Presence Of Arbuscular Mycorrhizal Fungi Research Articles

Addition of polyester microplastic fibers to soil alters the diversity and abundance of arbuscular mycorrhizal fungi and affects plant growth and nutrition

Microplastics (MPs) represent an emerging factor in global environmental change and are increasingly found in soils. However, the extent to which they affect plants and their interactions with the soil microbiome is poorly understood. Here, we test the hypothesis that increasing levels of polyester MP fibers in soil alter plant growth and nutrient acquisition responses to arbuscular mycorrhizal (AM) fungi via changes in AM fungal colonization and community composition. We used Sorghum drummondii as a model species in a fully factorial greenhouse experiment. Plants were exposed to soil treatments with 0, 0.2, 1, and 3% MP polyester fibers either in the presence or absence of an assembled AM fungal community comprising 13 species across three families with contrasting life-history strategies. We found that the 1% MP treatment promoted plant biomass irrespective of the presence of AM fungi. While no changes in macronutrient concentrations in plant tissues were seen, there was a significant increase in B and Mn when relatively low amounts of MPs were added, and this effect was modulated by AM fungi. Furthermore, there were shifts in AM fungal community composition in response to MP, favoring taxa such as Gigaspora sp. while negatively affecting ruderal taxa like Glomus sp. Overall, our data indicate that MP polyester fibers present in soil can in some cases be beneficial to plants and AM fungal interactions. However, the implications of these findings over the long-term and in the context of ecological repercussions of MP pollution in the environment remain to be seen.

Enhancing olive tree (Olea europaea) rhizosphere dynamics: Co-inoculation effects of arbuscular mycorrhizal fungi and plant growth- promoting rhizobacteria in field experiments

We investigated the outcome of the interaction between the arbuscular mycorrhizal fungus (AMF) Rhizophagus (R) irregularis DAOM 197198 and the Plant-Growth-Promoting Rhizobacteria (PGPR) (mix of Bacillus megaterium, Burkholdria cedrus and Streptomyces beta-vulgaris) by conducting an olive field experiment. Our data provide evidence that the co-inoculation of R. irregularis and PGPR has important effects on the rhizosphere microbial community. The largest proportional increase was found for the PLFA biomarkers indicative of Gram-negative bacteria (16:1ω9, 18:1ω7 and 18:1ω9), fungi (18:2ω6) and actinobacteria (10Me16:0 and 10Me18:0). Microbial inoculants application of all tested treatments caused a significant decrease in the level of trehalose in the olive rhizosphere. The most pronounced decrease was observed in the plant inoculated with R. intraradices only, suggesting that the presence of AMF may have relaxed the bacterial stress. Co-inoculation of PGPR and AMF significantly improved the nutritional status of olive roots. Specifically, the interaction of PGPR and R. intraradices led to an increase in N (26 %), P (60 %), Fe (25 %), Mn (18 %), Zn (26 %), B (22 %) and Cu (14 %) compared with the control. We also found that the co-inoculation of AMF with PGPR causes a shift in the accumulation of secondary metabolites in olive roots. In particular, the most important effect induced by AMF was an improvement of oleuropein concentration, while co-inoculation of R. irregularis and PGPR positively modulated verbascoside concentration. The novelty of the present work lies in the use of microbial inoculants in the field of olive trees. This approach provided direct information regarding the advantages of using AMF and PGPR inoculants, allowing the reduction of chemical inputs and positively influencing the olive tree performance.

Testing the joint effects of arbuscular mycorrhizal fungi and ants on insect herbivory on potato plants

