of inoculated fungi in roots of planted seedlings was examined at the end of the second growing season. Although the inoculation with H. crustuliniforme triggered growth responses, the fungus was not found in the roots of seedlings at the end of the second growing season suggesting a possibility that the observed growth-promoting effect of H. crustuliniforme may be transient. The results suggest that the inoculation of conifer seedlings with ectomycorrhizal fungi could potentially be carried out on a large scale in tree nurseries to benefit postplanting performance in oil sands reclamation sites. However, these practices should take into consideration the differences in responses between the different plant species and fungal strains.

Growth response of Pinus densiflora seedlings inoculated with three indigenous ectomycorrhizal fungi in combination

Pinus densiflora seedlings were inoculated with three indigenous ectomycorrhizal fungi (Cenococcum geophilum, Rhizopogon roseolus and Russula densifolia) in single-, two-, and three-species treatments. After 8 months, the colonization rates of each ectomycorrhizal species, seedling growth and the nutrition were assessed in each treatment. P. densiflora seedlings inoculated with different ECM species composition showed an increase in height and basal diameter and improved seedling root and shoot nutrition concentrations compared to control treatment. Generally, combined inoculation had a more positive influence on the seedlings than the single inoculation. The three-species inoculation presented the highest growth and basal diameter and concentration of most nutrients except potassium. In conclusion, the results provided strong evidence for benefits of combined inoculation with the indigenous ectomycorrhizal fungi on P. densiflora seedlings under controlled conditions.

Fungi in roots of nursery grown Pinus sylvestris: ectomycorrhizal colonisation, genetic diversity and spatial distribution

The aims of this study were to investigate patterns of ectomycorrhizal (ECM) colonisation and community structure on nursery grown seedlings of Pinus sylvestris, spatial distribution of ECMs in the nursery plot and genetic diversity of commonly isolated ECM basidiomycete Hebeloma cavipes. One hundred seedlings were sampled in 225 m(2) area using a systematic grid design. For each seedling, 20 individual root tips were randomly collected, morphotyped, and surface sterilised for fungal isolation in pure culture. Results showed that ECM community was comprised of nine distinct morphotypes among which Thelephora terrestris (39.7%), Hebeloma sp. (17.8%) and Suillus luteus (6.1%) were the most abundant. Spatial distribution of ECMs in the nursery plot was determined by their relative abundance: even in common ECMs and random in rare ones. Fungal isolation yielded 606 pure cultures, representing 71 distinct taxa. The most commonly isolated fungi were the ascomycetes Neonectria macrodidyma (20.3%), Phialocephala fortinii (13.5%), Neonectria radicicola (6.3%) and the ECM basidiomycete H. cavipes (4.5%). Intraspecific genetic diversity within 27 H. cavipes isolates was studied using two methods: restriction digestion of the amplified intergenic spacer of nuclear ribosomal DNA and genealogical concordance of five genetic markers. Five and eight genotypes were revealed by each respective method, but both of those were largely consistent, in particular, in determining the largest genotype (A) composed of 18 isolates. Mapping positions for each H. cavipes isolate and genotype in the field showed that isolates of the A genotype covered a large part of the nursery plot. This suggests that H. cavipes is largely disseminated by vegetative means of local genotypes and that nursery cultivation practices are likely to contribute to the dissemination of this species in the forest nursery soils.

Effects of stump and slash removal on growth and mycorrhization of Picea abies seedlings outplanted on a forest clear-cut

The objectives of this study were to investigate impact of stump and slash removal on growth and mycorrhization of Picea abies seedlings outplanted on a forest clear-cut. Four non-replicated site preparation treatments included: (1) mounding (M), (2) removal of stumps (K), (3) mounding and removal of logging slash (HM) and (4) removal of logging slash and stumps (HK). Results showed that height increment of the seedlings was highest in K and lowest in M after the third growing season, and similar pattern remained after the fourth season. Ectomycorrhizal (ECM) colonisation of seedling roots was highest in M (96.6%) and lowest in K (72.3%), and even in HK (76.0%) and HM (76.3%). Morphotyping and sequencing of internal transcribed spacer of fungal ribosomal DNA revealed a total of 13 ECM species. Among those, Thelephora terrestris and Cenococcum geophilum were the most common, found on 27.4% and 26.3% of roots, respectively. The rest of species colonised 26.6% of roots. Richness of ECM species was highest in M (10 species) and lowest in K (three species). Consequently, stump and slash removal from clear-felled sites had a positive effect on growth of outplanted spruce seedlings, but negative effect on their mycorrhization. This suggests that altered soil conditions due to site disturbance by stump and slash removal might be more favourable for tree growth than more abundant mycorrhization of their root systems in less disturbed soil.

Ectomycorrhizal community structure of different genotypes of Scots pine under forest nursery conditions

In this paper, we report the effect of Scots pine genotypes on ectomycorrhizal (ECM) community and growth, survival, and foliar nutrient composition of 2-year-old seedlings grown in forest bare-root nursery conditions in Lithuania. The Scots pine seeds originated from five stands from Latvia (P1), Lithuania (P2 and P3), Belarus (P4), and Poland (P5). Based on molecular identification, seven ECM fungal taxa were identified: Suillus luteus and Suillus variegatus (within the Suilloid type), Wilcoxina mikolae, Tuber sp., Thelephora terrestris, Cenococcum geophilum, and Russuloid type. The fungal species richness varied between five and seven morphotypes, depending on seed origin. The average species richness and relative abundance of most ECM morphotypes differed significantly depending on pine origin. The most essential finding of our study is the shift in dominance from an ascomycetous fungus like W. mikolae in P2 and P4 seedlings to basidiomycetous Suilloid species like S. luteus and S. variegatus in P1 and P5 seedlings. Significant differences between Scots pine origin were also found in seedling height, root dry weight, survival, and concentration of C, K, Ca, and Mg in the needles. The Spearman rank correlation coefficient revealed that survival and nutritional status of pine seedlings were positively correlated with abundance of Suilloid mycorrhizas and negatively linked with W. mikolae abundance. However, stepwise multiple regression analysis showed that only survival and magnesium content in pine needles were significantly correlated with abundance of ECM fungi, and Suilloid mycorrhizas were a main significant predictor. Our results may have implications for understanding the physiological and genetic relationship between the host tree and fungi and should be considered in management decisions in forestry and ECM fungus inoculation programs.