Ecology and Diversity of Arbuscular Mycorrhizal Fungi (AMF) in Rice (Oryza sativa L.) in South India: An Ecological Analysis of Factors Influencing AMF in Rice Fields.

AIMS: This study examined the diversity of arbuscular mycorrhizal fungi (AMF), mean spore density (MSD), and root colonization in relation to factors such as agroclimatic zones, rice varieties, soil types, and rice varieties in paddy fields of South India. The aim was to understand how these factors influence AMF, facilitating their effective use as a biological tool in agriculture. METHODS AND RESULTS: AMF were identified through light microscopy of spores, while MSD and percentage-root-length colonization (PRLC) were measured using standard methods. Correlation and principal component analyses were performed to explore the interrelationships between AMF characteristics and various environmental, soil, and plant variables. Sixteen AMF species were identified across 29 rice varieties from three agroclimatic zones, six soil orders, and 18 soil series over two seasons. Notably, 70% of chemicalized rice fields lacked AMF spores, and only 50% exhibited root colonization. This study offers new insights into the role of AMF in rice cultivation. CONCLUSIONS: The AMF diversity and root colonization in relation to environmental variables underscores their significant impact on AMF in particular crop fields.

Assessing the potential role of arbuscular mycorrhizal fungi in improving the phytochemical content and antioxidant properties in Gomphrena globosa.

Strategies to increase the secondary metabolite production, obtained from medicinal plants has been the topic of research in recent years. The symbiotic interaction between arbuscular mycorrhizal fungi and plants allows host-fungus pairings to enhance secondary metabolite synthesis. Therefore, the current study investigated the effect of inoculating two distinct AMF species discretely as well as in conjunction on the flower-derived secondary metabolites in Gomphrena globosa. The findings showed that the plants inoculated with combined treatment exhibited higher total phenolic (50.11 mg GAE/g DW), flavonoids (29.67 mg QE/g DW), saponins (122.55 mg DE/g DW), tannins (165.71 TAE/g DW) and terpenoid (8.24 mg LE/g DW) content in the methanolic extract. HPTLC examination showed the existence of kaempferol and benzoic acid with the highest amount (0.90% and 5.83% respectively) observed in the same treatment. FTIR analysis revealed functional group peaks with increased peak intensity in the combination treatment. Higher antioxidant activities such as DPPH (IC50: 401.39 µg/mL), ABTS (IC50: 71.18 µg/mL) and FRAP (8774.73 µM Fe (II) equivalent) were observed in the methanolic extract of combined treatment. To our knowledge, this is the first study on the impact of AMF inoculation on bioactive compounds and antioxidant activities in G. globosa flowers. Moreover, this study could lead to the development of novel pharmaceuticals and herbal remedies for various diseases.

Recycling steel slag as fertiliser proxy in agriculture is good circular economy but disrupts plant microbial symbioses in the soil.

Modern agriculture depends on synthetic fertilisers to ensure food security but their manufacture and use accounts for ~5 % of the global greenhouse gas emissions. Achieving climate change targets therefore requires alternatives, that while maintaining crop productivity, reduce emissions across the lifecycle of fertiliser utilisation. Steel slag, a nutrient-rich by-product of steel manufacture, offers a viable alternative. Being substantially cheaper than fertilisers, it is economically attractive for farmers, particularly in low-middle income countries of the Global South. However, slag application in agriculture poses risk of pollutant transfer to the human food chain and disruption of key plant-microbe symbioses like the arbuscular mycorrhizal fungi (AMF). Here, using barley as a model crop, we tested the suitability of slag as a fertiliser proxy. Mycorrhizal and non-mycorrhizal barley were grown in soils ameliorated with slag in concentrations of 0, 2, 5 and 10 t ha-1. We analysed slag-mycorrhiza interaction and their combined effects on crop yield and risks to human nourishment. Slag increased grain yield by respective 32 and 21 % in mycorrhizal and non-mycorrhizal barley. Grain concentration of metal pollutants in mycorrhizal and non-mycorrhizal barley fertilised with slag were within the WHO recommended limits. But slag reduced mycorrhizal colonisation in barley roots and extraradical hyphal spread in the soil. The consequent decline in symbiont function lowered AMF-mediated plant nutrient uptake and increased mineral losses in leachates. AMF are keystone species of the soil microbiome. Loss of AMF function presents long-term ecological consequences for agriculture and necessitates a careful evaluation of slag application to soil.

