Arbuscular mycorrhizal fungi increase grain yields: a meta-analysis

TaLAC129 is a negative regulator of arbuscular mycorrhizal symbiosis but enhanced the growth and yield of bread wheat

Arbuscular mycorrhizal (AM) symbiosis enhances nutrient acquisition and stress resilience in plants, yet the genetic mechanisms regulating this interaction in wheat remain poorly understood. This study explores the variation in AM colonization rates across a diverse set of wheat varieties and aims to identify key genes that regulate the wheat-AM symbiosis. Understanding these molecular mechanisms is crucial for improving nutrient uptake efficiency and stress resistance in wheat breeding programs. Here, we conducted a genome-wide association study (GWAS) of 291 wheat varieties and integrated transcriptomic data to identify TaLAC129, a laccase (LAC)-encoding gene, as a critical negative regulator of AM colonization in wheat roots. Overexpression of TaLAC129 significantly increased root LAC activity and lignin content, concurrently suppressing AM colonization. While this suppression reduced nitrogen (N), phosphorus (P), and potassium (K) uptake in stems, leaves, and glumes, it markedly enhanced nutrient utilization efficiency (NUE) in grains. Furthermore, TaLAC129 overexpression improved agronomic traits, including grains per panicle, 1000-grain weight, and overall yield. Our findings reveal the dual role of TaLAC129 in balancing AM symbiosis and nutrient allocation, offering a novel genetic target for breeding wheat varieties with improved yield and nutrient efficiency. This study provides critical insights into the molecular coordination between symbiotic trade-offs and agricultural productivity in cereal crops.

Symbiotic synergy: How Arbuscular Mycorrhizal Fungi enhance nutrient uptake, stress tolerance, and soil health through molecular mechanisms and hormonal regulation

Arbuscular Mycorrhizal (AM) symbiosis is integral to sustainable agriculture and enhances plant resilience to abiotic and biotic stressors. Through their symbiotic association with plant roots, AM improves nutrient and water uptake, activates antioxidant defenses, and facilitates hormonal regulation, contributing to improved plant health and productivity. Plants release strigolactones, which trigger AM spore germination and hyphal branching, a process regulated by genes, such as D27, CCD7, CCD8, and MAX1. AM recognition by plants is mediated by receptor-like kinases (RLKs) and LysM domains, leading to the formation of arbuscules that optimize nutrient exchange. Hormonal regulation plays a pivotal role in this symbiosis; cytokinins enhance AM colonization, auxins support arbuscule formation, and brassinosteroids regulate root growth. Other hormones, such as salicylic acid, gibberellins, ethylene, jasmonic acid, and abscisic acid, also influence AM colonization and stress responses, further bolstering plant resilience. In addition to plant health, AM enhances soil health by improving microbial diversity, soil structure, nutrient cycling, and carbon sequestration. This symbiosis supports soil pH regulation and pathogen suppression, offering a sustainable alternative to chemical fertilizers and improving soil fertility. To maximize AM 's potential of AM in agriculture, future research should focus on refining inoculation strategies, enhancing compatibility with different crops, and assessing the long-term ecological and economic benefits. Optimizing AM applications is critical for improving agricultural resilience, food security, and sustainable farming practices.

Considerations for Domestication of Novel Strains of Filamentous Fungi

Fungi, especially filamentous fungi, are a relatively understudied, biotechnologically useful resource with incredible potential for commercial applications. These multicellular eukaryotic organisms have long been exploited for their natural production of useful commodity chemicals and proteins such as enzymes used in starch processing, detergents, food and feed production, pulping and paper making and biofuels production. The ability of filamentous fungi to use a wide range of feedstocks is another key advantage. As chassis organisms, filamentous fungi can express cellular machinery, and metabolic and signal transduction pathways from both prokaryotic and eukaryotic origins. Their genomes abound with novel genetic elements and metabolic processes that can be harnessed for biotechnology applications. Synthetic biology tools are becoming inexpensive, modular, and expansive while systems biology is beginning to provide the level of understanding required to design increasingly complex synthetic systems. This review covers the challenges of working in filamentous fungi and offers a perspective on the approaches needed to exploit fungi as microbial cell factories.

Mechanisms of cooperation in the plants-arbuscular mycorrhizal fungi-bacteria continuum

In nature, cooperation is an essential way for species, whether they belong to the same kingdom or to different kingdoms, to overcome the scarcity of resources and improve their fitness. Arbuscular mycorrhizal fungi are symbiotic microorganisms whose origin date back 400 million years. They form symbiotic associations with the vast majority of terrestrial plants, helping them to obtain nutrients from the soil in exchange for carbon. At the more complex level, soil bacteria participate in the symbiosis between arbuscular mycorrhizal fungi and plants: they obtain carbon from the exudation of hyphae connected to the roots and compensate for the limited saprophytic capacity of arbuscular mycorrhizal fungi by mineralizing organic compounds. Therefore, plants, arbuscular mycorrhizal fungi and soil bacteria constitute a continuum that may be accompanied by multiple forms of cooperation. In this review, we first analyzed the functional complementarities and differences between plants and arbuscular mycorrhizal fungi in arbuscular mycorrhizal symbiosis. Secondly, we discussed the resource exchange relationship between plants and arbuscular mycorrhizal fungi from the perspective of biological market theory and "surplus carbon" hypothesis. Finally, on the basis of mechanisms for maintaining cooperation, direct and indirect reciprocity in the hyphosphere, induced by the availability of external resource and species fitness, were examined. Exploring these reciprocal cooperations will provide a better understanding of the intricate ecological relationships between plants, arbuscular mycorrhizal fungi and soil bacteria as well as their evolutionary implications.

Root microbes can improve plant tolerance to insect damage: A systematic review and meta-analysis

To limit damage from insect herbivores, plants rely on a blend of defensive mechanisms that includes partnerships with beneficial microbes, particularly those inhabiting roots. While ample evidence exists for microbially mediated resistance responses that directly target insects through changing phytotoxin and volatile profiles, we know surprisingly little about the microbial underpinnings of plant tolerance. Tolerance defenses counteract insect damage via shifts in plant physiology that reallocate resources to fuel compensatory growth, improve photosynthetic efficiency, and reduce oxidative stress. Despite being a powerful mitigator of insect damage, tolerance remains an understudied realm of plant defenses. Here, we propose a novel conceptual framework that can be broadly applied across study systems to characterize microbial impacts on expression of tolerance defenses. We conducted a systematic review of studies quantifying the impact of rhizosphere microbial inoculants on plant tolerance to herbivory based on several measures-biomass, oxidative stress mitigation, or photosynthesis. We identified 40 studies, most of which focused on chewing herbivores (n = 31) and plant growth parameters (e.g., biomass). Next, we performed a meta-analysis investigating the impact of microbial inoculants on plant tolerance to herbivory, which was measured via differences in plant biomass, and compared across key microbe, insect, and plant traits. Thirty-five papers comprising 113 observations were included in this meta-analysis, with effect sizes (Hedges' d) ranging from -4.67 (susceptible) to 18.38 (overcompensation). Overall, microbial inoculants significantly reduce the cost of herbivory via plant growth promotion, with overcompensation and compensation comprising 25% of observations of microbial-mediated tolerance. The grand mean effect size 0.99 [0.49; 1.49] indicates that the addition of a microbial inoculant increased plant biomass by ~1 SD under herbivore stress, thus improving tolerance. This effect was influenced most by microbial attributes, including functional guild and total soil community diversity. Overall, results highlight the need for additional investigation of microbially mediated plant tolerance, particularly in sap-feeding insects and across a more comprehensive range of tolerance mechanisms. Such attention would round out our current understanding of anti-herbivore plant defenses, offer insight into the underlying mechanisms that promote resilience to insect stress, and inform the application of microbial biotechnology to support sustainable agricultural practices.

Is arbuscular mycorrhizal fungal addition beneficial to potato systems? A meta-analysis

The application of arbuscular mycorrhizal (AM) fungi has been reported to confer multiple agronomic benefits to crop plants including cereals, vegetables, and fruit trees, as well as to improve soil structure and health. In this study, we conducted a meta-analysis to investigate whether AM fungal addition enhances potato yield. We further examined whether several experimental conditions (type of experiment, inoculation method, and source of AM fungi) and potato cultivar may explain the outcomes. We calculated the effect sizes of seven plant parameters by including a total of 106 independent pot and field experimental studies from 37 peer reviewed publications. Our results show that the addition of AM fungi has an overall positive effect on all potato plant parameters included in our analyses except for aboveground plant biomass. Potato cultivar was the main significant moderator explaining our findings, with some cultivars benefiting more from AM fungal presence than others. Our findings agree with several other global meta-analyses reporting positive effects of AM fungi on other important crops and highlights the potential application of these fungal symbionts in potato agro-ecosystems.

