Glomus Intraradices Research Articles

Variability in Chemical Composition and Biochemical Activities of Mentha x piperita L. Essential Oil, in Response to Mycorrhizal Symbiosis and Heavy Metal Stress.

The present paper highlights the effect of Pb/Cd-stress and/or mycorrhizal colonization by Glomus Intraradices on yield, chemical composition, cytotoxicity and antimicrobial activity of Mentha x piperita L. essential oil. Our findings showed that mycorrhizal colonization could be used to improve the essential oil yield of M. x piperita, either in non-stressed or Pb/Cd-stressed plants. GC-MS analysis revealed three chemotypes: linalool/pulegone (32.6/30.8 %) chemotype in essential oils of non-mycorrhizal Pb-stressed plants, menthone/menthyl acetate (30.3/25.1 %) chemotype in essential oils of non-mycorrhizal Cd-stressed plants and menthol (44.6 %) chemotype in essential oils of non-mycorrhizal non-stressed plants, mycorrhizal non-stressed plants and mycorrhizal Pb/Cd-stressed plants. The cytotoxicity of M. x piperita essential oil, evaluated by brine shrimp lethality bioassay, was increased in presence of Pb/Cd-stress (from 379.58 to 72.84 μm/mL) and decreased in mycorrhizal plants (from 379.58 to 482.32 μm/mL). The antimicrobial activity of M. x piperita essential oil, evaluated by disc diffusion method and determination of Minimum Inhibitory Concentration against ten microorganisms, was enhanced by the mycorrhizal colonization and deceased by the Pb/Cd-stress. In conclusion, the inoculation of medicinal plants with mycorrhizal fungi is a real avenue for alleviating abiotic stress and/or increasing the quantity and quality of secondary metabolites in terms of biological activities.

IPD3, a master regulator of arbuscular mycorrhizal symbiosis, affects genes for immunity and metabolism of non-host Arabidopsis when restored long after its evolutionary loss

Arbuscular mycorrhizal symbiosis (AM) is a beneficial trait originating with the first land plants, which has subsequently been lost by species scattered throughout the radiation of plant diversity to the present day, including the model Arabidopsis thaliana. To explore if elements of this apparently beneficial trait are still present and could be reactivated we generated Arabidopsis plants expressing a constitutively active form of Interacting Protein of DMI3, a key transcription factor that enables AM within the Common Symbiosis Pathway, which was lost from Arabidopsis along with the AM host trait. We characterize the transcriptomic effect of expressing IPD3 in Arabidopsis with and without exposure to the AM fungus (AMF) Rhizophagus irregularis, and compare these results to the AM model Lotus japonicus and its ipd3 knockout mutant cyclops-4. Despite its long history as a non-AM species, restoring IPD3 in the form of its constitutively active DNA-binding domain to Arabidopsis altered expression of specific gene networks. Surprisingly, the effect of expressing IPD3 in Arabidopsis and knocking it out in Lotus was strongest in plants not exposed to AMF, which is revealed to be due to changes in IPD3 genotype causing a transcriptional state, which partially mimics AMF exposure in non-inoculated plants. Our results indicate that molecular connections to symbiosis machinery remain in place in this nonAM species, with implications for both basic science and the prospect of engineering this trait for agriculture.

Integrated approaches for heavy metal-contaminated soil remediation: harnessing the potential of Paulownia elongata S. Y. Hu, Oscillatoria sp., arbuscular mycorrhizal fungi (Glomus mosseae and Glomus intraradices), and iron nanoparticles.

