Effects of nitrogen deposition on carbon and nutrient cycling along a natural soil acidity gradient as revealed by metagenomics.

Nitrogen (N) deposition and soil acidification are environmental challenges affecting ecosystem functioning, health, and biodiversity, but their effects on functional genes are poorly understood. Here, we utilized metabarcoding and metagenomics to investigate the responses of soil functional genes to N deposition along a natural soil pH gradient. Soil N content was uncorrelated with pH, enabling us to investigate their effects separately. Soil acidity strongly and negatively affected the relative abundances of most cluster of orthologous gene categories of the metabolism supercategory. Similarly, soil acidity negatively affected the diversity of functional genes related to carbon and N but not phosphorus cycling. Multivariate analyses showed that soil pH was the most important factor affecting microbial and functional gene composition, while the effects of N deposition were less important. Relative abundance of KEGG functional modules related to different parts of the studied cycles showed variable responses to soil acidity and N deposition. Furthermore, our results suggested that the diversity-function relationship reported for other organisms also applies to soil microbiomes. Since N deposition and soil pH affected microbial taxonomic and functional composition to a different extent, we conclude that N deposition effects might be primarily mediated through soil acidification in forest ecosystems.

Global patterns in endemicity and vulnerability of soil fungi.

Fungi are highly diverse organisms, which provide multiple ecosystem services. However, compared with charismatic animals and plants, the distribution patterns and conservation needs of fungi have been little explored. Here, we examined endemicity patterns, global change vulnerability and conservation priority areas for functional groups of soil fungi based on six global surveys using a high-resolution, long-read metabarcoding approach. We found that the endemicity of all fungi and most functional groups peaks in tropical habitats, including Amazonia, Yucatan, West-Central Africa, Sri Lanka, and New Caledonia, with a negligible island effect compared with plants and animals. We also found that fungi are predominantly vulnerable to drought, heat and land-cover change, particularly in dry tropical regions with high human population density. Fungal conservation areas of highest priority include herbaceous wetlands, tropical forests, and woodlands. We stress that more attention should be focused on the conservation of fungi, especially root symbiotic arbuscular mycorrhizal and ectomycorrhizal fungi in tropical regions as well as unicellular early-diverging groups and macrofungi in general. Given the low overlap between the endemicity of fungi and macroorganisms, but high conservation needs in both groups, detailed analyses on distribution and conservation requirements are warranted for other microorganisms and soil organisms.

The influence of tree genus, phylogeny, and richness on the specificity, rarity, and diversity of ectomycorrhizal fungi.

Partner specificity is a well-documented phenomenon in biotic interactions, yet the factors that determine specificity in plant-fungal associations remain largely unknown. By utilizing composite soil samples, we identified the predictors that drive partner specificity in both plants and fungi, with a particular focus on ectomycorrhizal associations. Fungal guilds exhibited significant differences in overall partner preference and avoidance, richness, and specificity to specific tree genera. The highest level of specificity was observed in root endophytic and ectomycorrhizal associations, while the lowest was found in arbuscular mycorrhizal associations. The majority of ectomycorrhizal fungal species showed a preference for one of their partner trees, primarily at the plant genus level. Specialist ectomycorrhizal fungi were dominant in belowground communities in terms of species richness and relative abundance. Moreover, all tree genera (and occasionally species) demonstrated a preference for certain fungal groups. Partner specificity was not related to the rarity of fungi or plants or environmental conditions, except for soil pH. Depending on the partner tree genus, specific fungi became more prevalent and relatively more abundant with increasing stand age, tree dominance, and soil pH conditions optimal for the partner tree genus. The richness of partner tree species and increased evenness of ectomycorrhizal fungi in multi-host communities enhanced the species richness of ectomycorrhizal fungi. However, it was primarily the partner-generalist fungi that contributed to the high diversity of ectomycorrhizal fungi in mixed forests.

Structure of plant-associated microeukaryotes in roots and leaves of aquatic and terrestrial plants revealed by blocking peptide-nucleic acid (PNA) amplification.

Studies of plant-microbe interactions, including mutualistic, antagonistic, parasitic, or commensal microbes, have greatly benefited our understanding of ecosystem functioning. New molecular identification tools have increasingly revealed the association patterns between microorganisms and plants. Here, we integrated long-read PacBio single-molecule sequencing technology with a blocking protein-nucleic acid (PNA) approach to minimise plant amplicons in a survey of plant-eukaryotic microbe relationships in roots and leaves of different aquatic and terrestrial plants to determine patterns of organ, host, and habitat preferences. The PNA approach reduced the samples' relative amounts of plant reads and did not distort the fungal and other microeukaryotic composition. Our analyses revealed that the eukaryotic microbiomes associated with leaves and roots of aquatic plants exhibit a much larger proportion of non-fungal microorganisms than terrestrial plants, and leaf and root microbiomes are similar. Terrestrial plants had much stronger differentiation of leaf and root microbiomes and stronger partner specificity than aquatic plants.

Connecting the multiple dimensions of global soil fungal diversity.

