An evidence-based consensus for the classification of arbuscular mycorrhizal fungi (Glomeromycota)

Isolation and characterization of non-rhizobial bacteria and arbuscular mycorrhizal fungi from legumes

This study investigates non-rhizobial endophytic bacteria in the root nodules of chickpea (Cicer arietinum L), faba bean (Vicia faba), and cowpea (Vigna unguiculata L. Walp), as well as arbuscular mycorrhizal fungi in the rhizospheric soil of chickpea and faba bean. Out of the 34 endophytic bacterial populations examined, 31 strains were identified as non-rhizobial based on nodulation tests. All strains were assessed for their plant growth-promoting (PGP) activities in vitro. The results revealed that most isolates exhibited multiple PGP activities, such as nitrogen fixation, indole-3-acetic acid (IAA) and ammonia (NH3) production, phosphate solubilization, and exopolysaccharide production. The most effective PGP bacteria were selected for 16S rRNA analysis. Additionally, a total of 36 species of native arbuscular mycorrhizal fungi (AMF) were identified. Acaulospora (100%) and Scutellospora (91.66%) were the most prevalent genera in Cicer arietinum L. and Vicia faba L. plants, respectively. Acaulospora also exhibited the highest spore density and relative abundance in both plants. Moreover, the root colonization of Cicer arietinum L. and Vicia faba L. plants by hyphae, vesicles, and arbuscules (HVA) was significant. The findings of this study provide valuable insights into non-rhizobial endophytic bacteria associated with legume root nodules and the diversity of AMF. These organisms have great potential for PGP and can be manipulated by co-inoculation with rhizobia to enhance their biofertilizer effectiveness. This manipulation is crucial for promoting sustainable agriculture, improving crop growth, and advancing biofertilizer technology.

Within-Site Variations in Soil Physicochemical Properties Explained the Spatiality and Cohabitation of Arbuscular Mycorrhizal Fungi in the Roots of Cryptomeria Japonica

Arbuscular mycorrhizal fungi (AMF) live in a community in the roots of host plants. Still, the patterns and factors that drive their spatiality and cohabitation remain uncovered, particularly that of trees in planted forests, which we aimed to clarify in Cryptomeria japonica, a major plantation tree in Japan. We analyzed 65 paired root and soil samples of Cryptomeria japonica trees collected from 11 microsite (MS) plots at two environmentally different forest sites in central Japan and measured soil pH, total phosphorus (TP), C, N, and the carbon-to-nitrogen ratio. Root AMF communities were recovered using Illumina's next-generation amplicon sequencing targeting the small subunit of ribosomal DNA. We detected more than 500 AMF OTUs at each site but only three belonging to Dominikia, Rhizophagus, and Sclerocystis were dominant in the roots of C. japonica, detected each at an average relative abundance higher than 20%. Two showed negatively correlated spatial distributions and different associations with soil pH. Similarly, the physicochemical properties at MSs significantly determined the AMF assemblages in the roots of C. japonica. Dominikia, Rhizophagus, and Sclerocystis coexist in the roots of C. japonica where soil physicochemical properties, particularly pH, determine their spatial dynamic, turnovers, and cohabitation patterns. These findings highlight the importance of simultaneous colonization of plants by multiple AMF.

Alleviation of NaCl Stress on Growth and Biochemical Traits of Cenchrus ciliaris L. via Arbuscular Mycorrhizal Fungi Symbiosis

Soil salinization, especially in arid and semi-arid regions, is one of the major abiotic stresses that affect plant growth. To mediate and boost plant tolerance against this abiotic stress, arbuscular mycorrhizal fungi (AMF) symbiosis is commonly thought to be an effective tool. So, the main purpose of this study was to estimate the role of AMF (applied as a consortium of Claroideoglomus etunicatum, Funneliformis mosseae, Rhizophagus fasciculatum, and R. intraradices species) symbiosis in mitigating deleterious salt stress effects on the growth parameters (shoot length (SL), root length (RL), shoot dry weight (SDW), root dry weight (RDW), root surface area (RSA), total root length (TRL), root volume (RV), root diameter (RD), number of nodes and leaves) of Cenchrus ciliaris L. plants through improved accumulations of photosynthetic pigments (chlorophyll a, chlorophyll b, total chlorophyll), proline and phenolic compounds. The results of this experiment revealed that the roots of C. ciliaris plants were colonized by AMF under all the applied salinity levels (0, 75, 150, 225, and 300 mM NaCl). However, the rate of colonization was negatively affected by increasing salinity as depicted by the varied colonization structures (mycelium, vesicles, arbuscules and spores) which were highest under non-saline conditions. This association of AMF induced an increase in the growth parameters of the plant which were reduced by salinity stress. The improved shoot/root indices are likely due to enhanced photosynthetic activities as the AMF-treated plants showed increased accumulation of pigments (chlorophyll a, chlorophyll b and total chlorophyll), under saline as well as non-saline conditions, compared to non-AMF (N-AMF) plants. Furthermore, the AMF-treated plants also exhibited enhanced accumulation of proline and phenolic compounds. These accumulated metabolites act as protective measures under salinity stress, hence explaining the improved photosynthetic and growth parameters of the plants. These results suggest that AMF could be a good tool for the restoration of salt-affected habitats. However, more research is needed to check the true efficacy of different AMF inoculants under field conditions.

Occurrence and diversity of arbuscular mycorrhizal fungi in yerba mate (Ilex paraguariensis - Aquifoliaceae) cultivation environments

Yerba mate (Ilex paraguariensis) represents a culture of economic, social, and ecological importance for the cultivation regions. Due to the chemical, physical, and biological variations that occur in the different soils where yerba mate is economically exploited, the symbiotic associations with arbuscular mycorrhizal fungi (AMF) guarantee the plant's ability to absorb nutrients. The purpose of this study was to identify and quantify the occurrence of arbuscular mycorrhizal fungi in different environments of yerba mate cultivation. The research was performed in four areas located in the rural area of the municipality of Seberi/RS: Environment with production of yerba mate in the conventional system, silvopastoral system, organic system, and native forest. The normality of residuals and homogeneity of variances assumptions were verified using the Lilliefors and Chi-square tests and the averages compared by the Tukey's test at 5% probability of error. In addition to calculations of diversity, equivalent species, and evenness indices. The presence of AMF spores showed a direct relationship with the phosphorus (P) availability in each treatment, with a count reduction in the organic system, with P content lower than 3 mg kg-1 of soil. The species with the highest predominance were the Acaulosporaceae (Acaulospora colombiana, A. delicata, and A. tuberculata), followed by the Glomaceae (Glomus ambisporum and Glomus pansihalos) in the conventional and silvopastoral systems. The silvopastoral and conventional systems showed the highest levels of Shannon-Weaver diversity (H') and Pielou's evenness, demonstrating greater diversity and consequently greater richness and uniformity.

Ecology and diversity of arbuscular mycorrhizal fungi (AMF) in rice (Oryza sativa L.) in South India: an ecological analysis of factors influencing AMF in rice fields

AIMS

This study examined the diversity of arbuscular mycorrhizal fungi (AMF), mean spore density (MSD), and root colonization in relation to factors such as agroclimatic zones, rice varieties and soil types in paddy fields of South India. The aim was to understand how these factors influence AMF association in rice, facilitating their effective use as a biological tool in paddy cultivation.

METHODS AND RESULTS

AMF were identified through light microscopy of spores, while MSD and percentage-root-length colonization (PRLC) were measured using standard methods. Correlation and principal component analyses were performed to explore the interrelationships between AMF characteristics and various environmental, soil, and plant variables. Sixteen AMF species were identified across 29 rice varieties from three agroclimatic zones, 6 soil orders, and 18 soil series over 2 seasons. Notably, 70% of chemicalized rice fields lacked AMF spores, and only 50% exhibited root colonization. This study offers new insights into the role of AMF in rice cultivation.

CONCLUSION

The AMF diversity and root colonization in relation to environmental variables underscore their significant impact on AMF in particular crop fields.

