Diversity and community structure of ectomycorrhizal fungi in a wooded meadow

Wooded meadows are seminatural plant communities that support high diversity of various taxa. Due to changes in land use, wooded meadows have severely declined during the last century. The dominant trees in wooded meadows acquire mineral nutrients via ectomycorrhizal fungi. Using anatomotyping and sequencing of root tips, interpolation and extrapolation methods, we studied the diversity and community structure of ectomycorrhizal fungi in two soil horizons of both managed and forested parts of a wooded meadow in Estonia. Species of Thelephoraceae, Sebacinaceae and the genus Inocybe dominated the whole ectomycorrhizal fungal community of 172 observed species. Forested and managed parts of the wooded meadow harboured different communities of ectomycorrhizal fungi, whereas soil horizon had a negligible effect on the fungal community composition. Diverse soil conditions and host trees likely support the high richness of ectomycorrhizal fungi in the wooded meadow ecosystem. Direct sequencing integrated with interpolation and extrapolation methods are promising to identify the fungi at the species level and to compare species richness between communities of ectomycorrhizal fungi.     

Experimental evidence for a delayed response of the above-ground vegetation and the seed bank to the invasion of an annual exotic plant in deciduous forests

Invasions by alien plants significantly affect native biodiversity and ecosystem functioning. We conducted a 5-year field experiment to investigate potential effects of the annual invasive plant Impatiens glandulifera on both the native above-ground vegetation and the soil seed bank in a deciduous forest in Switzerland. Eight years after the establishment of I. glandulifera, we set up plots in patches invaded by the alien plant, in plots from which the invasive plant had been manually removed and in plots which were not yet colonized by the invasive plant. We examined plant species richness, diversity and plant species composition in the above-ground vegetation and soil seed bank in all plots one year and five years after the initiation of the experiment. The 36 plots (3 plot types × 6 replicates × 2 sites) were equally distributed over two forest sites. Neither the native above-ground vegetation nor the soil seed bank was influenced by the presence of I. glandulifera one year after the start of the field experiment. After five years, however, plant species richness of both the above-ground vegetation and the soil seed bank was reduced by 25% and 30%, respectively, in plots invaded by the alien plant compared to plots from which I. glandulifera had been removed or uninvaded plots. Furthermore, plots invaded by the alien plant had a lower total seedling density (reduction by 60%) and an altered plant species composition in the soil seed bank compared to control plots. Our field experiment indicates that negative effects of the annual invasive plant on the native above-ground vegetation and soil seed bank of deciduous forests become visible with a delay of several years.     

Ectomycorrhizal-Dominated Boreal and Tropical Forests Have Distinct Fungal Communities,but Analogous Spatial Patterns across Soil Horizons

Fungi regulate key nutrient cycling processes in many forest ecosystems, but their diversity and distribution within and across ecosystems are poorly understood. Here, we examine the spatial distribution of fungi across a boreal and tropical ecosystem, focusing on ectomycorrhizal fungi. We analyzed fungal community composition across litter (organic horizons) and underlying soil horizons (0–20 cm) using 454 pyrosequencing and clone library sequencing. In both forests, we found significant clustering of fungal communities by site and soil horizons with analogous patterns detected by both sequencing technologies. Free-living saprotrophic fungi dominated the recently-shed leaf litter and ectomycorrhizal fungi dominated the underlying soil horizons. This vertical pattern of fungal segregation has also been found in temperate and European boreal forests, suggesting that these results apply broadly to ectomycorrhizal-dominated systems, including tropical rain forests. Since ectomycorrhizal and free-living saprotrophic fungi have different influences on soil carbon and nitrogen dynamics, information on the spatial distribution of these functional groups will improve our understanding of forest nutrient cycling.     