How the multiple facets of soil fungal diversity vary worldwide remains virtually unknown, hindering the management of this essential species-rich group. By sequencing high-resolution DNA markers in over 4000 topsoil samples from natural and human-altered ecosystems across all continents, we illustrate the distributions and drivers of different levels of taxonomic and phylogenetic diversity of fungi and their ecological groups. We show the impact of precipitation and temperature interactions on local fungal species richness (alpha diversity) across different climates. Our findings reveal how temperature drives fungal compositional turnover (beta diversity) and phylogenetic diversity, linking them with regional species richness (gamma diversity). We integrate fungi into the principles of global biodiversity distribution and present detailed maps for biodiversity conservation and modeling of global ecological processes.

Inducing Tolerance to Abiotic Stress in Hordeum vulgare L. by Halotolerant Endophytic Fungi Associated With Salt Lake Plants.

A characteristic trait of plants living in harsh environments is their association with fungal endophytes, which enable them to survive under extreme stress. Abiotic stress resistance in agro-ecosystems, particularly in arid and semi-arid regions, can be increased by inoculating these fungal endophytes on plants other than their original hosts. The present study is therefore focused on the possible role of three halotolerant endophytic fungi, i.e., Periconia macrospinosa, Neocamarosporium goegapense, and N. chichastianum, isolated from roots of salt lake plants growing in the central desert of Iran, in alleviating the adverse effects of salinity and drought stresses on barley under greenhouse conditions. To perform this experiment, a randomized block design was applied with three factors: fungi (four levels including three halotolerant endophytic species and control), salinity (three levels including 8, 12, and 16 dS/m), and drought (four levels including 100, 80, 60, 40 percent field capacity). All plants were measured for growth characteristics, chlorophyll concentration, proline content, and antioxidant enzyme activities. A three-way analysis of variance indicated that all three fungal endophytes, to varying extents, induced the barley plants' resistance to salinity and drought, and their combined effects. Additionally, we found that fungal endophytes were more effective when the barley plants were subjected to higher levels of salinity and drought. Under the stress of salinity and drought, a strong relationship between inoculation of fungal endophytes and enhancement of biomass, shoot length, chlorophyll concentration, proline content, and activity of catalase, peroxidase, and superoxide dismutase was indicated. We discussed that increased root growth, proline content, and antioxidant enzyme activity are the main physiological and biochemical mechanisms causing stress resistance in barley plants inoculated with endophytes. Our research findings illustrate that fungal endophytes have a substantial potential for increasing abiotic stress tolerance in barley plants, which can be applied in agricultural ecosystems.

Desert-adapted fungal endophytes induce salinity and drought stress resistance in model crops.

Abiotic stresses are among the most damaging and ever-increasing threats to crop production worldwide. Utilizing extreme-habitat-adapted symbiotic microorganisms is a well-known strategy to mitigate the destructive effects of abiotic stresses on agricultural products. Here, we show the effects of the inoculation of halotolerant endophytic fungi recovered from desert plants on drought and salinity stress tolerance in two model agricultural plants A Periconia and two Neocamarosporium species were selected for this study after an in vitro halotolerant assay. Then, a random block design with three factors including fungi, salinity, and drought treatments was used to investigate the ability of these endophytes to induce stress resistance in tomato and cucumber plants. Physiological markers including proline content and activities of superoxide dismutase, catalase and peroxidase enzymes; as well as growth parameters and chlorophyll contents were assessed in all model plants. Fungal symbiosis increased chlorophyll concentration and plant growth, under all levels of salinity and drought stress. In model plants associated with P. macrospinosa significant increase in proline content and antioxidant enzymatic activities was observed under all levels of the salinity and drought stresses compared to the endophyte-free plants, while plants associated with the two Neocamarosporium species, indicated significant increasing proline content and antioxidant enzymatic activities only in high levels of the salinity and drought stresses. Our findings provide novel insights into the eco-physiological mechanisms of halotolerant fungal endophyte-mediated drought and salinity stress tolerance in cucumber and tomato plants, which signify the prospective applications of arid and saline habitat adapted endophytes in agricultural systems.

Regional-Scale In-Depth Analysis of Soil Fungal Diversity Reveals Strong pH and Plant Species Effects in Northern Europe.

Soil microbiome has a pivotal role in ecosystem functioning, yet little is known about its build-up from local to regional scales. In a multi-year regional-scale survey involving 1251 plots and long-read third-generation sequencing, we found that soil pH has the strongest effect on the diversity of fungi and its multiple taxonomic and functional groups. The pH effects were typically unimodal, usually both direct and indirect through tree species, soil nutrients or mold abundance. Individual tree species, particularly Pinus sylvestris, Picea abies, and Populus x wettsteinii, and overall ectomycorrhizal plant proportion had relatively stronger effects on the diversity of biotrophic fungi than saprotrophic fungi. We found strong temporal sampling and investigator biases for the abundance of molds, but generally all spatial, temporal and microclimatic effects were weak. Richness of fungi and several functional groups was highest in woodlands and around ruins of buildings but lowest in bogs, with marked group-specific trends. In contrast to our expectations, diversity of soil fungi tended to be higher in forest island habitats potentially due to the edge effect, but fungal richness declined with island distance and in response to forest fragmentation. Virgin forests supported somewhat higher fungal diversity than old non-pristine forests, but there were no differences in richness between natural and anthropogenic habitats such as parks and coppiced gardens. Diversity of most fungal groups suffered from management of seminatural woodlands and parks and thinning of forests, but especially for forests the results depended on fungal group and time since partial harvesting. We conclude that the positive effects of tree diversity on overall fungal richness represent a combined niche effect of soil properties and intimate associations.