The mid-domain effect in ectomycorrhizal fungi: range overlap along an elevation gradient on Mount Fuji, Japan

Compositional shifts and co-occurrence patterns of topsoil bacteria and micro-eukaryotes across a permafrost thaw gradient in alpine meadows of the Qilian Mountains, China

Soil microorganisms play a pivotal role in the biogeochemical cycles of alpine meadow ecosystems, especially in the context of permafrost thaw. However, the mechanisms driving microbial community responses to environmental changes, such as variations in active layer thickness (ALT) of permafrost, remain poorly understood. This study utilized next-generation sequencing to explore the composition and co-occurrence patterns of soil microbial communities, focusing on bacteria and micro-eukaryotes along a permafrost thaw gradient. The results showed a decline in bacterial alpha diversity with increasing permafrost thaw, whereas micro-eukaryotic diversity exhibited an opposite trend. Although changes in microbial community composition were observed in permafrost and seasonally frozen soils, these shifts were not statistically significant. Bacterial communities exhibited a greater differentiation between frozen and seasonally frozen soils, a pattern not mirrored in eukaryotic communities. Linear discriminant analysis effect size analysis revealed a higher number of potential biomarkers in bacterial communities compared with micro-eukaryotes. Bacterial co-occurrence networks were more complex, with more nodes, edges, and positive linkages than those of micro-eukaryotes. Key factors such as soil texture, ALT, and bulk density significantly influenced bacterial community structures, particularly affecting the relative abundances of the Acidobacteria, Proteobacteria, and Actinobacteria phyla. In contrast, fungal communities (e.g., Nucletmycea, Rhizaria, Chloroplastida, and Discosea groups) were more affected by electrical conductivity, vegetation coverage, and ALT. This study highlights the distinct responses of soil bacteria and micro-eukaryotes to permafrost thaw, offering insights into microbial community stability under global climate change.IMPORTANCEThis study sheds light on how permafrost thaw affects microbial life in the soil, with broader implications for understanding climate change impacts. As permafrost degrades, it alters the types and numbers of microbes in the soil. These microbes play essential roles in environmental processes, such as nutrient cycling and greenhouse gas emissions. By observing shifts from bacteria-dominated to fungi-dominated communities as permafrost thaws, the study highlights potential changes in these processes. Importantly, this research suggests that the stability of microbial networks decreases with permafrost degradation, potentially disrupting the delicate balance of these ecosystems. The findings not only deepen our understanding of microbial responses to changing climates but also support the development of strategies to monitor and potentially mitigate the effects of climate change on fragile high-altitude ecosystems.

Contributions to the Inocybe umbratica-paludinella (Agaricales) Group in China: Taxonomy, Species Diversity, and Molecular Phylogeny

Inocybe is the largest genus in the family Inocybaceae, with approximately 1000 species worldwide. Basic data on the species diversity, geographic distribution, and the infrageneric framework of Inocybe are still incomplete because of the intricate nature of this genus, which includes numerous unrecognized taxa that exist around the world. A multigene phylogeny of the I. umbratica-paludinella group, initially designated as the "I. angustifolia subgroup", was conducted using the ITS-28S-rpb2 nucleotide datasets. The seven species, I. alabamensis, I. angustifolia, I. argenteolutea, I. olivaceonigra, I. paludinella, I. subangustifolia, and I. umbratica, were confirmed as members of this species group. At the genus level, the I. umbratica-paludinella group is a sister to the lineage of the unifying I. castanea and an undescribed species. Inocybe sect. Umbraticae sect. nov. was proposed to accommodate species in the I. umbratica-paludinella group and the I. castanea lineage. This section now comprises eight documented species and nine new species from China, as described in this paper. Additionally, new geographical distributions of I. angustifolia and I. castanea in China are reported. The nine new species and I. angustifolia, I. castanea, I. olivaceonigra, and I. umbratica are described in detail and illustrated herein with color plates based on Chinese materials. A global key to 17 species in the section Umbraticae is provided. The results of the current study provide a more detailed basis for the accurate identification of species in the I. umbratica-paludinella group and a better understanding of their phylogenetic placement.

Community composition of phytopathogenic fungi significantly influences ectomycorrhizal fungal communities during subtropical forest succession

Ectomycorrhizal fungi (EMF) can form symbiotic relationships with plants, aiding in plant growth by providing access to nutrients and defense against phytopathogenic fungi. In this context, factors such as plant assemblages and soil properties can impact the interaction between EMF and phytopathogenic fungi in forest soil. However, there is little understanding of how these fungal interactions evolve as forests move through succession stages. In this study, we used high-throughput sequencing to investigate fungal communities in young, intermediate, and old subtropical forests. At the genus level, EMF communities were dominated by Sebacina, Russula, and Lactarius, while Mycena was the most abundant genus in pathogenic fungal communities. The relative abundances of EMF and phytopathogenic fungi in different stages showed no significant difference with the regulation of different factors. We discovered that interactions between phytopathogenic fungi and EMF maintained a dynamic balance under the influence of the differences in soil quality attributed to each forest successional stage. The community composition of phytopathogenic fungi is one of the strong drivers in shaping EMF communities over successions. In addition, the EMF diversity was significantly related to plant diversity, and these relationships varied among successional stages. Despite the regulation of various factors, the positive relationship between the diversity of phytopathogenic fungi and EMF remained unchanged. However, there is no significant difference in the ratio of the abundance of EMF and phytopathogenic fungi over the course of successions. These results will advance our understanding of the biodiversity-ecosystem functioning during forest succession. KEY POINTS: •Community composition of both EMF and phytopathogenic fungi changed significantly over forest succession. •Phytopathogenic fungi is a key driver in shaping EMF community. •The effect of plant Shannon's diversity on EMF communities changed during the forest aging process.

Topography- and depth-dependent rhizosphere microbial community characteristics drive ecosystem multifunctionality in Juglans mandshurica forest

Rhizosphere microbial community characteristics and ecosystem multifunctionality (EMF), both affected by topographic factors, are closely correlated. However, more targeted exploration is yet required to fully understand the variations of rhizosphere microbial communities along topographic gradients in different soil layers, as well as whether and how they regulate EMF under specific site conditions. Here, we conducted relevant research on Juglans mandshurica forests at six elevation gradients and two slope positions ranging from 310 to 750 m in Tianjin Baxian Mountain. Results demonstrated that rhizosphere soil physicochemical properties and enzyme activities of both layers (0-20 cm and 20-40 cm) varied significantly with elevation, while only at top layer did slope position have significant impacts on most indicators. Bacterial richness and diversity were higher in the top layer at slope bottom and middle-high elevation, the difference in fungi was not as noticeable. Both topographic factors and soil depth significantly impacted microbial community structure, with Candidatus_Udaeobacter of bacteria, Mortierella, Sebacina, and Hygrocybe of fungi mainly contributing to the dissimilarity between communities. EMF rose with increasing elevation, bacteria were more critical drivers of this process than fungi, and topographic factors could affect EMF by altering bacterial diversity and dominant taxa abundance. For evaluating EMF, the aggregate structure of sub layer and the carbon cycle-related indicators of top layer were of higher importance. Our results revealed the depth-dependent characteristics of the rhizosphere microbial community along topographic gradients in studied stands, as well as the pivotal regulatory role of bacteria on EMF, while also highlighting depth as an important variable for analyzing soil properties and EMF. This work helps us better understand the response of individuals and communities of J. mandshurica to changing environmental conditions, further providing a scientific reference for the management and protection of secondary forests locally and in North China.

Elevational Variation in and Environmental Determinants of Fungal Diversity in Forest Ecosystems of Korean Peninsula

Exploring species diversity along elevational gradients is important for understanding the underlying mechanisms. Our study focused on analyzing the species diversity of fungal communities and their subcommunities at different trophic and taxonomic levels across three high mountains of the Korean Peninsula, each situated in a different climatic zone. Using high-throughput sequencing, we aimed to assess fungal diversity patterns and investigate the primary environmental factors influencing fungal diversity. Our results indicate that soil fungal diversity exhibits different elevational distribution patterns on different mountains, highlighting the combined effects of climate, soil properties, and geographic topology. Notably, the total and available phosphorus contents in the soil emerged as key determinants in explaining the differences in diversity attributed to soil properties. Despite the varied responses of fungal diversity to elevational gradients among different trophic guilds and taxonomic levels, their primary environmental determinants remained remarkably consistent. In particular, total and available phosphorus contents showed significant correlations with the diversity of the majority of the trophic guilds and taxonomic levels. Our study reveals the absence of a uniform diversity pattern along elevational gradients, underscoring the general sensitivity of fungi to soil conditions. By enriching our understanding of fungal diversity dynamics, this research enhances our comprehension of the formation and maintenance of elevational fungal diversity and the response of microbial communities in mountain ecosystems to climate change. This study provides valuable insights for future ecological studies of similar biotic communities.