Summer-Wet Hydrologic Cycle during the Middle Miocene of the United States: New Evidence from Fossil Fungi

Hydrologic reconstructions from North America are largely unknown for the Middle Miocene. Examination of fungal palynomorph assemblages coupled with traditional plant-based palynology permits delineation of local, as opposed to regional, climate signals and provides a baseline for study of ancient fungas. Here, the Fungi in a Warmer World project presents paleoecology and paleoclimatology of 351 fungal morphotypes from 3 sites in the United States: the Clarkia Konservat-Lagerstätte site (Idaho), the Alum Bluff site (Florida), and the Bouie River site (Mississippi). Of these, 83 fungi are identified as extant taxa and 41 are newly reported from the Miocene. Combining new plant-based paleoclimatic reconstructions with funga-based paleoclimate reconstructions, we demonstrate cooling and hydrologic changes from the Miocene climate optimum to the Serravallian. In the southeastern United States, this is comparable to that reconstructed with pollen and paleobotany alone. In the northwestern United States, cooling is greater than indicated by other reconstructions and hydrology shifts seasonally, from no dry season to a dry summer season. Our results demonstrate the utility of fossil fungi as paleoecologic and paleoclimatic proxies and that warmer than modern geological time intervals do not match the "wet gets wetter, dry gets drier" paradigm. Instead, both plants and fungi show an invigorated hydrological cycle across mid-latitude North America.

Phylogenetic classification of arbuscular mycorrhizal fungi: new species and higher-ranking taxa in Glomeromycota and Mucoromycota (class Endogonomycetes)

Arbuscular mycorrhizal (AM) fungi - Glomeromycota and Endogonomycetes - comprise multiple species and higher-level taxa that have remained undescribed. We propose a mixed morphology- and DNA-based classification framework to promote taxonomic communication and shed light into the phylogenetic structure of these ecologically essential fungi. Based on eDNA samples and long reads as type materials, we describe 15 new species and corresponding genera (Pseudoentrophosporakesseensis, Hoforsarebekkae, Kahvenarebeccae, Kelottijaerviashannonae, Kungsaengenashadiae, Langduoadianae, Lehetuaindrekii, Lokrumastenii, Moosteastephanieae, Nikkaluoktamahdiehiae, Parniguacraigii, Riederbergasylviae, Ruuacoralieae, Tammsaareavivikae and Unemaeeanathalieae), the genus Parvocarpum as well as 19 families (Pseudoentrophosporaceae, Hoforsaceae, Kahvenaceae, Kelottijaerviaceae, Kungsaengenaceae, Langduoaceae, Lehetuaceae, Lokrumaceae, Moosteaceae, Nikkaluoktaceae, Parniguaceae, Riederbergaceae, Ruuaceae, Tammsaareaceae, Unemaeeaceae, Bifigurataceae, Planticonsortiaceae, Jimgerdemanniaceae and Vinositunicaceae) and 17 orders (Hoforsales, Kahvenales, Kelottijaerviales, Kungsaengenales, Langduoales, Lehetuales, Lokrumales, Moosteales, Nikkaluoktales, Parniguales, Riederbergales, Ruuales, Tammsaareales, Unemaeeales, Bifiguratales and Densosporales), and propose six combinations (Diversisporabareae, Diversisporanevadensis, Fuscutatacerradensis, Fuscutatareticulata, Viscosporadeserticola and Parvocarpumbadium) based on phylogenetic evidence. We highlight further knowledge gaps in the phylogenetic structure of AM fungi and propose an alphanumeric coding system for preliminary communication and reference-based eDNA quality-filtering of the remaining undescribed genus- and family-level groups. Using AM fungi as examples, we hope to offer a sound, mixed framework for classification to boost research in the alpha taxonomy of fungi, especially the "dark matter fungi".

The rootstock modifies the arbuscular mycorrhizal community of the root system, while the influence of the scion is limited in grapevines

Understanding the effects of grapevine rootstock and scion genotypes on arbuscular mycorrhizal fungi (AMF), as well as the roles of these fungi in plant development, could provide new avenues for adapting viticulture to climate change and reducing agrochemical inputs. The root colonization of 10 rootstock/scion combinations was studied using microscopy and metabarcoding approaches and linked to plant development phenotypes. The AMF communities were analysed using 18S rRNA gene sequencing. The 28S rRNA gene was also sequenced for some combinations to evaluate whether the method changed the results. Root colonization indexes measured by microscopy were not significantly different between genotypes. Metabarcoding analyses showed an effect of the rootstock genotype on the β-diversity and the enrichment of several taxa with both target genes, as well as an effect on the Chao1 index with the 18S rRNA gene. We confirm that rootstocks recruit different AMF communities when subjected to the same pedoclimatic conditions, while the scion has little or no effect. Significant correlations were observed between AMF community composition and grapevine development, suggesting that AMF have a positive effect on plant growth. Given these results, it will be important to define consensus methods for studying the role of these beneficial micro-organisms in vineyards.

Arbuscular Mycorrhizal Fungi as Biostimulant and Biocontrol Agents: A Review

Arbuscular mycorrhizal fungi (AMF) are soil microorganisms living in symbiosis with most terrestrial plants. They are known to improve plant tolerance to numerous abiotic and biotic stresses through the systemic induction of resistance mechanisms. With the aim of developing more sustainable agriculture, reducing the use of chemical inputs is becoming a major concern. After providing an overview on AMF history, phylogeny, development cycle and symbiosis benefits, the current review aims to explore the potential of AMF as biostimulants and/or biocontrol agents. Nowadays, AMF inoculums are already increasingly used as biostimulants, improving mineral nutrient plant acquisition. However, their role as a promising tool in the biocontrol market, as an alternative to chemical phytosanitary products, is underexplored and underdiscussed. Thus, in the current review, we will address the mechanisms of mycorrhized plant resistance to biotic stresses induced by AMF, and highlight the various factors in favor of inoculum application, but also the challenges that remain to be overcome.

Evolutionary history of arbuscular mycorrhizal fungi and genomic signatures of obligate symbiosis

BACKGROUND

The colonization of land and the diversification of terrestrial plants is intimately linked to the evolutionary history of their symbiotic fungal partners. Extant representatives of these fungal lineages include mutualistic plant symbionts, the arbuscular mycorrhizal (AM) fungi in Glomeromycota and fine root endophytes in Endogonales (Mucoromycota), as well as fungi with saprotrophic, pathogenic and endophytic lifestyles. These fungal groups separate into three monophyletic lineages but their evolutionary relationships remain enigmatic confounding ancestral reconstructions. Their taxonomic ranks are currently fluid.

RESULTS

In this study, we recognize these three monophyletic linages as phyla, and use a balanced taxon sampling and broad taxonomic representation for phylogenomic analysis that rejects a hard polytomy and resolves Glomeromycota as sister to a clade composed of Mucoromycota and Mortierellomycota. Low copy numbers of genes associated with plant cell wall degradation could not be assigned to the transition to a plant symbiotic lifestyle but appears to be an ancestral phylogenetic signal. Both plant symbiotic lineages, Glomeromycota and Endogonales, lack numerous thiamine metabolism genes but the lack of fatty acid synthesis genes is specific to AM fungi. Many genes previously thought to be missing specifically in Glomeromycota are either missing in all analyzed phyla, or in some cases, are actually present in some of the analyzed AM fungal lineages, e.g. the high affinity phosphorus transporter Pho89.

CONCLUSION

Based on a broad taxon sampling of fungal genomes we present a well-supported phylogeny for AM fungi and their sister lineages. We show that among these lineages, two independent evolutionary transitions to mutualistic plant symbiosis happened in a genomic background profoundly different from that known from the emergence of ectomycorrhizal fungi in Dikarya. These results call for further reevaluation of genomic signatures associated with plant symbiosis.