Main conclusionAnts, but not mycorrhizae, significantly affected insect leaf-chewing herbivory on potato plants. However, there was no evidence of mutualistic interactive effects on herbivory.Plants associate with both aboveground and belowground mutualists, two prominent examples being ants and arbuscular mycorrhizal fungi (AMF), respectively. While both of these mutualisms have been extensively studied, joint manipulations testing their independent and interactive (non-additive) effects on plants are rare. To address this gap, we conducted a joint test of ant and AMF effects on herbivory by leaf-chewing insects attacking potato (Solanum tuberosum) plants, and further measured plant traits likely mediating mutualist effects on herbivory. In a field experiment, we factorially manipulated the presence of AMF (two levels: control and mycorrhization) and ants (two levels: exclusion and presence) and quantified the concentration of leaf phenolic compounds acting as direct defenses, as well as plant volatile organic compound (VOC) emissions potentially mediating direct (e.g., herbivore repellents) or indirect (e.g., ant attractants) defense. Moreover, we measured ant abundance and performed a dual-choice greenhouse experiment testing for effects of VOC blends (mimicking those emitted by control vs. AMF-inoculated plants) on ant attraction as a mechanism for indirect defense. Ant presence significantly reduced herbivory whereas mycorrhization had no detectable influence on herbivory and mutualist effects operated independently. Plant trait measurements indicated that mycorrhization had no effect on leaf phenolics but significantly increased VOC emissions. However, mycorrhization did not affect ant abundance and there was no evidence of AMF effects on herbivory operating via ant-mediated defense. Consistently, the dual-choice assay showed no effect of AMF-induced volatile blends on ant attraction. Together, these results suggest that herbivory on potato plants responds mainly to top-down (ant-mediated) rather than bottom-up (AMF-mediated) control, an asymmetry in effects which could have precluded mutualist non-additive effects on herbivory. Further research on this, as well as other plant systems, is needed to examine the ecological contexts under which mutualist interactive effects are more or less likely to emerge and their impacts on plant fitness and associated communities.

Arbuscular Mycorrhizal Fungi Mediate the Acclimation of Rice to Submergence.

Flooding is a critical factor that limits the establishment of a symbiosis between rice and arbuscular mycorrhizal fungi (AMF) in wetland ecosystems. The distribution of carbon resources in roots and the acclimation strategies of rice to flooding stress in the presence of AMF are poorly understood. We conducted a root box experiment, employing nylon sheets or nylon meshes to create separate fungal chambers that either prevented or allowed the roots and any molecules to pass through. We found that the mycorrhizal colonization rate and the expression of genes OsD14L and OsCERK1, which are involved in fungal perception during symbiosis, both increased in mycorrhizal rice roots following intermittent flooding compared to continuous flooding. Furthermore, AMF inoculation affected root morphological traits, facilitating both shallower and deeper soil exploration. Increased submergence intensity led to carbohydrate deprivation in roots, while high mycorrhizal colonization increased soil oxygen consumption and decreased the neutral lipid concentration in roots. However, mycorrhizal inoculation increased the rice photosynthesis rate and facilitated acclimation to submergence by mediating the expression of the genes OsCIPK15 and OsSUB1A to enhance rice shoot elongation and the sugar concentration in roots as a result of reduced competition for carbon between rice and AMF under different flooding conditions.

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.

Crab bioturbation reduces carbon storage in salt marshes under more robust mechanisms than plant invasiveness

IntroductionThe macrobenthos are crucial for the stability of estuarine ecosystems due to their burrowing behavior in the sediment and their uptake of nutrients from plants. These activities lead to significant alterations in both the morphological and biogeochemical processes within the region.MethodsHowever, there is limited investigation into carbon cycling processes specifically related to crab bioturbation. Additionally, few studies have examined enzymatic activities and carbon fractions in sediments from crab burrow walls at different crab growth stages. This study aims to explore the impact of both plant invasiveness and crab bioturbation on carbon storage.ResultsOur findings suggest that plant invasion leads to higher organic accumulation due to the reduction of recalcitrant organic carbon (ROC) (decreased by 11.6% in invasive and 62.6% in native site from April to December), faster photosynthetic rates (25.8 μmol/m2 s in invasive and 10.7 μmol/m2 s in native site), and an increased presence of arbuscular mycorrhizal fungi (AMF) in the soil over time. However, the increase of easy oxidized carbon (EOC) may lead to less carbon storage in soil (increase by 67.7% in invasive and 48.8% in native site from April to December). In addition to invasiveness, the bioturbation activities of macrobenthos also affect carbon storage. Sediments from crab burrows exhibit higher EOC content (33.6% more than the bulk soil) and higher levels of carbon cycling-related enzymes, including S-ACT, S-β-GC, and S-ACP activities (24.2%, 8.99%, and 135.6% higher than the bulk soil, respectively).DiscussionThese changes contribute to reduced carbon accumulation in the soil. Therefore, crab bioturbation is a more significant factor affecting carbon sink capacity than plant invasion.