Corrigendum: Drought-induced adaptive and ameliorative strategies in plants [Chemosphere 364 (2024) 143134].

Drought stress (DS) is a hazardous abiotic prerequisite that is becoming increasingly severe around the world. As a result, new management measures to reduce the negative effects of DS are desperately needed to ensure improved agricultural productivity. This review focuses primarily on various DS mitigation strategies that can be utilized to overcome DS. In recent years, the application of biochar, plant growth promoting rhizobacteria (PGPR), and arbuscular mycorrhizal fungi (AMF) have emerged as major strategies for improving crop yields under DS conditions. PGPR increases osmolyte buildup, increases the aminocyclopropane-1-carboxylate (ACC) deaminase enzyme, and provides inaccessible nutrients to plants, hence boosting drought tolerance. Different genetic approaches, including as transcriptional engineering, miRNA engineering, and quantitative trait loci (QTL) mapping, have emerged as an incredibly efficient method for making drought-resistant plants. Drought-related phytohormones, signaling molecules, transcription factors, and transcriptional and translational changes are all affected by genomic intervention. It is critical for enhancing tolerance response to identify prospective transcription factors and target them for engineering the abiotic stress tolerance response in crop plants. Investigating novel QTLs for drought tolerance features using a fresh genetic resource would also be beneficial in dissecting the mechanisms governing the trait's diversity. This review aims to provide information to readers about drought mitigation measures including the usage of PGPR, AMF, biochar, phytohormones, chemicals, and genetic approaches.

Arbuscular mycorrhizal fungal inoculum and N2-fixing plants in ecological reclamation of arid mining areas: nutrient limitation of the moss biocrust microbiome.

Ecoenzymatic stoichiometry can reflect the ability of soil microorganisms to acquire energy and nutrients and to determine their response to environmental stresses. However, the drivers of metabolic limitation of the moss biocrust microbiome during the ecological restoration of coal mining areas are poorly understood. Therefore, in this study, enzymatic stoichiometry modeling and high-throughput sequencing were used to simultaneously determine moss biocrust microbial metabolic limitation and its relationship with moss biocrust nutrients and arbuscular mycorrhizal fungal (AMF) diversity in five arid and semi-arid revegetation types (Hippophae rhamnoides, Amorpha fruticosa, Cerasus humilis, Cerasus szechuanica, and Xanthoceras sorbifolium) and two microbial treatments (AMF-inoculated and uninoculated). The activities of moss biocrust carbon (C)-, nitrogen (N)-, and phosphorus (P)-acquiring enzymes and organic carbon fractions in the AMF-inoculated treatment were significantly higher than those in the uninoculated control. Moss biocrust microbial community C and P limitations were observed in the five revegetation types, with lower limitation in general in the AMF-inoculated treatment. Dinitrogen-fixing plants (Amorpha fruticosa and Hippophae rhamnoides) significantly mitigated moss biocrust microbiome C and P limitation, especially in the AMF-inoculated treatment. Furthermore, partial least squares path modeling (PLS-PM) shows that moss biocrust organic carbon fractions (- 0.73 and - 0.81 of the total effects, respectively) and AMF diversity (- 0.73 and - 0.81 of the total effects) had negative effect on microbial C and P limitation, suggesting that more efficient active nutrients and AMF diversity are important factors alleviating limitation of moss biocrust microbial metabolism. This indicates that moss biocrust microbial communities under N2-fixing species with AMF inoculation were more stable under environmental stress; thus, AMF inoculation and/or N2-fixing plants may be recommended as preferred options for the ecological restoration of arid mining areas.

Microbial necromass and glycoproteins for determining soil carbon formation under arbuscular mycorrhiza symbiosis.