Cross-kingdom nutrient exchange in the plant-arbuscular mycorrhizal fungus-bacterium continuum

The association between plants and arbuscular mycorrhizal fungi (AMF) affects plant performance and ecosystem functioning. Recent studies have identified AMF-associated bacteria as cooperative partners that participate in AMF-plant symbiosis: specific endobacteria live inside AMF, and hyphospheric bacteria colonize the soil that surrounds the extraradical hyphae. In this Review, we describe the concept of a plant-AMF-bacterium continuum, summarize current advances and provide perspectives on soil microbiology. First, we review the top-down carbon flow and the bottom-up mineral flow (especially phosphorus and nitrogen) in this continuum, as well as how AMF-bacteria interactions influence the biogeochemical cycling of nutrients (for example, carbon, phosphorus and nitrogen). Second, we discuss how AMF interact with hyphospheric bacteria or endobacteria to regulate nutrient exchange between plants and AMF, and the possible molecular mechanisms that underpin this continuum. Finally, we explore future prospects for studies on the hyphosphere to facilitate the utilization of AMF and hyphospheric bacteria in sustainable agriculture.

Protecting plants from pathogens through arbuscular mycorrhiza: Role of fungal diversity

Arbuscular mycorrhizal (AM) fungi play a crucial role in protecting host plants from pathogens. AM fungal taxa show varying abilities to hinder the development of plant pathogens with various underlying mechanisms of action, and plant defense through mycorrhization should be viewed to have a continuum of several possible mechanisms. However, an additive or synergistic effect is not always achieved. This review examines the potential mechanisms by which AM fungi enhance plant tolerance and defense against pathogens, as well as the possible interactive mechanisms among AM fungal traits that may lead to facilitative and antagonistic effect on plant defense outcomes. It also provides evidence demonstrating the benefits of AM fungal consortia used so far to protect crop plants from various pathogens. It concludes by proposing some biotechnological applications aimed at unraveling the connections between AM fungal diversity and their function to enhance efficacy of plant pathogen protection.

Garlic stalk waste and arbuscular mycorrhizae mitigate challenges in continuously monocropping eggplant obstacles by modulating physiochemical properties and fungal community structure

BACKGROUND AND AIMS

Continuous vegetable production under plastic tunnels faces challenges like soil degradation, increased soil-borne pathogens, and diminished eggplant yield. These factors collectively threaten the long-term sustainability of food security by diminishing the productivity and resilience of agricultural soils. This research examined the use of raw garlic stalk (RGS) waste and arbuscular mycorrhizal fungi (AMF) as a sustainable solution for these issues in eggplant monoculture. We hypothesized that the combined application of RGS waste and AMF would improve soil physicochemical properties compared to untreated soil in eggplant monoculture. The combined use of RGS and AMF was expected to suppress soil-borne pathogens, increase the abundance of soil beneficial microorganisms and alter fungal community structure. The combined application of RGS and AMF will significantly enhance eggplant yield compared to untreated plots. This study aimed to determine whether AMF and RGS, individually or in combination, can ameliorate the adverse effects of monoculture on eggplant soil. We also investigated whether these treatments could enhance eggplant yield.

METHODS

The experiment was arranged in a completely randomized design with four treatments: AMF, RGS, and a combined treatment of AMF + RGS (ARGS), along with a control. Each treatment was replicated three times, Eggplant seedlings inoculated with AMF and treated with RGS amendments, both individually and combined. The effects on root traits, soil physicochemical properties, soil enzyme activity, and fungal community structure were investigated.

RESULTS

RGS amendments and AMF inoculation improved root length, volume, and mycorrhizal colonization. The combined treatment showed the most significant improvement. RGS and AMF application increased soil nutrient availability (N, P, K) and organic matter content. Enzyme activities also increased with RGS and AMF treatments, with the combined application showing the highest activity. Soil electrical conductivity (EC) increased, while soil pH decreased with RGS and AMF amendments. Sequencing revealed a shift in the fungal community structure. Ascomycota abundance decreased, while Basidiomycota abundance increased with RGS and AMF application. The combined treatment reduced the abundance of pathogenic genera (Fusarium) and enriched beneficial taxa (Chaetomium, Coprinellus, Aspergillus). Pearson correlations supported the hypothesis that soil physicochemical properties influence fungal community composition.

CONCLUSIONS

This study demonstrates the potential of co-applying RGS and AMF in continuous cropping systems. It enhances soil physicochemical properties, reduces soil-borne pathogens, and promotes beneficial microbial communities and eggplant yield. This combined approach offers a sustainable strategy to address the challenges associated with eggplant monoculture under plastic tunnels.

New fungal primers reveal the diversity of Mucoromycotinian arbuscular mycorrhizal fungi and their response to nitrogen application

BACKGROUND

Arbuscular mycorrhizas (AM) are the most widespread terrestrial symbiosis and are both a key determinant of plant health and a major contributor to ecosystem processes through their role in biogeochemical cycling. Until recently, it was assumed that the fungi which form AM comprise the subphylum Glomeromycotina (G-AMF), and our understanding of the diversity and ecosystem roles of AM is based almost exclusively on this group. However recent evidence shows that fungi which form the distinctive 'fine root endophyte' (FRE) AM morphotype are members of the subphylum Mucoromycotina (M-AMF), so that AM symbioses are actually formed by two distinct groups of fungi.

RESULTS

We investigated the influence of nitrogen (N) addition and wheat variety on the assembly of AM communities under field conditions. Visual assessment of roots showed co-occurrence of G-AMF and M-AMF, providing an opportunity to compare the responses of these two groups. Existing 'AM' 18S rRNA primers which co-amplify G-AMF and M-AMF were modified to reduce bias against Mucoromycotina, and compared against a new 'FRE' primer set which selectively amplifies Mucoromycotina. Using the AM-primers, no significant effect of either N-addition or wheat variety on G-AMF or M-AMF diversity or community composition was detected. In contrast, using the FRE-primers, N-addition was shown to reduce M-AMF diversity and altered community composition. The ASV which responded to N-addition were closely related, demonstrating a clear phylogenetic signal which was identified only by the new FRE-primers. The most abundant Mucoromycotina sequences we detected belonged to the same Endogonales clades as dominant sequences associated with FRE morphology in Australia, indicating that closely related M-AMF may be globally distributed.

CONCLUSIONS

The results demonstrate the need to consider both G-AMF and M-AMF when investigating AM communities, and highlight the importance of primer choice when investigating AMF community dynamics.

The ancestral environment of teosinte populations shapes their root microbiome

BACKGROUND

The composition of the root microbiome affects the host's growth, with variation in the host genome associated with microbiome variation. However, it is not known whether this intra-specific variation of root microbiomes is a consequence of plants performing targeted manipulations of them to adapt to their local environment or varying passively with other traits. To explore the relationship between the genome, environment and microbiome, we sampled seeds from teosinte populations across its native range in Mexico. We then grew teosinte accessions alongside two modern maize lines in a common garden experiment. Metabarcoding was performed using universal bacterial and fungal primers to profile their root microbiomes.

RESULTS

The root microbiome varied between the two modern maize lines and the teosinte accessions. We further found that variation of the teosinte genome, the ancestral environment (temperature/elevation) and root microbiome were all correlated. Multiple microbial groups significantly varied in relative abundance with temperature/elevation, with an increased abundance of bacteria associated with cold tolerance found in teosinte accessions taken from high elevations.

CONCLUSIONS

Our results suggest that variation in the root microbiome is pre-conditioned by the genome for the local environment (i.e. non-random). Ultimately, these claims would be strengthened by confirming that these differences in the root microbiome impact host phenotype, for example, by confirming that the root microbiomes of high-elevation teosinte populations enhance cold tolerance.

Mycorrhizal inoculation and fertilizer microdosing interactions in pearl millet (Pennisetum glaucum) under greenhouse conditions

Introduction

Soil fertility is a major constraint to agricultural development in the Sahel region of Africa. One alternative to reducing the use of mineral fertilizers is to partially replace them with microbes that promote nutrition and growth, such as arbuscular mycorrhizal fungi (AMF). Mineral fertilizer microdosing is a technique developed to enhance fertilizer efficiency and encourage smallholder farmers to adopt higher mineral fertilizer applications.