In recent years, researchers have extensively investigated the remediation of heavy metal-contaminated soil using plants, microorganisms, and iron nanoparticles. The objective of this study was to investigate and compare the individual and simultaneous effects of Paulownia elongata S. Y. Hu, cyanobacteria (Oscillatoria sp.), arbuscular mycorrhizal fungi (AMF) including Glomus mosseae and Glomus intraradices, and zero-valent iron nanoparticles (nZVI) on the remediation of heavy metal-contaminated soil containing chromium (Cr VI and Cr III) and nickel (Ni). The study found significant variations in parameters such as pH (acidity), electrical conductivity (EC), nitrogen (N), phosphorus (P), potassium (K), and organic carbon (OC) among different treatments. The addition of cyanobacteria, AMF, and nZVI influenced these properties, resulting in both increases and decreases compared to the control treatment. The treatment involving a combination of cyanobacteria, AMF, and nZVI (CCAN25) exhibited the highest increase in growth parameters, such as total dry mass, root length, stem diameter, and leaf area, while other treatments showed varied effects on plant growth. Moreover, the CCAN25 treatment demonstrated the highest increase in chlorophyll a, chlorophyll b, and carotenoid levels, whereas other treatments displayed reductions in these pigments compared to the control. Moderate phytoaccumulation of Cr and Ni in P. elongata samples across all treatments was observed, as indicated by the bioconcentration factor and bioaccumulation coefficient values being less than 1.0 for both metals. The findings provide insights into the potential application of these treatments for soil remediation and plant growth enhancement in contaminated environments.

Arbuscular Mycorrhizal Fungi Inducing Tomato Plant Resistance and Its Role in Control of Bemisia tabaci Under Greenhouse Conditions.

Arbuscular mycorrhizal fungi (AMF) are one of the environment-friendly organisms that enhance plant performance. AMF affect the herbivorous insect community by indirectly modifying host plant nutrient uptake, growth, and defense, also known as priming. In the current study, under greenhouse conditions, the effects of inoculating tomato seedlings with four species of AMF, i.e., Funneliformis mosseae, Rhizophagus intraradices, Rhizophagus irregularis, and Glomus iranicus, were studied in relation to tomato plant growth parameters, plant defense enzymes, and total phenol content, and additionally, the life table of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) feeding on these plants was determined. The results demonstrated that the growth parameters of tomato plants, including plant height, stem diameter, number of leaves, root volume, leaf surface area, weight of the root, and aerial organs (containing the leaves and stem), were greater and larger in the AMF-inoculated plants compared to the non-inoculated plants. Furthermore, there were higher defense enzyme activities, including peroxidase, phenylalanine ammonia lyase and polyphenol oxidase, and also higher total phenol contents in the AMF-inoculated plants. The whitefly life table characteristics were decreased in the group feeding on the AMF-inoculated plants. All together, the AMF colonization made the tomato plants more resistant against B. tabaci by improving plant growth and increasing defense enzymes. The degree of priming observed here suggests the potential of AMF to have expansive applications, including their implementation in sustainable agriculture.

COI1-mediated jasmonic acid signalling regulates mycorrhizal colonisation intensity and is an indispensable component of mycorrhiza-induced resistance.

Hormonal signalling plays an elementary role in the regulation of plant-microbe interactions. Jasmonic acid (JA) signalling is one of the major regulators that decides the fate of these interactions in plants. However, the role of JA is not unanimous and varies from neutral to positive or negative regulation. In the present study, we targeted SlCOI1, a key gene in JA signalling, by silencing (using artificial miRNA approach) and overexpressing constitutively in tomato transgenic hairy roots (HR) system. We developed in-vitro colonisation of these hairy roots with model arbuscular mycorrhizal fungi (AMF) Rhizophagus irregularis. The colonised HR exhibited a stronger induction of PAMPs-triggered immunity (PTI) response and reactive oxygen species (ROS) homeostasis against Fusarium oxysporum f. sp. lycopersici (FOL). The ROS signalling key gene RBOH-B and the PTI response marker genes LRR22 and PTI5 were expressed at an earlier stage and at a higher amplitude in the colonised HR, providing evidence for mycorrhiza-induced resistance (MIR). Further, SlCOI1 silencing resulted in a higher degree of R. irregularis colonisation, while overexpression restricted its proliferation. Intriguingly, despite a higher degree of colonisation, the SlCOI1-silenced HR lines manifested a weakened MIR compared to its control colonised HR line. This univocally indicates an indispensable role of COI1-mediated JA signalling in MIR. This is one of the few studies conducted using in-vitro AMF-colonised HR system to understand how signalling events occurred during AMF colonisation and tripartite interactions, specifically MIR.