Soil compaction reversed the effect of arbuscular mycorrhizal fungi on soil hydraulic properties

Arbuscular mycorrhizal fungi (AMF) typically provide a wide range of nutritional benefits to their host plants, and their role in plant water uptake, although still controversial, is often cited as one of the hallmarks of this symbiosis. Less attention has been dedicated to other effects relating to water dynamics that the presence of AMF in soils may have. Evidence that AMF can affect soil hydraulic properties is only beginning to emerge. In one of our recent experiments with dwarf tomato plants, we serendipitously found that the arbuscular mycorrhizal fungus (Rhizophagus irregularis ‘PH5’) can slightly but significantly reduce water holding capacity (WHC) of the substrate (a sand–zeolite–soil mixture). This was further investigated in a subsequent experiment, but there we found exactly the opposite effect as mycorrhizal substrate retained more water than did the non-mycorrhizal substrate. Because the same substrate was used and other conditions were mostly comparable in the two experiments, we explain the contrasting results by different substrate compaction, most likely caused by different pot shapes. It seems that in compacted substrates, AMF may have no effect upon or even decrease the substrates’ WHC. On the other hand, the AMF hyphae interweaving the pores of less compacted substrates may increase the capillary movement of water throughout such substrates and cause slightly more water to remain in the pores after the free water has drained. We believe that this phenomenon is worthy of mycorrhizologists’ attention and merits further investigation as to the role of AMF in soil hydraulic properties.

Computer vision models enable mixed linear modeling to predict arbuscular mycorrhizal fungal colonization using fungal morphology

The presence of Arbuscular Mycorrhizal Fungi (AMF) in vascular land plant roots is one of the most ancient of symbioses supporting nitrogen and phosphorus exchange for photosynthetically derived carbon. Here we provide a multi-scale modeling approach to predict AMF colonization of a worldwide crop from a Recombinant Inbred Line (RIL) population derived from Sorghum bicolor and S. propinquum. The high-throughput phenotyping methods of fungal structures here rely on a Mask Region-based Convolutional Neural Network (Mask R-CNN) in computer vision for pixel-wise fungal structure segmentations and mixed linear models to explore the relations of AMF colonization, root niche, and fungal structure allocation. Models proposed capture over 95% of the variation in AMF colonization as a function of root niche and relative abundance of fungal structures in each plant. Arbuscule allocation is a significant predictor of AMF colonization among sibling plants. Arbuscules and extraradical hyphae implicated in nutrient exchange predict highest AMF colonization in the top root section. Our work demonstrates that deep learning can be used by the community for the high-throughput phenotyping of AMF in plant roots. Mixed linear modeling provides a framework for testing hypotheses about AMF colonization phenotypes as a function of root niche and fungal structure allocations.

Arbuscular mycorrhizal fungi reduce soil N2O emissions by altering root traits and soil denitrifier community composition