Methods

A pot experiment was set up to study the effects of AMF inoculation on the mineral nutrition of pearl millet under mineral fertilizer microdosing conditions. The experimental setup followed a randomized complete block design with five replicates. The treatments tested on millet were an absolute control and eight microdoses derived from the combination of three doses of 15- 10-10 [nitrogen, phosphorus, and potassium (NPK)] mineral fertilizer (2 g, 3 g, and 5 g per pot), three doses of urea (1 g, 2 g, and 3 g per pot), and three doses of organic manure (OM) (200 g, 400 g, and 600 g), combined with and without AMF (Rhizophagus irregularis and Rhizophagus aggregatum). The parameters studied were growth, root colonization by AMF, and mineral nutrition. Plant height, stem diameter, root dry biomass, and percentage of root mycorrhization were measured.

Results and discussion

The results revealed a significant effect of the fertilizers on the growth of pearl millet compared to the control. AMF and OM treatments resulted in the highest biomass production. AMF combined with microdoses of NPK improved N and calcium (Ca) concentrations, while their combination with organic matter mainly improved the K concentration. Combining AMF with microdosed NPK and compost enhanced zinc (Zn) and nickel (Ni) concentrations. Root colonization varied from 0.55 to 56.4%. This investigation highlights the positive effects of AMF inoculation on nutrient uptake efficiency when combined with microdosing fertilization.

Effect of AMF Inoculation on Reducing Excessive Fertilizer Use

Excessive use of chemical fertilizer is a global concern. Arbuscular mycorrhizal fungi (AMF) are considered a potential solution due to their symbiotic association with crops. This study assessed AMF's effects on maize yield, fertilizer efficiency, plant traits, and soil nutrients under different reduced-fertilizer regimes in medium-low fertility fields. We found that phosphorus supplementation after a 30% fertilizer reduction enhanced AMF's positive impact on grain yield, increasing it by 3.47% with pure chemical fertilizers and 6.65% with mixed fertilizers. The AMF inoculation did not significantly affect the nitrogen and phosphorus fertilizer use efficiency, but significantly increased root colonization and soil mycelium density. Mixed fertilizer treatments with phosphorus supplementation after fertilizer reduction showed greater mycorrhizal effects on plant traits and soil nutrient contents compared to chemical fertilizer treatments. This study highlights that AMF inoculation, closely linked to fertilization regimes, can effectively reduce fertilizer use while sustaining or enhancing maize yields.

Building blocks toward sustainable biofertilizers: variation in arbuscular mycorrhizal spore germination when immobilized with diazotrophic bacteria in biodegradable hydrogel beads

AIM

We investigated whether there was interspecies and intraspecies variation in spore germination of 12 strains of arbuscular mycorrhizal fungi when co-entrapped with the diazotrophic plant growth-promoting bacteria, Azospirillum brasilense Sp7 in alginate hydrogel beads.

METHODS AND RESULTS

Twelve Rhizophagus irregularis, Rhizophagus intraradices, and Funneliformis mosseae strains were separately combined with a live culture of Azospirillum brasilense Sp7. Each fungal-bacterial consortia was supplemented with sodium alginate to a 2% concentration (v/v) and cross-linked in calcium chloride (2% w/v) to form biodegradable hydrogel beads. One hundred beads from each combination (total of 1200) were fixed in solidified modified Strullu and Romand media. Beads were observed for successful spore germination and bacterial growth over 14 days. In all cases, successful growth of A. brasilense was observed. For arbuscular mycorrhizal fungi, interspecies variation in spore germination was observed, with R. intraradices having the highest germination rate (64.3%), followed by R. irregularis (45.5%) and F. mosseae (40.3%). However, a difference in intraspecies germination was only observed among strains of R. irregularis and F. mosseae. Despite having varying levels of germination, even the strains with the lowest potential were still able to establish with the plant host Brachypodium distachyon in a model system.

CONCLUSIONS

Arbuscular mycorrhizal spore germination varied across strains when co-entrapped with a diazotrophic plant growth-promoting bacteria. This demonstrates that hydrogel beads containing a mixed consortium hold potential as a sustainable biofertilizer and that compatibility tests remain an important building block when aiming to create a hydrogel biofertilizer that encases a diversity of bacteria and fungi. Moving forward, further studies should be conducted to test the efficacy of these hydrogel biofertilizers on different crops across varying climatic conditions in order to optimize their potential.

Meta-analysis reveals the effects of microbial inoculants on the biomass and diversity of soil microbial communities

Microbial inoculation involves transplanting microorganisms from their natural habitat to new plants or soils to improve plant performance, and it is being increasingly used in agriculture and ecological restoration. However, microbial inoculants can invade and alter the composition of native microbial communities; thus, a comprehensive analysis is urgently needed to understand the overall impact of microbial inoculants on the biomass, diversity, structure and network complexity of native communities. Here we provide a meta-analysis of 335 studies revealing a positive effect of microbial inoculants on soil microbial biomass. This positive effect was weakened by environmental stress and enhanced by the use of fertilizers and native inoculants. Although microbial inoculants did not alter microbial diversity, they induced major changes in the structure and bacterial composition of soil microbial communities, reducing the complexity of bacterial networks and increasing network stability. Finally, higher initial levels of soil nutrients amplified the positive impact of microbial inoculants on fungal biomass, actinobacterial biomass, microbial biomass carbon and microbial biomass nitrogen. Together, our results highlight the positive effects of microbial inoculants on soil microbial biomass, emphasizing the benefits of native inoculants and the important regulatory roles of soil nutrient levels and environmental stress.

Insect-microbe interactions and their influence on organisms and ecosystems

Microorganisms are important associates of insect and arthropod species. Insect-associated microbes, including bacteria, fungi, and viruses, can drastically impact host physiology, ecology, and fitness, while many microbes still have no known role. Over the past decade, we have increased our knowledge of the taxonomic composition and functional roles of insect-associated microbiomes and viromes. There has been a more recent shift toward examining the complexity of microbial communities, including how they vary in response to different factors (e.g., host genome, microbial strain, environment, and time), and the consequences of this variation for the host and the wider ecological community. We provide an overview of insect-microbe interactions, the variety of associated microbial functions, and the evolutionary ecology of these relationships. We explore the influence of the environment and the interactive effects of insects and their microbiomes across trophic levels. Additionally, we discuss the potential for subsequent synergistic and reciprocal impacts on the associated microbiomes, ecological interactions, and communities. Lastly, we discuss some potential avenues for the future of insect-microbe interactions that include the modification of existing microbial symbionts as well as the construction of synthetic microbial communities.

Wheat dwarfing reshapes plant and fungal development in arbuscular mycorrhizal symbiosis

The introduction of Reduced height (Rht) dwarfing genes into elite wheat varieties has contributed to enhanced yield gain in high input agrosystems by preventing lodging. Yet, how modern selection for dwarfing has affected symbiosis remains poorly documented. In this study, we evaluated the response of both the plant and the arbuscular mycorrhizal fungus to plant genetic variation at a major Quantitative Trait Locus called QTL 4B2, known to harbor a Rht dwarfing gene, when forming the symbiosis. We used twelve inbred genotypes derived from a diversity base broadened durum wheat Evolutionary Pre-breeding Population and genotyped with a high-throughput Single Nucleotide Polymorphism (SNP) genotyping array. In a microcosm setup segregating roots and the extra-radical mycelium, each wheat genotype was grown with or without the presence of Rhizophagus irregularis. To characterize arbuscular mycorrhizal symbiosis, we assessed hyphal density, root colonization, spore production, and plant biomass. Additionally, we split the variation of these variables due either to genotypes or to the Rht dwarfing genes alone. The fungus exhibited greater development in the roots of Dwarf plants compared to non-Dwarf plants, showing increases of 27%, 37% and 51% in root colonization, arbuscules, and vesicles, respectively. In addition, the biomass of the extra-radical fungal structures increased by around 31% in Dwarf plants. The biomass of plant roots decreased by about 43% in mycorrhizal Dwarf plants. Interestingly, extraradical hyphal production was found to be partly genetically determined with no significant effect of Rht, as for plant biomasses. In contrast, variations in root colonization, arbuscules and extraradical spore production were explained by Rht dwarfing genes. Finally, when mycorrhizal, Dwarf plants had significantly lower total P content, pointing towards a less beneficial symbiosis for the plant and increased profit for the fungus. These results highlight the effect of Rht dwarfing genes on both root and fungal development. This calls for further research into the molecular mechanisms governing these effects, as well as changes in plant physiology, and their implications for fostering arbuscular mycorrhizal symbiosis in sustainable agrosystems.