Nitrogen isotopes in ectomycorrhizal sporocarps correspond to belowground exploration types

Nitrogen isotope values (δ¹⁵N) are higher in ectomycorrhizal fungi than in their plant hosts but the wide variability in δ¹⁵N among sporocarps of different fungal taxa is unexplained. We propose that fungal δ¹⁵N reflects sequestration of fungal nitrogen to build fungal biomass, and should accordingly reflect fungal exploration strategies and hyphal properties. To test this, we compared δ¹⁵N to exploration types, hyphal hydrophobicity, and the presence of rhizomorphs in ectomycorrhizal species from surveys at four sites in temperate and boreal coniferous forests. Fungi with exploration types of high biomass, such as long-distance (e.g., Suillus), medium-distance mat (e.g., Hydnellum), and medium-distance fringe (e.g., Cortinarius) were 4–7‰ more enriched in ¹⁵N than fungi with exploration types of low biomass [medium-distance smooth (e.g., Amanita), short-distance (e.g., Inocybe), and contact (e.g., Hygrophorus)]. High biomass types comprised 79% (Åheden, northern Sweden), 65% (Deer Park, Pacific Northwest, USA), 45% (Stadsskogen, central Sweden), and 39% (Hoh, Pacific Northwest, USA) of ectomycorrhizal species, with these types more prevalent at sites of lower nitrogen availability. Species with hydrophobic hyphae or with rhizomorphs were 3–4‰ more enriched in ¹⁵N than taxa with hydrophilic hyphae or without rhizomorphs. The consistency of these patterns suggest that δ¹⁵N measurements could provide insights into belowground functioning of poorly known taxa of ectomycorrhizal fungi and into relative fungal biomass across ectomycorrhizal communities.     

Ectomycorrhizal fungal diversity and saprotrophic fungal diversity are linked to different tree community attributes in a field‐based tree experiment

Exploring the link between above‐ and belowground biodiversity has been a major theme of recent ecological research, due in large part to the increasingly well‐recognized role that soil microorganisms play in driving plant community processes. In this study, we utilized a field‐based tree experiment in Minnesota, USA, to assess the effect of changes in plant species richness and phylogenetic diversity on the richness and composition of both ectomycorrhizal and saprotrophic fungal communities. We found that ectomycorrhizal fungal species richness was significantly positively influenced by increasing plant phylogenetic diversity, while saprotrophic fungal species richness was significantly affected by plant leaf nitrogen content, specific root length and standing biomass. The increasing ectomycorrhizal fungal richness associated with increasing plant phylogenetic diversity was driven by the combined presence of ectomycorrhizal fungal specialists in plots with both gymnosperm and angiosperm hosts. Although the species composition of both the ectomycorrhizal and saprotrophic fungal communities changed significantly in response to changes in plant species composition, the effect was much greater for ectomycorrhizal fungi. In addition, ectomycorrhizal but not saprotrophic fungal species composition was significantly influenced by both plant phylum (angiosperm, gymnosperm, both) and origin (Europe, America, both). The phylum effect was caused by differences in ectomycorrhizal fungal community composition, while the origin effect was attributable to differences in community heterogeneity. Taken together, this study emphasizes that plant‐associated effects on soil fungal communities are largely guild‐specific and provides a mechanistic basis for the positive link between plant phylogenetic diversity and ectomycorrhizal fungal richness.     

Forest Age and Plant Species Composition Determine the Soil Fungal Community Composition in a Chinese Subtropical Forest

Fungal diversity and community composition are mainly related to soil and vegetation factors. However, the relative contribution of the different drivers remains largely unexplored, especially in subtropical forest ecosystems. We studied the fungal diversity and community composition of soils sampled from 12 comparative study plots representing three forest age classes (Young: 10–40 yrs; Medium: 40–80 yrs; Old: ≥80 yrs) in Gutianshan National Nature Reserve in South-eastern China. Soil fungal communities were assessed employing ITS rDNA pyrotag sequencing. Members of Basidiomycota and Ascomycota dominated the fungal community, with 22 putative ectomycorrhizal fungal families, where Russulaceae and Thelephoraceae were the most abundant taxa. Analysis of similarity showed that the fungal community composition significantly differed among the three forest age classes. Forest age class, elevation of the study plots, and soil organic carbon (SOC) were the most important factors shaping the fungal community composition. We found a significant correlation between plant and fungal communities at different taxonomic and functional group levels, including a strong relationship between ectomycorrhizal fungal and non-ectomycorrhizal plant communities. Our results suggest that in subtropical forests, plant species community composition is the main driver of the soil fungal diversity and community composition.     