Arbuscular mycorrhizal fungi (AMF) increase the ability of plants to obtain nitrogen (N) from the soil, and thus can affect emissions of nitrous oxide (N2O), a long-lived potent greenhouse gas. However, the mechanisms underlying the effects of AMF on N2O emissions are still poorly understood, particularly in agroecosystems with different forms of N fertilizer inputs. Utilizing a mesocosm experiment in field, we examined the effects of AMF on N2O emissions via their influence on maize root traits and denitrifying microorganisms under ammonia and nitrate fertilizer input using 15N isotope tracer. Here we show that the presence of AMF alone or both maize roots and AMF increased maize biomass and their 15N uptake, root length, root surface area, and root volume, but led to a reduction in N2O emissions under both N input forms. Random forest model showed that root length and surface area were the most important predictors of N2O emissions. Additionally, the presence of AMF reduced the (nirK + nirS)/nosZ ratio by increasing the relative abundance of nirS-Bradyrhizobium and Rubrivivax with ammonia input, but reducing nosZ-Azospirillum, Cupriavidus and Rhodopseudomonas under both fertilizer input. Further, N2O emissions were significantly and positively correlated with the nosZ-type Azospirillum, Cupriavidus and Rhodopseudomonas, but negatively correlated with the nirS-type Bradyrhizobium and Rubrivivax. These results indicate that AMF reduce N2O emissions by increasing root length to explore N nutrients and altering the community composition of denitrifiers, suggesting that effective management of N fertilizer forms interacting with the rhizosphere microbiome may help mitigate N2O emissions under future N input scenarios.

Improving plant adaptation to soil antimony contamination: the synergistic contribution of arbuscular mycorrhizal fungus and olive mill waste

BackgroundThis study aimed to investigate the alterations in biochemical and physiological responses of oat plants exposed to antimony (Sb) contamination in soil. Specifically, we evaluated the effectiveness of an arbuscular mycorrhizal fungus (AMF) and olive mill waste (OMW) in mitigating the effects of Sb contamination. The soil was treated with a commercial strain of AMF (Rhizophagus irregularis) and OMW (4% w/w) under two different levels of Sb (0 and 1500 mg kg−1 soil).ResultsThe combined treatment (OMW + AMF) enhanced the photosynthetic rate (+ 40%) and chlorophyll a (+ 91%) and chlorophyll b (+ 50%) content under Sb condition, which in turn induced more biomass production (+ 67–78%) compared to the contaminated control plants. More photosynthesis in OMW + AMF-treated plants gives a route for phenylalanine amino acid synthesis (+ 69%), which is used as a precursor for the biosynthesis of secondary metabolites, including flavonoids (+ 110%), polyphenols (+ 26%), and anthocyanins (+ 63%) compared to control plants. More activation of phenylalanine ammonia-lyase (+ 38%) and chalcone synthase (+ 26%) enzymes in OMW + AMF-treated plants under Sb stress indicated the activation of phenylpropanoid pathways in antioxidant metabolites biosynthesis. There was also improved shifting of antioxidant enzyme activities in the ASC/GSH and catalytic pathways in plants in response to OMW + AMF and Sb contamination, remarkably reducing oxidative damage markers.ConclusionsWhile individual applications of OMW and AMF also demonstrated some degree of plant tolerance induction, the combined presence of AMF with OMW supplementation significantly enhanced plant biomass production and adaptability to oxidative stress induced by soil Sb contamination.

Tripartite interactions among free‐living, N‐fixing bacteria, arbuscular mycorrhizal fungi, and plants: Mutualistic benefits and community response to co‐inoculation

AbstractInteractions between arbuscular mycorrhizal (AM) fungi and free‐living nitrogen fixers (FLNF) occur in the rhizosphere where they can enhance plant nutrient acquisition, impact plant growth, and affect soil processes. Tripartite mutualism commonly occurs between nodule‐forming plants, symbiotic diazotrophs, and AM fungi, and can occur between non‐nodulating plants, FLNF, and AM fungi. However, information on the extent of, and controls on, tripartite mutualism in non‐nodulating plant systems is limited to a small number of crop plants and culturable microbial inoculum, mostly in greenhouse growing conditions. We conducted a systematic literature review to synthesize the current understanding of the responses of plants, AM fungi, and FLNF to co‐inoculation, as well as the conditions affecting tripartite mutualism and the magnitude and range of benefits conferred. Our review shows that plants generally benefit from co‐inoculation with AM fungi and FLNF taxa, but benefits are highly variable and context dependent, ranging from 94% reduction in plant shoot biomass to 255% increase in total plant biomass. Additionally, the presence of AM fungi can increase abundance of FLNF and the presence of FLNF can increase AM fungal root colonization, but these responses also vary widely. Major factors influencing variation in response to co‐inoculation by all organisms include plant phenology/age, soil type and nutrient availability, and partner pairing. There is potential for leveraging these tripartite mutualisms to improve plant productivity and soil microbial function, but successful application is more likely with a thorough understanding of the environmental and mechanistic controls on these relationships and testing of field‐scale implementation.