Native Arbuscular Mycorrhizal Fungi Promote Plukenetia volubilis Growth and Decrease the Infection Levels of Meloidogyne incognita

The use of arbuscular mycorrhizal fungi (AMF) offers promising benefits to agriculture in the Amazon regions, where soils are characteristically acidic and nutrient-poor. The purpose of this research was to investigate the potential effects of two recently described species of AMF (Nanoglomus plukenetiae and Rhizoglomus variabile) native to the Peruvian Amazon for improving the plant growth of Plukenetia volubilis (inka nut or sacha inchi) and protecting the roots against soil pathogens. Two assays were simultaneously conducted under greenhouse conditions in Peru. The first focused on evaluating the biofertilizer effect of AMF inoculation, while the second examined the bioprotective effect against the root knot nematode, Meloidogyne incognita. Overall, the results showed that AMF inoculation of P. volubilis seedlings positively improved their development, particularly their biomass, height, and the leaf nutrient contents. When seedlings were exposed to M. incognita, plant growth was also noticeably higher for AMF-inoculated plants than those without AMF inoculation. Nematode reproduction was significantly suppressed by the presence of AMF, in particular R. variabile, and especially when inoculated prior to nematode exposure. The dual AMF inoculation did not necessarily lead to improved crop growth but notably improved P and K leaf contents. The findings provide strong justification for the development of products based on AMF as agro-inputs to catalyze nutrient use and uptake and protect crops against pests and diseases, especially those that are locally adapted to local crops and cropping conditions.

Arbuscular Mycorrhizal inoculants and its regulatory landscape

One of the most prominent means for sustainable agriculture and ecosystem management are Arbuscular Mycorrhizal (AM) inoculants. These inoculants establish beneficial symbiotic relationships with land plant roots, offering a wide range of benefits, from enhanced nutrient absorption to improved resilience against environmental stressors. However, several currently available commercial AM inoculants face challenges such as inconsistency in field applications, ecological risks associated with non-native strains, and the absence of universal regulations. Currently, regulations for AM inoculants vary globally, with some regions leading efforts to standardize and ensure quality control. Proposed regulatory frameworks aim to establish parameters for composition, safety, and efficacy. Nevertheless, challenges persist in terms of scientific data, standardization, testing under real conditions, and the ecological impact of these inoculants. To address these challenges and unlock the full potential of AM inoculants, increased research funding, public-private partnerships, monitoring, awareness, and ecosystem impact studies are recommended. Future regulations have the potential to improve product quality, soil health, and crop productivity while reducing reliance on chemical inputs and benefiting the environment. However, addressing issues related to compliance, standardization, education, certification, monitoring, and cost is essential for realizing these benefits. Global harmonization and collaborative efforts are vital to maximize their impact on agriculture and ecosystem management, leading to healthier soils, increased crop yields, and a more sustainable agricultural industry.

Testing the trade-balance model: resource stoichiometry does not sufficiently explain AM effects

Variations in arbuscular mycorrhizae (AM) effects on plant growth (MGR) are commonly assumed to result from cost : benefit balances, with C as the cost and, most frequently, P as the benefit. The trade-balance model (TBM) adopts these assumptions and hypothesizes that mycorrhizal benefit depends on C : N : P stoichiometry. Although widely accepted, the TBM has not been experimentally tested. We isolated the parameters included in the TBM and tested these assumptions using it as framework. Oryza sativa plants were supplied with different N : P ratios at low light level, establishing different C : P and C : N exchange rates, and C, N or P limitation. MGR and effects on nutrient uptake, %M, ERM, photosynthesis and shoot starch were measured. C distribution to AM fungi played no role in MGR, and N was essential for all AM effects, including on P nutrition. C distribution to AM and MGR varied with the limiting nutrient (N or P), and evidence of extensive interplay between N and P was observed. The TBM was not confirmed. The results agreed with the exchange of surplus resources and source-sink regulation of resource distribution among plants and AMF. Rather than depending on exchange rates, resource exchange may simply obey both symbiont needs, not requiring further regulation.

Plant-microbe interactions through a lens: tales from the mycorrhizosphere

BACKGROUND

The soil microbiome plays a pivotal role in maintaining ecological balance, supporting food production, preserving water quality and safeguarding human health. Understanding the intricate dynamics within the soil microbiome necessitates unravelling complex bacterial-fungal interactions (BFIs). BFIs occur in diverse habitats, such as the phyllosphere, rhizosphere and bulk soil, where they exert substantial influence on plant-microbe associations, nutrient cycling and overall ecosystem functions. In various symbiotic associations, fungi form mycorrhizal connections with plant roots, enhancing nutrient uptake through the root and mycorrhizal pathways. Concurrently, specific soil bacteria, including mycorrhiza helper bacteria, play a pivotal role in nutrient acquisition and promoting plant growth. Chemical communication and biofilm formation further shape plant-microbial interactions, affecting plant growth, disease resistance and nutrient acquisition processes.

SCOPE

Promoting synergistic interactions between mycorrhizal fungi and soil microbes holds immense potential for advancing ecological knowledge and conservation. However, despite the significant progress, gaps remain in our understanding of the evolutionary significance, perception, functional traits and ecological relevance of BFIs. Here we review recent findings obtained with respect to complex microbial communities - particularly in the mycorrhizosphere - and include the latest advances in the field, outlining their profound impacts on our understanding of ecosystem dynamics and plant physiology and function.

CONCLUSIONS

Deepening our understanding of plant BFIs can help assess their capabilities with regard to ecological and agricultural safe-guarding, in particular buffering soil stresses, and ensuring sustainable land management practices. Preserving and enhancing soil biodiversity emerge as critical imperatives in sustaining life on Earth amidst pressures of anthropogenic climate change. A holistic approach integrates scientific knowledge on bacteria and fungi, which includes their potential to foster resilient soil ecosystems for present and future generations.

Rational management of the plant microbiome for the Second Green Revolution

The Green Revolution of the mid-20th century transformed agriculture worldwide and has resulted in environmental challenges. A new approach, the Second Green Revolution, seeks to enhance agricultural productivity while minimizing negative environmental impacts. Plant microbiomes play critical roles in plant growth and stress responses, and understanding plant-microbiome interactions is essential for developing sustainable agricultural practices that meet food security and safety challenges, which are among the United Nations Sustainable Development Goals. This review provides a comprehensive exploration of key deterministic processes crucial for developing microbiome management strategies, including the host effect, the facilitator effect, and microbe-microbe interactions. A hierarchical framework for plant microbiome modulation is proposed to bridge the gap between basic research and agricultural applications. This framework emphasizes three levels of modulation: single-strain, synthetic community, and in situ microbiome modulation. Overall, rational management of plant microbiomes has wide-ranging applications in agriculture and can potentially be a core technology for the Second Green Revolution.

Molecular and Systems Biology Approaches for Harnessing the Symbiotic Interaction in Mycorrhizal Symbiosis for Grain and Oil Crop Cultivation

Mycorrhizal symbiosis, the mutually beneficial association between plants and fungi, has gained significant attention in recent years due to its widespread significance in agricultural productivity. Specifically, arbuscular mycorrhizal fungi (AMF) provide a range of benefits to grain and oil crops, including improved nutrient uptake, growth, and resistance to (a)biotic stressors. Harnessing this symbiotic interaction using molecular and systems biology approaches presents promising opportunities for sustainable and economically-viable agricultural practices. Research in this area aims to identify and manipulate specific genes and pathways involved in the symbiotic interaction, leading to improved cereal and oilseed crop yields and nutrient acquisition. This review provides an overview of the research frontier on utilizing molecular and systems biology approaches for harnessing the symbiotic interaction in mycorrhizal symbiosis for grain and oil crop cultivation. Moreover, we address the mechanistic insights and molecular determinants underpinning this exchange. We conclude with an overview of current efforts to harness mycorrhizal diversity to improve cereal and oilseed health through systems biology.