Restoration of belowground fungal communities in reclaimed landscapes of the Canadian boreal forest

The trajectory of forests establishing on reclaimed oil sands mines in the Canadian boreal forest is uncertain. Soil microbes, namely mycorrhizal fungi, partly underlie successional trajectories of plant communities, yet their role in restoration is often overlooked. Here, we tested the relative importance of common management tools used in restoration—species planted and soil placement—on the recovery of ectomycorrhizal fungal communities over 4 years. Importantly, we further compared the community assembly of fungi on reclaimed landscapes to that in reference ecosystems disturbed to different degrees. This latter test addresses whether disturbance intensity is more important than common management interventions to restore fungal communities in these ecosystems. Three main findings emerged. (1) The effect of tree species planted and soil placement on ectomycorrhizal fungal communities establishing on reclaimed landscapes was dynamic through time. (2) Disturbances that remove or disrupt the organic layer of soils substantially affect the composition of ectomycorrhizal fungal communities. (3) Shifts in the community composition of ectomycorrhizal fungi were driven to a greater extent by disturbance severity than either tree species planted or soil placement.     

Fungal soil communities in a young transgenic poplar plantation form a rich reservoir for fungal root communities

Fungal communities play a key role in ecosystem functioning. However, only little is known about their composition in plant roots and the soil of biomass plantations. The goal of this study was to analyze fungal biodiversity in their belowground habitats and to gain information on the strategies by which ectomycorrhizal (ECM) fungi form colonies. In a 2-year-old plantation, fungal communities in the soil and roots of three different poplar genotypes (Populus × canescens, wildtype and two transgenic lines with suppressed cinnamyl alcohol dehydrogenase activity) were analyzed by 454 pyrosequencing targeting the rDNA internal transcribed spacer 1 (ITS) region. The results were compared with the dynamics of the root-associated ECM community studied by morphotyping/Sanger sequencing in two subsequent years. Fungal species and family richness in the soil were surprisingly high in this simple plantation ecosystem, with 5944 operational taxonomic units (OTUs) and 186 described fungal families. These findings indicate the importance that fungal species are already available for colonization of plant roots (2399 OTUs and 115 families). The transgenic modification of poplar plants had no influence on fungal root or soil communities. Fungal families and OTUs were more evenly distributed in the soil than in roots, probably as a result of soil plowing before the establishment of the plantation. Saprophytic, pathogenic, and endophytic fungi were the dominating groups in soil, whereas ECMs were dominant in roots (87%). Arbuscular mycorrhizal diversity was higher in soil than in roots. Species richness of the root-associated ECM community, which was low compared with ECM fungi detected by 454 analyses, increased after 1 year. This increase was mainly caused by ECM fungal species already traced in the preceding year in roots. This result supports the priority concept that ECMs present on roots have a competitive advantage over soil-localized ECM fungi.     

Changes in Soil Fungal Communities, Extracellular Enzyme Activities, and Litter Decomposition Across a Fire Chronosequence in Alaskan Boreal Forests

Wildfires are a pervasive disturbance in boreal forests, and the frequency and intensity of boreal wildfires is expected to increase with climate warming. Boreal forests store a large fraction of global soil organic carbon (C), but relatively few studies have documented how wildfires affect soil microbial communities and soil C dynamics. We used a fire chronosequence in upland boreal forests of interior Alaska with sites that were 1, 7, 12, 24, 55, ~90, and ~100 years post-fire to examine the short- and long-term responses of fungal community composition, fungal abundance, extracellular enzyme activity, and litter decomposition to wildfires. We hypothesized that post-fire changes in fungal abundance and community composition would constrain decomposition following fires. We found that wildfires altered the composition of soil fungal communities. The relative abundance of ascomycetes significantly increased following fire whereas basidiomycetes decreased. Post-fire decreases in basidiomycete fungi were likely attributable to declines in ectomycorrhizal fungi. Fungal hyphal lengths in the organic horizon significantly declined in response to wildfire, and they required at least 24 years to return to pre-fire levels. Post-fire reductions in fungal hyphal length were associated with decreased activities of hydrolytic extracellular enzymes. In support of our hypothesis, the decomposition rate of aspen and black spruce litter significantly increased as forests recovered from fire. Our results indicate that post-fire reductions in soil fungal abundance and activity likely inhibit litter decomposition following boreal wildfires. Slower rates of litter decay may lead to decreased heterotrophic respiration from soil following fires and contribute to a negative feedback to climate warming.     