Effect of Arbuscular Mycorrhizal Fungi and Rock Phosphate on Growth, Physiology, and Biochemistry of Carob under Water Stress and after Rehydration in Vermicompost-Amended Soil.

In the Mediterranean region, reforestation programs record failures following successive drought periods. The use of different plant-growth-promoting amendments and the understanding of drought-induced physiological and biochemical responses of carob will contribute to the reforestation program's success. In this study, the effects of arbuscular-mycorrhizal-fungi (AMF), vermicompost (VC), and rock phosphate (RP) on carob seedlings under drought stress (DS) and recovery (REC) conditions were evaluated. A greenhouse experiment was conducted with carob seedlings grown in the presence of AMF, VC, and RP, applied alone or in combination under well-watered (WW), DS (by stopping irrigation for 12 days), and recovery (REC) conditions. The obtained results indicated that the triple combination (AMF + VC + RP) presented the highest improvement in water potential, photosynthetic pigment content, stomatal conductance, and chlorophyll fluorescence compared to the controls under DS and after REC. In addition, this combination resulted in improved tolerance of carob seedlings to DS and a high potential for rapid recovery after rehydration due to a high accumulation of sugars, proteins, and antioxidant enzymes. In summary, the results underline the importance of inoculating carob with AMF in combination with (in)-organic amendments in improving its tolerance to DS and its recovery performances.

Mycorrhizosphere bacteria inhibit chromium uptake and phytotoxicity by regulating proline metabolism, antioxidant defense system, and aquaporin gene expression in tomato.

Chromium (Cr) contamination in soil-plant systems poses a pressing environmental challenge due to its detrimental impacts on plant growth and human health. Results exhibited that Cr stress decreased shoot biomass, root biomass, leaf relative water content, and plant height. However, single and co-application of Bacillus subtilis (BS) and arbuscular mycorrhizal fungi (AMF) considerably enhanced shoot biomass (+ 21%), root biomass (+ 2%), leaf relative water content (+ 26%), and plant height (+ 13) under Cr stress. The frequency of mycorrhizal (F) association (+ 5%), mycorrhizal colonization (+ 13%), and abundance of arbuscules (+ 5%) in the non-stressed soil was enhanced when inoculated with combined BS and AMF as compared to Cr-stressed soil. The co-inoculation with BS and AMF considerably enhanced total chlorophyll, carotenoids, and proline content in Cr-stressed plants. Cr-stressed plants resulted in attenuated response in SOD, POD, CAT, and GR activities when inoculated with BS and AMF consortia by altering oxidative stress biomarkers (H2O2 and MDA). In Cr-stressed plants, the combined application of BS and AMF considerably enhanced proline metabolism, for instance, P5CR (+ 17%), P5CS (+ 28%), OAT (- 22%), and ProDH (- 113%) as compared to control. Sole inoculation with AMF downregulated the expression of SIPIP2;1, SIPIP2;5, and SIPIP2;7 in Cr-stressed plants. However, the expression of NCED1 was downregulated with the application of sole AMF. In contrast, the relative expression of Le4 was upregulated in the presence of AMF and BS combination in Cr-stressed plants. Therefore, it is concluded that co-application of BS and AMF enhanced Cr tolerance by enhancing proline metabolism, antioxidant enzymes, and aquaporin gene expression. Future study might concentrate on elucidating the molecular processes behind the synergistic benefits of BS and AMF, as well as affirming their effectiveness in field experiments under a variety of environmental situations. Long-term research on the effect of microbial inoculation on soil health and plant production might also help to design sustainable chromium remediation solutions.

A Critical Review of the Effectiveness of Biochar Coupled with Arbuscular Mycorrhizal Fungi in Soil Cadmium Immobilization.