Arbuscular mycorrhizal fungi suppress ammonia-oxidizing bacteria but not archaea across agricultural soils

Arbuscular mycorrhizal (AM) fungi are supposedly competing with ammonia-oxidizing microorganisms (AO) for soil nitrogen in form of ammonium. Despite a few studies directly addressing AM fungal and AO interactions, mostly in artificial cultivation substrates, it is not yet clear whether AM fungi can effectively suppress AO in field soils containing complex indigenous microbiomes. To fill this knowledge gap, we conducted compartmentalized pot experiments using four pairs of cropland and grassland soils with varying physicochemical properties. To exclude the interference of roots, a fine nylon mesh was used to separate the rhizosphere and mesh bags, with the latter being filled with unsterile field soils. Inoculation of plants with AM fungus Rhizophagus irregularis LPA9 suppressed AO bacteria (AOB) but not archaea (AOA) in the soils, indicating how soil nitrification could be suppressed by AM fungal presence/activity. In addition, in rhizosphere filled with artificial substrate, AM inoculation did suppress both AOB and AOA, implying more complex interactions between roots, AO, and AM fungi. Besides, we also observed that indigenous AM fungi contained in the field soils eventually did colonize the roots of plants behind the root barrier, and that the extent of such colonization was higher if the soil has previously been taken from cropland than from grassland. Despite this, the effect of experimental AM fungal inoculation on suppression of indigenous AOB in the unsterile field soils did not vanish. It seems that studying processes at a finer temporal scale, using larger buffer zones between rhizosphere and mesh bags, and/or detailed characterization of indigenous AM fungal and AO communities would be needed to uncover further details of the biotic interactions between the AM fungi and indigenous soil AO.

Intraspecific competition hinders drought recovery in a resident but not in its range-expanding congener plant independent of mycorrhizal symbiosis

Background and aimsUnderstanding biotic interactions within plant populations and with their symbiotic partners is crucial for elucidating plant responses to drought. While many studies have highlighted the importance of intraspecific plant or mutualistic fungal interactions in predicting drought responses, we know little about the combined effects of these two interactions on the recovery of plants after drought.MethodsWe conducted an experiment to study the recovery after an extreme drought event of a native European plant species (Centaurea jacea) and its range-expanding congener (Centaurea stoebe), across a gradient of plant density and in association with an AM fungal species (Rhizophagus irregularis).ResultsOur results showed strong intraspecific competition in C. jacea, which constrained their post-drought recovery. We further found that AM fungi constrained root biomass recovery of C. jacea after drought under high intraspecific competition. The post-drought recovery in C. stoebe was high potentially due to its greater plasticity in the root diameter under drought conditions.ConclusionStrong intraspecific competition can constrain recovery in plants like C. jacea with lesser root trait plasticity after drought, independent of mycorrhizal symbiosis.

Arbuscular Mycorrhizal Fungi as Biofertilizers to Increase the Plant Quality of Sour-Orange Seedlings

In addressing the agricultural challenges posed by climate change, the use of biofertilizers, derived from living organisms, promotes environmentally friendly crop cultivation, and represents an adaptive strategy for sustainable agriculture in the face of climate uncertainty. Careful selection of the arbuscular mycorrhizal fungus (AMF) would represent a crucial step in mycorrhizal inoculation, considering the varying levels of compatibility between the AMF and the host plant. This study aimed to assess the impact of two AMF species that are prevalent in citrus soils of south-eastern Spain (Rhizophagus irregularis and Funneliformis mosseae) on the Citrus aurantium seedlings’ behavior. Sour-orange plants showed a high mycorrhizal dependence regardless of the specific AMF species. Both R. irregularis and F. mosseae fungi exhibited high colonization percentages, with R. irregularis outperforming F. mosseae in root colonization. Inoculation with both AMF yielded notable growth improvements, but R. irregularis exhibited higher positive effects in the long term. The heightened P nutrition and increased chlorophyll concentration significantly enhanced the performance of AMF-inoculated plants. With F. mosseae, plants showed more pronounced improvements in P nutrition and a stronger correlation of their dry mass with P concentration; however, in general, inoculation with R. irregularis produced a higher sour-orange-plant performance. Both R. irregularis and F. mosseae fungi produced strong positive effects in sour-orange growth, which positioned them as viable biofertilizer options. These results can contribute to enhancing understanding for the development of an improved design of biofertilizers used in regions that are vulnerable to climate change, such as south-eastern Spain. This promotes a shift towards more sustainable and environmentally friendly agricultural practices by reducing dependence on chemical fertilizers.