Late Quaternary climate change explains soil fungal community composition rather than fungal richness in forest ecosystems

The dramatic climate fluctuations of the late Quaternary have influenced the diversity and composition of macroorganism communities, but how they structure belowground microbial communities is less well known. Fungi constitute an important component of soil microorganism communities. They play an important role in biodiversity maintenance, community assembly, and ecosystem functioning, and differ from many macroorganisms in many traits. Here, we examined soil fungal communities in Chinese temperate, subtropical, and tropic forests using Illumina MiSeq sequencing of the fungal ITS1 region. The relative effect of late Quaternary climate change and contemporary environment (plant, soil, current climate, and geographic distance) on the soil fungal community was analyzed. The richness of the total fungal community, along with saprotrophic, ectomycorrhizal (EM), and pathogenic fungal communities, was influenced primarily by the contemporary environment (plant and/or soil) but not by late Quaternary climate change. Late Quaternary climate change acted in concert with the contemporary environment to shape total, saprotrophic, EM, and pathogenic fungal community compositions and with a stronger effect in temperate forest than in tropic–subtropical forest ecosystems. Some contemporary environmental factors influencing total, saprotrophic, EM, and pathogenic fungal communities in temperate and tropic–subtropical forests were different. We demonstrate that late Quaternary climate change can help to explain current soil fungal community composition and argue that climatic legacies can help to predict soil fungal responses to climate change.     

Digging mammals contribute to rhizosphere fungal community composition and seedling growth

Bioturbation is an important ecosystem process, and the loss of native digging mammals due to introduced predators and habitat loss may have detrimental consequences for ecosystem health. The mycophagous woylie (Bettongia penicillata ogilbyi) was once widespread across the Australian continent and currently exists in a greatly reduced range, while the omnivorous quenda (Isoodon fusciventer), which once occurred across the southern part of Western Australia (WA), remains common in south west WA over a reduced range. Populations of these two digging marsupials are currently maintained within sanctuaries where they can reach high densities. To assess the influence these digging marsupials have on fungal assemblages, we investigated fungal root associations among seedlings of a key mycorrhizal forest canopy species, Corymbia calophylla, R. Br. K. D. Hill and L. A. S. Johnson. Seedlings were grown in soil collected from inside (heavily-dug soil) and outside (minimally-dug soil) two predator-proof sanctuaries. Our results showed that above-ground seedling biomass was significantly greater for seedlings grown in soil collected from inside the sanctuaries. There were no differences in the diversity or species richness of rhizosphere fungal communities isolated from these seedlings; however, the community composition was significantly different. This was most obvious for the predator-proof enclosure that had been in place for 20 years (Karakamia Sanctuary) compared with the more recently-installed Perup Sanctuary (fenced in 2010; 4 years before this study). At Karakamia, there were greater numbers of putatively hypogeous ectomycorrhizal fungi inside the enclosure and four times the number of operational taxonomic units of arbuscular mycorrhizal fungi outside the enclosure. The differences in fungal communities suggest that digging mammals play a pivotal role in ecosystem functioning by influencing the rhizosphere of this key forest canopy species, which has implications for maintaining the health and persistence of forests.     

Effects of maternal genotypic identity and genetic diversity of the red mangrove Rhizophora mangle on associated soil bacterial communities: A field‐based experiment

Loss of plant biodiversity can result in reduced abundance and diversity of associated species with implications for ecosystem functioning. In ecosystems low in plant species diversity, such as Neotropical mangrove forests, it is thought that genetic diversity within the dominant plant species could play an important role in shaping associated communities. Here, we used a manipulative field experiment to study the effects of maternal genotypic identity and genetic diversity of the red mangrove Rhizophora mangle on the composition and richness of associated soil bacterial communities. Using terminal restriction fragment length polymorphism (T‐RFLP) community fingerprinting, we found that bacterial community composition differed among R. mangle maternal genotypes but not with genetic diversity. Bacterial taxa richness, total soil nitrogen, and total soil carbon were not significantly affected by maternal genotypic identity or genetic diversity of R. mangle. Our findings show that genotype selection in reforestation projects could influence soil bacterial community composition. Further research is needed to determine what impact these bacterial community differences might have on ecosystem processes, such as carbon and nitrogen cycling.     