Biogeographic and co-occurrence network differentiation of fungal communities in warm-temperate montane soils

Studying the biogeographic patterns of fungal communities across altitudinal and soil depth gradients is essential for understanding how environmental variations shape the diversity and functionality of these complex ecological assemblages. Here, we evaluated the response and assembly patterns of fungal communities to altitude and soil depth, and the co-occurrence patterns influencing soil fungal metabolic preferences on Dongling Mountain. We observed significant variations in fungal β-diversity, driven by elevation and soil depth, with climatic parameters (MAT and MAP) and nutrient concentrations (TOC, TP, and TN) serving as prominent influencers. Additionally, we found that the multiple substrate-induced respiration rate of fungi degrading various carbon substrates was diminished in high-altitude and subsurface soils compared to low-altitude and surface soils. Stochastic processes play a more important role in controlling fungal community assembly than deterministic processes, with dispersal limitation emerging as the main driver of community assembly. While greater network complexity was evident in the topsoil compared to the subsoil, both layers harbored altitude-sensitive OTUs (asOTUs) that belonging to distinct modules. Moreover, fungal groups sensitive to the same altitude exhibited similar metabolic preferences. The asOTUs designated for lower altitude areas favored unstable carbon substrates (glucose and sucrose), while those designated as higher altitude areas exhibited a preference for recalcitrant carbon (xylan and lignin). This evidence suggests that soil fungal communities respond to environmental changes by trading off their life strategies and metabolic characteristics.

Experimental evidence that root-associated fungi improve plant growth at high altitude

Unravelling how species communities change along environmental gradients requires a dual understanding: the direct responses of the species to their abiotic surroundings and the indirect variation of these responses through biotic interactions. Here, we focus on the interactive relationships between plants and their symbiotic root-associated fungi (RAF) along stressful abiotic gradients. We investigate whether variations in RAF community composition along altitudinal gradients influence plant growth at high altitudes, where both plants and fungi face harsher abiotic conditions. We established a translocation experiment between pairs of Bistorta vivipara populations across altitudinal gradients. To separate the impact of shifting fungal communities from the overall influence of changing abiotic conditions, we used a root barrier to prevent new colonization by RAF following translocation. To characterize the RAF communities, we applied DNA barcoding to the root samples. Through the utilization of joint species distribution modelling, we assessed the relationship between changes in plant functional traits resulting from experimental treatments and the corresponding changes in the RAF communities. Our findings indicate that RAF communities influence plant responses to stressful abiotic conditions. Plants translocated from low to high altitudes grew more when they were able to associate with the resident high-altitude RAF compared to those plants that were not allowed to associate with the resident RAF. We conclude that interactions with RAF impact how plants respond to stressful abiotic conditions. Our results provide experimental support that interactions with RAF improve plant stress tolerance to altitudinal stressors such as colder temperatures and less nutrient availability.

Interplay of biotic and abiotic factors shapes tree seedling growth and root-associated microbial communities

Root-associated microbes can alleviate plant abiotic stresses, thus potentially supporting adaptation to a changing climate or to novel environments during range expansion. While climate change is extending plant species fundamental niches northward, the distribution and colonization of mutualists (e.g., arbuscular mycorrhizal fungi) and pathogens may constrain plant growth and regeneration. Yet, the degree to which biotic and abiotic factors impact plant performance and associated microbial communities at the edge of their distribution remains unclear. Here, we use root microscopy, coupled with amplicon sequencing, to study bacterial, fungal, and mycorrhizal root-associated microbial communities from sugar maple seedlings distributed across two temperate-to-boreal elevational gradients in southern Québec, Canada. Our findings demonstrate that soil pH, soil Ca, and distance to sugar maple trees are key drivers of root-associated microbial communities, overshadowing the influence of elevation. Interestingly, changes in root fungal community composition mediate an indirect effect of soil pH on seedling growth, a pattern consistent at both sites. Overall, our findings highlight a complex role of biotic and abiotic factors in shaping tree-microbe interactions, which are in turn correlated with seedling growth. These findings have important ramifications for tree range expansion in response to shifting climatic niches.

Response of the C-fixing bacteria community to precipitation changes and its impact on bacterial necromass accumulation in semiarid grassland

Climate change-induced warming has the potential to intensify drought conditions in certain regions, resulting in uneven precipitation patterns. However, the impact of precipitation-induced changes on soil C-fixing bacterial community composition to changes and their subsequent effect on the accumulation of microbial necromass in the soil remains unclear. To address this knowledge gap, we conducted an in-situ simulated precipitation control experiment in semi-arid grasslands, encompassing five primary precipitation gradients: ambient precipitation as a control (contr), decreased precipitation by 80% and 40% (DP80, DP40), and increased precipitation by 40% and 80% (IP80, IP40). Our findings indicate that while an increase in precipitation promotes greater total bacterial diversity, it reduces the diversity of cbbM-harboring bacteria. The dominance of drought-tolerant Proteobacteria within the cbbM-harboring bacterial community was responsible for the observed increase in their relative abundance, ranging from 8.9% to 15.6%, under conditions of decreased precipitation. In arid environments characterized by limited soil moisture and nutrient availability, certain dominant genera such as Thiobacillus, Sulfuritalea, and Halothiobacillus, which possess cbbM genes, exhibit strong synergistic effects with other bacteria, thereby leading to a high nutrient use efficiency. Linear regression analysis shows that bacterial necromass C was significantly negatively correlated with cbbM-harboring bacterial diversity but positively correlated with cbbM-harboring bacterial community composition. Consequently, in the extreme drought environment of DP80, the contribution of bacterial necromass C to SOC was dramatically reduced by 75% relative to the control. Although bacterial necromass C was preferentially consumed as nutrients and energy for microorganisms, C-fixing microorganisms supplemented the soil C pool by assimilating atmospheric CO2. Bacterial necromass was primarily controlled by accessible C and N rather than by the total bacterial community composition and relative abundance. Our results provide compelling evidence for the critical role of the composition of the bacterial community and its necromass in the accumulation of SOC in semiarid grassland ecosystems.

Interplay between edaphic and climatic factors unravels plant and microbial diversity along an altitudinal gradient

Altitude influences biodiversity and physiochemical soil attributes in terrestrial ecosystems. It is of immense importance to know the patterns of how interactions among climatic and edaphic factors influence plant and microbial diversity in various ecosystems, particularly along the gradients. We hypothesize that altitudinal variation determines the distribution of plant and microbial species as well as their interactions. To test the hypothesis, different sites with variable altitudes were selected. Analyses of edaphic factors revealed significant (p < 0.001) effects of the altitude. Soil ammonium and nitrate were strongly affected by it contrary to potassium (K), soil organic matter and carbon. The response patterns of individual taxonomic groups differed across the altitudinal gradient. Plant species and soil fungal diversity increased with increasing altitude, while soil archaeal and bacterial diversity decreased with increasing altitude. Plant species richness showed significant positive and negative interactions with edaphic and climatic factors. Fungal species richness was also significantly influenced by the soil ammonium, nitrate, available phosphorus, available potassium, electrical conductivity, and the pH of the soil, but showed non-significant interactions with other edaphic factors. Similarly, soil variables had limited impact on soil bacterial and archaeal species richness along the altitude gradient. Proteobacteria, Ascomycota, and Thaumarchaeota dominate soil bacterial, fungal, and archaeal communities, with relative abundance of 27.4%, 70.56%, and 81.55%, respectively. Additionally, Cynodon dactylon is most abundant plant species, comprising 22.33% of the recorded plant taxa in various study sites. RDA revealed that these communities influenced by certain edaphic and climatic factors, e.g., Actinobacteria strongly respond to MAT, EC, and C/N ratio, Ascomycota and Basidiomycota show strong associations with EC and MAP, respectively. Thaumarcheota are linked to pH, and OM, while Cyperus rotundus are sensitive to AI and EC. In conclusion, the observed variations in microbial as well as plant species richness and changes in soil properties at different elevations provide valuable insights into the factors determining ecosystem stability and multifunctionality in different regions.

