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Summary: Mycorrhizal associations are key mutualisms that shape the structure of forest communities and multiple ecosystem functions. However, we lack a framework for predicting the varying dominance of distinct mycorrhizal associations in an integrated proxy of multifunctionality across ecosystems.Here, we used the datasets containing diversity of mycorrhizal associations and 18 ecosystem processes related to supporting, provisioning, and regulating services to examine how the dominance of ectomycorrhiza (EcM) associations affects ecosystem multifunctionality in subtropical mountain forests in Southwest China. Meanwhile, we synthesized the prevalence of EcM‐dominant effects on ecosystem functioning in forest biomes.Our results demonstrated that elevation significantly modified the distributions of EcM trees and fungal dominance, which in turn influenced multiple functions simultaneously. Multifunctionality increased with increasing proportion of EcM associations, supporting the ectomycorrhizal‐dominance hypothesis. Meanwhile, we observed that the impacts of EcM dominance on individual ecosystem functions exhibited different relationships among forest biomes.Our findings highlight the importance of ectomycorrhizal dominance in regulating multifunctionality in subtropical forests. However, this ectomycorrhizal feedback in shaping ecosystem functions cannot necessarily be generalized across forests. Therefore, we argue that the predictions for ecosystem multifunctionality in response to the shifts of mycorrhizal composition could vary across space and time. [ABSTRACT FROM AUTHOR]

This article is a Commentary on Giovannetti et al., 241: 1393–1400. [ABSTRACT FROM AUTHOR]

Summary: Phosphorus (P) for carbon (C) exchange is the pivotal function of arbuscular mycorrhiza (AM), but how this exchange varies with soil P availability and among co‐occurring plants in complex communities is still largely unknown.We collected intact plant communities in two regions differing c. 10‐fold in labile inorganic P. After a 2‐month glasshouse incubation, we measured 32P transfer from AM fungi (AMF) to shoots and 13C transfer from shoots to AMF using an AMF‐specific fatty acid. AMF communities were assessed using molecular methods.AMF delivered a larger proportion of total shoot P in communities from high‐P soils despite similar 13C allocation to AMF in roots and soil. Within communities, 13C concentration in AMF was consistently higher in grass than in blanketflower (Gaillardia aristata Pursh) roots, that is P appeared more costly for grasses. This coincided with differences in AMF taxa composition and a trend of more vesicles (storage structures) but fewer arbuscules (exchange structures) in grass roots. Additionally, 32P‐for‐13C exchange ratios increased with soil P for blanketflower but not grasses.Contrary to predictions, AMF transferred proportionally more P to plants in communities from high‐P soils. However, the 32P‐for‐13C exchange differed among co‐occurring plants, suggesting differential regulation of the AM symbiosis. [ABSTRACT FROM AUTHOR]

Summary: Arbuscular (AM) and orchid (OrM) mycorrhiza are the most widespread mycorrhizal symbioses among flowering plants, formed by distinct fungal and plant species. They are both endosymbioses because the fungal hyphae can enter inside the plant cell to develop intracellular fungal structures that are surrounded by the plant membrane. The symbiotic plant–fungus interface is considered to be the major site of nutrient transfer to the host plant. We summarize recent data on nutrient transfer in OrM and compare the development and function of the arbuscules formed in AM and the pelotons formed in OrM in order to outline differences and conserved traits. We further describe the unexpected similarities in the form and function of the intracellular mycorrhizal fungal structures observed in orchids and in the roots of mycoheterotrophic plants forming AM. We speculate that these similarities may be the result of convergent evolution of mycorrhizal types in mycoheterotrophic plants and highlight knowledge gaps and new research directions to explore this scenario. [ABSTRACT FROM AUTHOR]