Antioxidant Response, Phenolic Compounds and Yield of Solanum tuberosum Tubers Inoculated with Arbuscular Mycorrhizal Fungi and Growing under Water Stress

Solanum tuberosum (potato) is one of the most common crops worldwide; however, it is sensitive to water stress, which necessitates the identification of alternative tools to improve their production. Here, we evaluated the inoculation of two arbuscular mycorrhizal fungi (AMF) strains, Claroideoglomus claroideum (CC), Claroideoglomus lamellosum (HMC26), and the MIX (CC + HMC26) in yield and phenolic and antioxidant response using chromatographic and spectroscopic methods in potato crops, at increasing levels of water stress, namely, with 100% (0), 70% (S1), and 40% (S2) soil humidity. Two caffeoylquinic acid isomers were detected and their levels showed a tendency to increase under stress together with the AMF inoculation, reaching up to 19.2 mg kg-1 of 5-caffeoylquinic acid and 7.4 mg kg-1 of caffeoylquinic acid isomer when CC was inoculated, and potato plants grew at the highest water starvation condition (S2). Regarding antioxidant activities, a differentiated response was detected depending on the AMF strain, highlighting the effect of HMC26 on Trolox equivalent antioxidant capacity (TEAC) method and CC in cupric reducing antioxidant capacity (CUPRAC) method, reaching up to 1.5 μmol g-1 of TEAC in plants inoculated with HMC26 and 0.9 μmol g-1 of CUPRAC in plants inoculated with CC, both in potato tubers of plants growing under the S2 stress condition. Meanwhile, the use of AMF did not influence the number and biomass of the tubers, but significant changes in the biochemical properties of tubers were observed. The results suggest that specific AMF adaptations to water stress must be considered when inoculation procedures are planned to improve the yield and quality of tubers in potato crops.

Crop rotation and inoculation increase soil bradyrhizobia population, soybean grain yields, and profitability

Crop rotation and rhizobial inoculation are strategies to increase yield by means of organic matter addition and modulation of microbial diversity. However, the extent to which these agricultural practices change soil Bradyrhizobium populations, soybean grain yield, and economic benefits to farmers is unclear. Thus, this study aimed to evaluate the interaction between crop rotation and inoculation of soybean (Glycine max) cultivated in two contrasting soils (clayey and sandy soil) on biological nitrogen fixation components, grain yields, and profits. Field experiments with a three-year crop rotation system were carried out to compare effects of inoculation and crop rotations on soil chemical attributes, bradyrhizobia most probable number (MPN) and diversity, soybean nodulation, grain yield, and economic indicators of inoculation in different crop rotations. The crop rotation did not affect the soil MPN cells of bradyrhizobia, but the inoculation and the soil sampling time did, ranging from 3.61-4.42 to 4.40-4.82 in the sandy soil, while in the clayey soil they were from 5.19-6.34 to 6.61-7.14 in Log10 per g of soil with higher population after harvest of summer crops. In the clayey soil, crop rotation influenced soybean nodulation. The grain yield of inoculated soybean in the clayey soil was higher than that in the sandy soil. Soybean inoculation with Bradyrhizobium spp. increased the profitability of agricultural production systems by up to 45% in clayey soil and up to 7% in sandy soil.

Soil microbiome indicators can predict crop growth response to large-scale inoculation with arbuscular mycorrhizal fungi

Alternative solutions to mineral fertilizers and pesticides that reduce the environmental impact of agriculture are urgently needed. Arbuscular mycorrhizal fungi (AMF) can enhance plant nutrient uptake and reduce plant stress; yet, large-scale field inoculation trials with AMF are missing, and so far, results remain unpredictable. We conducted on-farm experiments in 54 fields in Switzerland and quantified the effects on maize growth. Growth response to AMF inoculation was highly variable, ranging from -12% to +40%. With few soil parameters and mainly soil microbiome indicators, we could successfully predict 86% of the variation in plant growth response to inoculation. The abundance of pathogenic fungi, rather than nutrient availability, best predicted (33%) AMF inoculation success. Our results indicate that soil microbiome indicators offer a sustainable biotechnological perspective to predict inoculation success at the beginning of the growing season. This predictability increases the profitability of microbiome engineering as a tool for sustainable agricultural management.

The Armillaria response to Gastrodia elata is partially mediated by strigolactone-induced changes in reactive oxygen species

Armillaria root diseases, caused by Armillaria spp., pose a significant threat to woody plants worldwide and result in substantial economic losses. However, certain species in the genus Armillaria can establish a unique symbiotic relationship with Gastrodia elata, which is the only known example of a plant benefiting from Armillaria. Although various plant signals that play a role in this interaction have been identified, the mechanism remains largely unknown from the Armillaria's perspective. In this study, we performed whole-genome sequencing of an Armillaria gallica strain named NRC001 isolated from G. elata. Comparative genomic analysis showed it is low-pathogenic Armillaria spp., which possesses 169 expanded gene families compared to high-pathogenic Armillaria spp. Among these expanded families, transcriptomic analysis revealed a significant increase in expression levels of four reactive oxygen species (ROS)-related gene families in A. gallica on G. elata compared to A. gallica on wood. Thus, a systematic survey of ROS-related gene families was carried out, and a total of 218 genes belonging to 44 ROS-related gene families in A. gallica were identified. Physiological experiments and transcriptome analysis showed that strigolactones (SLs) released by G. elata have a mediation impact on ROS, particularly enhancing the ROS scavenging activities by increasing the expression level and activity of several enzymes, such as catalase and glutathione reductase. Among the ROS-related genes, the aquaporin (AQP) is crucial as it is responsible for transporting hydrogen peroxide (H2O2) across the cell membrane. Five orthologs of AQP genes in A. gallica were identified and overexpressed in yeast. Only AgAQPA from the so-called 'other aquaglyceroporin' subfamily was demonstrated to be capable of mediating H2O2 transport in A. gallica. To our best knowledge, this is the first 'other aquaglyceroporins' gene in fungi to be identified as having transporter capacity. This study not only provides new insights into the mechanisms by which SL signaling regulates interactions between Armillaria and G. elata, but also sheds light on the function of fungal AQPs.

Arbuscular mycorrhizal fungi enhance active ingredients of medicinal plants: a quantitative analysis

Medicinal plants are invaluable resources for mankind and play a crucial role in combating diseases. Arbuscular mycorrhizal fungi (AMF) are widely recognized for enhancing the production of medicinal active ingredients in medicinal plants. However, there is still a lack of comprehensive understanding regarding the quantitative effects of AMF on the accumulation of medicinal active ingredients. Here we conducted a comprehensive global analysis using 233 paired observations to investigate the impact of AMF inoculation on the accumulation of medicinal active ingredients. This study revealed that AMF inoculation significantly increased the contents of medicinal active ingredients by 27%, with a particularly notable enhancement observed in flavonoids (68%) and terpenoids (53%). Furthermore, the response of medicinal active ingredients in belowground organs (32%) to AMF was more pronounced than that in aboveground organs (18%). Notably, the AMF genus Rhizophagus exhibited the strongest effect in improving the contents of medicinal active ingredients, resulting in an increase of over 50% in both aboveground and belowground organs. Additionally, the promotion of medicinal active ingredients by AMF was attributed to improvements in physiological factors, such as chlorophyll, stomatal conductance and net photosynthetic rate. Collectively, this research substantially advanced our comprehension of the pivotal role of AMF in improving the medicinal active ingredients of plants and provided valuable insights into the potential mechanisms driving these enhancements.

Effects of Agricultural Intensification on Mediterranean Diets: A Narrative Review

INTRODUCTION

Mediterranean diets (MedDiets) are linked to substantial health benefits. However, there is also growing evidence that the intensification of food production over the last 60 years has resulted in nutritionally relevant changes in the composition of foods that may augment the health benefits of MedDiets.

OBJECTIVE

To synthesize, summarize, and critically evaluate the currently available evidence for changes in food composition resulting from agricultural intensification practices and their potential impact on the health benefits of MedDiets.

METHODS

We summarized/synthesized information from (i) systematic literature reviews/meta-analyses and more recently published articles on composition differences between conventional and organic foods, (ii) desk studies which compared food composition data from before and after agricultural intensification, (iii) recent retail and farm surveys and/or factorial field experiments that identified specific agronomic practices responsible for nutritionally relevant changes in food composition, and (iv) a recent systematic literature review and a small number of subsequently published observational and dietary intervention studies that investigated the potential health impacts of changes in food composition resulting from agricultural intensification.

