Co-occurring Fungal Functional Groups Respond Differently to Tree Neighborhoods and Soil Properties Across Three Tropical Rainforests in Panama

Characterization of ectomycorrhizal fungal communities associated with tree species on an iron tailings deposit undergoing restoration

Vegetation restoration is an effective method to improve the ecological environment of mine tailings, which has a profound impact on the potential ecological functions of soil fungal communities; yet, little is known about its beneficial effect on soil ectomycorrhizal fungal community. In this study, the responses of soil characteristics and soil ectomycorrhizal fungal community diversity and structure to different revegetation, as well as the contribution of soil factors to soil ectomycorrhizal community were investigated in Liaoning Province, China. As we anticipated, the presence of vegetation significantly improved most soil properties we studied. What's more, compared to Korean pine (Pinus koraiensis Sieb. et Zucc.), Chinese poplar (Populus simonii Carr), and black locust (Robinia pseudoacacia L) could better improve soil total carbon, total nitrogen, total phosphorus, and available phosphorus. In addition, soil ectomycorrhizal fungal community diversity in black locust was greater than Korean pine and Populus simonii. Nonmetric multidimensional scaling analyses indicated that soil ectomycorrhizal community significantly differed depending on different revegetation types. Thus, these results indicated that black locust could be a suitable species for the revegetation of iron mine tailings. The study provided theoretical basis for ecological restoration of iron mine tailings using local plant species.

Changes in litter input exert divergent effects on the soil microbial community and function in stands of different densities

Soil microbial communities influence soil biogeochemical cycling by affecting the production of extracellular enzymes and the release of carbon dioxide. Changes in litter input or stand density due to thinning can affect soil microbial communities and their function by altering soil biochemical properties. However, it is unclear how or to what extent different amounts of litter input affect soil microbial communities and their function in forest stands with different densities. Therefore, we simulated litter removal, 50 % litter reduction, normal litter input, and double litter increase under field conditions by applying different amounts of litter to soils with different stand densities in the laboratory. We then measured soil biochemical properties, microbial communities, enzyme activity, and respiration rate. Our results revealed that the responses of soil dissolved organic carbon and total nitrogen to litter input were more pronounced in the high-density forest stand with poor soil than in the low-density forest stand with nutrient-rich soil, which was mainly reflected in that the addition of litter significantly decreased the concentration of dissolved organic carbon while increasing the content of total nitrogen in the soil of the high-density forest stand. In comparison to the soil carbon component, the nitrogen component of the soil was more affected by stand density. The responses of soil fungal and bacterial communities to leaf litter treatment varied with stand density, as reflected primarily in changes in the relative abundances of Ascomycota, unclassified_K_fungi, and Proteobacteria, and changes in the relative abundances of their functional groups (ectomycorrhizal fungi, saprophytic fungi, pathogens, parasites, and bacteria involved in the nitrogen cycle). Soil fungal community responses to changes in litter input are more sensitive in the high-density forest with nutrient-poor soil than in the low-density forest stand. Furthermore, litter input inhibited the activities of soil β-glucuronidase, N-acetyl-β-d-glucosaminidase, and acid phosphatase more strongly in the low-density forest stand. Litter manipulation primarily affected enzymatic activity in the high-density forest stand by changing the diversity and composition of the soil fungal community. However, in the low-density forest stand, litter treatment affected soil enzyme activity, primarily through changes in soil bacterial and fungal community composition, as well as soil respiration through changes in bacterial richness (Chao 1) and community composition. We conclude that how the change in litter input impacts the soil microbial community and its function, or the magnitude of the effects, is largely dependent on soil quality. Relationships among soil variables, microbial communities, and function differ between stand densities. Our study contributes to an enhanced understanding of the impact of changes in litter input due to climate change or anthropogenic activities on soil biogeochemical cycles and can also guide rationally formulating forest management approaches to improve microbial function under climate change.