Species composition of root-associated mycobiome of ruderal invasive Anthemis cotula L. varies with elevation in Kashmir Himalaya

Investigating the microbial communities associated with invasive plant species can provide insights into how these species establish and thrive in new environments. Here, we explored the fungal species associated with the roots of the invasive species Anthemis cotula L. at 12 sites with varying elevations in the Kashmir Himalaya. Illumina MiSeq platform was used to identify the species composition, diversity, and guild structure of these root-associated fungi. The study found a total of 706 fungal operational taxonomic units (OTUs) belonging to 8 phyla, 20 classes, 53 orders, 109 families, and 160 genera associated with roots of A. cotula, with the most common genus being Funneliformis. Arbuscular mycorrhizal fungi (AMF) constituted the largest guild at higher elevations. The study also revealed that out of the 12 OTUs comprising the core mycobiome, 4 OTUs constituted the stable component while the remaining 8 OTUs comprised the dynamic component. While α-diversity did not vary across sites, significant variation was noted in β-diversity. The study confirmed the facilitative role of the microbiome through a greenhouse trial in which a significant effect of soil microbiome on height, shoot biomass, root biomass, number of flower heads, and internal CO2 concentration of the host plant was observed. The study indicates that diverse fungal mutualists get associated with this invasive alien species even in nutrient-rich ruderal habitats and may be contributing to its spread into higher elevations. This study highlights the importance of understanding the role of root-associated fungi in invasion dynamics and the potential use of mycobiome management strategies to control invasive species.

The subfamily Xerocomoideae (Boletaceae, Boletales) in China

Xerocomoideae is an ecologically and economically important Boletaceae subfamily (Boletales) comprising 10 genera. Although many studies have focused on Xerocomoideae in China, the diversity, taxonomy and molecular phylogeny still remained incompletely understood. In the present study, taxonomic and phylogenetic studies on Chinese species of Xerocomoideae were carried out by morphological examinations and molecular phylogenetic analyses. Eight genera in Xerocomoideae, viz. Aureoboletus, Boletellus, Heimioporus, Hemileccinum, Hourangia, Phylloporus, Pulchroboletus, and Xerocomus were confirmed to be distributed in China; 97 species of the subfamily were accepted as being distributed in China; one ambiguous taxon was tentatively named Bol. aff. putuoensis; two synonyms, viz. A. marroninus and P. dimorphus were defined. Among the Chinese accepted species, 13 were newly described, viz. A. albipes, A. conicus, A. ornatipes, Bol. erythrolepis, Bol. rubidus, Bol. sinochrysenteroides, Bol. subglobosus, Bol. zenghuoxingii, H. squamipes, P. hainanensis, Pul. erubescens, X. albotomentosus, and X. fuscatus, 36 known species were redescribed, and the other 48 species were reviewed. Keys to accepted species of Aureoboletus, Boletellus, Heimioporus, Hemileccinum, Hourangia, Phylloporus, and Xerocomus in China were also provided. Taxonomic novelties: New species: Aureoboletus albipes N.K. Zeng, Xu Zhang & Zhi Q. Liang, A. conicus N.K. Zeng, Xu Zhang & Zhi Q. Liang, A. ornatipes N.K. Zeng, Xu Zhang & Zhi Q. Liang, Boletellus erythrolepis N.K. Zeng, R. Xue, S. Jiang & Zhi Q. Liang, Bol. rubidus N.K. Zeng, R. Xue, Y.J. Hao & Zhi Q. Liang, Bol. sinochrysenteroides N.K. Zeng, R. Xue & Kuan Zhao, Bol. subglobosus N.K. Zeng, R. Xue, S. Jiang & Zhi Q. Liang, Bol. zenghuoxingii N.K. Zeng, R. Xue, S. Jiang & Zhi Q. Liang, Hemileccinum squamipes N.K. Zeng, Chang Xu & Zhi Q. Liang, Phylloporus hainanensis N.K. Zeng, L.L. Wu, & Zhi Q. Liang, Pulchroboletus erubescens N.K. Zeng, Chang Xu & Zhi Q. Liang, Xerocomus albotomentosus N.K. Zeng, H.J. Xie, Chang Xu & Zhi Q. Liang, and X. fuscatus N.K. Zeng, H.J. Xie, Chang Xu & Zhi Q. Liang. Citation: Xue R, Zhang X, Xu C, Xie HJ, Wu LL, Wang Y, Tang LP, Hao YJ, Zhao K, Jiang S, Li Y, Yang YY, Li Z, Liang ZQ, Zeng NK (2023). The subfamily Xerocomoideae (Boletaceae, Boletales) in China. Studies in Mycology 106: 95-197. doi: 10.3114/sim.2022.106.03.

Elevational patterns of microbial species richness and evenness across climatic zones and taxonomic scales

Understanding the elevational patterns of soil microbial diversity is crucial for microbial biogeography, yet the elevational patterns of diversity across different climatic zones, trophic levels, and taxonomic levels remain unclear. In this study, we investigated the elevational patterns of species richness, species evenness and the relationship between species richness and evenness (RRE) in the forest soil bacterial and fungal communities and individual phyla across three climatic zones (tropical, subtropical, and cold temperate). Our results revealed that soil bacterial richness (alpha diversity) decreased with elevation, while fungal richness exhibited a hump-shaped pattern in the tropical and cold-temperate forests. Elevational patterns of evenness in bacterial and fungal communities showed the hump-shaped pattern across climatic zones, except for bacterial evenness in the tropical forest. Both bacterial and fungal richness and evenness were positively correlated in the subtropical and cold-temperate forests, while negatively correlated for bacteria in the tropical forest. The richness and evenness of soil microorganisms across different regions were controlled by climatic and edaphic factors. Soil pH was the most important factor associated with the variations in bacterial richness and evenness, while mean annual temperature explained the major variations in fungal richness. Our results addressed that the varieties of elevational patterns of microbial diversity in climatic zones and taxonomic levels, further indicating that richness and evenness may respond differently to environmental gradients.

Ectomycorrhizal community associated with Cedrus deodara in four urban forests of Nantong in East China

Ectomycorrhizal (ECM) fungi play fundamental roles in host plant growth and terrestrial ecosystems. Cedrus deodara is cultivated in several regions in China, has high ecological, economic and medicinal value, for its afforestation and providing timber and wood oil. Here, we investigated ECM colonization status of four urban C. deodara forests in Nantong, East China. We also characterized soil spore banks by conducting bioassay experiments using soils collected from these forests. In total, we identified 19 ECM fungal species, of which 13 species were found in mature forests and 9 species were identified in bioassay experiments, with only 3 species shared. Soil pH and available P content had significant effects on species occurrence in both mature trees and bioassay seedlings on local scales. ECM communities clearly (A = 0.391, p = 0.006) separated mature forests from spore banks. Thelephoracae was the richest family we detected associated with C. deodara, while Trichophaea sp. was the most dominant in mature forests, and Wilcoxina sp. was dominant in spore banks. ECM richness affected the growth of bioassay seedlings, especially after inoculation with 2 ECM species, promoting root growth, significantly (F = 3.028, p = 0.050), but it had no effects on shoots (F = 1.778, p = 0.177). No effect of inoculation rate was found on seedlings growth. To conserve this important tree species, the ECM fungi that are associated with it should be considered.

Discrepant diversity patterns and function of bacterial and fungal communities on an earthquake-prone mountain gradient in Northwest Sichuan, China

Patterns of microbial diversity on elevational gradients have been extensively studied, but little is known about those patterns during the restoration of earthquake-fractured alpine ecosystems. In this study, soil properties, soil enzyme activities, abundance and diversity of soil bacterial and fungal communities at four positions along a 2.6-km elevational gradient in the Snow Treasure Summit National Nature Reserve, located in Pingwu County, Southwest China. Although there were no significant changes in the soil chemical environment, bacterial and fungal communities were significantly different at different elevations. The overall fungal community presented an N-shaped diversity pattern with increasing elevation, while bacterial diversity decreased significantly with elevation. Changes in microbial diversity were associated with soil phosphorus, plant litter, and variations in dominant microbial taxa. Differences in enzyme activities among elevations were regulated by microbial communities, with changes in catalase and acid phosphatase activities mainly controlled by Acidobacteria and Planctomycetaceae bacteria, respectively (catalase: p < 0.001; acid phosphatase: p < 0.01), and those in β-glucosidase, sucrase, and urease activities mainly controlled by fungi. The β-glucosidase and sucrase were both positively correlated with Herpotrichiellaceae, and urease was positively correlated with Sebacinaceae (p < 0.05). These findings contribute to the conservation and management of mountain ecosystems in the face of changing environmental conditions. Further research can delve into the specific interactions between microbial communities, soil properties, and vegetation to gain deeper insights into the intricate ecological dynamics within earthquake-prone mountain ecosystems.