Arbuscular mycorrhizal fungi (AMF) form symbioses with most terrestrial plants and critically modulate soil organic carbon (C) dynamics. Whether AMF promote soil C storage and stability is, however, largely unknown. Since microbial necromass C (MNC) and glomalin-related soil protein (GRSP) are stable microbial-derived C in soils, we therefore evaluated how AMF symbiosis alters both soil C pools and their contributions to soil organic C (SOC) under nitrogen fertilization, based on a 16-weeks mesocosm experiment using a mutant tomato with highly reduced AMF symbiosis. Results showed that SOC content is 4.5 % higher following AMF symbiosis. Additionally, the content of MNC and total GRSP were 47.5 % and 22.3 % higher under AMF symbiosis than at AMF absence, respectively. The accumulations of GRSP and microbial necromass in soil were closely associated with mineral-associated organic C and the abundance of AMF. The increased soil living microbial biomass under AMF symbiosis was mainly derived from AMF biomass, and fungal necromass C significantly contributed to SOC accumulation, as evidenced by the higher fungal:bacterial necromass C ratio under AMF symbiosis. On the contrary, bacterial necromass was degraded to compensate for the increased microbial nutrient demand because of the aggravated nutrient limitation under AMF symbiosis, leading to a decrease in bacterial necromass. Redundancy analysis showing that bacterial necromass was negatively correlated with soil C:N ratio supported this argument. Moreover, the relative change rate of total GRSP was consistently greater in nitrogen-limited soil than that of microbial necromass. Our findings suggested GRSP accumulates faster and contributes more to SOC pools under AMF symbiosis than microbial necromass. The positive correlation between the contributions of GRSP and MNC to SOC further provided valuable information in terms of enhancing our understanding of mechanisms underlying the maintenance of SOC stocks through microbial-derived C.

Inoculation with arbuscular mycorrhizal fungi improves plant biomass and nitrogen and phosphorus nutrients: a meta-analysis.

Arbuscular mycorrhizal fungi (AMF) have profound effects on plant growth and nitrogen (N) and phosphorus (P) nutrition. However, a comprehensive evaluation of how plant N and P respond to AMF inoculation is still unavailable. Here, we complied data from 187 original researches and carried out a meta-analysis to assess the effects of AMF inoculation on plant growth and N and P nutrition. We observe overall positive effects of AMF inoculation on plant performance. The mean increases of plant biomass, N concentration, P concentration, N and P uptake of whole plant are 47%, 16%, 27%, 67%, and 105%, respectively. AMF inoculation induces more increases in plant concentrations and storage of P than N. Plant responses to AMF inoculation are substantially higher with single AMF species than with mixed AMF species, in laboratory experiments than in field experiments, and in legumes than in non-legumes. The response ratios of plant N and P nutrition are positively correlated with AMF colonization rate, N addition, P addition, and water condition, while unvaried with experiment duration. The biggest and smallest effect sizes of AMF inoculation on plant performance are observed in the application of nitrate and ammonium, respectively. Accordingly, this meta-analysis study clearly suggests that AMF inoculation improves both plant N and P nutrients and systematically clarifies the variation patterns in AMF effects with various biotic and abiotic factors. These findings highlight the important role of AMF inoculation in enhancing plant N and P resource acquisitions and provide useful references for evaluating the AMF functions under the future global changes.

A mycoheterotrophic orchid uses very limited soil inorganic nitrogen in its natural habitat.

Mycoheterotrophic plants acquire nitrogen (N) directly from the soil and through their symbiotic fungi. The fungi-derived N has received considerable attention, but the contribution of soil-derived N has been largely overlooked. We investigated how the leafless, rootless, and almost mycoheterotrophic orchid Cymbidium macrorhizon obtains soil N by applying 15N-labeled ammonium nitrate in its natural habitat, and tracking metabolite accumulation and mycorrhizal fungal association after N application. The decline of N in the rhizome from flowering to fruiting indicated a transfer of N from the rhizome to fruits. At current dose of N application (0.6 g NH4NO3 each plant), only 1.5% of the plant's N was derived from fertilizer, resulting in a low nitrogen use efficiency of 0.27%. The majority of those newly absorbed N (88.89%) was found sank in the rhizome. Amino acids (or their derivatives) and alkaloids were predominant differentially accumulated nitrogenous metabolites after N application, with amino acids occurring in both fruits and the rhizome, and alkaloids primarily in the fruits. The addition of N did not alter the richness of mycorrhizal fungi, but did affect their relative abundance. Our findings suggest that Cymbidium macrorhizon uses very limited soil inorganic nitrogen in its natural habitat, and the root-like rhizome primarily stores N rather than absorbs its inorganic forms, offering new insights into how mycoheterotrophic plants utilize soil N, and the influence of nutrient availability on the orchid-fungi association.