Diversity and distribution of tropical ectomycorrhizal fungi

The tropics were long considered to have few ectomycorrhizal fungi, presumably due to a paucity of ectomycorrhizal host plants relative to higher-latitude ecosystems. However, an increase in research in tropical regions over the past 30 years has greatly expanded knowledge about the occurrence of tropical ectomycorrhizal fungi. To assess their broad biogeographic and diversity patterns, we conducted a comprehensive review and quantitative data analysis of 49 studies with 80 individual data sets along with additional data from GlobalFungi to elucidate tropical diversity patterns and biogeography of ectomycorrhizal fungi across the four main tropical regions: the Afrotropics, the Neotropics, Southeast Asia, and Oceania. Generalized linear models were used to explore biotic and abiotic influences on the relative abundance of the 10 most frequently occurring lineages. We also reviewed the available literature and synthesized current knowledge about responses of fungi to anthropogenic disturbances, and their conservation status and threats. We found that /russula-lactarius and /tomentella-thelephora were the most abundant lineages in the Afrotropics, the Neotropics, and Southeast Asia, whereas /cortinarius was the most abundant lineage in Oceania, and that /russula-lactarius, /inocybe, and /tomentella-thelephora were the most species-rich lineages across all of the tropical regions. Based on these analyses, we highlight knowledge gaps for each tropical region. Increased sampling of tropical regions, collaborative efforts, and use of molecular methodologies are needed for a more comprehensive view of the ecology and diversity of tropical ectomycorrhizal fungi.

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 Closer Examination of the 'Abundant-Center' for Ectomycorrhizal Fungal Community Associated With Picea crassifolia in China

A long-standing hypothesis in biogeography predicts that a species' abundance is highest at the center of its geographical range and decreases toward its edges. In this study, we test the abundant-center hypothesis of ectomycorrhizal (ECM) fungal communities associated with Picea crassifolia, an endemic species widely distributed in northwest China. We analyzed the taxonomic richness and the relative abundance of ECM fungi in four main distribution areas, from center to edges. In total, 234 species of ECM fungi were detected, and of these, 137 species were shared among all four sites. Inocybe, Sebacina, Tomentella, and Cortinarius were the dominant genera. ECM fungal richness and biodiversity were highest at the central and lower at peripheral sites. Our results indicated that ECM fungal species richness was consistent with the abundant-center hypothesis, while the relative abundances of individual fungal genera shifted inconsistently across the plant's range.

Influence of Tourism Disturbance on Soil Microbial Community Structure in Dawei Mountain National Forest Park

This research aimed to reveal the response characteristics of soil microbial community structure to different degrees of tourism disturbance. To explore the soil microbial community structure’s response mechanism, we set up continuous plots with different interference intensities: high disturbance, middle disturbance, and the control area. We collected 0–10 cm topsoil in all plots and used Illumina MiSeq high-throughput sequencing method to obtain and analyze the response characteristics of soil microbial community composition and structure under different tourism disturbances. These results were then combined with alpha diversity and environmental factors to explore the microbial response mechanism. In the tested soil, Acidobacteria, Chlorocurve, and Proteobacteria were the main bacterial phyla, while Basidiomycota and Ascomycota were the main fungal phyla. Based on the phylum, the relative abundance of the microbial community between the interference groups was compared using a significance test, with significant differences found between the interference groups in the phyla Chloroflexus, GAL15, Rokubacteria, and Blastomonas (p < 0.05). The relative abundance of the dominant phyla in the fungal community was significantly different among the groups (p < 0.05). A principal component analysis of the soil microbial community structure suggested that the soil microbial community structure was significantly different for different interference levels.

