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Summary: Arbuscular mycorrhizal fungi (AMF) are ubiquitous plant root symbionts, which can house two endobacteria: Ca. Moeniiplasma glomeromycotorum (CaMg) and Ca. Glomeribacter gigasporarum (CaGg). However, little is known about their distribution and population structure in natural AMF populations and whether AMF can harbour other endobacteria.We isolated AMF from two environments and conducted detailed analyses of endobacterial communities associated with surface‐sterilised AMF spores.Consistent with the previous reports, we found that CaMg were extremely abundant (80%) and CaGg were extremely rare (2%) in both environments. Unexpectedly, we discovered an additional and previously unknown level of bacterial diversity within AMF spores, which extended beyond the known endosymbionts, with bacteria belonging to 10 other phyla detected across our spore data set. Detailed analysis revealed that: CaGg were not limited in distribution to the Gigasporaceae family of AMF, as previously thought; CaMg population structure was driven by AMF host genotype; and a significant inverse correlation existed between the diversity of CaMg and diversity of all other endobacteria.Based on these data, we generate novel testable hypotheses regarding the function of CaMg in AMF biology by proposing that they might act as conditional mutualists of AMF. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) provide plants with vital mineral nutrients and co‐exist inside the roots alongside a complex community of bacterial endophytes. These co‐existing AMF and bacterial root communities have been studied individually and are known to be influenced in structure by different environmental parameters. However, the extent to which they are affected by environmental parameters and by each other is completely unknown. The current study addressed this knowledge gap by characterising AMF and bacterial communities inside plant roots from a natural and an agricultural ecosystem. Using multivariate modelling, the relative contribution of environmental parameters in structuring the two communities was quantified at different spatial scales. Using this model, it was possible to then remove the contribution of environmental parameters and show that the co‐existing AMF and bacterial communities were significantly correlated with each other, explaining up to 36% of each other's variance. Notably, this was not due to the presence of know AMF endobacteria, as removal of endobacterial reads maintained the significance of correlation. These findings provide the first empirical evidence of a selective and bi‐directional relationship between AMF and bacteria co‐inhibiting plant roots and indicate that a significant fraction of this covariation is due to biological and ecological interactions between them. [ABSTRACT FROM AUTHOR]

The availability of global microbial diversity data, collected using standardized metabarcoding techniques, makes microorganisms promising models for investigating the role of regional and local factors in driving biodiversity., Here we modelled the global diversity of symbiotic arbuscular mycorrhizal ( AM) fungi using currently available data on AM fungal molecular diversity (small subunit ( SSU) ribosomal RNA ( rRNA) gene sequences) in field samples. To differentiate between regional and local effects, we estimated species pools (sets of potentially suitable taxa) for each site, which are expected to reflect regional processes. We then calculated community completeness, an index showing the fraction of the species pool present, which is expected to reflect local processes., We found significant spatial variation, globally in species pool size, as well as in local and dark diversity (absent members of the species pool). Species pool size was larger close to areas containing tropical grasslands during the last glacial maximum, which are possible centres of diversification. Community completeness was greater in regions of high wilderness (remoteness from human disturbance). Local diversity was correlated with wilderness and current connectivity to mountain grasslands., Applying the species pool concept to symbiotic fungi facilitated a better understanding of how biodiversity can be jointly shaped by large-scale historical processes and recent human disturbance. [ABSTRACT FROM AUTHOR]

This article is a Commentary on Rasmussen et al., 220: 1247–1260. [ABSTRACT FROM AUTHOR]

The role of arbuscular mycorrhizal fungi (AMF) in resisting surface flow soil erosion has never been tested experimentally. We set up a full factorial greenhouse experiment using Achillea millefolium with treatments consisting of addition of AMF inoculum and non-microbial filtrate, non-AMF inoculum and microbial filtrate, AMF inoculum and microbial filtrate, and non-AMF inoculum and non-microbial filtrate (control) which were subjected to a constant shear stress in the form of surface water flow to quantify the soil detachment rate through time. We found that soil loss can be explained by the combined effect of roots and AMF extraradical hyphae and we could disentangle the unique effect of AMF hyphal length, which significantly reduced soil loss, highlighting their potential importance in riparian systems. [ABSTRACT FROM AUTHOR]

Next-generation sequencing technologies with markers covering the full Glomeromycota phylum were used to uncover phylogenetic community structure of arbuscular mycorrhizal fungi (AMF) associated with Festuca brevipila. The study system was a semi-arid grassland with high plant diversity and a steep environmental gradient in pH, C, N, P and soil water content. The AMF community in roots and rhizosphere soil were analyzed separately and consisted of 74 distinct operational taxonomic units (OTUs) in total. Community-level variance partitioning showed that the role of environmental factors in determining AM species composition was marginal when controlling for spatial autocorrelation at multiple scales. Instead, phylogenetic distance and spatial distance were major correlates of AMF communities: OTUs that were more closely related (and which therefore may have similar traits) were more likely to co-occur. This pattern was insensitive to phylogenetic sampling breadth. Given the minor effects of the environment, we propose that at small scales closely related AMF positively associate through biotic factors such as plant-AMF filtering and interactions within the soil biota. [ABSTRACT FROM AUTHOR]