Differential distribution patterns and assembly processes of soil microbial communities under contrasting vegetation types at distinctive altitudes in the Changbai Mountain

Diversity patterns and community assembly of soil microorganisms are essential for understanding soil biodiversity and ecosystem processes. Investigating the impacts of environmental factors on microbial community assembly is crucial for comprehending the functions of microbial biodiversity and ecosystem processes. However, these issues remain insufficiently investigated in related studies despite their fundamental significance. The present study aimed to assess the diversity and assembly of soil bacterial and fungal communities to altitude and soil depth variations in mountain ecosystems by using 16S and ITS rRNA gene sequence analyses. In addition, the major roles of environmental factors in determining soil microbial communities and assembly processes were further investigated. The results showed a U-shaped pattern of the soil bacterial diversity at 0-10  cm soil depth along altitudes, reaching a minimum value at 1800 m, while the fungal diversity exhibited a monotonically decreasing trend with increasing altitude. At 10-20  cm soil depth, the soil bacterial diversity showed no apparent changes along altitudinal gradients, while the fungal Chao1 and phylogenetic diversity (PD) indices exhibited hump-shaped patterns with increasing altitude, reaching a maximum value at 1200 m. Soil bacterial and fungal communities were distinctively distributed with altitude at the same depth of soil, and the spatial turnover rates in fungi was greater than in bacteria. Mantel tests suggested soil physiochemical and climate variables significantly correlated with the β diversity of microbial community at two soil depths, suggesting both soil and climate heterogeneity contributed to the variation of bacterial and fungal community. Correspondingly, a novel phylogenetic null model analysis demonstrated that the community assembly of soil bacterial and fungal communities were dominated by deterministic and stochastic processes, respectively. The assembly processes of bacterial community were significantly related to the soil DOC and C:N ratio, while the fungal community assembly processes were significantly related to the soil C:N ratio. Our results provide a new perspective to assess the responses of soil microbial communities to variations with altitude and soil depth.

The spatial patterns of diversity and their relationships with environments in rhizosphere microorganisms and host plants differ along elevational gradients

Introduction

Identifying spatial patterns of biodiversity along elevational gradients provides a unified framework for understanding these patterns and predicting ecological responses to climate change. Moreover, microorganisms and plants are closely interconnected (e.g., via the rhizosphere) and thus may share spatial patterns of diversity and show similar relationships with environments.

Methods

This study compared diversity patterns and relationships with environments in host plants and rhizosphere microorganisms (including various functional groups) along elevational gradients across three climatic zones.

Results

We found that above-and belowground diversity decreased monotonically or showed a hump-shaped or U-shaped pattern along elevation gradients. However, the diversity patterns of plants, bacteria, and fungi varied depending on the taxon and climatic zone. Temperature and humidity strongly contribute to above-and belowground diversity patterns and community composition along elevational gradients. Nonetheless, soil factors might be important regulators of diversity patterns and the community composition of plants and microorganisms along these gradients. Structural equation modeling revealed that environmental factors had a stronger direct effect on rhizosphere microbial diversity than host plant diversity.

Discussion

In sum, spatial patterns of diversity and their relationships with environments in rhizosphere microorganisms and their host plants differed at the regional scale. Different functional groups (e.g., pathogen, mycorrhiza and nitrifier) of soil microorganisms may have divergent elevational patterns and environmental responses. These data improve our understanding of elevational diversity patterns, and provide new insights into the conservation of biodiversity and ecosystem management, especially under climate change.

Temperature and Precipitation Drive Elevational Patterns of Microbial Beta Diversity in Alpine Grasslands

Understanding the mechanisms underlying biodiversity patterns is a central issue in ecology, while how temperature and precipitation jointly control the elevational patterns of microbes is understudied. Here, we studied the effects of temperature, precipitation and their interactions on the alpha and beta diversity of soil archaea and bacteria in alpine grasslands along an elevational gradient of 4300-5200 m on the Tibetan Plateau. Alpha diversity was examined on the basis of species richness and evenness, and beta diversity was quantified with the recently developed metric of local contributions to beta diversity (LCBD). Typical alpine steppe and meadow ecosystems were distributed below and above 4850 m, respectively, which was consistent with the two main constraints of mean annual temperature (MAT) and mean annual precipitation (MAP). Species richness and evenness showed decreasing elevational patterns in archaea and nonsignificant or U-shaped patterns in bacteria. The LCBD of both groups exhibited significant U-shaped elevational patterns, with the lowest values occurring at 4800 m. For the three diversity metrics, soil pH was the primary explanatory variable in archaea, explaining over 20.1% of the observed variation, whereas vegetation richness, total nitrogen and the K/Al ratio presented the strongest effects on bacteria, with relative importance values of 16.1%, 12.5% and 11.6%, respectively. For the microbial community composition of both archaea and bacteria, the moisture index showed the dominant effect, explaining 17.6% of the observed variation, followed by MAT and MAP. Taken together, temperature and precipitation exerted considerable indirect effects on microbial richness and evenness through local environmental and energy supply-related variables, such as vegetation richness, whereas temperature exerted a larger direct influence on LCBD and the community composition. Our findings highlighted the profound influence of temperature and precipitation interactions on microbial beta diversity in alpine grasslands on the Tibetan Plateau.

View from the Top: Insights into the Diversity and Community Assembly of Ectomycorrhizal and Saprotrophic Fungi along an Altitudinal Gradient in Chinese Boreal Larix gmelinii-Dominated Forests

The altitudinal patterns of soil fungi have attracted considerable attention; however, few studies have investigated the diversity and community assembly of fungal functional guilds along an altitudinal gradient. Here, we explored ectomycorrhizal (EcM) and saprotrophic (SAP) fungal diversity and community assembly along a 470 m vertical gradient (ranging from 830 to 1300 m) on Oakley Mountain, sampling bulk soils in the 0-10 cm and 10-20 cm soil layers of Larix gmelinii-dominated forests. Illumina MiSeq sequencing of the ITS genes was employed to explore the fungal community composition and diversity. The relative abundance of EcM and SAP fungi showed a divergent pattern along an altitudinal gradient, while we observed a consistent altitudinal tendency for EcM and SAP fungal diversity and community assembly. The diversity of both fungal guilds increased with increasing altitude. Altitude and soil moisture were the key factors affecting the community composition of both fungal guilds. In addition, the plant community composition significantly affected the EcM fungal community composition, whereas the dissolved organic nitrogen and ammonium nitrogen contents were the driving factors of SAP fungal community. Despite the effects of vegetation and soil factors, EcM and SAP fungal communities were mainly governed by stochastic processes (especially drift) at different altitudes and soil depths. These results shed new light on the ecology of different fungal functional guilds along an altitudinal gradient, which will provide a deeper understanding of the biogeography of soil fungi.

Response of cbbL-harboring microorganisms to precipitation changes in a naturally-restored grassland

The impact of the long-term uneven precipitation distribution model on the diversity and community composition of soil C-fixing microorganisms in arid and semiarid grasslands remains unclear. In 2015, we randomly set up five experimental plots with precipitation gradients on the natural restoration grassland of the Loess Plateau (natural precipitation, NP; ± 40% natural precipitation: decreased precipitation (DP), DP40; increased precipitation (IP), IP40; ± 80% natural precipitation: DP80; IP80). In the third and fifth years after the experimental layout (spanned two years), we explored the cbbL-genes, which are functional genes in the Calvin cycle, harboring microbial diversity and community composition under different precipitation treatments. The results showed that the increase in mean annual precipitation significantly changed the cbbL-harboring microbial alpha diversity, especially when controlling for 40% natural precipitation. The response of the dominant microbial communities to interannual increased precipitation variation shifted from Gammaproteobacteria (Bradyrhizobium) to Betaproteobacteria (Variovorax). The structural equation model showed that precipitation directly affected the cbbL-harboring microbial diversity and community composition and indirectly by affecting soil NO₃^- (mg N kg ^-1), soil organic matter, dissolved organic N content, and above- and underground biomass. In conclusion, studying how cbbL-harboring microbial diversity and community composition respond to uneven precipitation variability provides new insights into the ecological processes of C-fixing microbes in semi-arid naturally-restored grasslands dominated by the Calvin cycle.