Microbial Consortia Versus Single-Strain Inoculants as Drought Stress Protectants in Potato Affected by the Form of N Supply

This study investigated the drought protection effects of six fungal and bacterial inoculants and ten consortia thereof on vegetative growth, nutritional status, and tuberization of potato under controlled and field conditions. It was hypothesized that microbial consortia offer improved drought protection as compared with single strains, due to complementary or synergistic effects, with differential impacts also of N fertilization management. Under NO3− fertilization, a 70% reduction in water supply over six weeks reduced shoot and tuber biomass of non-inoculated plants by 30% and 50%, respectively, and induced phosphate (P) limitation compared to the well-watered control. The P nutritional status was significantly increased above the deficiency threshold by three single-strain inoculants and eight consortia. This was associated with the presence of the arbuscular mycorrhizal fungus (AMF) inoculant Rhizophagus irregularis MUCL41833 (five cases) and stimulation of root growth (five cases). Additionally, Bacillus amyloliquefaciens FZB42 and AMF + Pseudomonas brassicacearum 3Re2-7 significantly reduced irreversible drought-induced leaf damage after recovery to well-watered conditions. However, the microbial inoculants did not mitigate drought-induced reductions in tuber biomass, neither in greenhouse nor in field experiments. By contrast, NH4+-dominated fertilization significantly increased tuber biomass under drought stress (534%), which was further increased by additional AMF inoculation (951%). This coincided with (i) improved enzymatic detoxification of drought-induced reactive oxygen species (ROS), (ii) improved osmotic adjustment in the shoot tissue (glycine betaine accumulation), (iii) increased shoot concentrations of ABA, jasmonic acid, and indole acetic acid, involved in drought stress signaling and tuberization, and (iv) reduced irreversible drought-induced leaf damage. Additional application of bacterial inoculants further improved ROS detoxification by increasing the production of antioxidants but stimulated biomass allocation towards shoot growth at the expense of tuber development. The results demonstrated that microbial consortia could increase the probability of drought protection effects influenced by the form of N supply. However, protective effects on vegetative growth do not necessarily translate into yield benefits, which can be achieved by adequate combination of inoculants and fertilizers.

The effect of arbuscular mycorrhizal fungi on carbon dioxide (CO2) emission from turfgrass soil under different irrigation intervals

AbstractIncreased nutrient and/or water uptake by arbuscular mycorrhizal (AM) symbiosis can affect soil biochemical properties and emission of the greenhouse gas carbon dioxide (CO2). Therefore, an experiment was designed to investigate the effect of AM fungi (AMF) on CO2 emissions from turfgrass. Three different AMF species (Funneliformis mosseae, Claroideoglomus etunicatum, and Rhizophagus irregularis) were used in this experiment. Turfgrass plants were cultivated in pots containing both mycorrhizal and non-mycorrhizal soils over a 10-week period. To mimic real-world conditions, the plants underwent irrigation cycles at intervals of 1, 2, and 3 days, replicating common irrigation practices in turfgrass fields. The research aimed to comprehensively understand the effects of AMF and varying irrigation intervals on CO2 emissions, soil characteristics, plant growth, and AMF parameters. It was observed that the changing irrigation intervals affected the AM symbiosis and this effect increased as the irrigation interval increased. It was determined that this AM symbiosis created with the plant significantly reduced CO2 emissions. In addition, it was determined that it regulates the soil structure and increases plant growth. In conclusion, it can be said that AMF species reduce CO2 emissions by reducing the need for water in the turfgrass.