Abrupt changes in the composition and function of fungal communities along an environmental gradient in the high Arctic

Fungi play a key role in soil–plant interactions, nutrient cycling and carbon flow and are essential for the functioning of arctic terrestrial ecosystems. Some studies have shown that the composition of fungal communities is highly sensitive to variations in environmental conditions, but little is known about how the conditions control the role of fungal communities (i.e., their ecosystem function). We used DNA metabarcoding to compare taxonomic and functional composition of fungal communities along a gradient of environmental severity in Northeast Greenland. We analysed soil samples from fell fields, heaths and snowbeds, three habitats with very contrasting abiotic conditions. We also assessed within‐habitat differences by comparing three widespread microhabitats (patches with high cover of Dryas, Salix, or bare soil). The data suggest that, along the sampled mesotopographic gradient, the greatest differences in both fungal richness and community composition are observed amongst habitats, while the effect of microhabitat is weaker, although still significant. Furthermore, we found that richness and community composition of fungi are shaped primarily by abiotic factors and to a lesser, though still significant extent, by floristic composition. Along this mesotopographic gradient, environmental severity is strongly correlated with richness in all fungal functional groups: positively in saprotrophic, pathogenic and lichenised fungi, and negatively in ectomycorrhizal and root endophytic fungi. Our results suggest complex interactions amongst functional groups, possibly due to nutrient limitation or competitive exclusion, with potential implications on soil carbon stocks. These findings are important in the light of the environmental changes predicted for the Arctic.     

Host plant species effects on arbuscular mycorrhizal fungal communities in tallgrass prairie

Symbiotic associations between plants and arbuscular mycorrhizal (AM) fungi are ubiquitous in many herbaceous plant communities and can have large effects on these communities and ecosystem processes. The extent of species-specificity between these plant and fungal symbionts in nature is poorly known, yet reciprocal effects of the composition of plant and soil microbe communities is an important assumption of recent theoretical models of plant community structure. In grassland ecosystems, host plant species may have an important role in determining development and sporulation of AM fungi and patterns of fungal species composition and diversity. In this study, the effects of five different host plant species [Poa pratensis L., Sporobolus heterolepis (A. Gray) A. Gray, Panicum virgatum L., Baptisia bracteata Muhl. ex Ell., Solidago missouriensis Nutt.] on spore communities of AM fungi in tallgrass prairie were examined. Spore abundances and species composition of fungal communities of soil samples collected from patches within tallgrass prairie were significantly influenced by the host plant species that dominated the patch. The AM fungal spore community associated with B. bracteata showed the highest species diversity and the fungi associated with Pa. virgatum showed the lowest diversity. Results from sorghum trap cultures using soil collected from under different host plant species showed differential sporulations of AM fungal species. In addition, a greenhouse study was conducted in which different host plant species were grown in similar tallgrass prairie soil. After 4 months of growth, AM fungal species composition was significantly different beneath each host species. These results strongly suggest that AM fungi show some degree of host-specificity and are not randomly distributed in tallgrass prairie. The demonstration that host plant species composition influences AM fungal species composition provides support for current feedback models predicting strong regulatory effects of soil communities on plant community structure. Differential responses of AM fungi to host plant species may also play an important role in the regulation of species composition and diversity in AM fungal communities. Received: 29 January 1999 / Accepted: 20 October 1999     

Plant identity strongly structures the root-associated fungal community in a diverse subtropical forest

Revealing the relationship between plants and root-associated fungi is very important in understanding diversity maintenance and community assembly in ecosystems. However, the community assembly of root-associated fungi of focal plant species along a subtropical plant species diversity gradient is less documented. Here, we examined root-associated fungal communities associated with five ectomycorrhizal (EM) plant species (Betula luminifera, Castanea henryi, Castanopsis fargesii, C. sclerophylla, and Quercus serrate) in a Chinese subtropical woody plant species diversity (1, 2, 4, 8, 16 and 24 species) experiment, using paired-end Illumina MiSeq sequencing of the ITS2 region. In total, we detected 1933 root-associated fungal operational taxonomic units (OTUs) at a 97% sequence similarity level. Plant identity had a significant effect on total and saprotrophic fungal OTU richness, but plant species diversity level had a significant effect on saprotrophic and pathogenic fungal OTU richness. The community composition of total, saprotrophic and EM fungi was structured by plant identity and plant species diversity level. However, the community composition of pathogenic fungi was only shaped by plant identity. This study highlights that plant identity has a stronger effect on the root-associated fungal community than plant species diversity level in a diverse subtropical forest ecosystem.     