Cadmium-contaminated soil significantly threatens global food security and human health. This scenario gives rise to significant worries regarding widespread environmental pollution. Biochar and arbuscular mycorrhizal fungi (AMF) can effectively immobilize cadmium in the soil in an environmentally friendly way. Existing studies have separately focused on the feasibility of each in remediating polluted soil. However, their association during the remediation of cadmium-polluted soils remains unclear. This review paper aims to elucidate the potential of biochar, in conjunction with AMF, as a strategy to remediate soil contaminated with cadmium. This paper comprehensively analyzes the current understanding of the processes in cadmium immobilization in the soil environment by examining the synergistic interactions between biochar and AMF. Key factors influencing the efficacy of this approach, such as biochar properties, AMF species, and soil conditions, are discussed. The influences of biochar-AMF interactions on plant growth, nutrient uptake, and overall ecosystem health in cadmium-contaminated environments are highlighted. This review indicates that combining biochar and AMF can improve cadmium immobilization. The presence of AMF in the soil can create numerous binding sites on biochar for cadmium ions, effectively immobilizing them in the soil. Insights from this review contribute to a deeper understanding of sustainable and eco-friendly approaches to remediate cadmium-contaminated soils, offering potential applications in agriculture and environmental management.

A survey on the composition and occurrence frequency of arbuscular mycorrhizal fungi in rhizospheric soils and roots of vegetables grown in Ho Chi Minh city

The study aimed to determine the presence and composition of arbuscular mycorrhizal fungi (AMF) in the rhizospheric soils and roots of vegetable plants (14 species of leafy vegetables) grown in Hoc Mon, Cu Chi, and Binh Chanh districts, Ho Chi Minh city. The results of the isolation of AMF spores based on the wet sieving method showed the presence of AMF in the rhizospheric soils of vegetables with an average spore density of 87.6 spores/50 g of soil. For the symbiotic ratio of AMF to the root tissues, there was no symbiosis in 4 vegetable crops, including amaranth, mustard green, leaf mustard, and bok choy. Still, there was symbiosis in the remaining 10 plants, with an average symbiotic rate of 6.6%. Identification of AMF spores based on the morphological characteristics recorded in all the soil samples appeared spore phenotypes of 5 fungal genera including Glomus, Acaulospora, Gigaspora, Scutellospora, and Sclerocystis. However, 3 morphological types were not yet identified. From the obtained results, two genera, Glomus and Acaulospora, have the highest frequency at 43.9 and 39.6%, respectively.

Effects of microplastic polystyrene, simulated acid rain and arbuscular mycorrhizal fungi on Trifolium repens growth and soil microbial community composition

Microplastic pollution is a global and ubiquitous environmental problem in the oceans as well as in the terrestrial environment. We examined the fate of polystyrene (PS) beads in experimental soil in the presence and absence of symbiotic arbuscular mycorrhizal fungi (AMF) and simulated acid rain to determine whether combinations of these three factors interact to alter growth of the white clover Trifolium repens. We found that PS, simulated acid rain or AMF added singly to soil did not alter T. repens growth or yields. In contrast, PS and AMF together significantly reduced shoot biomass while simulated acid rain and PS together significantly reduced available soil phosphorus independent of AMF presence. PS, AMF and simulated acid rain together significantly reduced soil NO3–-N. AMF added singly also enriched for beneficial soil bacteria of the genus Solirubrobacter while PS combined with AMF significantly enriched the potential plant pathogenic fungus Spiromastix spp. AMF innoculated with PS increased the abundance of soil hydrocarbon degraders independent of the presence of simulated acid rain. In addition, the abundance of soil nitrate reducers was increased by the presence of PS especially in the presence of AMF and simulated acid rain. Moreover, the latter increased the abundance of soil pathogens within the fungal community including antibiotic producers. These findings indicate that the coexistence of microplastics, acid rain and AMF may exacerbate the adverse effects of microplastics on soil and plant health.

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.