Altitudinal Variation Influences Soil Fungal Community Composition and Diversity in Alpine-Gorge Region on the Eastern Qinghai-Tibetan Plateau

Soil fungi play an integral and essential role in maintaining soil ecosystem functions. The understanding of altitude variations and their drivers of soil fungal community composition and diversity remains relatively unclear. Mountains provide an open, natural platform for studying how the soil fungal community responds to climatic variability at a short altitude distance. Using the Illumina MiSeq high-throughput sequencing technique, we examined soil fungal community composition and diversity among seven vegetation types (dry valley shrub, valley-mountain ecotone broadleaved mixed forest, subalpine broadleaved mixed forest, subalpine coniferous-broadleaved mixed forest, subalpine coniferous forest, alpine shrub meadow, alpine meadow) along a 2582 m altitude gradient in the alpine-gorge region on the eastern Qinghai-Tibetan Plateau. Ascomycota (47.72%), Basidiomycota (36.58%), and Mortierellomycota (12.14%) were the top three soil fungal dominant phyla in all samples. Soil fungal community composition differed significantly among the seven vegetation types along altitude gradients. The α-diversity of soil total fungi and symbiotic fungi had a distinct hollow pattern, while saprophytic fungi and pathogenic fungi showed no obvious pattern along altitude gradients. The β-diversity of soil total fungi, symbiotic fungi, saprophytic fungi, and pathogenic fungi was derived mainly from species turnover processes and exhibited a significant altitude distance-decay pattern. Soil properties explained 31.27-34.91% of variation in soil fungal (total and trophic modes) community composition along altitude gradients, and the effects of soil nutrients on fungal community composition varied by trophic modes. Soil pH was the main factor affecting α-diversity of soil fungi along altitude gradients. The β-diversity and turnover components of soil total fungi and saprophytic fungi were affected by soil properties and geographic distance, while those of symbiotic fungi and pathogenic fungi were affected only by soil properties. This study deepens our knowledge regarding altitude variations and their drivers of soil fungal community composition and diversity, and confirms that the effects of soil properties on soil fungal community composition and diversity vary by trophic modes along altitude gradients in the alpine-gorge region.

A Contribution to Knowledge of Craterellus (Hydnaceae, Cantharellales) in China: Three New Taxa and Amended Descriptions of Two Previous Species

Species of Craterellus (Hydnaceae, Cantharellales) in China are investigated on the basis of morphological and molecular phylogenetic analyses of DNA sequences from nuc 28S rDNA D1-D2 domains (28S) and nuc rDNA internal transcribed spacer ITS1-5.8S-ITS2 region. Five species are recognized in China, of which three of them are described as new, viz. C. fulviceps, C. minor, and C. parvopullus, while two of them are previously described taxa, viz. C. aureus, and C. lutescens. A key to the known Chinese taxa of the genus is also provided.

Diversity and distribution of CO2-fixing microbial community along elevation gradients in meadow soils on the Tibetan Plateau

Soil CO₂-fixing microbes play a significant role in CO₂-fixation in the terrestrial ecosystems, particularly in the Tibetan Plateau. To understand carbon sequestration by soil CO₂-fixing microbes and the carbon cycling in alpine meadow soils, microbial diversity and their driving environmental factors were explored along an elevation gradient from 3900 to 5100 m, on both east and west slopes of Mila Mountain region on the Tibetan Plateau. The CO₂-fixing microbial communities were characterized by high-throughput sequencing targeting the cbbL gene, encoding the large subunit for the CO₂-fixing protein ribulose 1, 5-bisphosphate carboxylase/oxygenase. The overall OTU (Operational Taxonomic Unit) abundance is concentrated at an altitude between 4300  and  4900 m. The diversity of CO₂-fixing microbes is the highest in the middle altitude area, and on the east slope is higher than those on the west slope. In terms of microbial community composition, Proteobacteria is dominant, and the most abundant genera are Cupriavidus, Rhodobacter, Sulfurifustis and Thiobacillus. Altitude has the greatest influence on the structural characteristics of CO₂-fixing microbes, and other environmental factors are significantly correlated with altitude. Therefore, altitude influences the structural characteristics of CO₂-fixing microbes by driving environmental factors. Our results are helpful to understand the variation in soil microbial community and its role in soil carbon cycling along elevation gradients.

Embracing mountain microbiome and ecosystem functions under global change

Mountains are pivotal to maintaining habitat heterogeneity, global biodiversity, ecosystem functions and services to humans. They have provided classic model natural systems for plant and animal diversity gradient studies for over 250 years. In the recent decade, the exploration of microorganisms on mountainsides has also achieved substantial progress. Here, we review the literature on microbial diversity across taxonomic groups and ecosystem types on global mountains. Microbial community shows climatic zonation with orderly successions along elevational gradients, which are largely consistent with traditional climatic hypotheses. However, elevational patterns are complicated for species richness without general rules in terrestrial and aquatic environments and are driven mainly by deterministic processes caused by abiotic and biotic factors. We see a major shift from documenting patterns of biodiversity towards identifying the mechanisms that shape microbial biogeographical patterns and how these patterns vary under global change by the inclusion of novel ecological theories, frameworks and approaches. We thus propose key questions and cutting-edge perspectives to advance future research in mountain microbial biogeography by focusing on biodiversity hypotheses, incorporating meta-ecosystem framework and novel key drivers, adapting recently developed approaches in trait-based ecology and manipulative field experiments, disentangling biodiversity-ecosystem functioning relationships and finally modelling and predicting their global change responses.

Contrasting elevational patterns and underlying drivers of stream bacteria and fungi at the regional scale on the Tibetan Plateau

Elevational gradients are the focus of development and evaluation of general theories on biodiversity. However, elevational studies of microorganisms and the underlying mechanisms remain understudied, especially at regional scales. Here, we examined stream bacterial and fungal communities along an elevational gradient of 990-4,600 m with a geographic distance up to 500 km in the southeastern Tibetan Plateau and further analyzed their elevational patterns and drivers of three biodiversity indicators, including species richness, ecological uniqueness and community composition. Bacteria and fungi showed distinct elevational trends in species richness and consistently decreasing patterns in their ecological uniqueness. The distance-decay relationships were concordant for the two microbial groups, while fungi showed higher dissimilarity and a lower turnover rate. Interestingly, bacterial and fungal compositions substantially differed between the elevations below and above 3,000 m. Climate predictors, such as the mean annual temperature and precipitation seasonality, had greater effects than local environment drivers. Notably, fungal diversity was mainly influenced by climate, while bacterial diversity was explained by the shared contributions of climate and local factors. Collectively, these findings revealed the elevational patterns of stream microbial biodiversity across mountains on a large spatial scale and highlight their underlying response mechanisms to environmental predictors.

Revisiting Hebeloma (Hymenogastraceae, Agaricales) in Japan: four species recombined into other genera but three new species discovered

Here, we present the results of studies of Japanese Hebeloma collections. The four species described by Imai as Hebeloma (H. fimicola, H. helvolescens, H. humosum, and H. tomoeae) are not from the genus Hebeloma, but are members of Agrocybe, Homophron, or Pholiota. Recombinations are made. Hebelomacrustuliniforme f. microspermum, described by Hongo, is a synonym of H. nanum. Three species of Hebeloma are described as new to science, all currently known only from Japan. Two of these species, H. asperosporum and H. cinnamomeum, are members of H. sect. Denudata while the third species H. citrisporum belongs to H. sect. Velutipes. Japanese records of H. cavipes, H. eburneum, H. hygrophilum, H. subtortum, and H. velutipes are validated. In total, fifteen species of Hebeloma are confirmed from Japan; this is compared with previous checklists.