Plant species richness and productivity determine the diversity of soil fungal guilds in temperate coniferous forest and bog habitats

Fungi have important roles as decomposers, mycorrhizal root symbionts and pathogens in forest ecosystems, but there is limited information about their diversity and composition at the landscape scale. This work aimed to disentangle the factors underlying fungal richness and composition along the landscape‐scale moisture, organic matter and productivity gradients. Using high‐throughput sequencing, we identified soil fungi from 54 low‐productivity Pinus sylvestris‐dominated plots across three study areas in Estonia and determined the main predictors of fungal richness based on edaphic, floristic and spatial variables. Fungal richness displayed unimodal relationship with organic matter and deduced soil moisture. Plant richness and productivity constituted the key predictors for taxonomic richness of functional guilds. Composition of fungi and the main ectomycorrhizal fungal lineages and hyphal exploration types was segregated by moisture availability and soil nitrogen. We conclude that plant productivity and diversity determine the richness and proportion of most functional groups of soil fungi in low‐productive pine forests on a landscape scale. Adjacent stands of pine forest may differ greatly in the dominance of functional guilds that have marked effects on soil carbon and nitrogen cycling in these forest ecosystems.     

Wildfire severity reduces richness and alters composition of soil fungal communities in boreal forests of western Canada

Wildfire is the dominant disturbance in boreal forests and fire activity is increasing in these regions. Soil fungal communities are important for plant growth and nutrient cycling postfire but there is little understanding of how fires impact fungal communities across landscapes, fire severity gradients, and stand types in boreal forests. Understanding relationships between fungal community composition, particularly mycorrhizas, and understory plant composition is therefore important in predicting how future fire regimes may affect vegetation. We used an extreme wildfire event in boreal forests of Canada's Northwest Territories to test drivers of fungal communities and assess relationships with plant communities. We sampled soils from 39 plots 1 year after fire and 8 unburned plots. High‐throughput sequencing (MiSeq, ITS) revealed 2,034 fungal operational taxonomic units. We found soil pH and fire severity (proportion soil organic layer combusted), and interactions between these drivers were important for fungal community structure (composition, richness, diversity, functional groups). Where fire severity was low, samples with low pH had higher total fungal, mycorrhizal, and saprotroph richness compared to where severity was high. Increased fire severity caused declines in richness of total fungi, mycorrhizas, and saprotrophs, and declines in diversity of total fungi and mycorrhizas. The importance of stand age (a surrogate for fire return interval) for fungal composition suggests we could detect long‐term successional patterns even after fire. Mycorrhizal and plant community composition, richness, and diversity were weakly but significantly correlated. These weak relationships and the distribution of fungi across plots suggest that the underlying driver of fungal community structure is pH, which is modified by fire severity. This study shows the importance of edaphic factors in determining fungal community structure at large scales, but suggests these patterns are mediated by interactions between fire and forest stand composition.     

Ectomycorrhizal fungal communities associated with Masson pine (Pinus massoniana Lamb.) in Pb–Zn mine sites of central south China