A gap in the recognition of two mycorrhizal factors: new insights into two LysM-type mycorrhizal receptors.

Arbuscular mycorrhizal (AM) fungi are crucial components of the plant microbiota and can form symbioses with 72% of land plants. Researchers have long known that AM symbioses have dramatic effects on plant performance and also provide multiple ecological services in terrestrial environments. The successful establishment of AM symbioses relies on the host plant recognition of the diffusible mycorrhizal (Myc) factors, lipo-chitooligosaccharides (LCOs) and chitooligosaccharides (COs). Among them, the short-chain COs such as CO4/5 secreted by AM fungi are the major Myc factors in COs. In this review, we summarize current advances, develop the concept of mycorrhizal biceptor complex (double receptor complexes for Myc-LCOs and CO4/5 in the same plant), and provide a perspective on the future development of mycorrhizal receptors. First, we focus on the distinct perception of two Myc factors by different host plant species, highlighting the essential role of Lysin-Motif (LysM)-type mycorrhizal receptors in perceiving them. Second, we propose the underlying molecular mechanisms by which LysM-type mycorrhizal receptors in various plants recognize both the Myc-LCOs and -COs. Finally, we explore future prospects for studies on the biceptor complex (Myc-LCO and -CO receptors) in dicots to facilitate the utilization of them in cereal crops (particularly in modern cultivated rice). In conclusion, our understanding of the precise perception processes during host plant interacting with AM fungi, where LysM-type mycorrhizal receptors act as recruiters, provides the tools to design biotechnological applications addressing agricultural challenges.

Enhanced Soil Fertility and Carbon Dynamics in Organic Farming Systems: The Role of Arbuscular Mycorrhizal Fungal Abundance.

Arbuscular mycorrhizal fungi (AMF) are critical for soil ecosystem services as they enhance plant growth and soil quality via nutrient cycling and carbon storage. Considering the growing emphasis on sustainable agricultural practices, this study investigated the effects of conventional and organic farming practices on AMF diversity, abundance, and ecological functions in maize, pepper, and potato-cultivated soils. Using next-generation sequencing and quantitative PCR, we assessed AMF diversity and abundance in addition to soil health indicators such as phosphorus content, total nitrogen, and soil organic carbon. Our findings revealed that, while no significant differences in soil physicochemical parameters or AMF diversity were observed across farming systems when all crop data were combined, organic farming significantly enhances AMF abundance and fosters beneficial microbial ecosystems. These ecosystems play vital roles in nutrient cycling and carbon storage, underscoring the importance of organic practices in promoting robust AMF communities that support ecosystem services. This study not only deepens our understanding of AMF's ecological roles but also highlights the potential of organic farming to leverage these benefits for improving sustainability in agricultural practices.

Progressing beyond colonization strategies to understand arbuscular mycorrhizal fungal life history.

Knowledge of differential life-history strategies in arbuscular mycorrhizal (AM) fungi is relevant for understanding the ecology of this group and its potential role in sustainable agriculture and carbon sequestration. At present, AM fungal life-history theories often focus on differential investment into intra- vs extraradical structures among AM fungal taxa, and its implications for plant benefits. With this Viewpoint we aim to expand these theories by integrating a mycocentric economics- and resource-based life-history framework. As in plants, AM fungal carbon and nutrient demands are stoichiometrically coupled, though uptake of these elements is spatially decoupled. Consequently, investment in morphological structures for carbon vs nutrient uptake is not in competition. We argue that understanding the ecology and evolution of AM fungal life-history trade-offs requires increased focus on variation among structures foraging for the same element, that is within intra- or extraradical structures (in our view a 'horizontal' axis), not just between them ('vertical' axis). Here, we elaborate on this argument and propose a range of plausible life-history trade-offs that could lead to the evolution of strategies in AM fungi, providing testable hypotheses and creating opportunities to explain AM fungal co-existence, and the context-dependent effects of AM fungi on plant growth and soil carbon dynamics.

The role of arbuscular mycorrhizal fungi in micronutrient homeostasis and cadmium uptake and transfer in rice under different flooding intensities.