RESULTS AND DISCUSSION

There has been growing evidence that the intensification of food production has resulted in (i) lower concentrations of nutritionally desirable compounds (e.g., phenolics, certain vitamins, mineral micronutrients including Se, Zn, and omega-3 fatty acids, α-tocopherol) and/or (ii) higher concentrations of nutritionally undesirable or toxic compounds (pesticide residues, cadmium, omega-6 fatty acids) in many of the foods (including wholegrain cereals, fruit and vegetables, olive oil, dairy products and meat from small ruminants, and fish) that are thought to contribute to the health benefits associated with MedDiets. The evidence for negative health impacts of consuming foods from intensified conventional production systems has also increased but is still limited and based primarily on evidence from observational studies. Limitations and gaps in the current evidence base are discussed. Conclusions: There is now substantial evidence that the intensification of agricultural food production has resulted in a decline in the nutritional quality of many of the foods that are recognized to contribute to the positive health impacts associated with adhering to traditional MedDiets. Further research is needed to quantify to what extent this decline augments the positive health impacts of adhering to a traditional MedDiet.

Mycorrhizal inoculation enhanced tillering in field grown wheat, nutritional enrichment and soil properties

To meet food security, commercial fertilizers are available to boost wheat yield, but there are serious ill effects associated with these fertilizers. Amongst various organic alternatives, inoculating crop fields with mycorrhizal species is the most promising option. Although, mycorrhizae are known to enhance wheat yield, but how the mycorrhizae influence different yield and quality parameters of wheat, is not clear. Therefore, this study was undertaken to investigate the influence of indigenous mycorrhizal species on the growth of wheat, its nutritional status and soil properties, in repeated set of field experiments. In total 11 species of mycorrhizae were isolated from the experimental sites with Claroideoglomus, being the most dominant one. Five different treatments were employed during the present study, keeping plot size for each replicate as 6 × 2 m. Introduction of consortia of mycorrhizae displayed a significant increase in number of tillers/plant (49.5%), dry biomass (17.4%), grain yield (21.2%) and hay weight (16.7%). However, there was non-significant effect of mycorrhizal inoculation on 1,000 grains weight. Moreover, protein contents were increased to 24.2%. Zinc, iron, phosphorus and potassium concentrations were also increased to 24%, 21%, 30.9% and 14.8%, respectively, in wheat grains. Enhancement effects were also noted on soil fertility such as soil organic carbon % age, available phosphorus and potassium were increased up to 64.7%, 35.8% and 23.9%, respectively. Herein, we concluded that mycorrhizal introduction in wheat fields significantly increased tillering in wheat and this increased tillering resulted in overall increase in wheat biomass/yield. Mycorrhizae also enhanced nutritional attributes of wheat grains as well as soil fertility. The use of mycorrhizae will help to reduce our dependance on synthetic fertilizers in sustainable agriculture.

The role of arbuscular mycorrhizal symbiosis in improving plant water status under drought

Arbuscular mycorrhizal fungi (AMF) have been presumed to ameliorate crop tolerance to drought. Here, we review the role of AMF in maintaining water supply to plants from drying soils and the underlying biophysical mechanisms. We used a soil-plant hydraulic model to illustrate the impact of several AMF mechanisms on plant responses to edaphic drought. The AMF enhance the soil's capability to transport water and extend the effective root length, thereby attenuating the drop in matric potential at the root surface during soil drying. The synthesized evidence and the corresponding simulations demonstrate that symbiosis with AMF postpones the stress onset limit, which is defined as the disproportionality between transpiration rates and leaf water potentials, during soil drying. The symbiosis can thus help crops survive extended intervals of limited water availability. We also provide our perspective on future research needs and call for reconciling the dynamic changes in soil and root hydraulics in order to better understand the role of AMF in plant water relations in the face of climate changes.

Crop Productivity Boosters: Native Mycorrhizal Fungi from an Old-Growth Grassland Benefits Tomato (Solanum lycopersicum) and Pepper (Capsicum annuum) Varieties in Organically Farmed Soils

This paper investigates the response of five tomato and five pepper varieties to native arbuscular mycorrhizal (AM) fungal inoculation in an organic farming system. The field experiment was conducted across a growing season at a working organic farm in Lawrence, KS, USA. The researchers hypothesized that native AM fungi inoculation would improve crop biomass production for both crop species, but that the magnitude of response would depend on crop cultivar. The results showed that both crops were significantly positively affected by inoculation. AM fungal inoculation consistently improved total pepper biomass throughout the experiment (range of +2% to +8% depending on the harvest date), with a +3.7% improvement at the final harvest for inoculated plants. An interaction between pepper variety and inoculation treatment was sometimes observed, indicating that some pepper varieties were more responsive to AM fungi than others. Beginning at the first harvest, tomatoes showed a consistent positive response to AM fungal inoculation among varieties. Across the experiment, AM fungi-inoculated tomatoes had +10% greater fruit biomass, which was driven by a +20% increase in fruit number. The study highlights the potential benefits of using native AM fungi as a soil amendment in organic farmed soils to improve pepper and tomato productivity.

Functional, not Taxonomic, Composition of Soil Fungi Reestablishes to Pre-mining Initial State After 52 Years of Recultivation

Open-cast mining leads to the loss of naturally developed soils and their ecosystem functions and services. Soil restoration after mining aims to restore the agricultural productivity in which the functions of the fungal community play a crucial role. Whether fungi reach a comparable functional state as in the soil before mining within half a century of recultivation is still unanswered. Here, we characterised the soil fungal community using ITS amplicon Illumina sequencing across a 52-year chronosequence of agricultural recultivation after open-cast mining in northern Europe. Both taxonomic and functional community composition showed profound shifts over time, which could be attributed to the changes in nutrient status, especially phosphorus availability. However, taxonomic composition did not reach the pre-mining state, whereas functional composition did. Importantly, we identified a positive development of arbuscular mycorrhizal root fungal symbionts after the initial three years of alfalfa cultivation, followed by a decline after conversion to conventional farming, with arbuscular mycorrhizal fungi being replaced by soil saprobes. We conclude that appropriate agricultural management can steer the fungal community to its functional pre-mining state despite stochasticity in the reestablishment of soil fungal communities. Nonetheless, conventional agricultural management results in the loss of plant symbionts, favouring non-symbiotic fungi.

Organ-specific responses during acclimation of mycorrhizal and non-mycorrhizal tomato plants to a mild water stress reveal differential local and systemic hormonal and nutritional adjustments

MAIN CONCLUSION

Tomato plant acclimation to a mild water stress implied tissue-specific hormonal and nutrient adjustments, being the root one of the main modulators of this response. Phytohormones are key regulators of plant acclimation to water stress. However, it is not yet clear if these hormonal responses follow specific patterns depending on the plant tissue. In this study, we evaluated the organ-specific physiological and hormonal responses to a 14 day-long mild water stress in tomato plants (Solanum lycopersicum cv. Moneymaker) in the presence or absence of the arbuscular mycorrhizal fungus Rhizoglomus irregulare, a frequently used microorganism in agriculture. Several physiological, production, and nutritional parameters were evaluated throughout the experiments. Additionally, endogenous hormone levels in roots, leaves, and fruits at different developmental stages were quantified by ultrahigh-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). Water deficit drastically reduced shoot growth, while it did not affect fruit production. In contrast, fruit production was enhanced by mycorrhization regardless of the water treatment. The main tissue affected by water stress was the root system, where huge rearrangements in different nutrients and stress-related and growth hormones took place. Abscisic acid content increased in every tissue and fruit developmental stage, suggesting a systemic response to drought. On the other hand, jasmonate and cytokinin levels were generally reduced upon water stress, although this response was dependent on the tissue and the hormonal form. Finally, mycorrhization improved plant nutritional status content of certain macro and microelements, specially at the roots and ripe fruits, while it affected jasmonate response in the roots. Altogether, our results suggest a complex response to drought that consists in systemic and local combined hormonal and nutrient responses.

A core microbiome in the hyphosphere of arbuscular mycorrhizal fungi has functional significance in organic phosphorus mineralization

The mycorrhizal pathway is an important phosphorus (P) uptake pathway for more than two-thirds of land plants. The arbuscular mycorrhizal (AM) fungi-associated hyphosphere microbiome has been considered as the second genome of mycorrhizal P uptake pathway and functionality in mobilizing soil organic P (Po). However, whether there is a core microbiome in the hyphosphere and how this is implicated in mining soil Po are less understood. We established on-site field trials located in humid, semiarid, and arid zones and a microcosm experiment in a glasshouse with specific AM fungi and varying soil types to answer the above questions. The hyphosphere microbiome of AM fungi enhanced soil phosphatase activity and promoted Po mineralization in all sites. Although the assemblage of hyphosphere microbiomes identified in three climate zones was mediated by environmental factors, we detected a core set in three sites and the subsequent microcosm experiment. The core members were co-enriched in the hyphosphere and dominated by Alphaproteobacteria, Actinobacteria, and Gammaproteobacteria. Moreover, these core bacterial members aggregate into stable guilds that contributed to phosphatase activity. The core hyphosphere microbiome is taxonomically conserved and provides functions, with respect to the mineralization of Po, that AM fungi lack.