To advance our understanding of ectomycorrhizal fungal communities in mining areas, the diversity and composition of ectomycorrhizal fungi associated with Masson pine (Pinus massoniana Lamb.) and soil chemistry were investigated in Taolin lead–zinc (Pb–Zn) mine tailings (TLT), two fragmented forest patches in a Huayuan Pb–Zn mineland (HY1 and HY2), and a non-polluted forest in Taolin in central south China. Ectomycorrhizal fungal species were identified by morphotyping and sequence analyses of the internally transcribed spacer regions of ribosomal DNA. The two study sites in the Huayuan mineland (HY1 and HY2) were significantly different in soil Pb, Zn, and cadmium (Cd) concentrations, but no significant difference was observed in ectomycorrhizal colonization, ectomycorrhizal fungal richness, diversity, or rank–abundance. In addition, the similarity of ectomycorrhizal fungal communities between HY1 and HY2 was quite high (S?rensen similarity index?=?0.47). Thus, the concentration of heavy metals may not be determining factors in the structure of these communities. In the tailings, however, significantly lower ectomycorrhizal colonization and ectomycorrhizal fungal richness were observed. The amounts of Pb and Zn in the tailing sand were higher than the non-polluted forest but far lower than in HY1. Thus, these heavy metals did not account for the reduced colonization and ectomycorrhizal fungal richness in TLT. The ectomycorrhizal fungal community in TLT was dominated by four pioneer species (Rhizopogon buenoi, Tomentella ellisii, Inocybe curvipes, and Suillus granulatus), which collectively accounted for 93.2?% of root tip colonization. The immature soil conditions in tailing (low N and P, sand texture, and lack of organic matter) may only allow certain pioneer ectomycorrhizal fungal species to colonize the site. When soil samples from four sites were combined, we found that the occurrences of major ectomycorrhizal fungal taxa were not clearly related to the concentrations of Pb, Zn, and Cd. In conclusion, our results suggest that ectomycorrhizal fungal communities in mining areas are not necessarily affected by heavy metals themselves but could be largely determined by soil maturity.     

Fungal Growth and Biomass Development is Boosted by Plants in Snow-Covered Soil

Soil microbial communities follow distinct seasonal cycles which result in drastic changes in processes involving soil nutrient availability. The biomass of fungi has been reported to be highest during winter, but is fungal growth really occurring in frozen soil? And what is the effect of plant cover on biomass formation and on the composition of fungal communities? To answer these questions, we monitored microbial biomass N, ergosterol, and the amount of fungal hyphae during summer and winter in vegetated and unvegetated soils of an alpine primary successional habitat. The winter fungal communities were identified by rDNA ITS clone libraries. Winter soil temperatures ranged between -0.6°C and -0.1°C in snow-covered soil. We found distinct seasonal patterns for all biomass parameters, with highest biomass concentrations during winter in snow-covered soil. The presence of plant cover had a significant positive effect on the amount of biomass in the soil, but the type of plant cover (plant species) was not a significant factor. A mean hyphal ingrowth of 5.6 m g(-1) soil was detected in snow-covered soil during winter, thus clearly proving fungal growth during winter in snow-covered soil. Winter fungal communities had a typical species composition: saprobial fungi were dominating, among them many basidiomycete yeasts. Plant cover had no influence on the composition of winter fungal communities.     

Nitrogen Uptake by Trees and Mycorrhizal Fungi in a Successional Northern Temperate Forest: Insights from Multiple Isotopic Methods

Forest succession may cause changes in nitrogen (N) availability, vegetation and fungal community composition that affect N uptake by trees and their mycorrhizal symbionts. Understanding how these changes affect the functioning of the mycorrhizal symbiosis is of interest to ecosystem ecology because of the fundamental roles mycorrhizae play in providing nutrition to trees and structuring forest ecosystems. We investigated changes in tree and mycorrhizal fungal community composition, the availability and uptake of N by trees and mycorrhizal fungi in a forest undergoing a successional transition (age-related loss of early successional tree taxa). In this system, 82–96% of mycorrhizal hyphae were ectomycorrhizal (EM). As biomass production of arbuscular mycorrhizal (AM) trees increased, AM hyphae comprised a significantly greater proportion of total fungal hyphae, and the EM contribution to the N requirement of EM-associated tree taxa declined from greater than 75% to less than 60%. Increasing N availability was associated with lower EM hyphal foraging and ¹⁵N tracer uptake, yet the EM-associated later-successional species Quercus rubra was nonetheless a stronger competitor for ¹⁵N than AM-associated Acer rubrum, likely due to the more extensive nature of the persistent EM hyphal network. These results indicate that successional increases in N availability and co-dominance by AM-associated trees have increased the importance of AM fungi in the mycorrhizal community, while down-regulating EM N acquisition and transfer processes. This work advances understanding of linkages between tree and fungal community composition, and indicates that successional changes in N availability may affect competition between tree taxa with divergent resource acquisition strategies.