Characterization of arbuscular mycorrhizal fungal species associating with Zea mays

Taxonomic identification of arbuscular mycorrhizal (AM) fungal spores extracted directly from the field is sometimes difficult because spores are often degraded or parasitized by other organisms. Single-spore inoculation of a suitable host plant allows for establishing monosporic cultures of AM fungi. This study aimed to propagate AM fungal spores isolated from maize soil using single spores for morphological characterization. First, trap cultures were established to trigger the sporulation of AM fungal species. Second, trap cultures were established with individual morphotypes by picking up only one spore under a dissecting microscope and transferring it to a small triangle of sterilized filter paper, which was then carefully inoculated below a root from germinated sorghum seeds in each pot and covered with a sterile substrate. All pots were placed in sunbags and maintained in a plant growth room for 120 days. Spores obtained from single spore trap cultures from each treatment, maize after oats (MO), maize after maize (MM), maize after peas (MP), and maize after soybean (MS), were extracted using the sieving method. Healthy spores were selected for morphological analysis. Direct PCR was conducted by crushing spores in RNAlater and applying three sets of primer pairs: ITS1 × ITS4, NS31 × AML2, and SSUmcf and LSUmBr. Nucleotide sequences obtained from Sanger sequencing were aligned on MEGA X. The phylogenetic tree showed that the closest neighbors of the propagated AM fungal species belonged to the genera Claroideoglomus, Funneliformis, Gigaspora, Paraglomus, and Rhizophagus. The morphological characteristics were compared to the descriptive features of described species posted on the INVAM website, and they included Acaulospora cavernata, Diversispora spurca, Funneliformis geosporus, Funneliformis mosseae, Gigaspora clarus, Gigaspora margarita, Glomus macrosporum, Paraglomus occultum, and Rhizophagus intraradices. These findings can provide a great contribution to crop productivity and sustainable management of the agricultural ecosystem. Also, the isolate analyzed could be grouped into efficient promoters of growth and mycorrhization of maize independent of their geographical location.

Year-round dynamics of arbuscular mycorrhizal fungi communities in the roots and surrounding soils of Cryptomeria japonica

Arbuscular mycorrhizal fungi (AMF) live simultaneously inside and outside of host plant roots for a functional mycorrhizal symbiosis. Still, the year-round dynamics and relationships between soil properties and AMF communities of trees in forest ecosystems remain unclear. We collected paired root and soil samples of the same Cryptomeria japonica trees at two forest sites (five trees at each site) every 2 months over a year. Total DNA was extracted from roots and soil separately and soil physicochemical properties were measured. With Illumina's next-generation amplicon sequencing targeting the small subunit of fungal ribosomal DNA, we clarified seasonal dynamics of soil properties and AMF communities. Soil pH and total phosphorus showed significant seasonality while total carbon, nitrogen, and C/N did not. Only pH was a good predictor of the composition and dynamics of the AMF community. The total AMF community (roots + soil) showed significant seasonality because of variation from May to September. Root and soil AMF communities were steady year-round, however, with similar species richness but contained significantly different AMF assemblages in any sampling month. Despite the weak seasonality in the communities, the top two dominant OTUs showed significant but different shifts between roots and soils across seasons with strong antagonistic relationships. In conclusion, few dominant AMF taxa are dynamically shifting between the roots and soils of C. japonica to respond to seasonal and phenological variations in their microhabitats. AMF inhabiting forest ecosystems may have high environmental plasticity to sustain a functional symbiosis regardless of seasonal variations that occur in the soil.

Three new species of arbuscular mycorrhizal fungi (Glomeromycota) and Acaulospora gedanensis revised

Studies of the morphology and the 45S nuc rDNA phylogeny of three potentially undescribed arbuscular mycorrhizal fungi (phylum Glomeromycota) grown in cultures showed that one of these fungi is a new species of the genus Diversispora in the family Diversisporaceae; the other two fungi are new Scutellospora species in Scutellosporaceae. Diversispora vistulana sp. nov. came from maritime sand dunes of the Vistula Spit in northern Poland, and S. graeca sp. nov. and S. intraundulata sp. nov. originally inhabited the Mediterranean dunes of the Peloponnese Peninsula, Greece. In addition, the morphological description of spores of Acaulospora gedanensis, originally described in 1988, was emended based on newly found specimens, and the so far unknown phylogeny of this species was determined. The phylogenetic analyses of 45S sequences placed this species among Acaulospora species with atypical phenotypic and histochemical features of components of the two inner germinal walls.

Comparative Analysis of Rhizosphere and Endosphere Fungal Communities in Healthy and Diseased Faba Bean Plants

This study used the ITS approach based on Illumina MiSeq sequencing to assess the endosphere and rhizosphere fungal communities in healthy and diseased faba bean plants. The findings indicate that the most predominant phyla in all samples were Ascomycota (49.89-99.56%) and Basidiomycota (0.33-25.78%). In healthy endosphere samples, Glomeromycota (0.08-1.17%) was the only predominant phylum. In diseased endosphere samples, Olpidiomycota (0.04-1.75%) was the only predominant phylum. At the genus level, Penicillium (0.47-35.21%) was more abundant in rhizosphere soil, while Paraphoma (3.48-91.16%) was predominant in the endosphere roots of faba bean plants. Significant differences were observed in the alpha diversity of rhizosphere samples from different germplasm resources (p < 0.05). The fungal community structures were clearly distinguished between rhizosphere and endosphere samples and between healthy and diseased endosphere samples (p < 0.05). Saccharomyces was significantly enriched in diseased endosphere samples, whereas Apiotrichum was enriched in healthy endosphere samples. Vishniacozyma and Phialophora were enriched in diseased rhizosphere samples, while Pseudogymnoascus was enriched in healthy rhizosphere samples. Diseased samples displayed more strongly correlated genera than healthy samples. Saprotrophs accounted for a larger proportion of the fungal microbes in rhizosphere soil than in endosphere roots. This study provides a better understanding of the composition and diversity of fungal communities in the rhizosphere and endosphere of faba bean plants as well as a theoretical guidance for future research on the prevention or control of faba bean root rot disease.

Keep in touch: the soil-root hydraulic continuum and its role in drought resistance in crops

Drought is a major threat to food security worldwide. Recently, the root-soil interface has emerged as a major site of hydraulic resistance during water stress. Here, we review the impact of soil drying on whole-plant hydraulics and discuss mechanisms by which plants can adapt by modifying the properties of the rhizosphere either directly or through interactions with the soil microbiome.

Mycorrhizal fungal communities associated with three metal accumulator plants growing in an abandoned Pb smelting factory

Plants associated with mycorrhizal fungi has the ability to establish on metal-contaminated soils playing an important role in phytoremediation programs. The objective of this study was to examine the presence of arbuscular mycorrhizal fungi (AMF) (spores density, diversity, indicator species, and root colonization) and dark septate endophytic fungi (DSE fungal root colonization) in three metal accumulator plants (Sorghum halepense, Bidens pilosa, and Tagetes minuta) growing in soils with high Pb content. The Pb content in AMF spores and plant biomass were also assessed. Rhizosphere soil samples were taken from the three dominant plant species at six study sites surrounding the abandoned Pb smelter and one uncontaminated site. The three studied plants were colonized by AMF and DSE fungi. A total of 24 AMF morphospecies were present in the Pb-contaminated areas. The AMF indicator species in the control site (non-contaminated area) was Funneliformis mosseae and in the most contaminated site were Gigaspora decipiens and Denticustata biornata. There was an increase in mycorrhizal variables such as the number of AMF vesicles, spore number, Pb content in AMF spores and plant biomass and DSE colonization (in Sorghum) with increasing soil Pb contamination, but a decrease in AMF diversity and richness was found. For upcoming soil restoration projects, it is crucial to understand the mycorrhizal fungi as well as the plant community that has adapted to the highly contaminated environment.

Effect the accumulation of bioactive constituents of a medicinal plant (Salvia Miltiorrhiza Bge.) by arbuscular mycorrhizal fungi community

BACKGROUND

Arbuscular mycorrhizal fungi (AMF) form symbiotic relationships with various terrestrial plants and have attracted considerable interest as biofertilizers for improving the quality and yield of medicinal plants. Despite the widespread distribution of AMFs in Salvia miltiorrhiza Bunge's roots, research on the impact of multiple AMFs on biomass and active ingredient accumulations has not been conducted. In this study, the effects of five native AMFs (Glomus formosanum, Septoglomus constrictum, Rhizophagus manihotis, Acaulospora laevis, and Ambispora gerdemannii) and twenty-six communities on the root biomass and active ingredient concentrations of S. miltiorrhiza were assessed using the total factor design method.