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Summary: Phosphate (Pi) is indispensable for life on this planet. However, for sessile land plants it is poorly accessible. Therefore, plants have developed a variety of strategies for enhanced acquisition and recycling of Pi. The mechanisms to cope with Pi limitation as well as direct uptake of Pi from the substrate via the root epidermis are regulated by a conserved Pi starvation response (PSR) system based on a family of key transcription factors (TFs) and their inhibitors. Furthermore, plants obtain Pi indirectly through symbiosis with mycorrhiza fungi, which employ their extensive hyphal network to drastically increase the soil volume that can be explored by plants for Pi. Besides mycorrhizal symbiosis, there is also a variety of other interactions with epiphytic, endophytic, and rhizospheric microbes that can indirectly or directly influence plant Pi uptake. It was recently discovered that the PSR pathway is involved in the regulation of genes that promote formation and maintenance of AM symbiosis. Furthermore, the PSR system influences plant immunity and can also be a target of microbial manipulation. It is known for decades that the nutritional status of plants influences the outcome of plant–microbe interactions. The first molecular explanations for these observations are now emerging. [ABSTRACT FROM AUTHOR]

Grasslands represent an essential part of terrestrial ecosystems. In particular, coastal grasslands are dominated by the influence of environmental factors resulting from sea–land interaction. Therefore, coastal grasslands are extremely heterogeneous both spatially and temporally. In this review, recent knowledge in the field of biotic interactions in coastal grassland soil is summarized. A detailed analysis of arbuscular mycorrhiza symbiosis, rhizobial symbiosis, plant–parasitic plant interactions, and plant–plant interactions is performed. The role of particular biotic interactions in the functioning of a coastal grassland ecosystem is characterized. Special emphasis is placed on future directions and development of practical applications for sustainable agriculture and environmental restoration. It is concluded that plant biotic interactions in soil are omnipresent and important constituents in different ecosystem services provided by coastal grasslands. [ABSTRACT FROM AUTHOR]

While mycorrhization rates have been studied in different contexts, not much is known about their temporal patterns across seasons. Here, we asked how mycorrhization rates of 10 deciduous trees assessed by microscopy changed from winter to spring to early summer. We made use of a tree diversity experiment on nutrient‐rich soil (former farmland) in Central Germany. In the experiment, saplings of host species with a preference for either arbuscular mycorrhiza (AM) or ectomycorrhiza (EM) were planted in monocultures, two‐species, and four‐species mixtures. In addition, mixtures were composed of tree species of only one mycorrhizal type or by AM/EM trees. For almost all species, with the exception of Aesculus hippocastanum and Acer pseudoplatanus (only AM), dual mycorrhization with both types (AM and EM) was found at every sampling time (December, March, and May), although the expected preferences for certain mycorrhizal types were confirmed. The sampling date had a significant influence on mycorrhization rates of both EM and AM tree species. Frequencies of EM and AM were lowest in May, but there were no differences between December and March. The causes of this seasonal variation may be associated with climate‐induced differences in carbon allocation to mycorrhizal tree roots in the temperate climate. Within individual trees, mycorrhization rates by AM and EM fungi were not correlated over time, pointing to asynchronous variation between both types and to independent drivers for AM and EM mycorrhization. At the community level, mycorrhiza frequency of either of the two types became more asynchronous from two‐species to four‐species mixtures. Thus, increased community asynchrony in mycorrhization could be another important mechanism in biodiversity–ecosystem functioning relationships. [ABSTRACT FROM AUTHOR]

Summary: The establishment of arbuscular mycorrhiza (AM) between plants and Glomeromycotina fungi is preceded by the exchange of chemical signals: fungal released Myc‐factors, including chitooligosaccharides (CO) and lipo‐chitooligosaccharides (LCO), activate plant symbiotic responses, while root‐exuded strigolactones stimulate hyphal branching and boost CO release. Furthermore, fungal signaling reinforcement through CO application was shown to promote AM development in Medicago truncatula, but the cellular and molecular bases of this effect remained unclear.Here, we focused on long‐term M. truncatula responses to CO treatment, demonstrating its impact on the transcriptome of both mycorrhizal and nonmycorrhizal roots over several weeks and providing an insight into the mechanistic bases of the CO‐dependent promotion of AM colonization.CO treatment caused the long‐lasting regulation of strigolactone biosynthesis and fungal accommodation‐related genes. This was mirrored by an increase in root didehydro‐orobanchol content, and the promotion of accommodation responses to AM fungi in root epidermal cells. Lastly, an advanced downregulation of AM symbiosis marker genes was observed at the latest time point in CO‐treated plants, in line with an increased number of senescent arbuscules.Overall, CO treatment triggered molecular, metabolic, and cellular responses underpinning a protracted acceleration of AM development. [ABSTRACT FROM AUTHOR]