Flooding intensity significantly alters the availability of iron (Fe), zinc (Zn), and cadmium (Cd) in paddy soil. However, the influence of arbuscular mycorrhizal fungi (AMF) on the uptake and transfer of Cd and micronutrients (Fe and Zn) under Cd stress in varying flooding conditions is not well understood. A pot experiment was conducted to investigate the micronutrient homeostasis and Cd uptake and transfer in rice cultivated in Cd-contaminated soil with AMF inoculation under continuous and intermittent flooding conditions. Compared to non-inoculation controls, mycorrhizal inoculation decreased Cd concentration in rice plants under continuous and intermittent flooding, and improved grain yield by 39.2 % for early season rice and 21.1 % for late season rice under continuous flooding. Mycorrhizal inoculation balanced the availability of Zn and Fe and decreased the availability of Cd in soil, lowering the ratios of soil-available Cd to both soil-available Zn and soil Fe2+. These changes led to a redistribution of Zn and Fe concentrations in rice, thereby reducing Cd acquisition in a soil-rice system. Structural equation model (SEM) analysis revealed that mycorrhizal inoculation had a strong direct negative effect on the expression of Zn and Fe-related genes OsNRAMP1, OsIRT1, and OsIRT2 in the roots of rice, which in turn directly affected root Cd concentration. Furthermore, mycorrhizal colonization decreased Cd transfer coefficients from leaves to grains under continuous flooding and from nodes and leaves to grains under intermittent flooding. In the nodes, the Fe concentration and the expression of genes OsIRT1 and OsHMA2 were associated with Cd transfer from the nodes to grains. Similarly, in the leaves, the expression of genes OsZIP1 and OsMTP1 corresponded with Cd transfer from leaves to grains. This study provides insights into the role of AMF in affecting micronutrient concentrations and Cd uptake in rice under varying flooding conditions.

Specialized protist communities on mycorrhizal fungal hyphae.

Arbuscular mycorrhizal (AM) fungi not only play a crucial role in acquiring nutrients for plants but also serve as a habitat for soil microbes. Recent studies observed that AM fungal hyphae are colonized by specific bacterial communities. However, so far it has not been explored whether fungal hyphae and mycorrhizal networks also harbor specific communities of protists, a key group of microbes in the soil microbiome. Here, we characterized protist communities in soil in a compartment with plant roots and on hyphae collected from hyphal compartments without plant roots. We detected specific protist communities on fungal hyphae. Fourteen protistan amplicon sequences variants (ASVs) were significantly associated with fungal hyphae, half of which belonged to the Cercozoa group. This research, for the first-time detected specific protist ASVs directly associated with abundant AM fungus hyphae, highlighting the complexity of the hyphal food web.

The crosstalk interaction of ethylene, gibberellins, and arbuscular mycorrhiza improves growth in salinized tomato plants by modulating the hormonal balance.

Ethylene (ET) and gibberellins (GAs) play key roles in controlling the biotic and abiotic interactions between plants and environment. To gain insights about the role of ET and GAs interactions in the mycorrization and response to salinity of tomato (Solanum lycopersicum L.) plants, the ET-insensitive (Never-ripe, Nr), and the ET-overproducer (Epinastic, Epi) mutants and their wild type cv. Micro-Tom (MT), were inoculated or not with the arbuscular mycorrhizal fungi (AMF) Rhizophagus irregularis and exposed to control (0 mM NaCl) and salinity (100 mM NaCl) conditions, with and without gibberellic acid (10-6 M GA3) application during four weeks. Exogenous GA3 enhanced plant growth irrespective of the genotype, AMF, and salinity conditions, while an additional effect on growth by AMF was only found in the ET-overproducer (Epi) mutant under control and salinity conditions. Epi almost doubled the AMF colonization level under both conditions but was the most affected by salinity and GA3 application compared to MT and Nr. In contrast, Nr registered the lowest AMF colonization level, but GA3 produced a positive effect, particularly under salinity, with the highest leaf growth recovery. Foliar GA3 application increased the endogenous concentration of GA1, GA3, and total GAs, more intensively in AMF-Epi plants, where induced levels of the ET-precursor ACC were also found. Interestingly, GA4 which is associated with AMF colonization, registered the strongest genotype x GA x AMF × salinity interactions. The different growth responses in relation to those interactions are discussed.