RESULTS

Thirty-one treatment groups formed symbiotic relationships with S. miltiorrhiza based on the pot culture results, and the colonization rate ranged from 54.83% to 89.97%. AMF communities had higher colonization rates and total phenolic acid concentration than single AMF, and communities also appeared to have higher root fresh weight, dry weight, and total phenolic acid concentration than single inoculations. As AMF richness increased, there was a rising trend in root biomass and total tanshinone accumulations (ATTS), while total phenolic acid accumulations (ATP) showed a decreasing trend. This suggests that plant productivity was influenced by the AMF richness, with higher inoculation benefits observed when the communities contained three or four AMFs. Additionally, the affinities of AMF members were also connected to plant productivity. The inoculation effect of closely related AMFs within the same family, such as G. formosanum, S. constrictum, and R. manihotis, consistently yielded lower than that of mono-inoculation when any combinations were applied. The co-inoculation of S. miltiorrhiza with nearby or distant AMFs from two families, such as G. formosanum, R. manihotis, and Ac. laevis or Am. gerdemannii resulted in an increase of ATP and ATTS by more than 50%. AMF communities appear to be more beneficial to the yield of bioactive constituents than the single AMF, but overall community inoculation effects are related to the composition of AMFs and the relationship between members.

CONCLUSION

This study reveals that the AMF community has great potential to improve the productivity and the accumulation of bioactive constituents in S. miltiorrhiza, indicating that it is an effective way to achieve sustainable agricultural development through using the AMF community.

Arbuscular mycorrhizal fungi alter rhizosphere fungal community characteristics of Acorus calamus to improve Cr resistance

To investigate changes in fungal community characteristics under different Cr(VI) concentration stresses and the advantages of adding arbuscular mycorrhizal fungi (AMF), we used high throughput sequencing to characterize the fungal communities. Cr(VI) stress reduced rhizosphere soil SOM (soil organic matter) content and AMF addition improved this stress phenomenon. There were significant differences in fungal community changes under different Cr(VI) concentrations. The fungal community characteristics changed through inhibition of fungal metabolic ability, as fungal abundance increased after AMF addition, and the fungal diversity increased under high Cr(VI) concentration. The dominant phyla were members of the Ascomycota, Basidiomycota, Mortierellomycota, and Rozellomycota. Dominant groups relevant to Cr resistance were Ascomycota and Basidiomycota fungi. Moreover, Fungal community characteristics were analyzed using high-throughput sequencing of the cytochrome c metabolic pathway, NADH dehydrogenase, and NADH: ubiquinone reductase and all these functions were enhanced after AMF addition. Therefore, Cr(VI) stress significantly affects fungal community structure, while AMF addition could increase its SOM content, and metabolic capacity, and improve fungal community tolerance to Cr stress. This study contributed to the understanding response of rhizosphere fungal community in AMF-assisted wetland phytoremediation under Cr stress.

Arbuscular Mycorrhizal Fungi Associated with Maize (Zea mays L.) in the Formation and Stability of Aggregates in Two Types of Soil

Knowledge of native Arbuscular Mycorrhizal Fungi (AMF) and their relationship with the edaphic characteristics where they live is important to establish the influence of allochthonous AMF, which were inoculated, on the development and stability of soil aggregates. The objectives of this research were to know the composition of native AMF species from two contrasting soils, and to establish the development and stability of aggregates in those soils with corn plants after inoculating them with allochthonous AMF. The experiment had three factors: Soil (two levels [S1 and S2]), HMA (three levels: without application [A0], with the application of Claroideoglomus claroideum [A1] and with the application of a consortium [A2]) and Fertilization (two levels (without fertilization [f0] and with fertilization [f1])). Twelve treatments were generated, with five replicates (60 experimental units [EU]). The EU consisted of a pot with a corn plant and the distribution was completely random. The results demonstrated that the Typic Ustifluvent presented nine species of native AMF, while the Typic Dystrustert had three; the native AMF in each soil influenced the activity of allochthonous AMF, such as their colonization and sporulation. Likewise, differences were found in the stability of macro-sized aggregates (0.5 to 2.0 mm).

Paired Root-Soil Samples and Metabarcoding Reveal Taxon-Based Colonization Strategies in Arbuscular Mycorrhizal Fungi Communities in Japanese Cedar and Cypress Stands

Arbuscular mycorrhizal fungi (AMF) in the roots and soil surrounding their hosts are typically independently investigated and little is known of the relationships between the communities of the two compartments. We simultaneously collected root and surrounding soil samples from Cryptomeria japonica (Cj) and Chamaecyparis obtusa (Co) at three environmentally different sites. Based on molecular and morphological analyses, we characterized their associated AMF communities. Cj was more densely colonized than Co and that root colonization intensity was significantly correlated with soil AMF diversity. The communities comprised 15 AMF genera dominated by Glomus and Paraglomus and 1443 operational taxonomic units (OTUs) of which 1067 and 1170 were in roots and soil, respectively. AMF communities were significantly different among sites, and the root AMF communities were significantly different from those of soil at each site. The root and soil AMF communities responded differently to soil pH. At the genus level, Glomus and Acaulospora were abundant in roots while Paraglomus and Redeckera were abundant in soil. Our findings suggest that AMF colonizing roots are protected from environmental stresses in soil. However, the root-soil-abundant taxa have adapted to both environments and represent a model AMF symbiont. This evidence of strategic exploitation of the rhizosphere by AMF supports prior hypotheses and provides insights into community ecology.

The Application of Arbuscular Mycorrhizal Fungi as Microbial Biostimulant, Sustainable Approaches in Modern Agriculture

Biostimulant application can be considered an effective, practical, and sustainable nutritional crop supplementation and may lessen the environmental problems related to excessive fertilization. Biostimulants provide beneficial properties to plants by increasing plant metabolism, which promotes crop yield and improves the quality of crops; protecting plants against environmental stresses such as water shortage, soil salinization, and exposure to sub-optimal growth temperatures; and promoting plant growth via higher nutrient uptake. Other important benefits include promoting soil enzymatic and microbial activities, changing the architecture of roots, increasing the solubility and mobility of micronutrients, and enhancing the fertility of the soil, predominantly by nurturing the development of complementary soil microbes. Biostimulants are classified as microbial, such as arbuscular mycorrhizae fungi (AMF), plant-growth-promoting rhizobacteria (PGPR), non-pathogenic fungi, protozoa, and nematodes, or non-microbial, such as seaweed extract, phosphite, humic acid, other inorganic salts, chitin and chitosan derivatives, protein hydrolysates and free amino acids, and complex organic materials. Arbuscular mycorrhizal fungi are among the most prominent microbial biostimulants and have an important role in cultivating better, healthier, and more functional foods in sustainable agriculture. AMF assist plant nutrient and water acquisition; enhance plant stress tolerance against salinity, drought, and heavy metals; and reduce soil erosion. AMF are proven to be a sustainable and environmentally friendly source of crop supplements. The current manuscript gives many examples of the potential of biostimulants for the production of different crops. However, further studies are needed to better understand the effectiveness of different biostimulants in sustainable agriculture. The review focuses on how AMF application can overcome nutrient limitations typical of organic systems by improving nutrient availability, uptake, and assimilation, consequently reducing the gap between organic and conventional yields. The aim of this literature review is to survey the impacts of AMF by presenting case studies and successful paradigms in different crops as well as introducing the main mechanisms of action of the different biostimulant products.

Role of Arbuscular Mycorrhizal Fungi in Regulating Growth, Enhancing Productivity, and Potentially Influencing Ecosystems under Abiotic and Biotic Stresses

Arbuscular mycorrhizal fungi (AMF) form symbiotic relationships with the roots of nearly all land-dwelling plants, increasing growth and productivity, especially during abiotic stress. AMF improves plant development by improving nutrient acquisition, such as phosphorus, water, and mineral uptake. AMF improves plant tolerance and resilience to abiotic stressors such as drought, salt, and heavy metal toxicity. These benefits come from the arbuscular mycorrhizal interface, which lets fungal and plant partners exchange nutrients, signalling molecules, and protective chemical compounds. Plants' antioxidant defence systems, osmotic adjustment, and hormone regulation are also affected by AMF infestation. These responses promote plant performance, photosynthetic efficiency, and biomass production in abiotic stress conditions. As a result of its positive effects on soil structure, nutrient cycling, and carbon sequestration, AMF contributes to the maintenance of resilient ecosystems. The effects of AMFs on plant growth and ecological stability are species- and environment-specific. AMF's growth-regulating, productivity-enhancing role in abiotic stress alleviation under abiotic stress is reviewed. More research is needed to understand the molecular mechanisms that drive AMF-plant interactions and their responses to abiotic stresses. AMF triggers plants' morphological, physiological, and molecular responses to abiotic stress. Water and nutrient acquisition, plant development, and abiotic stress tolerance are improved by arbuscular mycorrhizal symbiosis. In plants, AMF colonization modulates antioxidant defense mechanisms, osmotic adjustment, and hormonal regulation. These responses promote plant performance, photosynthetic efficiency, and biomass production in abiotic stress circumstances. AMF-mediated effects are also enhanced by essential oils (EOs), superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), hydrogen peroxide (H2O2), malondialdehyde (MDA), and phosphorus (P). Understanding how AMF increases plant adaptation and reduces abiotic stress will help sustain agriculture, ecosystem management, and climate change mitigation. Arbuscular mycorrhizal fungi (AMF) have gained prominence in agriculture due to their multifaceted roles in promoting plant health and productivity. This review delves into how AMF influences plant growth and nutrient absorption, especially under challenging environmental conditions. We further explore the extent to which AMF bolsters plant resilience and growth during stress.