Introduction: Plants and arbuscular mycorrhizal fungi (AMF) mutualistic interactions are essential for sustainable agriculture production. Although it is shown that AMF inoculation improves cassava physiological performances and yield traits, the molecular mechanisms involved in AM symbiosis remain largely unknown. Herein, we integrated metabolomics and transcriptomics analyses of symbiotic (Ri) and asymbiotic (CK) cassava roots and explored AM-induced biochemical and transcriptional changes. Results: Three weeks (3w) after AMF inoculations, proliferating fungal hyphae were observable, and plant height and root length were significantly increased. In total, we identified 1,016 metabolites, of which 25 were differentially accumulated (DAMs) at 3w. The most highly induced metabolites were 5-aminolevulinic acid, L-glutamic acid, and lysoPC 18:2. Transcriptome analysis identified 693 and 6,481 differentially expressed genes (DEGs) in the comparison between CK (3w) against Ri at 3w and 6w, respectively. Functional enrichment analyses of DAMs and DEGs unveiled transport, amino acids and sugar metabolisms, biosynthesis of secondary metabolites, plant hormone signal transduction, phenylpropanoid biosynthesis, and plant-pathogen interactions as the most differentially regulated pathways. Potential candidate genes, including nitrogen and phosphate transporters, transcription factors, phytohormone, sugar metabolism-related, and SYM (symbiosis) signaling pathway-related, were identified for future functional studies. Discussion: Our results provide molecular insights into AM symbiosis and valuable resources for improving cassava production. [ABSTRACT FROM AUTHOR]

Mycorrhizas are widespread below‐ground symbioses formed between plant roots and soil fungi. This plant–fungal partnership impacts terrestrial ecosystems by mediating plant performance and biogeochemical processes. The influence of mycorrhizas on plant and ecosystem functioning is ultimately driven by the biological processes that regulate plant–mycorrhizal interactions. Although convergent patterns in morphological and genetic traits of mycorrhizas have been well‐documented and reflect key selection forces that shape the biology of mycorrhizas, generalizable traits of mycorrhizal‐associated root metabolome, which are more intimately linked to plant and ecosystem functioning, remain unexplored.Here, we compared mycorrhizal‐associated metabolome alterations across multiple plant–mycorrhizal fungus combinations. Specifically, we inoculated a phylogenetically diverse set of temperate tree species with either arbuscular mycorrhizal or ectomycorrhizal fungi (the two major mycorrhizal lifestyles). Using comprehensive metabolomics approaches, we then assessed the metabolome in mycorrhizal and non‐mycorrhizal roots and the corresponding leaves.Comparing across multiple plant–mycorrhizal fungus combinations, our data revealed metabolite alterations unique to mycorrhizal lifestyle as well as those common across plant–fungus combinations irrespective of lifestyles. Roots colonized by arbuscular mycorrhizal and ectomycorrhizal fungi accumulated different sets of carbohydrates, reflecting unique carbon allocation strategies for mycorrhizas. Arbuscular mycorrhizal roots accumulated cyclic polyols (e.g. inositols) inaccessible to their fungal partners, suggesting tight regulation of carbon partitioning. Such accumulation did not occur in ectomycorrhizal‐colonized roots, which instead accrued acyclic polyols (e.g. mannitol and arabitol) that were undetected in non‐mycorrhizal roots and likely of fungal origin. Mycorrhizas also altered specialized metabolism, featuring frequent increases in flavan‐3‐ols (e.g. catechins, gallocatechins, and their oligomers) but decreases in flavanols irrespective of mycorrhizal lifestyles, suggesting tactical reconfiguration of specialized metabolites to both facilitate and restrain the symbiont. These characteristic metabolite alterations were largely root specific and were not mirrored in leaves.Synthesis. Using multiple plant–mycorrhizal systems and metabolomics approaches, our study demonstrates that part of the metabolite alterations occurring during root–mycorrhizal interactions were relatively common across plant–mycorrhizal systems, with implications for both carbon partitioning and tissue protection strategies important for successful symbiosis. These generalizable patterns appear robust to the phylogenetic history of host plants and thus may be widespread in land plants. [ABSTRACT FROM AUTHOR]