Deep Soil Layers of Drought-Exposed Forests Harbor Poorly Known Bacterial and Fungal Communities

Soil microorganisms such as bacteria and fungi play important roles in the biogeochemical cycling of soil nutrients, because they act as decomposers or are mutualistic or antagonistic symbionts, thereby influencing plant growth and health. In the present study, we investigated the vertical distribution of the soil microbiome to a depth of 2 m in Swiss drought-exposed forests of European beech and oaks on calcareous bedrock. We aimed to disentangle the effects of soil depth, tree (beech, oak), and substrate (soil, roots) on microbial abundance, diversity, and community structure. With increasing soil depth, organic carbon, nitrogen, and clay content decreased significantly. Similarly, fine root biomass, microbial biomass (DNA content, fungal abundance), and microbial alpha-diversity decreased and were consequently significantly related to these physicochemical parameters. In contrast, bacterial abundance tended to increase with soil depth, and the bacteria to fungi ratio increased significantly with greater depth. Tree species was only significantly related to the fungal Shannon index but not to the bacterial Shannon index. Microbial community analyses revealed that bacterial and fungal communities varied significantly across the soil layers, more strongly for bacteria than for fungi. Both communities were also significantly affected by tree species and substrate. In deep soil layers, poorly known bacterial taxa from Nitrospirae, Chloroflexi, Rokubacteria, Gemmatimonadetes, Firmicutes and GAL 15 were overrepresented. Furthermore, archaeal phyla such as Thaumarchaeota and Euryarchaeota were more abundant in subsoils than topsoils. Fungal taxa that were predominantly found in deep soil layers belong to the ectomycorrhizal Boletus luridus and Hydnum vesterholtii. Both taxa are reported for the first time in such deep soil layers. Saprotrophic fungal taxa predominantly recorded in deep soil layers were unknown species of Xylaria. Finally, our results show that the microbial community structure found in fine roots was well represented in the bulk soil. Overall, we recorded poorly known bacterial and archaeal phyla, as well as ectomycorrhizal fungi that were not previously known to colonize deep soil layers. Our study contributes to an integrated perspective on the vertical distribution of the soil microbiome at a fine spatial scale in drought-exposed forests.

Fungal guilds and soil functionality respond to tree community traits rather than to tree diversity in European forests

At the global scale, most forest research on biodiversity focuses on aboveground organisms. However, understanding the structural associations between aboveground and belowground communities provides relevant information about important functions linked to biogeochemical cycles. Microorganisms such as soil fungi are known to be closely coupled to the dominant tree vegetation, and we hypothesize that tree traits affect fungal guilds and soil functionality in multiple ways. By analysing fungal diversity of 64 plots from four European forest types using Illumina DNA sequencing, we show that soil fungal communities respond to tree community traits rather than to tree species diversity. To explain changes in fungal community structure and measured soil enzymatic activities, we used a trait-based ecological approach and community-weighted means of tree traits to define 'fast' (acquisitive) versus 'slow' (conservative) tree communities. We found specific tree trait effects on different soil fungal guilds and soil enzymatic activities: tree traits associated with litter and absorptive roots correlated with fungal, especially pathogen diversity, and influenced community composition of soil fungi. Relative abundance of the symbiotrophic and saprotrophic guilds mirrored the litter quality, while the root traits of fast tree communities enhanced symbiotrophic abundance. We found that forest types of higher latitudes, which are dominated by fast tree communities, correlated with high carbon-cycling enzymatic activities. In contrast, Mediterranean forests with slow tree communities showed high enzymatic activities related to nitrogen and phosphorous. Our findings highlight that tree trait effects of either 'fast' or 'slow' tree communities drive different fungal guilds and influence biogeochemical cycles.

Mutualist and pathogen traits interact to affect plant community structure in a spatially explicit model

Empirical studies show that plant-soil feedbacks (PSF) can generate negative density dependent (NDD) recruitment capable of maintaining plant community diversity at landscape scales. However, the observation that common plants often exhibit relatively weaker NDD than rare plants at local scales is difficult to reconcile with the maintenance of overall plant diversity. We develop a spatially explicit simulation model that tracks the community dynamics of microbial mutualists, pathogens, and their plant hosts. We find that net PSF effects vary as a function of both host abundance and key microbial traits (e.g., host affinity) in ways that are compatible with both common plants exhibiting relatively weaker local NDD, while promoting overall species diversity. The model generates a series of testable predictions linking key microbial traits and the relative abundance of host species, to the strength and scale of PSF and overall plant community diversity.