Mycorrhizal and non-mycorrhizal perennial ryegrass roots exhibit differential regulation of lipid and Ca2+ signaling pathways in response to low and high temperature stresses.

Lipids and Ca2+ are involved as intermediate messengers in temperature-sensing signaling pathways. Arbuscular mycorrhizal (AM) symbiosis is a mutualistic symbiosis between fungi and terrestrial plants that helps host plants cope with adverse environmental conditions. Nonetheless, the regulatory mechanisms of lipid- and Ca2+-mediated signaling pathways in mycorrhizal plants under cold and heat stress have not been determined. The present work focused on investigating the lipid- and Ca2+-mediated signaling pathways in arbuscular mycorrhizal (AM) and non-mycorrhizal (NM) roots under temperature stress and determining the role of Ca2+ levels in AM symbiosis and temperature stress tolerance in perennial ryegrass (Lolium perenne L.) Compared with NM plants, AM symbiosis increased phosphatidic acid (PA) and Ca2+ signaling in the roots of perennial ryegrass, increasing the expression of genes associated with low temperature (LT) stress, including LpICE1, LpCBF3, LpCOR27, LpCOR47, LpIRI, and LpAFP, and high temperature (HT) stress, including LpHSFC1b, LpHSFC2b, LpsHSP17.8, LpHSP22, LpHSP70, and LpHSP90, under LT and HT conditions. These effects result in modulated antioxidant enzyme activities, reduced lipid peroxidation, and suppressed growth inhibition caused by LT and HT stresses. Furthermore, exogenous Ca2+ application enhanced AM symbiosis, leading to the upregulation of Ca2+ signaling pathway genes in roots and ultimately promoting the growth of perennial ryegrass under LT and HT stresses. These findings shed light on lipid and Ca2+ signal transduction in AM-associated plants under LT and HT stresses, emphasizing that Ca2+ enhances cold and heat tolerance in mycorrhizal plants.

Phosphatases: Decoding the Role of Mycorrhizal Fungi in Plant Disease Resistance.

Mycorrhizal fungi, a category of fungi that form symbiotic relationships with plant roots, can participate in the induction of plant disease resistance by secreting phosphatase enzymes. While extensive research exists on the mechanisms by which mycorrhizal fungi induce resistance, the specific contributions of phosphatases to these processes require further elucidation. This article reviews the spectrum of mycorrhizal fungi-induced resistance mechanisms and synthesizes a current understanding of how phosphatases mediate these effects, such as the induction of defense structures in plants, the negative regulation of plant immune responses, and the limitation of pathogen invasion and spread. It explores the role of phosphatases in the resistance induced by mycorrhizal fungi and provides prospective future research directions in this field.

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.

Arbuscular mycorrhizal hyphae facilitate rhizobia dispersal and nodulation in legumes.

In soil ecosystems, rhizobia occupy the rhizosphere of legume roots to form nodules, a process triggered by microbial recognition of specific root-derived signals (i.e., flavonoids). However, soil conditions can limit bacterial motility, restricting signal perception to the area directly influenced by roots. Legumes, like most plants of agricultural interest, associate with arbuscular mycorrhizal fungi, whose hyphae develop extensively in the soil, potentially providing an effective dispersal network for rhizobia. We hypothesized that mycelial networks of arbuscular mycorrhizal fungi play a role in signal transmission and act as a highway, enabling rhizobia to migrate from distant soil to the roots of leguminous plants. Using in vitro and greenhouse microcosm systems, we demonstrated that Rhizophagus irregularis helps Shinorhizobium meliloti to migrate towards the legume Medicago truncatula, triggering nodulation, a mechanism absent without the arbuscular mycorrhizal fungus. Metabolomics analysis revealed eight flavonoids unique to the compartment containing extraradical hyphae of the arbuscular mycorrhizal fungus linked to M. truncatula roots, associated with S. meliloti growth and nod gene expression. Rhizobia plated on the extraradical hyphae connecting two plants (the legume M. truncatula and non-legume Solanum tuberosum) by a common mycelium network, showed preference for the legume, suggesting the chemoattraction by specific signals transported by the fungus connected to the legume. Simultaneously, S. meliloti stimulated the cytoplasmic/protoplasmic flow in the hyphae, likely increasing the release of nutrients and signals. Our results highlight the importance of extraradical hyphae (i.e. the mycorrhizal pathway) of arbuscular mycorrhizal fungi for the migration of rhizobia over long distances to the roots, leading to nodulation.