Association of mycoheterotrophic Gentianaceae with specific Glomus lineages

Some plant species took an alternative evolutionary pathway in which they lost their photosynthetic capacity to depend exclusively on carbon supplied by arbuscular mycorrhizal fungi (AMF) in an association called mycoheterotrophy. Among them is Voyriella parviflora, a species of the family Gentianaceae, which is found in tropical regions such as the Amazon basin. Here, we assessed the identity of AMF symbionts associated with this species. DNA was isolated from eight Gentianaceae specimens and from litter and surrounding roots of photosynthetic plants. The atp1 gene was amplified by Sanger sequencing to determine the taxonomic affiliation of the mycoheterotrophic plants. A 280 bp region of the 18S rRNA gene of AMF was amplified with primers NS31/AML2 by high-throughput sequencing. The mycoheterotrophic specimens were assigned to V. parviflora with a bootstrap support of 72%. Glomus was the most abundant AMF genus, both in the mycoheterotrophic plants and in the litter and roots of photosynthetic plants. In addition, a few Glomus genotypes were abundantly enriched in the mycoheterotrophic plants, with only a few specimens colonized by Gigaspora, Acaulospora, and Scutellospora in a low proportion. These genotypes formed a cluster within a larger clade, suggesting that V. parviflora shows a preferential association with a narrow Glomus lineage which is not phylogenetically close to a previously identified V. parviflora's associated lineage. Furthermore, detecting fungi from other families suggests that V. parviflora is colonized by other genera, although with low frequency. These findings provide new insights into the association between AMF and mycoheterotrophic species and highlight the importance of considering trap culture-independent approaches in understanding this symbiosis.

Isolation and identification of arbuscular mycorrhizal fungi from an abandoned uranium mine and their role in soil-to-plant transfer of radionuclides and metals

Arbuscular mycorrhizal fungi were recovered from soil samples from the naturally radioactive soil at the long-abandoned South Terras uranium mine in Cornwall, UK. Species of Rhizophagus, Claroideoglomus, Paraglomus, Septoglomus, and Ambispora were recovered, and pot cultures from all except Ambispora were established. Cultures were identified to species level using morphological observation and rRNA gene sequencing combined with phylogenetic analysis. These cultures were used in pot experiments designed with a compartmentalised system to assess the contribution of fungal hyphae to the accumulation of essential elements, such as copper and zinc, and non-essential elements, such as lead, arsenic, thorium, and uranium into root and shoot tissues of Plantago lanceolata. The results indicated that none of the treatments had any positive or negative impact on shoot and root biomass. However, Rhizophagus irregularis treatments showed higher accumulation of copper and zinc in shoots, while R. irregularis and Septoglomus constrictum enhanced arsenic accumulation in roots. Moreover, R. irregularis increased uranium concentration in roots and shoots of the P. lanceolata plant. This study provides useful insight into fungal-plant interactions that determine metal and radionuclide transfer from soil into the biosphere at contaminated sites such as mine workings.

Arbuscular mycorrhizae reduce the response of important plant functional traits to drought and salinity. A meta-analysis study

We aimed at exploring the plant functional traits whose responses to drought or salinity are altered by the presence of arbuscular mycorrhiza (AM). We performed a meta-analysis across 114 articles spanning 110 plant species or cultivars. We quantified the size effect of AM symbiosis on the stress response of several functional traits, using linear mixed model analysis (LMM). Correlation analysis between functional traits and total biomass responses to stresses were also performed through LMM. The literature search and further selection yielded seven functional traits, extracted from 114 laboratory studies, including 888 observations and 110 plant species/cultivars. Evidence for significant effects of predictor variables (type of stress, AM symbiosis and/or their interaction) on functional trait response were found for leaf area ratio (LAR), root mass fraction (RMF) and root-shoot (R:S) ratio. Our results provided evidence to accept the hypothesis that AM fungal inoculation may reduce the stress response of these plant functional traits by decreasing its magnitude. We also found a weak correlation between stress responses of these traits and total biomass variation. Although our literature search and data collection were intensive and our results robust, the scope of our conclusions is limited by the agronomical bias of plant species targeted by the meta-analysis. Further knowledge on non-cultivable plant species and better understanding of the mechanisms ruling resources allocation in plants would allow more generalised conclusions.

A metabarcoding protocol targeting two DNA regions to analyze root-associated fungal communities in ferns and lycophytes

Premise

Detailed studies of the fungi associated with lycophytes and ferns provide crucial insights into the early evolution of land plants. However, most investigations to date have assessed fern-fungus interactions based only on visual root inspection. In the present research, we establish and evaluate a metabarcoding protocol to analyze the fungal communities associated with fern and lycophyte roots.

Methods

We used two primer pairs focused on the ITS rRNA region to screen the general fungal communities, and the 18S rRNA to target Glomeromycota fungi (i.e., arbuscular mycorrhizal fungi). To test these approaches, we collected and processed roots from 12 phylogenetically distant fern and lycophyte species.

Results

We found marked compositional differences between the ITS and 18S data sets. While the ITS data set demonstrated the dominance of orders Glomerales (phylum Glomeromycota), Pleosporales, and Helotiales (both in phylum Ascomycota), the 18S data set revealed the greatest diversity of Glomeromycota. Non-metric multidimensional scaling (NMDS) ordination suggested an important geographical effect in sample similarities.

Discussion

The ITS-based approach is a reliable and effective method to analyze the fungal communities associated with fern and lycophyte roots. The 18S approach is more appropriate for studies focused on the detailed screening of arbuscular mycorrhizal fungi.

Arbuscular mycorrhizal fungal communities with contrasting life-history traits influence host nutrient acquisition

Life-history traits differ substantially among arbuscular mycorrhizal (AM) fungal families, potentially affecting hyphal nutrient acquisition efficiency, host nutrition, and thereby plant health and ecosystem function. Despite these implications, AM fungal community life-history strategies and community trait diversity effects on host nutrient acquisition are poorly understood. To address this knowledge gap, we grew sudangrass with AM fungal communities representing contrasting life-history traits and diversity: either (1) five species in the AM family Gigasporaceae, representing competitor traits, (2) five Glomerales species, representing ruderal traits, or (3) a mixed-trait community combining all ten AM fungal species. After 12 weeks, we measured above and belowground plant biomass and aboveground nutrient uptake and concentration. Overall, AM fungal colonization increased host nutrition, biomass, and foliar δ⁵nitrogen enrichment compared to the uncolonized control. Between the single-trait communities, the Glomeraceae community generally outperformed the Gigasporaceae community in host nutrition and plant growth, increasing plant phosphorus (P) uptake 1.5 times more than the Gigasporaceae community. We saw weak evidence for a synergistic effect of the mixed community, which was only higher for plant P concentration (1.26 times higher) and root colonization (1.26 times higher) compared to the single-trait communities. However, this higher P concentration did not translate to more P uptake or the highest plant biomass for the mixed community. These findings demonstrate that the AM symbiosis is affected by community differences at high taxonomic levels and provide insight into how different AM fungal communities and their associated traits affect host nutrition for fast-growing plant species.