Plant-soil microbial interactions have moved into focus as an important mechanism for understanding plant coexistence and composition of communities. Both arbuscular mycorrhizal (AM) as well as other root endophytic fungi co-occur in plant roots, and therefore have the potential to influence relative abundances of plant species in local assemblages. However, no study has experimentally examined how these key root endosymbiont groups might interact and affect plant community composition. Here, using an assemblage of five plant species in mesocosms in a fully factorial experiment, we added an assemblage of AM fungi and/or a mixture of root endophytic fungal isolates, all obtained from the same grassland field site. The results demonstrate that the AM fungi and root endophytes interact to affect plant community composition by changing relative species abundance, and consequently aboveground productivity. Our study highlights the need to explicitly consider interactions of root-inhabiting fungal groups in studies of plant assemblages. [ABSTRACT FROM AUTHOR]

Aims: Arbuscular mycorrhizal (AM) fungi, a group of obligate symbionts of terrestrial plants, have a global distribution range. Yet, we lack concrete synthetic and empirical evidence that could reveal whether distinct ecological niches are distributed across Glomeromycota through determining linkages between environmental factors and the distribution of these taxa. Methods: We have modelled the probability of occurrence of Gigasporaceae and Acaulosporaceae as a function of candidate environmental factors. These families are among the most common but non-ubiquitous taxa in AM-driven ecosystems. We have constructed our database using studies with a global scope and carried out our analysis through a logistic regression approach. Results: The probability of occurrence of Acaulosporacae increased in acidic environments and soils with high bulk density. By contrast, a key factor that affected probability of occurrence of Gigasporaceae was precipitation. Conclusions: Through the analysis of an unprecedentedly large amount of data we could infer that niche processes mediate occurrence of a group of fungi at scales broader than the local scale of the individual studies gathered in the analysed dataset. Knowledge of well-supported niche features could enhance discovery of new taxa of AM fungi, and would facilitate development of study designs with greater ecological realism. [ABSTRACT FROM AUTHOR]

Abstract: The study of interrelationships between soil structure and its functional properties is complicated by the fact that the quantitative description of soil structure is challenging. Soil scientists have tackled this challenge by taking advantage of approaches such as fractal geometry, which describes soil architectural complexity through a scaling exponent (D) relating mass and numbers of particles/aggregates to particle/aggregate size. Typically, soil biologists use empirical indices such as mean weight diameters (MWD) and percent of water stable aggregates (WSA), or the entire size distribution, and they have successfully related these indices to key soil features such as C and N dynamics and biological promoters of soil structure. Here, we focused on D, WSA and MWD and we tested whether: D estimated by the exponent of the power law of number-size distributions is a good and consistent correlate of MWD and WSA; D carries information that differs from MWD and WSA; the fraction of variation in D that is uncorrelated with MWD and WSA is related to soil chemical and biological properties that are thought to establish interdependence with soil structure (e.g., organic C, N, arbuscular mycorrhizal fungi). We analysed observational data from a broad scale field study and results from a greenhouse experiment where arbuscular mycorrhizal fungi (AMF) and collembola altered soil structure. We were able to develop empirical models that account for a highly significant and large portion of the correlation observed between WSA and MWD but we did not uncover the mechanisms that underlie this correlation. We conclude that most of the covariance between D and soil biotic (AMF, plant roots) and abiotic (C, N) properties can be accounted for by WSA and MWD. This result implies that the ecological effects of the fragmentation properties described by D and generally discussed under the framework of fractal models can be interpreted under the intuitive perspective of simpler indices and we suggest that the biotic components mostly impacted the largest size fractions, which dominate MWD, WSA and the scaling exponent ruling number-size distributions. [Copyright &y& Elsevier]

A letter to the editor is presented related to the fungi arbuscular mycorrhizal.

The article focuses the use of network theory in understanding the nature arbuscular mycorrhizal (AM) fungi-plant interactions. It discusses Chagnon and colleagues and Montesinos-Navarro and colleagues' research and arguments concerning bipartite networks. It also recall the basic theory on interaction matrix and the basic facts implying that co-occurrence ≠ interaction.

Abstract: Soil aggregation is a principal ecosystem process mediated by soil biota. Collembola and arbuscular mycorrhizal (AM) fungi are important groups in the soil, and can interact in various ways. Few studies have examined collembola effects on soil aggregation, while many have quantified AM effects. Here, we asked if collembola have any effect on soil aggregation, and if they alter AM fungi-mediated effects on soil aggregation. We carried out a factorial greenhouse study, manipulating the presence of both collembola and AM fungi, using two different plant species, Sorghum vulgare and Daucus carota. We measured root length and biomass, AMF (and non-AMF) soil hyphal length, root colonization, and collembolan populations, and quantified water stable soil aggregates (WSA) in four size classes. Soil exposed to growth of AMF hyphae and collembola individually had higher WSA than control treatments. Moreover, the interaction effects between AMF and collembola were significant, with non-additive increases in the combined application compared to the single treatments. Our findings show that collembola can play a crucial role in maintaining ecological sustainability through promoting soil aggregation, and point to the importance of considering organism interactions in understanding formation of soil structure. [Copyright &y& Elsevier]

Arbuscular mycorrhizal fungi are recognized as important drivers of plant health and productivity in agriculture but very often existing knowledge is limited to the topsoil. With growing interest in the role of subsoil in sustainable agriculture, we used high-throughput Illumina sequencing on a set of samples encompassing drilosphere, rhizosphere and bulk soil, in both top- and subsoil. Our results show subsoil AMF communities harbor unique Operational Taxonomic Units (OTUs) and that both soil depths differ in community structure both at the OTU and family level. Our results emphasize the distinctness of subsoil AMF communities and the potential role of subsoil as a biodiversity reservoir. [ABSTRACT FROM AUTHOR]