Evaluating the Interaction between Arbuscular Mycorrhizal Fungi (AMF) and Plant Pathogens

The presence of arbuscular mycorrhizal fungi (AMF) in the rhizosphere has been shown to exert a substantial influence on plant disease resistance. The colonization of AMF induces a cascade of defense responses in plants, resulting in heightened resistance to pathogen invasion. The current study unveils the essential role of AMF in initiating systemic defense responses in plants. When plants undergo colonization by AMF, they initiate a variety of molecular and biochemical mechanisms that enhance their immune system. These systemic defense responses equip the plant with the ability to both withstand invading pathogens and ready neighboring uninfected tissues for potential future attacks. In addition, the establishment of AMF in the roots can induce physical alterations in the root architecture, thereby increasing the difficulty for pathogens to infiltrate and infect plants. While there have been notable advancements in understanding the overall impact of AMF colonization on plant disease resistance, further investigation is needed. Future investigations should delve into the mechanisms of AMF colonization on plant disease resistance, with a particular emphasis on elucidating the signaling pathways and biochemical factors that trigger systemic defense responses. This will offer valuable insights into the molecular foundation of plant immunity and aid in the development of precise disease management strategies. AMF can also serve as biocontrol agents for sustainable management of plant diseases, thereby decreasing dependency on chemical pesticides and encouraging environmentally-conscious practices. The efficiency of AMF colonization and the expression of plant defense responses can be significantly altered by environmental factors, such as soil conditions and nutrient availability. Comprehending these factors will facilitate the formulation of efficient management tactics to enhance biotic interactions in agricultural systems.

Soil Physicochemical Characteristics and Spore Density of Indigenous Arbuscular Mycorrhizal Fungi (AMF) in Different Vegetation Patches of a Marginal Upland in Central Philippines

To show the importance of plant-microbe association in stressed tropical landscapes, the study evaluated the physicochemical characteristics and indigenous arbuscular mycorrhizal fungi (AMF) spore density in selected vegetation patches of marginal upland soils in Central Philippines. Five quadrats were used in the study, namely Andropogon aciculatus (control plot), Imperata cylindrica, Chromolaena odorata, Melastoma malabathricum and mixed vegetation patch. Results showed that soils in the studied vegetation patches had different physicochemical characteristics and AMF spore density. Although all patches had clay soil texture and comparable water-holding capacity, mixed vegetation patch had moderate compaction (1.33 g cm-3) and higher porosity (50.31%) compared with the other patches, which had extreme compaction (1.37-1.65 g cm-3) and lower porosity (37.74-48.76%). In terms of chemical properties, soils in different patches had moderate (5.69) to strongly acidic pH (5.13), moderate organic matter (2.69-2.91%) levels, low P (2.67-3.94 ppm) content and above critical K levels (0.2-1.2 cmol+ kg-1). Results also revealed that C. odorata patch had the highest spore density count (11.33 spores 100 g-1), followed by mixed vegetation (9 spores 100 g-1), M. malabathricum (8.33 spores 100 g-1), and A. aciculatus patch having the lowest spore density count (4 spores 100 g-1). The significant spore density variability was attributed to the differences in soil’s physicochemical characteristics among the different vegetation patches and AMF host specificity. Spores detection, therefore, indicated AMF presence and helped the adaptation mechanism of the natural vegetation in this degraded upland.

Divergent response of maize and soybean rhizosphere to arbuscular mycorrhiza

Maize and soybean are capable of forming symbiotic relationship with arbuscular mycorrhizal fungi (AMF), which enables the plants to overcome P limitations and resist drought effects. The results indicate that the activities of β-glucosidase, chitinase and acid phosphatase in the rhizosphere were double those in the bulk soil, regardless of plant species. Both soybean and maize demonstrated a decrease in β-glucosidase activity. However, chitinase activity displayed a divergent pattern between the two plant species under AMF influence, with a notable 18.5% increase in maize compared to a substantial 44.8% decrease in soybean. The presence of AMF resulted in a 50% reduction in rhizosphere microbial biomass phosphorus (MBP) in soybean, whereas this effect was not observed in maize. The distinct nutrient demands of each plant species appear to regulate the impact of AMF on the characteristics of microbial activities in the rhizosphere.