Effects of nitrogen addition and seasonal change on arbuscular mycorrhizal fungi community diversity in a poplar plantation

Arbuscular mycorrhizal (AM) fungi play a crucial role in carbon (C), nitrogen (N), and phosphorous (P) biogeochemical cycling. Therefore, it is essential to determine the seasonal responses of the AM fungal community to N addition to understanding better the ecological processes against a background of intensified N deposition. Based on an ongoing field simulation experiment with five N addition levels (0, 5, 10, 15, and 30 gN·m−2·a−1) in a 5-year-old poplar plantation at Dongtai Forest Farm in Yancheng, Jiangsu province, eastern China, soil physicochemical properties, the root colonization rate, and the rhizosphere soil AM fungal community diversity and composition in four seasons (summer, autumn, winter, and spring) were investigated. Meanwhile, the relationships between the characteristics of the AM fungal community and soil environmental factors were analyzed. High-throughput sequencing showed that the dominant genera in the poplar plantation were Glomus (average relative abundance 87.52%), Diversispora (9.62%), and Acaulospora (1.85%). The addition of N significantly increased the root colonization rate in spring. The diversity of the AM fungal community (Chao and Shannon indexes) was primarily affected by seasonal change rather than N addition, and the diversity in summer was significantly lower than in the other three seasons. Redundancy analysis showed that soil temperature, available P, total P, and pH significantly affected the structure of the AM fungal community. It can be concluded N addition primarily influenced the root colonization rate, whereas seasonal change had a notable effect on the AM fungal community diversity. Although seasonal change and N addition greatly influenced the composition, seasonal change exerted a more substantial effect than N addition. These results will improve our understanding of the underground ecological processes in poplar plantation ecosystems.

Glomerales Dominate Arbuscular Mycorrhizal Fungal Communities Associated with Spontaneous Plants in Phosphate-Rich Soils of Former Rock Phosphate Mining Sites

Arbuscular mycorrhizal fungi (AMF) are key drivers of soil functioning. They interact with multiple soil parameters, notably, phosphorus (P). In this work, AMF communities of native plants grown spontaneously on former mining sites either enriched (P sites) or not enriched with P (nP sites) by mining cuttings of rock phosphate (RP) were studied. No significant differences were observed in the root mycorrhizal rates of the plants when comparing P and nP sites. The assessment of AMF diversity and community structure using Illumina MiSeq metabarcoding and targeting 18S rDNA in roots and rhizospheric soils showed a total of 318 Amplicon Sequence Variants (ASVs) of Glomeromycota phylum. No significant difference in the diversity was found between P and nP sites. Glomeraceae species were largely dominant, formed a fungal core of 26 ASVs, and were persistent and abundant in all sites. In the P soils, eight ASVs were identified by indicator species analysis. A trend towards an increase in Diversisporaceae and Claroideoglomeraceae and a reduction in Paraglomeraceae and Glomeraceae were noticed. These results provide new insights into AMF ecology in former RP mining sites; they document that P concentration is a driver of AMF community structures in soils enriched in RP long term but also suggest an influence of land disturbance, ecosystem self-restoration, and AMF life history strategies as drivers of AMF community profiles.

A new order, Entrophosporales, and three new Entrophospora species in Glomeromycota

As a result of phylogenomic, phylogenetic, and morphological analyses of members of the genus Claroideoglomus, four potential new glomoid spore-producing species and Entrophospora infrequens, a new order, Entrophosporales, with one family, Entrophosporaceae (=Claroideoglomeraceae), was erected in the phylum Glomeromycota. The phylogenomic analyses recovered the Entrophosporales as sister to a clade formed by Diversisporales and Glomeraceae. The strongly conserved entrophosporoid morph of E. infrequens, provided with a newly designated epitype, was shown to represent a group of cryptic species with the potential to produce different glomoid morphs. Of the four potential new species, three enriched the Entrophosporales as new Entrophospora species, E. argentinensis, E. glacialis, and E. furrazolae, which originated from Argentina, Sweden, Oman, and Poland. The fourth fungus appeared to be a glomoid morph of the E. infrequens epitype. The physical association of the E. infrequens entrophosporoid and glomoid morphs was reported and illustrated here for the first time. The phylogenetic analyses, using nuc rDNA and rpb1 concatenated sequences, confirmed the previous conclusion that the genus Albahypha in the family Entrophosporaceae sensu Oehl et al. is an unsupported taxon. Finally, the descriptions of the Glomerales, Entrophosporaceae, and Entrophospora were emended and new nomenclatural combinations were introduced.

Composition and seasonal variation of the arbuscular mycorrhizal fungi spore community in litter, root mat, and soil from a subtropical rain forest

Community composition and seasonal variation of sporulation of arbuscular mycorrhizal fungi (AMF) have been studied in soils from many ecosystems including subtropical forest. Yet, AMF community composition has been surveyed only from the mineral soil but not from the litter layer and the root mat, and long-term variation in sporulation is not fully understood. We sampled a 75-m² plot from a subtropical forest to determine AMF community composition in the following habitats: the litter layer, the root mat, and the mineral soil. Moreover, samples were taken in fall, winter, spring, and summer over a 2-year period to follow the seasonal variation of AMF sporulation. We detected 47 AMF species belonging to six families and 14 genera, Glomeraceae and Acaulosporaceae being the most represented families. Sixteen species were common to all three habitats, five species were shared between two habitats, and 26 species were recovered exclusively from single habitats. While species richness was not significantly different among habitats, AMF total spore numbers were significantly higher in the litter and root mat compared to the soil. PERMANOVA did not detect a significant effect of habitats on community composition when species presence/absence was considered, but significant differences between litter versus soil and root mat versus soil were detected when spore abundance was considered. A seasonal pattern of spore abundance for species was not observed over the 2-year sampling period regardless of habitat. This study revealed that (i) different AMF species sporulate in the different habitats; thus, field surveys considering only the mineral soil might underestimate species richness and (ii) AMF species sporulate asynchronously in subtropical forest.

Clonal spore populations in sporocarps of arbuscular mycorrhizal fungi

Some arbuscular mycorrhizal (AM) fungal species known to form sporocarps (i.e., aggregations of spores) are polyphyletic in two orders, Glomerales and Diversisporales. Spore clusters (sporocarp-like structures) often formed in pot cultures or in vitro conditions are supposed to be clonal populations, while sporocarps in natural habitats with a fungal peridium are morphologically similar to those of epigeous sexual (zygosporic) sporocarps of Endogone species. Thus, in this study, we explored the genetics of sporocarpic spores of two AM fungi with a view to possibilities of clonal or sexual reproduction during sporocarps formation. To examine these possibilities, we investigated single-nucleotide polymorphisms (SNPs) in reduced genomic libraries of spores isolated from sporocarps molecularly identified as Rhizophagus irregularis and Diversispora epigaea. In addition, partial sequences of the MAT locus HD2 gene of R. irregularis were phylogenetically analyzed to determine the nuclear status of the spores. We found that most SNPs were shared among the spores isolated from each sporocarp in both species. Furthermore, all HD2 sequences from spores isolated from three R. irregularis sporocarps were identical. These results indicate that those sporocarps comprise clonal spores. Therefore, sporocarps with clonal spores may have different functions than sexual reproduction, such as massive spore production or spore dispersal via mycophagy.

The efficiency of arbuscular mycorrhiza in increasing tolerance of Triticum aestivum L. to alkaline stress

BACKGROUND

Evaluation of native soil microbes is a realistic way to develop bio-agents for ecological restoration. Soil alkalinity, which has a high pH, is one of the most common concerns in dry and semi-arid climates. Alkaline soils face problems due to poor physical properties, which affect plant growth and crop production. A pot experiment was carried out to investigate the impact of native mycorrhizal fungi (AMF) on the wheat plant (Triticum aestivum L.) under two levels of alkalinity stress -T1 (37 mM NaHCO3), T2 (74 mM NaHCO3) - at two developmental stages (the vegetative and productive stages).

RESULTS

Alkalinity stress significantly inhibited the germination percentage, plant biomass, photosynthetic pigments, and some nutrients (K, N, and P). Mycorrhizal inoculation improved growth parameters and productivity of wheat-stressed plants. However, lipid peroxidation was significantly lowered in mycorrhizal-inoculated plants compared to non-inoculated plants. Catalase and peroxidase were inhibited in wheat leaves and roots by alkalinity, while mycorrhiza promoted the activity of these enzymes.

CONCLUSION

The results of this study demonstrated that alkalinity stress had highly negative effects on some growth parameters of the wheat plant, while AMF inoculation attenuated these detrimental effects of alkalinity stress at two stages by reducing the pH and Na concentration and increasing the availability of P and the productivity of wheat in particular crop yield parameters.