Status of endogenous endomycorrhizal fungi associated with cowpea (<i>Vigna unguiculata</i> L.) in the Sudano-Sahelian zone of Cameroon

The Sudano-Sahelian part of Cameroon is known for its severe climatic conditions and low soil fertility. Local farmers use chemical fertilisers to increase crop production, usually without moderation. As a result, there is environmental pollution such as soil acidification, production of greenhouse gases, and increased eutrophication. To face this situation, scientific research recommends ecological solutions such as bio-fertilisers to enhance soil fertility. In this context, the mycorrhiza symbiosis technology deserves special attention. Indeed, it is a beneficial association between soil fungi (Glomeromycota) and the roots of more than 85% of plants; the evaluation of the agronomic potential of these microorganisms has shown spectacular results under field conditions. This study analyses the status of indigenous arbuscular mycorrhizal fungi in the cowpea rhizosphere in the agro-ecological zone 1 of Cameroon. For this purpose, soil samples were collected from the Far North and North regions of Cameroon. Composite soil samples were obtained by mixing soils collected from three divisions per region. Cowpea was grown in pots on these composite soil samples for 3 months. At maturity, spores of mycorrhizal fungi were isolated and parameters including mycorrhization frequency and intensity, the specific spore’s density and richness were evaluated. The spores were characterised according to morpho-anatomical criteria. The results established that between localities, mycorrhization frequency varied between 7-19%; mycorrhization intensity, 7-17.28%; specific density, 0.66-44% and specific richness, 2-4%. Eight specimens of arbuscular mycorrhizal fungi in six genera were characterised: Acaulospora (A. kentinensis, A. myriocarpa); Ambispora sp; Diversispora epigae, Funneliformis mossea, Glomus (G. constrictum, G. manihotis, and G. maculosum) and Rhizophagus intraradices. G. constritum was predominant in all the studied sites, followed by R. intraradices, while Acaulospora myriocarpa was the rarest. These results pave the way for the selection of indigenous arbuscular mycorrhiza fungi for ecological cowpea production in this area.

Effects of Different Vesicular - arbuscular Mycorrhizal (VAM) Fungi on the Seedling Growth of Tecomella undulata

Tecomella undulata (Sm.) Seem. (family Bignoniaceae) is a tree found in desert parts of India, and Arabia. The cultivation of high-quality seedlings is vital for establishing a successful plantation and the contribution of arbuscular mycorrhizal fungi (AMF) in the soil plays a vital role in the nursery phase. A study conducted during the periods of 2021-22 and 2022-23 scrutinised the effect of four distinct species of Glomus spp. (G. mosseae, G. intraradices, G. fasciculatum and Glomus hoi) on Tecomella undulata seedlings in AMF-inoculated soil. The inoculation involved applying of 400-500 sporocarps/kg of soil during sowing and the evaluation encompassed growth and survival parameters. Results revealed that among the 4 Glomus species, soil inoculated with Glomus fasiculatum at 180 days after sowing, significantly increased the root colonization percentage with (50.69 and 46.71 %) in year (2021-22) and (2022-23) compared to the uninoculated control. Additionally, seedlings exhibited significantly higher no. of spores per 100g of soil, when treated with (Glomus fasiculatum) inoculated soil, which was statistically at par with soil inoculated with (Glomus intraradices) at (103.67 and 98.65). During both the experimental year, in terms of germination percentage, root length and root: shoot ratio were found non- significantly with (44.45 %), root length at 360 DAS, (26.67 and 25.74) respectively, root shoot ratio at 360 days after sowing. While, plant survival percentage (30.63 and 25.41%) at 90 DAS. Whereas, at 360 DAS, collar diameter (6.14 and 10.07 mm), shoot length (33.36 and 32.19 cm), plant biomass (8.31 and 8.05 g), leaf area (196.29 and 185.46 cm 2) was observed significantly higher in treatment T3 (Glomus fasiculatum) which was statistically at par with treatment T1 (G. intraradices). It is concluded from study that Glomus fasiculatum were found best for growth and survival of seedlings followed by Glomus intraradices as compare to control.

Influence of plant species, mycorrhizal inoculant, and soil phosphorus level on arbuscular mycorrhizal communities in onion and carrot roots.