Elevation Matters More than Season in Shaping the Heterogeneity of Soil and Root Associated Ectomycorrhizal Fungal Community

Ectomycorrhizal (EcM) fungi play important roles in forest ecosystems, and their richness and composition can change along with elevation and season changes. However, no study has estimated the relative importance of altitudinal and seasonal heterogeneity in predicting the distribution of EcM fungal communities by simultaneously considering different sample types (root versus soil). In this study, we collected root and soil samples along a > 1,500-m elevation gradient during wet and dry seasons from Baima Snow Mountain, located in "the Mountains of Southwest China," one of the 34 biodiversity hot spots, and we analyzed them using next-generation sequencing. Regardless of the sample type, similar EcM fungal richness pattern with increasing elevation (decline in the forest zone, and an increase at the alpine meadow zone) and strong community turnovers among different elevational zones and between two seasons were detected, and changes of EcM fungal community similarity on 400-m altitude gradient were equivalent to the community turnover between dry and wet seasons. Elevation and edaphic factors were shown to have the largest effects on EcM fungal community. The heterogeneity of richness and community composition was stronger among different elevational zones than across different seasons, mainly because the elevation variations in the EcM fungal community were shaped by the combined effects of different environmental factors, while seasonal changes were mainly controlled by temperature and fast-changing soil nutrients. IMPORTANCE Altitude and season represent two important environmental gradients that shape the structure of biome, including the heterogeneity of EcM fungi. Previous studies have separately considered the influences of altitude and season on EcM fungal communities, but the relative importance of altitude and season is still unknown. The present study revealed that elevation influences the heterogeneity of EcM fungal community more than season; this may be because the variability of environmental factors is higher across different elevations than that across seasons.

Community dynamics of soil-borne fungal communities along elevation gradients in neotropical and paleotropical forests

Because of their steep gradients in abiotic and biotic factors, mountains offer an ideal setting to illuminate the mechanisms that underlie patterns of species distributions and community assembly. We compared the composition of taxonomically and functionally diverse fungal communities in soils along five elevational gradients in mountains of the Neo- and Paleotropics (northern Argentina, southern Brazil, Panama, Malaysian Borneo, and Papua New Guinea). Both richness and composition of soil fungal communities reflect environmental factors, particularly temperature and soil pH, with some shared patterns among neotropical and paleotropical regions. Community dynamics are characterized by replacement of species along elevation gradients, implying a relatively narrow elevation range for most fungi, which appears to be driven by contrasting environmental preferences among both functional and taxonomic groups. For functional groups dependent on symbioses with plants (especially ectomycorrhizal fungi), the distribution of host plants drives richness and community composition, resulting in important differences in elevational patterns between neotropical and paleotropical montane communities. The pronounced compositional and functional turnover along elevation gradients implies that tropical montane forest fungi will be sensitive to climate change, resulting in shifts in composition and functionality over time.

Distribution and Assembly Processes of Soil Fungal Communities along an Altitudinal Gradient in Tibetan Plateau

In soil ecosystems, fungi exhibit diverse biodiversity and play an essential role in soil biogeochemical cycling. Fungal diversity and assembly processes across soil strata along altitudinal gradients are still unclear. In this study, we investigated the structure and abundance of soil fungal communities among soil strata and elevational gradients on the Tibetan Plateau using Illumina MiSeq sequencing of internal transcribed spacer1 (ITS1). The contribution of neutral and niche ecological processes were quantified using a neutral community model and a null model-based methodology. Our results showed that fungal gene abundance increased along altitudinal gradients, while decreasing across soil strata. Along with altitudinal gradients, fungal α-diversity (richness) decreased from surface to deeper soil layers, while β-diversity showed weak correlations with elevations. The neutral community model showed an excellent fit for neutral processes and the lowest migration rate (R² = 0.75). The null model showed that stochastic processes dominate in all samples (95.55%), dispersal limitations were dominated at the surface layer and decreased significantly with soil strata, while undominated processes (ecological drift) show a contrary trend. The log-normal model and the null model (βNTI) correlation analysis also neglect the role of niche-based processes. We conclude that stochastic dispersal limitations, together with ecological drifts, drive fungal communities.

Seasonal dynamics of soil microbial diversity and functions along elevations across the treeline

Although microbial diversity patterns along elevations have been extensively studied, little is known about whether the patterns are influenced by seasonality. To test the seasonal and elevational effects on microbial communities and functions, we collected soil samples across a mountain gradient above and below the treeline in three seasons (spring, summer and autumn). Microbial diversity based on the sequencing of 16S rRNA, 18S rRNA and nifH genes was measured, and microbial functions represented by soil basal respiration and microbial biomass were analyzed. As expected, we found significant seasonal and elevational effects on microbial α- and β-diversity and functions, and the effects of elevations were greater than seasonal effects. Elevational patterns of microbial β-diversity and functions were not influenced by seasonality. However, the elevational α-diversity patterns showed by specific groups (bacteria, protist and metazoa) changed among seasons. Further, we identified key soil properties (i.e. moisture, total carbon, total nitrogen and nitrate) which had higher seasonal and elevational variations, mainly contributing to the spatiotemporal variations of microbial diversity and functions. The findings of higher soil nutrients, archaeal and metazoan richness, and microbial functions at the treeline elevation, imply a strong edge effect of treeline on microbial diversity and functions. Together, our study highlights that seasonality influences the elevational patterns of soil microbial α-diversity, rather than that of β-diversity and functions, thus provides new insights into the seasonal and elevational effects on microbial communities and functions.

Different patterns of belowground fungal diversity along altitudinal gradients with respect to microhabitat and guild types

Fungi are key components of belowground ecosystems with various ecological roles in forests. Although the changes in the richness and composition of belowground fungi across altitudinal gradients have been widely reported, only a few studies have focused on the microhabitat types along altitudinal gradients. Here, we analysed the effect of altitude on the ectomycorrhizal and non-ectomycorrhizal fungal communities in belowground microhabitats. We collected root and soil samples from 16 Pinus densiflora forests at various altitudes across Korea, and measured the soil properties as potential factors. Fungal communities were analysed by high-throughput sequencing of the internal transcribed spacer 2 (ITS2) region. We found that altitude negatively affected the species richness of root-inhabiting fungi but did not influence that of soil-inhabiting fungi. In addition, the composition of ectomycorrhizal (ECM) fungi was less influenced by altitude than non-ECM fungi. Most of the soil properties did not show a significant relationship with altitude, but the effect of soil properties was different across microhabitat types and ecological roles of fungi. Our results reveal that microhabitat types and altitudinal gradients differently affect the richness and composition of fungal communities associated with P. densiflora, providing a better understanding of plant-associated fungal communities.

Saprotrophic fungal diversity predicts ectomycorrhizal fungal diversity along the timberline in the framework of island biogeography theory

Island biogeography theory (IBT) is one of the most fruitful paradigms in macroecology, positing positive species-area and negative species-isolation relationships for the distribution of organisms. Biotic interactions are also crucial for diversity maintenance on islands. In the context of a timberline tree species (Betula ermanii) as "virtual island", we surveyed ectomycorrhizal (EcM) fungal diversity along a 430-m vertical gradient on the top of Changbai Mountain, China, sampling fine roots and neighboring soils of B. ermanii. Besides elevation, soil properties and plant functional traits, endophytic and saprotrophic fungal diversity were assessed as candidate predictors to construct integrative models. EcM fungal diversity decreased with increasing elevation, and exhibited positive diversity to diameter at breast height and negative diversity to distance from forest edge relationships in both roots and soils. Integrative models further showed that saprotrophic fungal diversity was the strongest predictor of EcM fungal diversity, directly enhancing EcM fungal diversity in roots and soils. Our study supports IBT as a basic framework to explain EcM fungal diversity. The diversity-begets-diversity hypothesis within the fungal kingdom is more predictive for EcM fungal diversity within the IBT framework, which reveals a tight association between saprotrophic and EcM fungal lineages in the timberline ecosystem.

Habitat specialisation controls ectomycorrhizal fungi above the treeline in the European Alps

Alpine habitats are one of the most vulnerable ecosystems to environmental change, however, little information is known about the drivers of plant-fungal interactions in these ecosystems and their resilience to climate change. We investigated the influence of the main drivers of ectomycorrhizal (EM) fungal communities along elevation and environmental gradients in the alpine zone of the European Alps and measured their degree of specialisation using network analysis. We sampled ectomycorrhizas of Dryas octopetala, Bistorta vivipara and Salix herbacea, and soil fungal communities at 28 locations across five countries, from the treeline to the nival zone. We found that: (1) EM fungal community composition, but not richness, changes along elevation, (2) there is no strong evidence of host specialisation, however, EM fungal networks in the alpine zone and within these, EM fungi associated with snowbed communities, are more specialised than in other alpine habitats, (3) plant host population structure does not influence EM fungal communities, and (4) most variability in EM fungal communities is explained by fine-scale changes in edaphic properties, like soil pH and total nitrogen. The higher specialisation and narrower ecological niches of these plant-fungal interactions in snowbed habitats make these habitats particularly vulnerable to environmental change in alpine ecosystems.