The effects of arbuscular mycorrhizal fungal species and taxonomic groups on stressed and unstressed plants: a global meta-analysis

The great majority of plants gain access to soil nutrients and enhance their performance under stressful conditions through symbiosis with arbuscular mycorrhizal fungi (AMF). The benefits that AMF confer vary among species and taxonomic groups. However, a comparative analysis of the different benefits among AMF has not yet been performed. We conducted a global meta-analysis of recent studies testing the benefits of individual AMF species and main taxonomic groups in terms of plant performance (growth and nutrition). Separately, we examined AMF benefits to plants facing biotic (pathogens, parasites, and herbivores) and abiotic (drought, salinity, and heavy metals) stress. AMF had stronger positive effects on phosphorus nutrition than on plant growth and nitrogen nutrition and the effects on the growth of plants facing biotic and abiotic stresses were similarly positive. While the AMF taxonomic groups showed positive effects on plant performance either with or without stress, Diversisporales were the most beneficial to plants without stress and Gigasporales to plants facing biotic stress. Our results provide a comprehensive analysis of the benefits of different AMF species and taxonomic groups on plant performance and useful insights for their management and use as bio-inoculants for agriculture and restoration.

Mycorrhizae Helper Bacteria: Unlocking Their Potential as Bioenhancers of Plant-Arbuscular Mycorrhizal Fungal Associations

The dynamic interactions of plants and arbuscular mycorrhizal fungi (AMF) that facilitate the efficient uptake of minerals from soil and provide protection from various environmental stresses (biotic and abiotic) are now also attributed to a third component of the symbiosis. These are the less investigated mycorrhizae helper bacteria (MHB), which constitute a dense, active bacterial community, tightly associated with AMF, and involved in the development and functioning of AMF. Although AMF spores are known to host several bacteria in their spore walls and cytoplasm, their role in promoting the ecological fitness and establishment of AMF symbiosis by influencing spore germination, mycelial growth, root colonization, metabolic diversity, and biocontrol of soil borne diseases is now being deciphered. MHB also promote the functioning of arbuscular mycorrhizal symbiosis by triggering various plant growth factors, leading to better availability of nutrients in the soil and uptake by plants. In order to develop strategies to promote mycorrhization by AMF, and particularly to stimulate the ability to utilize phosphorus from the soil, there is a need to decipher crucial metabolic signalling pathways of MHB and elucidate their functional significance as mycorrhiza helper bacteria. MHB, also referred to as AMF bioenhancers, also improve agronomic efficiency and formulations using AMF along with enriched population of MHB are a promising option. This review covers the aspects related to the specificity and mechanisms of action of MHB, which positively impact the formation and functioning of AMF in mycorrhizal symbiosis, and the need to advocate MHB as AMF bioenhancers towards their inclusion in integrated nutrient management practices in sustainable agriculture.

Influence of different irrigation methods on the alfalfa rhizosphere soil fungal communities in an arid region

Xinjiang is the largest arid and saline agricultural region in China. The common irrigation methods in this area are traditional flood irrigation and drip irrigation. In this study, we investigated the effects of these two irrigation methods on the fungal diversity, community structures, and functions in alfalfa rhizosphere soil as well as the associated environmental factors in northern Tianshan Mountain (Xinjiang, China). Soil enzyme activities (urease and neutral phosphatase) were significantly higher in the drip-irrigated alfalfa rhizosphere soil than in the flood-irrigated alfalfa rhizosphere soil, whereas the fungal alpha diversity in the drip-irrigated alfalfa rhizosphere soil was significantly lower than that in the flood-irrigated alfalfa rhizosphere soil. Six dominant fungal phyla were identified (>0.1%), with Ascomycota being the most abundant in all soils, followed by Basidiomycota (5.47%), Mortierellomycota (1.07%), Glomeromycota (0.55%), Rozellomycota (0.27%), and Chytridiomycota (0.14%). Ascomycota and Glomeromycota species were significantly less abundant in drip-irrigated alfalfa rhizosphere soil than in flood-irrigated alfalfa rhizosphere soil. A LEFSe analysis identified Cladosporiaceae (20.8%) species as the most abundant marker fungi in drip-irrigated alfalfa rhizosphere soil. Of the 13 fungal functional groups identified on the basis of the functional annotation using the FUNGuild database, Ectomycorrhizal (22.29%) was the primary functional group. Compared with flood irrigation, drip irrigation significantly decreased the relative abundance of Ectomycorrhizal and Arbuscular_Mycorrhizal, while increasing the relative abundance of Plant_Pathogen, although not significantly (P = 0.19). Available potassium was revealed to be the main environmental factor influencing soil enzyme activities, fungal alpha diversity, fungal community structures, and fungal functions in response to the different irrigation methods. In conclusion, drip irrigation may be more appropriate than flood irrigation in the Tianshan dryland agricultural area for enhancing soil enzyme activities, but it may also increase the abundance of plant pathogenic fungi in the soil.

Early branching arbuscular mycorrhizal fungus Paraglomus occultum carries a small and repeat-poor genome compared to relatives in the Glomeromycotina

The arbuscular mycorrhizal fungi (AMFs) are obligate root symbionts in the subphylum Glomeromycotina that can benefit land plants by increasing their soil nutrient uptake in exchange for photosynthetically fixed carbon sources. To date, annotated genome data from representatives of the AMF orders Glomerales, Diversisporales and Archaeosporales have shown that these organisms have large and highly repeated genomes, and no genes to produce sugars and fatty acids. This led to the hypothesis that the most recent common ancestor (MRCA) of Glomeromycotina was fully dependent on plants for nutrition. Here, we aimed to further test this hypothesis by obtaining annotated genome data from a member of the early diverging order Paraglomerales (Paraglomus occultum). Genome analyses showed this species carries a 39.6 Mb genome and considerably fewer genes and repeats compared to most AMF relatives with annotated genomes. Consistent with phylogenies based on ribosomal genes, our phylogenetic analyses suggest P. occultum as the earliest diverged branch within Glomeromycotina. Overall, our analyses support the view that the MRCA of Glomeromycotina carried hallmarks of obligate plant biotrophy. The small genome size and content of P. occultum could either reflect adaptive reductive processes affecting some early AMF lineages, or indicate that the high gene and repeat family diversity thought to drive AMF adaptability to host and environmental change was not an ancestral feature of these prominent plant symbionts.

Arbuscular mycorrhizal fungi conducting the hyphosphere bacterial orchestra

More than two-thirds of terrestrial plants acquire nutrients by forming a symbiosis with arbuscular mycorrhizal (AM) fungi. AM fungal hyphae recruit distinct microbes into their hyphosphere, the narrow region of soil influenced by hyphal exudates. They thereby shape this so-called second genome of AM fungi, which significantly contributes to nutrient mobilization and turnover. We summarize current insights into characteristics of the hyphosphere microbiome and the role of hyphal exudates on orchestrating its composition. The hyphal exudates not only contain carbon-rich compounds but also promote bacterial growth and activity and influence the microbial community structure. These effects lead to shifts in function and cause changes in organic nutrient cycling, making the hyphosphere a unique and largely overlooked functional zone in ecosystems.

Effects of Antimony on Rice Growth and Its Existing Forms in Rice Under Arbuscular Mycorrhizal Fungi Environment

Arbuscular mycorrhizal fungi (AMF) can form symbiotic relationships with most terrestrial plants and regulate the uptake and distribution of antimony (Sb) in rice. The effect of AMF on the uptake and transport of Sb in rice was observed using pot experiments in the greenhouse. The results showed that AMF inoculation increased the contact area between roots and metals by forming mycelium, and changed the pH and Eh of the root soil, leading to more Sb entering various parts of the rice, especially at an Sb concentration of 1,200 mg/kg. The increase in metal toxicity further led to a decrease in the rice chlorophyll content, which directly resulted in a 22.7% decrease in aboveground biomass, 21.7% in underground biomass, and 11.3% in grain biomass. In addition, the antioxidant enzyme results showed that inoculation of AMF decreased 22.3% in superoxide dismutase, 9.9% in catalase, and 20.7% in peroxidase compared to the non-inoculation groups, further verifying the negative synergistic effect of AMF inoculation on the uptake of Sb in rice. The present study demonstrated the effect of AMF on the uptake and transport of Sb in the soil–rice system, facilitating future research on the related mechanism in the soil–rice system under Sb stress.