Arbuscular mycorrhizal fungi (AMF) are ancient and ecologically important symbionts that colonize plant roots. These symbionts assist in the uptake of water and nutrients, particularly phosphorus, from the soil. This important role has led to the development of AMF inoculants for use as biofertilizers in agriculture. Commercial mycorrhizal inoculants are increasingly popular to produce onion and carrot, but their specific effects on native mycorrhizal communities under field conditions are not known. Furthermore, adequate availability of nutrients in soils, specifically phosphorus, can reduce the diversity and abundance of AMF communities in the roots. The type of crop grown can also influence the composition of AMF communities colonizing the plant roots. This study aimed to investigate how AMF inoculants, soil phosphorus levels, and plant species influence the diversity of AMF communities that colonize the roots of onion and carrot plants. Field trials were conducted on high organic matter (muck) soil in the Holland Marsh, Ontario, Canada. The treatments included AMF-coated seeds (three to five propagules of Rhizophagus irregularis per seed) and non-treated onion and carrot seeds grown in soil with low (~46 ppm) and high (~78 ppm) phosphorus levels. The mycorrhizal communities colonizing the onion and carrot roots were identified by Illumina sequencing. Five genera, Diversispora, Claroideoglomus, Funneliformis, Rhizophagus, and Glomus, were identified in roots of both plant species. AMF communities colonizing carrot roots were more diverse and richer than those colonizing onion roots. Diversispora and Funneliformis had a 1.3-fold and 2.9-fold greater abundance, respectively, in onion roots compared to carrots. Claroideoglomus was 1.4-fold more abundant in carrot roots than in onions. Inoculation with R. irregularis increased the abundance and richness of Rhizophagus in AMF communities of onion roots but not in carrot roots. The soil phosphorus level had no effect on the richness and diversity of AMF in the roots of either crop. In summary, AMF inoculant and soil phosphorus levels influenced the composition of AMF communities colonizing the roots of onion and carrot plants, but the effects varied between plant species.

Regulation of nitric oxide by phytoglobins in Lotus japonicus is involved in mycorrhizal symbiosis with Rhizophagus irregularis

Various reactive molecular species are generated in plant–microbe interactions, and these species participate in defense and symbiotic responses. Leguminous plants successfully establish symbiosis by maintaining an appropriate level of nitric oxide (NO), which is generated in the roots and nodules during root nodule symbiosis. Phytoglobin (plant hemoglobin) controls NO levels in plants. In this study, we investigated mycorrhizal symbiosis, which occurs in more than 80% of land plants, between Rhizophagus irregularis and Lotus japonicus to clarify the involvement of phytoglobin-mediated NO regulation. The mycorrhizae of L. japonicus exhibited higher NO levels in the presence of R. irregularis than in its absence, especially at the infection site. LjGlb1–1, a phytoglobin that regulates NO level in L. japonicus, was upregulated during symbiosis with R. irregularis. In transformed hairy roots carrying the ProLjGlb1–1:GUS construct, LjGlb1–1 expression was observed at the R. irregularis infection site. We further examined the symbiotic phenotypes of L. japonicus lines with high and low LjGlb1–1 expression with R. irregularis. During mycorrhizal symbiosis, the high LjGlb1–1 expression line exhibited better growth than the wild-type, whereas the low expression line exhibited poor growth. In addition, the expression of LjPT4, a phosphate transporter specific to mycorrhizal symbiosis, was higher in the high LjGlb1–1 expression line, whereas that of the tubulin gene of R. irregularis was lower in the low LjGlb1–1 expression line than in the wild-type. These results confirm that NO regulation by LjGlb1–1 is involved in mycorrhizal symbiosis in L. japonicus, as it is reportedly in nitrogen-fixing symbiosis.

Synergistic effects of arbuscular mycorrhizal fungi and biochar are highly beneficial to Ligustrum lucidum seedlings in Cd-contaminated soil.