Taxonomic revision of Russula subsection Amoeninae from South Korea

RussulasubsectionAmoeninae is morphologically defined by a dry velvety pileus surface, a complete absence of cystidia with heteromorphous contents in all tissues, and spores without amyloid suprahilar spot. Thirty-four species within subsection Amoeninae have been published worldwide. Although most Russula species in South Korea have been assigned European or North American names, recent molecular studies have shown that Russula species from different continents are not conspecific. Therefore, the present study aims to: 1) define which species of RussulasubsectionAmoeninae occur on each continent using molecular phylogenetic analyses; 2) revise the taxonomy of Korean Amoeninae. The phylogenetic analyses using the internal transcribed spacer (ITS) and multilocus sequences showed that subsection Amoeninae is monophyletic within subgenus HeterophyllidiaesectionHeterophyllae. A total of 21 RussulasubsectionAmoeninae species were confirmed from Asia, Australia, Europe, North America, and Central America, and species from different continents formed separate clades. Three species were recognized from South Korea and were clearly separated from the European and North American species. These species are R.bella, also reported from Japan, a new species described herein, Russulaorientipurpurea, and a new species undescribed due to insufficient material.

Higher host plant specialization of root-associated endophytes than mycorrhizal fungi along an arctic elevational gradient

How community-level specialization differs among groups of organisms, and changes along environmental gradients, is fundamental to understanding the mechanisms influencing ecological communities. In this paper, we investigate the specialization of root-associated fungi for plant species, asking whether the level of specialization varies with elevation. For this, we applied DNA barcoding based on the ITS region to root samples of five plant species equivalently sampled along an elevational gradient at a high arctic site. To assess whether the level of specialization changed with elevation and whether the observed patterns varied between mycorrhizal and endophytic fungi, we applied a joint species distribution modeling approach. Our results show that host plant specialization is not environmentally constrained in arctic root-associated fungal communities, since there was no evidence for changing specialization with elevation, even if the composition of root-associated fungal communities changed substantially. However, the level of specialization for particular plant species differed among fungal groups, root-associated endophytic fungal communities being highly specialized on particular host species, and mycorrhizal fungi showing almost no signs of specialization. Our results suggest that plant identity affects associated mycorrhizal and endophytic fungi differently, highlighting the need of considering both endophytic and mycorrhizal fungi when studying specialization in root-associated fungal communities.

Contrasting patterns and drivers of soil bacterial and fungal diversity across a mountain gradient

Microbial elevational diversity patterns have been extensively studied, but their shaping mechanisms remain to be explored. Here, we examined soil bacterial and fungal diversity and community compositions across a 3.4 km elevational gradient (consists of five elevations) on Mt. Kilimanjaro located in East Africa. Bacteria and fungi had different diversity patterns across this extensive mountain gradient-bacterial diversity had a U shaped pattern while fungal diversity monotonically decreased. Random forest analysis revealed that pH (12.61% importance) was the most important factor affecting bacterial diversity, whereas mean annual temperature (9.84% importance) had the largest impact on fungal diversity, which was consistent with results obtained from mixed-effects model. Meanwhile, the diversity patterns and drivers of those diversity patterns differ among taxonomic groups (phyla/classes) within bacterial or fungal communities. Taken together, our study demonstrated that bacterial and fungal diversity and community composition responded differently to climate and edaphic properties along an extensive mountain gradient, and suggests that the elevational diversity patterns across microbial groups are determined by distinct environmental variables. These findings enhanced our understanding of the formation and maintenance of microbial diversity along elevation, as well as microbial responses to climate change in montane ecosystems.

Host plant phylogeny and geographic distance strongly structure Betulaceae-associated ectomycorrhizal fungal communities in Chinese secondary forest ecosystems

Environmental filtering and dispersal limitation are two of the primary drivers of community assembly in ecosystems, but their effects on ectomycorrhizal (EM) fungal communities associated with wide ranges of Betulaceae taxa at a large scale are poorly documented. In this study, we examined EM fungal communities associated with 23 species from four genera (Alnus, Betula, Carpinus and Corylus) of Betulaceae in Chinese secondary forest ecosystems, using Illumina MiSeq sequencing of the ITS2 region. Effects of host plant phylogeny, soil, climate and geographic distance on EM fungal community were explored. In total, we distinguished 1738 EM fungal operational taxonomic units (OTUs) at a 97% sequence similarity level. The EM fungal communities of Alnus had significantly lower OTU richness than those associated with the other three plant genera. The EM fungal OTU richness was significantly affected by geographic distance, host plant phylogeny, soil and climate. The EM fungal community composition was significantly influenced by host plant phylogeny (12.1% of variation explained in EM fungal community), geographic distance (7.7%), soil (4.6%) and climate (1.1%). This finding highlights that environmental filtering linked to host plant phylogeny and dispersal limitation strongly influence EM fungal communities associated with Betulaceae plants in Chinese secondary forest ecosystems.

Soil Microbial Biogeography in a Changing World: Recent Advances and Future Perspectives

Soil microbial communities are fundamental to maintaining key soil processes associated with litter decomposition, nutrient cycling, and plant productivity and are thus integral to human well-being. Recent technological advances have exponentially increased our knowledge concerning the global ecological distributions of microbial communities across space and time and have provided evidence for their contribution to ecosystem functions. However, major knowledge gaps in soil biogeography remain to be addressed over the coming years as technology and research questions continue to evolve. In this minireview, we state recent advances and future directions in the study of soil microbial biogeography and discuss the need for a clearer concept of microbial species, projections of soil microbial distributions toward future global change scenarios, and the importance of embracing culture and isolation approaches to determine microbial functional profiles. This knowledge will be critical to better predict ecosystem functions in a changing world.

Expansion of the genus Imleria in North America to include Imleria floridana, sp. nov., and Imleria pallida, comb. nov

Imleria is a small genus of Boletaceae found primarily in the Northern Hemisphere characterized by the light to dark brown hymenophore that stains blue. In Florida, specimens of Imleria were collected that resembled I. badia, a species known primarily from northeastern North America and Europe. Five nuclear loci of these Florida specimens were sequenced and phylogenetically analyzed. A nuc rDNA internal transcribed spacer ITS1-5.8S-ITS2 (ITS) phylogeny of Imleria was generated using primarily uncultured environmental sequences to confirm ectomycorrhizal associations. Based on morphological and molecular data, we describe a new species, Imleria floridana. Results from these analyses also support the new combination Imleria pallida. A lectotype of I. pallida is also established from Charles H. Peck's original material. We discuss the distinguishing characters and species of Imleria found in North America and provide a key to the known worldwide species of Imleria.

Ectomycorrhizal fungal communities in ice-age relict forests of Pinus pumila on nine mountains correspond to summer temperature

Ectomycorrhizal (ECM) fungi are critical symbionts of major forest trees, and their communities are affected by various environmental factors including temperature. However, previous knowledge concerning temperature effects does not exclude the effects of host species and coexisting plants, which usually change with temperature, and should be rigorously tested under the same vegetation type. Herein we examined ECM fungal communities in ice-age relict forests dominated by a single host species (Pinus pumila) distributed on nine mountains across >1000 km in Japan. Direct sequencing of rDNA ITS regions identified 154 ECM fungal species from 4134 ECM root-tip samples. Gradient analyses revealed a large contribution of temperature, especially summer temperature, to ECM fungal communities. Additionally, we explored global sequence records of each fungal species to infer its potential temperature niche, and used it to estimate the temperature of the observed communities. The estimated temperature was significantly correlated with the actual temperature of the research sites, especially in summer seasons, indicating inherent temperature niches of the fungal components could determine their distribution among the sites. These results indicate that temperature is still a significant determinant in structuring ECM fungal communities after excluding the effects of host species and coexisting plants. The results also imply that the rising temperature under global warming may have been affecting soil microbes unnoticeably, while such microbial community change may have been contributing to the resilience of the same vegetation.