Mycorrhizas drive the evolution of plant adaptation to drought

Plant adaptation to drought facilitates major ecological transitions, and will likely play a vital role under looming climate change. Mycorrhizas, i.e. strategic associations between plant roots and soil-borne symbiotic fungi, can exert strong influence on the tolerance to drought of extant plants. Here, I show how mycorrhizal strategy and drought adaptation have been shaping one another throughout the course of plant evolution. To characterize the evolutions of both plant characters, I applied a phylogenetic comparative method using data of 1,638 extant species globally distributed. The detected correlated evolution unveiled gains and losses of drought tolerance occurring at faster rates in lineages with ecto- or ericoid mycorrhizas, which were on average about 15 and 300 times faster than in lineages with the arbuscular mycorrhizal and naked root (non-mycorrhizal alone or with facultatively arbuscular mycorrhizal) strategy, respectively. My study suggests that mycorrhizas can play a key facilitator role in the evolutionary processes of plant adaptation to critical changes in water availability across global climates.

The multifaceted roles of Arbuscular Mycorrhizal Fungi in peanut responses to salt, drought, and cold stress

BACKGROUND

Arbuscular Mycorrhizal Fungi (AMF) are beneficial microorganisms in soil-plant interactions; however, the underlying mechanisms regarding their roles in legumes environmental stress remain elusive. Present trials were undertaken to study the effect of AMF on the ameliorating of salt, drought, and cold stress in peanut (Arachis hypogaea L.) plants. A new product of AMF combined with Rhizophagus irregularis SA, Rhizophagus clarus BEG142, Glomus lamellosum ON393, and Funneliformis mosseae BEG95 (1: 1: 1: 1, w/w/w/w) was inoculated with peanut and the physiological and metabolomic responses of the AMF-inoculated and non-inoculated peanut plants to salt, drought, and cold stress were comprehensively characterized, respectively.

RESULTS

AMF-inoculated plants exhibited higher plant growth, leaf relative water content (RWC), net photosynthetic rate, maximal photochemical efficiency of photosystem II (PSII) (Fv/Fm), activities of antioxidant enzymes, and K⁺: Na⁺ ratio while lower leaf relative electrolyte conductivity (REC), concentration of malondialdehyde (MDA), and the accumulation of reactive oxygen species (ROS) under stressful conditions. Moreover, the structures of chloroplast thylakoids and mitochondria in AMF-inoculated plants were less damaged by these stresses. Non-targeted metabolomics indicated that AMF altered numerous pathways associated with organic acids and amino acid metabolisms in peanut roots under both normal-growth and stressful conditions, which were further improved by the osmolytes accumulation data.

CONCLUSION

This study provides a promising AMF product and demonstrates that this AMF combination could enhance peanut salt, drought, and cold stress tolerance through improving plant growth, protecting photosystem, enhancing antioxidant system, and regulating osmotic adjustment.

Population Response of Rhizosphere Microbiota of Garden Pea Genotypes to Inoculation with Arbuscular Mycorrhizal Fungi

This study of a legume's rhizosphere in tripartite symbiosis focused on the relationships between the symbionts and less on the overall rhizosphere microbiome. We used an experimental model with different garden pea genotypes inoculated with AM fungi (Rhizophagus irregularis and with a mix of AM species) to study their influence on the population levels of main trophic groups of soil microorganisms as well as their structure and functional relationships in the rhizosphere microbial community. The experiments were carried out at two phenological cycles of the plants. Analyzes were performed according to classical methods: microbial population density defined as CUF/g a.d.s. and root colonization rate with AMF (%). We found a proven dominant effect of AMF on the densities of micromycetes and actinomycetes in the direction of reduction, suggesting antagonism, and on ammonifying, phosphate-solubilizing and free-living diazotrophic Azotobacter bacteria in the direction of stimulation, an indicator of mutualistic relationships. We determined that the genotype was decisive for the formation of populations of bacteria immobilizing mineral NH4+-N and bacteria Rhizobium. We reported significant two-way relationships between trophic groups related associated with soil nitrogen and phosphorus ions availability. The preserved proportions between trophic groups in the microbial communities were indicative of structural and functional stability.

Microbiomes in agroecosystem: Diversity, function and assembly mechanisms

Soils are a main repository of biodiversity harbouring immense diversity of microbial species that plays a central role in fundamental ecological processes and acts as the seed bank for emergence of the plant microbiome in cropland ecosystems. Crop-associated microbiomes play an important role in shaping plant performance, which includes but not limited to nutrient uptake, disease resistance, and abiotic stress tolerance. Although our understanding of structure and function of soil and plant microbiomes has been rapidly advancing, most of our knowledge comes from ecosystems in natural environment. In this review, we present an overview of the current knowledge of diversity and function of microbial communities along the soil-plant continuum in agroecosystems. To characterize the ecological mechanisms for community assembly of soil and crop microbiomes, we explore how crop host and environmental factors such as plant species and developmental stage, pathogen invasion, and land management shape microbiome structure, microbial co-occurrence patterns, and crop-microbiome interactions. Particularly, the relative importance of deterministic and stochastic processes in microbial community assembly is illustrated under different environmental conditions, and potential sources and keystone taxa of the crop microbiome are described. Finally, we highlight a few important questions and perspectives in future crop microbiome research.

Integrating plant and fungal quantitative genetics to improve the ecological and agricultural applications of mycorrhizal symbioses

Finding and targeting genes that quantitatively contribute to agricultural and ecological processes progresses food production and conservation efforts. Typically, quantitative genetic approaches link variants in a single organism's genome with a trait of interest. Recently, genome-to-genome mapping has found genome variants interacting between species to produce the result of a multiorganism (including multikingdom) interaction. These were plant and bacterial pathogen genome interactions; plant-fungal coquantitative genetics have not yet been applied. Plant-mycorrhizae symbioses exist across most biomes, for a majority of land plants, including crop plants, and manipulate many traits from single organisms to ecosystems for which knowing the genetic basis would be useful. The availability of Rhizophagus irregularis mycorrhizal isolates, with genomic information, makes dual-genome methods with beneficial mutualists accessible and imminent.

Transcriptome analysis reveals the regulatory mode by which NAA promotes the growth of Armillaria gallica

A symbiotic relationship is observed between Armillaria and the Chinese herbal medicine Gastrodia elata (G. elata). Armillaria is a nutrient source for the growth of G. elata, and its nutrient metabolism efficiency affects the growth and development of G. elata. Auxin has been reported to stimulate Armillaria species, but the molecular mechanism remains unknown. We found that naphthalene acetic acid (NAA) can also promote the growth of A. gallica. Moreover, we identified a total of 2071 differentially expressed genes (DEGs) by analyzing the transcriptome sequencing data of A. gallica at 5 and 10 hour of NAA treatment. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that these unigenes were significantly enriched in the metabolism pathways of arginine, proline, propanoate, phenylalanine and tryptophan. The expression levels of the general amino acid permease (Gap), ammonium transporter (AMT), glutamate dehydrogenase (GDH), glutamine synthetase (GS), Zn(II) 2Cys6 and C2H2 transcription factor genes were upregulated. Our transcriptome analysis showed that the amino acid and nitrogen metabolism pathways in Armillaria were rapidly induced within hours after NAA treatment. These results provide valuable insights into the molecular mechanisms by which NAA promotes the growth of Armillaria species.

Experimental duration determines the effect of arbuscular mycorrhizal fungi on plant biomass in pot experiments: A meta-analysis

Arbuscular mycorrhizal fungi (AMF) play various important roles in promoting plant growth. Numerous environmental and evolutionary factors influence the response of plants to AMF. However, the importance of the individual factors on the effects of AMF on plant biomass is not clearly understood. In this study, a meta-analysis using 1,640 observations from 639 published articles related to the influence of AMF on the plant shoot, root, and total biomass was performed; 13 different experimental setting factors that had an impact on the influence of AMF and their importance were quantitatively synthesized. The meta-analysis showed that AMF had positive effects on the plant shoot, root, and total biomass; moreover, the experimental duration, plant root-to-shoot ratio (R/S), AMF root length colonization, plant family, pot size, soil texture, and the soil pH all influenced the effects of AMF on the shoot, root, and total biomass. In addition, the plant root system and plant functional type had impacts on the effect of AMF on shoot biomass; AMF guild also impacted the effect of AMF on root biomass. Of these factors, the experimental duration, plant R/S, and pot size were the three most important predicting the effects of AMF on the plant shoot, root, and total biomass. This study comprehensively assessed the importance of the different factors that influenced the response of plants to AMF, highlighting that the experimental duration, plant R/S, and pot size should be taken into consideration in pot experiments in studies of the functions of AMF. Multiple unfavorable factors that may obscure or confound the observed functions of AMF should be excluded.