Cadmium (Cd) contamination is a widespread environmental issue. There is a lack of knowledge about the impacts of applying arbuscular mycorrhizal fungi (AMF) and biochar, either alone or in their combination, on alleviating Cd phytotoxicity in Ligustrum lucidum. Therefore, a pot experiment was conducted in a greenhouse, where L. lucidum seedlings were randomly subjected to four regimes of AMF treatments (inoculation with sterilized AMF, with Rhizophagus irregularis, Diversispora versiformis, alone or a mixture of these two fungi), and two regimes of biochar treatments (with or without rice-husk biochar), as well as three regimes of Cd treatments (0, 15, and 150mgkg-1), to examine the responses of growth, photosynthetic capabilities, soil enzymatic activities, nutritional concentrations, and Cd absorption of L. lucidum plants to the interactive effects of AMF, biochar, and Cd. The results demonstrated that under Cd contaminations, AMF alone significantly increased plant total dry weight, soil pH, and plant nitrogen (N) concentration by 84%, 3.2%, and 13.2%, respectively, and inhibited soil Cd transferring to plant shoot by 42.2%; biochar alone significantly enhanced net photosynthetic rate, soil pH, and soil catalase of non-mycorrhizal plants by 16.4%, 9%, and 11.9%, respectively, and reduced the soil Cd transferring to plant shoot by 44.7%; the additive effect between AMF and biochar greatly enhanced plant total dry weight by 101.9%, and reduced the soil Cd transferring to plant shoot by 51.6%. Furthermore, dual inoculation with D. versiformis and R. irregularis conferred more benefits on plants than the single fungal species did. Accordingly, amending Cd-contaminated soil with the combination of mixed-fungi inoculation and biochar application performed the best than either AMF or biochar alone. These responses may have been attributed to higher mycorrhizal colonization, soil pH, biomass accumulation, and biomass allocation to the roots, as well as photosynthetic capabilities. In conclusion, the combined use of mixed-fungi involving D. versiformis and R. irregularis and biochar addition had significant synergistic effects on enhancing plant performance and reducing Cd uptake of L. lucidum plants in Cd-contaminated soil.

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 Sinorhizobium 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.

Nutrient-dependent cross-kingdom interactions in the hyphosphere of an arbuscular mycorrhizal fungus.

The hyphosphere of arbuscular mycorrhizal (AM) fungi is teeming with microbial life. Yet, the influence of nutrient availability or nutrient forms on the hyphosphere microbiomes is still poorly understood. Here, we examined how the microbial community (prokaryotic, fungal, protistan) was affected by the presence of the AM fungus Rhizophagus irregularis in the rhizosphere and the root-free zone, and how different nitrogen (N) and phosphorus (P) supplements into the root-free compartment influenced the communities. The presence of AM fungus greatly affected microbial communities both in the rhizosphere and the root-free zone, with prokaryotic communities being affected the most. Protists were the only group of microbes whose richness and diversity were significantly reduced by the presence of the AM fungus. Our results showed that the type of nutrients AM fungi encounter in localized patches modulate the structure of hyphosphere microbial communities. In contrast we did not observe any effects of the AM fungus on (non-mycorrhizal) fungal community composition. Compared to the non-mycorrhizal control, the root-free zone with the AM fungus (i.e., the AM fungal hyphosphere) was enriched with Alphaproteobacteria, some micropredatory and copiotroph bacterial taxa (e.g., Xanthomonadaceae and Bacteroidota), and the poorly characterized and not yet cultured Acidobacteriota subgroup GP17, especially when phytate was added. Ammonia-oxidizing Nitrosomonas and nitrite-oxidizing Nitrospira were significantly suppressed in the presence of the AM fungus in the root-free compartment, especially upon addition of inorganic N. Co-occurrence network analyses revealed that microbial communities in the root-free compartment were complex and interconnected with more keystone species when AM fungus was present, especially when the root-free compartment was amended with phytate. Our study showed that the form of nutrients is an important driver of prokaryotic and eukaryotic community assembly in the AM fungal hyphosphere, despite the assumed presence of a stable and specific AM fungal hyphoplane microbiome. Predictable responses of specific microbial taxa will open the possibility of using them as co-inoculants with AM fungi, e.g., to improve crop performance.

In Vitro Hyphal Branching Assay Using Rhizophagus irregularis.