Roles of Arbuscular Mycorrhizal Fungi on Soil Fertility: Contribution in the Improvement of Physical, Chemical, and Biological Properties of the Soil

Many of the world's soils are experiencing degradation at an alarming rate. Climate change and some agricultural management practices, such as tillage and excessive use of chemicals, have all contributed to the degradation of soil fertility. Arbuscular Mycorrhizal Fungi (AMFs) contribute to the improvement of soil fertility. Here, a short review focusing on the role of AMF in improving soil fertility is presented. The aim of this review was to explore the role of AMF in improving the chemical, physical, and biological properties of the soil. We highlight some beneficial effects of AMF on soil carbon sequestration, nutrient contents, microbial activities, and soil structure. AMF has a positive impact on the soil by producing organic acids and glomalin, which protect from soil erosion, chelate heavy metals, improve carbon sequestration, and stabilize soil macro-aggregation. AMF also recruits bacteria that produce alkaline phosphatase, a mineralization soil enzyme associated with organic phosphorus availability. Moreover, AMFs influence the composition, diversity, and activity of microbial communities in the soil through mechanisms of antagonism or cooperation. All of these AMF activities contribute to improve soil fertility. Knowledge gaps are identified and discussed in the context of future research in this review. This will help us better understand AMF, stimulate further research, and help in sustaining the soil fertility.

Combined Bioremediation of Bensulfuron-Methyl Contaminated Soils With Arbuscular Mycorrhizal Fungus and Hansschlegelia zhihuaiae S113

Over the past decades, because of large-scale bensulfuron-methyl (BSM) application, environmental residues of BSM have massively increased, causing severe toxicity in rotation-sensitive crops. The removal of BSM from the environment has become essential. In this study, the combined bioremediation of the arbuscular mycorrhizal fungi (AMF) Rhizophagus intraradices and BSM-degrading strain Hansschlegelia zhihuaiae S113 of BSM-polluted soil was investigated. BSM degradation by S113 in the maize rhizosphere could better promote AMF infection in the roots of maize, achieving an infection rate of 86.70% on the 36th day in the AMF + S113 + BSM group. Similarly, AMF enhanced the colonization and survival of S113 in maize rhizosphere, contributing 4.65 × 105 cells/g soil on the 15th day and 3.78 × 104 cells/g soil on the 20th day to a population of colonized-S113 (based possibly on the strong root system established by promoting plant-growth AMF). Both S113 and AMF coexisted in rhizosphere soil. The BSM-degrading strain S113 could completely remove BSM at 3 mg/kg from the maize rhizosphere soil within 12 days. AMF also promoted the growth of maize seedlings. When planted in BSM-contaminated soil, maize roots had a fresh weight of 2.59 ± 0.26 g in group S113 + AMF, 2.54 ± 0.20 g in group S113 + AMF + BSM, 2.02 ± 0.16 g in group S113 + BSM, and 2.61 ± 0.25 g in the AMF group, all of which exceeded weights of the control group on the 36th day except for the S113 + BSM group. Additionally, high-throughput sequencing results indicated that simultaneous inoculation with AMF and strain S113 of BSM-polluted maize root-soil almost left the indigenous bacterial community diversity and richness in maize rhizosphere soil unaltered. This represents a major advantage of bioremediation approaches resulting from the existing vital interactions among local microorganisms and plants in the soil. These findings may provide theoretical guidance for utilizing novel joint-bioremediation technologies, and constitute an important contribution to environmental pollution bioremediation while simultaneously ensuring crop safety and yield.

The Native Arbuscular Mycorrhizal Fungi and Vermicompost-Based Organic Amendments Enhance Soil Fertility, Growth Performance, and the Drought Stress Tolerance of Quinoa

The present study aimed to determine the effects of biostimulants on the physicochemical parameters of the agricultural soil of quinoa under two water regimes and to understand the mode of action of the biostimulants on quinoa for drought adaptation. We investigated the impact of two doses of vermicompost (5 and 10 t/ha) and arbuscular mycorrhizal fungi applied individually, or in joint application, on attenuating the negative impacts of water shortage and improving the agro-physiological and biochemical traits of quinoa, as well as soil fertility, under two water regimes (well-watered and drought stress) in open field conditions. Exposure to drought decreased biomass, leaf water potential, and stomatal conductance, and increased malondialdehyde and hydrogen peroxide content. Mycorrhiza and/or vermicompost promoted plant growth by activating photosynthesis machinery and nutrient assimilation, leading to increased total soluble sugars, proteins, and antioxidant enzyme activities in the leaf and root. After the experiment, the soil's total organic matter, phosphorus, nitrogen, calcium, and soil glomalin content improved by the single or combined application of mycorrhiza and vermicompost. This knowledge suggests that the combination of mycorrhiza and vermicompost regulates the physiological and biochemical processes employed by quinoa in coping with drought and improves the understanding of soil-plant interaction.

Zinc nutrition and arbuscular mycorrhizal symbiosis effects on maize (Zea mays L.) growth and productivity

Zinc (Zn) is an essential micronutrient required to enhance crop growth and yield. In the arid – semiarid region, Zn deficiency is expected due to alkaline calcareous soil. Contrarily, Zn toxicity is also becoming an environmental concern due to increasing anthropogenic activities (metal smelting, copper industry, etc.). Therefore, balanced Zn application is necessary to save resources and achieve optimum crop growth and yield. Most scientists suggest biological approaches to overcome the problem of Zn toxicity and deficiency. These biological approaches are mostly environment-friendly and cost-effective. In these biological approaches, the use of arbuscular mycorrhizae fungi (AMF) symbiosis is becoming popular. It can provide tolerance to the host plant against Zn-induced stress. Inoculation of AMF helps in balance uptake of Zn and enhances the growth and yield of crops. On the other hand, maize (Zea mays L.) is an important cereal crop due to its multifarious uses. As maize is an effective host for mycorrhizae symbiosis, that’s why this review was written to elaborate on the beneficial role of arbuscular mycorrhizal fungi (AMF). The review aimed to glance at the recent advances in the use of AMF to enhance nutrient uptake, especially Zn. It was also aimed to discuss the mechanism of AMF to overcome the toxic effect of Zn. We have also discussed the detailed mechanism and physiological improvement in the maize plant. In conclusion, AMF can play an imperative role in improving maize growth, yield, and balance uptake of Zn by alleviating Zn stress and mitigating its toxicity.

Biogeographic Patterns of Arbuscular Mycorrhizal Fungal Communities Along a Land-Use Intensification Gradient in the Subtropical Atlantic Forest Biome

Information concerning arbuscular mycorrhizal (AM) fungal geographical distribution in tropical and subtropical soils from the Atlantic Forest (a global hotspot of biodiversity) are scarce and often restricted to the evaluation of richness and abundance of AM fungal species at specific ecosystems or local landscapes. In this study, we hypothesized that AM fungal diversity and community composition in subtropical soils would display fundamental differences in their geographical patterns, shaped by spatial distance and land-use change, at local and regional scales. AM fungal community composition was examined by spore-based taxonomic analysis, using soil trap cultures. Acaulospora koskei and Glomus were found as generalists, regardless of mesoregions and land uses. Other Acaulospora species were also found generalists within mesoregions. Land-use change and intensification did not influence AM fungal composition, partially rejecting our first hypothesis. We then calculated the distance-decay of similarities among pairs of AM fungal communities and the distance-decay relationship within and over mesoregions. We also performed the Mantel test and redundancy analysis to discriminate the main environmental drivers of AM fungal diversity and composition turnover. Overall, we found significant distance-decays for all land uses. We also observed a distance-decay relationship within the mesoregion scale (< 104 km) and these changes were correlated mainly to soil type (not land use), with the secondary influence of both total organic carbon and clay contents. AM fungal species distribution presented significant distance-decays, regardless of land uses, which was indicative of dispersal limitation, a stochastic neutral process. Although, we found evidence that, coupled with dispersal limitation, niche differentiation also played a role in structuring AM fungal communities, driven by long-term historical contingencies, as represented by soil type, resulting from different soil origin and mineralogy across mesoregions.