Temporal complementarity between roots and mycorrhizal fungi drives wheat nitrogen use efficiency

Improving nitrogen (N) use efficiency (NUE) to reduce the application of N fertilisers in a way that benefits the environment and reduces farmers' costs is an ongoing objective for sustainable wheat production. However, whether and how arbuscular mycorrhizal fungi (AMF) affect NUE in wheat is still not well explored. Three independent but complementary experiments were conducted to decipher the contribution of roots and AMF to the N uptake and utilisation efficiency in wheat. We show a temporal complementarity pattern between roots and AMF in shaping NUE of wheat. Pre-anthesis N uptake efficiency mainly depends on root functional traits, but the efficiency to utilise the N taken up during pre-anthesis for producing grains (E_N,g ) is strongly affected by AMF, which might increase the uptake of phosphorus and thereby improve photosynthetic carbon assimilation. Root association with AMF reduced the N remobilisation efficiency in varieties with high E_N,g ; whilst the overall grain N concentration increased, due to a large improvement in post-anthesis N uptake supported by AMF and/or other microbes. The findings provide evidence for the importance of managing AMF in agroecosystems, and an opportunity to tackle the contradiction between maximising grain yield and protein concentration in wheat breeding.

The mycorrhiza-specific ammonium transporter ZmAMT3;1 mediates mycorrhiza-dependent nitrogen uptake in maize roots

Most plant species can form symbioses with arbuscular mycorrhizal fungi (AMFs), which may enhance the host plant's acquisition of soil nutrients. In contrast to phosphorus nutrition, the molecular mechanism of mycorrhizal nitrogen (N) uptake remains largely unknown, and its physiological relevance is unclear. Here, we identified a gene encoding an AMF-inducible ammonium transporter, ZmAMT3;1, in maize (Zea mays) roots. ZmAMT3;1 was specifically expressed in arbuscule-containing cortical cells and the encoded protein was localized at the peri-arbuscular membrane. Functional analysis in yeast and Xenopus oocytes indicated that ZmAMT3;1 mediated high-affinity ammonium transport, with the substrate NH4+ being accessed, but likely translocating uncharged NH3. Phosphorylation of ZmAMT3;1 at the C-terminus suppressed transport activity. Using ZmAMT3;1-RNAi transgenic maize lines grown in compartmented pot experiments, we demonstrated that substantial quantities of N were transferred from AMF to plants, and 68%-74% of this capacity was conferred by ZmAMT3;1. Under field conditions, the ZmAMT3;1-dependent mycorrhizal N pathway contributed >30% of postsilking N uptake. Furthermore, AMFs downregulated ZmAMT1;1a and ZmAMT1;3 protein abundance and transport activities expressed in the root epidermis, suggesting a trade-off between mycorrhizal and direct root N-uptake pathways. Taken together, our results provide a comprehensive understanding of mycorrhiza-dependent N uptake in maize and present a promising approach to improve N-acquisition efficiency via plant-microbe interactions.

Effects of Commercial Arbuscular Mycorrhizal Inoculants on Plant Productivity and Intra-Radical Colonization in Native Grassland: Unintentional De-Coupling of a Symbiosis?

There has been a surge in industries built on the production of arbuscular mycorrhizal (AM) fungal-based inoculants in the past few decades. This is not surprising, given the positive effects of AM fungi on plant growth and nutritional status. However, there is growing concern regarding the quality and efficacy of commercial inoculants. To assess the potential benefits and negative consequences of commercial AM fungal inoculants in grasslands, we conducted a controlled growth chamber study assessing the productivity and AM fungal root colonization of nine grassland plant species grown in grassland soil with or without one of six commercial AM fungal products. Our research showed no evidence of benefit; commercial inoculants never increased native plant biomass, although several inoculants decreased the growth of native species and increased the growth of invasive plant species. In addition, two commercial products contained excessive levels of phosphorus or nitrogen and consistently reduced AM fungal root colonization, indicating an unintentional de-coupling of the symbiosis. As there is little knowledge of the ecological consequences of inoculation with commercial AM fungal products, it is critical for restoration practitioners, scientists, and native plant growers to assess the presence of local AM fungal communities before investing in unnecessary, or possibly detrimental, AM fungal products.

Impacts of Drought Stress and Mycorrhizal Inoculation on the Performance of Two Spring Wheat Cultivars

Cereal production is becoming challenging, given ongoing climate change. Arbuscular mycorrhizal fungi (AMF) are discussed to mitigate effects of drought for plants and enhance nutrient uptake. Thus, we investigated the impacts of drought and mycorrhiza on the growth and allocation patterns of two cultivars of spring wheat (Triticum aestivum). Plants were grown under three irrigation regimes (well-watered, continuous or pulsed drought) and in three substrates (absence or presence of one or three AMF species). Applied water use efficiency (WUEapplied), harvest index (HI) and contents of carbon (C), nitrogen (N) and phosphorous (P) were determined when grains were watery ripe. When grains were hard, again, WUEapplied, HI and the thousand-kernel weight were measured. The WUEapplied and HI were lowest in plants under pulsed drought stress at the second harvest, while the thousand-kernel weight was lower in mycorrhized compared to non-mycorrhized plants. The C/N ratio dropped with increasing drought stress but was enhanced by mycorrhiza, while the P content was surprisingly unaffected by mycorrhiza. The total root length colonization was higher in substrates with the AMF mix, but overall, fungal presence could not alleviate the effects of drought. Our results highlight the complexity of responses to challenging environments in this highly domesticated species.

Amendment with Burkina Faso phosphate rock-enriched composts alters soil chemical properties and microbial structure, and enhances sorghum agronomic performance

Low soil available phosphorus (P) severely limits crop production in sub-Saharan Africa. The present study evaluated phosphate rock-enriched composts as locally available low-cost fertilizers for sorghum production. The treatments consisted of sorghum straw, compost (COMP), phosphate rock (BPR), BPR-enriched compost (P-COMP), BPR-rhizosphere soil-enriched compost (P-COMP-SOIL), nitrogen-phosphorus-potassium treatment (NPK, 60–39–25), and control (NK, 60–25). Sorghum straw and compost were applied at 1.34 tons ha⁻¹. N, P, and K in all treatments, excluding the control, were adjusted to 60, 39, and 25 kg ha⁻¹, with urea, BPR, and KCl, respectively. Sorghum vr. kapelga was cultivated and soil samples were collected at the S5, S8, and S9 growth stages. P-COMP-SOIL and NPK yielded better sorghum yields than the other treatments. The rhizosphere soil of P-COMP-SOIL had high abundance of soil bacteria and AMF, and genes involved in P solubilization, such as: acid phosphatase (aphA), phosphonatase (phnX), glucose dehydrogenase (gcd), pyrroloquinoline quinone (pqqE), phosphate-specific transporter (pstS). The superior performance of the P-COMP-SOIL was associated with its higher available P content and microbial abundance. Multivariate analysis also revealed vital contributions of N, carbon, and exchangeable cations to sorghum growth. Soils could be amended with phosphate rock-rhizosphere soil-enriched composts, as an alternative to chemical fertilizers.

Agricultural management and pesticide use reduce the functioning of beneficial plant symbionts

Phosphorus (P) acquisition is key for plant growth. Arbuscular mycorrhizal fungi (AMF) help plants acquire P from soil. Understanding which factors drive AMF-supported nutrient uptake is essential to develop more sustainable agroecosystems. Here we collected soils from 150 cereal fields and 60 non-cropped grassland sites across a 3,000 km trans-European gradient. In a greenhouse experiment, we tested the ability of AMF in these soils to forage for the radioisotope 33P from a hyphal compartment. AMF communities in grassland soils were much more efficient in acquiring 33P and transferred 64% more 33P to plants compared with AMF in cropland soils. Fungicide application best explained hyphal 33P transfer in cropland soils. The use of fungicides and subsequent decline in AMF richness in croplands reduced 33P uptake by 43%. Our results suggest that land-use intensity and fungicide use are major deterrents to the functioning and natural nutrient uptake capacity of AMF in agroecosystems.