Most terrestrial plants are associated with symbiotic Glomeromycotina fungi, commonly known as arbuscular mycorrhizal (AM) fungi. AM fungi increase plant biomass in phosphate-depleted conditions by allocating mineral nutrients to the host; therefore, host roots actively exude various specialized metabolites and orchestrate symbiotic partners. The hyphal branching activity induced by strigolactones (SLs), a category of plant hormones, was previously discovered using an in vitro assay system. For this bioassay, AM fungi of the Gigaspora genus (Gigasporaeae) are commonly used due to their linear hyphal elongation and because the simple branching pattern is convenient for microscopic observation. However, many researchers have also used Glomeraceae fungi, such as Rhizophagus species, as the symbiotic partner of host plants, although they often exhibit a complex hyphal branching pattern. Here, we describe a method to produce and quantify the hyphal branches of the popular model AM fungus Rhizophagus irregularis. In this system, R. irregularis spores are sandwiched between gels, and chemicals of interest are diffused from the surface of the gel to the germinating spores. This method enables the positive effect of a synthetic SL on R. irregularis hyphal branching to be reproduced. This method could thus be useful to quantify the physiological effects of synthesized chemicals or plant-derived specialized metabolites on R. irregularis. Key features • Development of an in vitro hyphal branching assay using germinating spores of Rhizophagus irregularis. • This in vitro assay system builds upon a method developed by Kameoka et al. [1] but modified to make it more applicable to hydrophilic compounds. • Optimized for R. irregularis to count the hyphal branches. • This bioassay requires at least 12 days to be done.

DROUGHT STRESS ALLEVIATION: THE CONTRIBUTION OF A SOIL BACTERIUM AND AN ARBUSCULAR MYCORRHIZAL FUNGUS IN SCALLION

Recent climate change and global warming have caused extreme heat and low rainfall which negatively affected soil nutrient, fertility status, decreased water content, and changed physiochemical properties of agricultural soils in many parts of the globe. As a result of drought, crop production is seriously reduced. The beneficial effects of soil microorganisms including arbuscular mycorrhizal fungi and rhizospheric bacteria on crop production and soil health are vital for the sustainable management of stressed agricultural practices. The present study evaluated the effects of an arbuscular mycorrhizal fungus, Rhizophagus irregularis, and a rhizospheric bacterium, Pseudomonas flourescens, alone and in dual inoculation on the survival, growth, mycorrhizal colonization, nutrient uptake, glomalin production, and soil aggregation of Allium fistulosum plants. In water-stressed soil, seedling survival, growth, total biomass, nutrient uptake, glomalin production, and soil aggregation were significantly increased when inoculated with R. irregularis and P. flourescens. Dual inoculation with R. irregularis and P. flourescens produced vigorous seedlings which contained higher amount of nitrogen, phosphorus, potassium contents, glomalin production, and soil aggregation compared to single inoculation. The present results indicate that arbuscular mycorrhizal fungi and beneficial rhizospheric bacteria offer potential for biofertilizers and mitigating drought in A. fistulosum plants.

Inoculantes on farm à base de fungos micorrízicos arbusculares no desempenho de trigo

Abstract The objective of this work was to evaluate whether the use of on-farm inoculants based on arbuscular mycorrhizal fungi (AMF) interferes with the agronomic performance of wheat cultivars. The following treatments were applied to cultivars TBIO Calibre and TBIO Sossego: eight on-farm inoculants, i.e., Acaulospora morrowiae, Cetraspora pellucida, Claroideoglomus etunicatum, Glomus intraradices, Rhizophagus clarus, Scutellospora heterogama, and two mycorrhizal communities from native forest (NF) obtained in the Bom Princípio (BP) and in the Flores da Cunha (FC) Brazilian municipalities; and no inoculant (control). A randomized complete block experimental design was used. Mycorrhizal colonization, root morphology, and thousand grain weight were evaluated. The association between 'TBIO Sossego' and S. heterogama provided the greatest root volume, while that between 'TBIO Calibre' and C. etunicatum and between 'TBIO Sossego' and the BP NF community resulted in the best thousand-grain weight. The use of AMF, especially C. etunicatum and S. heterogama, enhances the development of the root system of wheat. 'TBIO Calibre' showed the greatest total length and quantity of very fine roots, while 'TBIO Sossego' developed a root system with the greatest surface area and quantity of thick roots. The use of on-farm inoculants affects the agronomic performance of wheat cultivars.