Mitigating gadolinium toxicity in guar (Cyamopsis tetragonoloba L.) through the symbiotic associations with arbuscular mycorrhizal fungi: physiological and biochemical insights.

BACKGROUND: Gadolinium (Gd) is an increasingly found lanthanide element in soil; thus, understanding its impact on plant physiology, biochemistry, and molecular responses is crucial. Here, we aimed to provide a comprehensive understanding of Gd (150 mg kg- 1) impacts on guar (Cyamopsis tetragonoloba L.) plant yield and metabolism and whether the symbiotic relationship with arbuscular mycorrhizal fungi (AMF) can mitigate Gd toxicity of soil contamination. RESULTS: AMF treatment improved mineral nutrient uptake and seed yield by 38-41% under Gd stress compared to non-inoculated stressed plants. Metabolic analysis unveiled the defense mechanisms adopted by AMF-treated plants, revealing carbon and nitrogen metabolism adaptations to withstand Gd contamination. This included an increase in the synthesis of primary metabolites, such as total sugar (+ 39% compared to control), soluble sugars (+ 29%), starch (+ 30%), and some main amino acids like proline (+ 57%) and phenylalanine (+ 87%) in the seeds of AMF-treated plants grown under Gd contamination. Furthermore, fatty acid and organic acid profile changes were accompanied by the production of secondary metabolites, including tocopherols, polyamines, phenolic acids, flavones, and anthocyanins. CONCLUSIONS: Overall, the coordinated synthesis of these compounds underscores the intricate regulatory mechanisms underlying plant-AMF interactions and highlights the potential of AMF to modulate plant secondary metabolism for enhanced Gd stress tolerance.

Arbuscular mycorrhizal fungi and exogenous Ca2+ application synergistically enhance salt and alkali resistance in perennial ryegrass through diverse adaptive strategies.

The challenge of soil salinization and alkalization, with its significant impact on crop productivity, has raised growing concerns with global population growth and enhanced environmental degradation. Although arbuscular mycorrhizal fungi (AMF) and calcium ions (Ca2+) are known to enhance plant resistance to stress, their combined effects on perennial ryegrass' tolerance to salt and alkali stress and the underlying mechanisms remain poorly understood. This study aimed to elucidate the roles of Arbuscular mycorrhizal (AM) fungus Rhizophagus irregularis and exogenous Ca2+ application in molecular and physiological responses to salt-alkali stress. AM symbiosis and exogenous Ca2+ application enhanced antioxidant enzyme activity and non-enzymatic components, promoting reactive oxygen species (ROS) scavenging and reducing lipid peroxidation while alleviating oxidative damage induced by salt-alkali stress. Furthermore, they enhanced osmotic balance by increasing soluble sugar content (Proportion of contribution of the osmotic adjustment were 34∼38 % in shoots and 30∼37 % in roots) under salt stress and organic acid content (Proportion of contribution of the osmotic adjustment were 32∼36 % in shoots and 37∼42 % in roots) under alkali stress. Changes in organic solute and inorganic cation-anion contents contributed to ion balance, while hormonal regulation played a role in these protective mechanisms. Moreover, the protective mechanisms involved activation of Ca2+-mediated signaling pathways, regulation of salt-alkali stress-related genes (including LpNHX1 and LpSOS1), increased ATPase activity, elevated ATP levels, enhanced Na+ extrusion, improved K+ absorption capacity, and a reduced Na+/K+ ratio, all contributing to the protection of photosynthetic pigments and the enhancement of photosynthetic efficiency. Ultimately, the combined application of exogenous Ca2+ and AMF synergistically alleviated the inhibitory effects of salt-alkali stress on perennial ryegrass growth. This finding suggested that exogenous Ca2+ may participate in the colonization of perennial ryegrass plants by R. irregularis, while AM symbiosis may activate Ca2+ pathways. Consequently, the combined treatment of AM and Ca2+ is beneficial for enhancing plant regulatory mechanisms and increasing crop yield under salt-alkali stress.