Notes, outline and divergence times of Basidiomycota

The Basidiomycota constitutes a major phylum of the kingdom Fungi and is second in species numbers to the Ascomycota. The present work provides an overview of all validly published, currently used basidiomycete genera to date in a single document. An outline of all genera of Basidiomycota is provided, which includes 1928 currently used genera names, with 1263 synonyms, which are distributed in 241 families, 68 orders, 18 classes and four subphyla. We provide brief notes for each accepted genus including information on classification, number of accepted species, type species, life mode, habitat, distribution, and sequence information. Furthermore, three phylogenetic analyses with combined LSU, SSU, 5.8s, rpb1, rpb2, and ef1 datasets for the subphyla Agaricomycotina, Pucciniomycotina and Ustilaginomycotina are conducted, respectively. Divergence time estimates are provided to the family level with 632 species from 62 orders, 168 families and 605 genera. Our study indicates that the divergence times of the subphyla in Basidiomycota are 406–430 Mya, classes are 211–383 Mya, and orders are 99–323 Mya, which are largely consistent with previous studies. In this study, all phylogenetically supported families were dated, with the families of Agaricomycotina diverging from 27–178 Mya, Pucciniomycotina from 85–222 Mya, and Ustilaginomycotina from 79–177 Mya. Divergence times as additional criterion in ranking provide additional evidence to resolve taxonomic problems in the Basidiomycota taxonomic system, and also provide a better understanding of their phylogeny and evolution.

Plant-microbe specificity varies as a function of elevation

Specialized associations between interacting species fundamentally determine the diversity and distribution of both partners. How the specialization of guilds of organisms varies along environmental gradients underpins popular theories of biogeography and macroecology, whereas the degree of specialization of a species is typically considered fixed. However, the extent to which environmental context impacts specialization dynamics is seldom examined empirically. In this study, we examine how specialization within a bipartite network consisting of three co-occurring plant species and their foliar fungal endophyte symbionts changes along a 1000-meter elevation gradient where host species were held constant. The gradient, along the slope of Mauna Loa shield volcano, represents almost the entire elevational range of two of the three plants. Network and plant specialization values displayed a parabolic relationship with elevation, and were highest at middle elevations, whereas bipartite associations were least specific at low and high elevations. Shannon's diversity of fungal endophytes correlated negatively with specificity, and was highest at the ends of the transects. Although plant host was a strong determinant of fungal community composition within sites, fungal species turnover was high among sites. There was no evidence of spatial or elevational patterning in fungal community compositon. Our work demonstrates that specificity can be a plastic trait, which is influenced by the environment and centrality of the host within its natural range.

Ectomycorrhizal fungi and soil enzymes exhibit contrasting patterns along elevation gradients in southern Patagonia

The biological and functional diversity of ectomycorrhizal (ECM) associations remain largely unknown in South America. In Patagonia, the ECM tree Nothofagus pumilio forms monospecific forests along mountain slopes without confounding effects of vegetation on plant-fungi interactions. To determine how fungal diversity and function are linked to elevation, we characterized fungal communities, edaphic variables, and eight extracellular enzyme activities along six elevation transects in Tierra del Fuego (Argentina and Chile). We also tested whether pairing ITS1 rDNA Illumina sequences generated taxonomic biases related to sequence length. Fungal community shifts across elevations were mediated primarily by soil pH with the most species-rich fungal families occurring mostly within a narrow pH range. By contrast, enzyme activities were minimally influenced by elevation but correlated with soil factors, especially total soil carbon. The activity of leucine aminopeptidase was positively correlated with ECM fungal richness and abundance, and acid phosphatase was correlated with nonECM fungal abundance. Several fungal lineages were undetected when using exclusively paired or unpaired forward ITS1 sequences, and these taxonomic biases need reconsideration for future studies. Our results suggest that soil fungi in N. pumilio forests are functionally similar across elevations and that these diverse communities help to maintain nutrient mobilization across the elevation gradient.

Fungal Elevational Rapoport pattern from a High Mountain in Japan

Little is known of how fungal distribution ranges vary with elevation. We studied fungal diversity and community composition from 740 to 2940 m above sea level on Mt. Norikura, Japan, sequencing the ITS2 region. There was a clear trend, repeated across each of the fungal phyla (Basidiomycota, Ascomycota, Zygomycota, Chytridomycota and Glomeromycota), and across the whole fungal community combined, towards an increased elevational range of higher elevation OTUs, conforming to the elevational Rapoport pattern. It appears that fungi from higher elevation environments are more generalized ecologically, at least in terms of climate-related gradients. These findings add to the picture from latitudinal studies of fungal ranges, which also suggest that the classic Rapoport Rule (broader ranges at higher latitudes) applies on a geographical scale. However, there was no mid-elevation maximum in diversity in any of the phyla studied, and different diversity trends for the different phyla, when different diversity indices were used. In terms of functional guilds, on Norikura there were trends towards increased saprotrophism (Zygomycota), symbiotrophism (Basidiomycota), symbiotrophism and saprotrophism (Ascomycota) and pathotrophism (Chytridiomycota) with elevation. The causes of each of these trends require further investigation from an ecological and evolutionary viewpoint.

Belowground fungal community diversity and composition associated with Norway spruce along an altitudinal gradient

Altitudinal gradients provide valuable information about the effects of environmental variables on changes in species richness and composition as well as the distribution of below ground fungal communities. Since most knowledge in this respect has been gathered on aboveground communities, we focused our study towards the characterization of belowground fungal communities associated with two different ages of Norway spruce (Picea abies) trees along an altitudinal gradient. By sequencing the internal transcribed spacer (ITS) region on the Illumina platform, we investigated the fungal communities in a floristically and geologically relatively well explored forest on the slope of Mt. Iseler of the Bavarian Alps. From fine roots and rhizosphere of a total of 90 of Norway spruce trees from 18 plots we detected 1285 taxa, with a range of 167 to 506 (average 377) taxa per plot. Fungal taxa are distributed over 96 different orders belonging to the phyla Ascomycota, Basidiomycota, Chrytridiomycota, Glomeromycota, and Mucoromycota. Overall the Agaricales (438 taxa) and Tremellales (81 taxa) belonging to the Basidiomycota and the Hypocreales (65 spp.) and Helotiales (61 taxa) belonging to the Ascomycota represented the taxon richest orders. The evaluation of our multivariate generalized mixed models indicate that the altitude has a significant influence on the composition of the fungal communities (p < 0.003) and that tree age determines community diversity (p < 0.05). A total of 47 ecological guilds were detected, of which the ectomycorrhizal and saprophytic guilds were the most taxon-rich. Our ITS amplicon Illumina sequencing approach allowed us to characterize a high fungal community diversity that would not be possible to capture with fruiting body surveys alone. We conclude that it is an invaluable tool for diverse monitoring tasks and inventorying biodiversity, especially in the detection of microorganisms developing very ephemeral and/or inconspicuous fruiting bodies or lacking them all together. Results suggest that the altitude mainly influences the community composition, whereas fungal diversity becomes higher in mature/older trees. Finally, we demonstrate that novel techniques from bacterial microbiome analyses are also useful for studying fungal diversity and community structure in a DNA metabarcoding approach, but that incomplete reference sequence databases so far limit effective identification.

Temperature niche position and breadth of ectomycorrhizal fungi: Reduced diversity under warming predicted by a nested community structure

Species with narrow niche breadths are assumed to be more susceptible to environmental changes than those with wide niche breadths. Although information on niche properties is necessary for predicting biological responses to environmental changes, such information is largely missing for soil microbes. In this study, we present the temperature niche positions and breadths of a functionally important group of eukaryotic soil microbes, ectomycorrhizal (EM) fungi. We compiled high-quality EM fungal sequence data from 26 forested sites in Japan (with mean annual temperatures ranging from 1.6 to 23.6°C) to create temperature niche profiles for each individual fungal species. Nested theory and a newly developed weighted-randomization null model were applied to 75 fungal operational taxonomic units (OTUs) with high occurrence records to examine potential preferences for certain temperature positions and breadths. Our analyses revealed that (a) many EM fungal OTUs were restricted to habitats with low mean annual temperatures, (b) fungal OTUs observed at colder sites exhibited narrower temperature breadths than expected by chance, (c) the composition of EM fungal OTUs exhibited a nested pattern along the temperature gradient, and (d) EM fungal richness was highest at colder sites, where the greatest degree of overlap in OTU occurrence was observed. These findings imply that future warming may limit the distribution of many EM fungal species that are currently adapted to only cold climates. This could eventually reduce EM fungal biodiversity, which is linked to forest function through symbiotic associations with trees. This study demonstrates the distribution and environmental ranges of various EM fungal species and can contribute to develop species distribution models with the aim of conserving microbes in the face of climate change.