Phaseolus vulgaris L. (Fabaceae) forms symbioses with arbuscular mycorrhizal fungi (AMF) and nitrogen-fixing rhizobia (NFB). The tripartite relationship uses molecular singals to establish intracellular symbioses in roots. The goal of this study was to determine if Rhizobium tropici CIAT 899 and exogenous riboflavin (vitamin B2) have an effect on AMF species selection and root colonization of P. vulgaris. Using SSU rRNA fragment amplification of DNA extracted from P. vulgaris roots, we found that the presence of R. tropici altered the relative distribution of AMF species. Dominikia bernensis (Ohel) was the most abundant AMF species in P. vulgaris roots but when R. tropici was co-inoculated, Glomus species dominated. Rhizobacteria such as R. tropici, secrete riboflavin and could affect AMF symbiosis. Addition of 50 μM riboflavin to P. vulgaris, increased plant growth (28%), dry nodule weight (18%), AMF colonization (248%) and mycorrhizal vesicle frequency (56%) in bean roots. 3.12 and 12.5 µM riboflavin favored the presence of Glomus macrocarpum in P. vulgaris roots. This work provides the basis to further study of rhizobial and mycorrhizal co-inoculation of Phaseolus vulgaris bean. [ABSTRACT FROM AUTHOR]

This study aimed to elucidate the role of bacteria colonising mycorrhizal hyphae in organically bound sulfur mobilisation, the dominant soil sulfur source that is not directly plant available. The effect of an intact mycorrhizal symbiosis with access to stable isotope organo-34S enriched soils encased in 35 µm mesh cores was tested in microcosms with Agrostis stolonifera and Plantago lanceolata. Hyphae and associated soil were sampled from static mesh cores with mycorrhizal ingrowth and rotating mesh cores that exclude mycorrhizal ingrowth as well as corresponding rhizosphere soil, while plant shoots were analysed for 34S uptake. Static cores increased uptake of 34S at early stages of plant growth when sulfur demand appeared to be high and harboured significantly larger populations of sulfonate mobilising bacteria. Bacterial and fungal communities were significantly different in the hyphospheres of static cores when compared to rotating cores, not associated with plant hosts. Shifts in bacterial and fungal communities occurred not only in rotated cores but also in the rhizosphere. Arylsulfatase activity was significantly higher in the rhizosphere when cores stayed static, while atsA and asfA gene diversity was distinct in the microcosms with static and rotating cores. This study demonstrated that AM symbioses can promote organo-S mobilization and plant uptake through interactions with hyphospheric bacteria, enabling AM fungal ingrowth into static cores creating a positive feedback-loop, detectable in the microbial rhizosphere communities. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal (AM) fungi are symbionts of most terrestrial plants and enhance their adaptability in metal-contaminated soils. In this study, mycorrhized and non-mycorrhized Eucalyptus grandis were grown under different Zn treatments. After 6 weeks of treatment, the growing status and ionome content of plants as well as the expression patterns of metal tolerance proteins and auxin biosynthesis-related genes were measured. In this study, mycorrhized E. grandis showed higher biomass and height at a high level of Zn compared with non-mycorrhized plants. In addition, AM plants accumulated P, Mg, and Mn in roots and P, Fe, and Cu in shoots, which indicate that AM fungi facilitate the uptake of ionome nutrients to promote plant growth. In addition, mycorrhiza upregulated the expression of EgMTP1 and EgMTP7, whose encoding proteins were predicted to be located at the vacuolar membrane. Meanwhile, Golgi membrane transporter EgMTP5 was also induced in AM shoot. Our results suggest that AM likely mitigates Zn toxicity through sequestrating excess Zn into vacuolar and Golgi. Furthermore, the expression of auxin biosynthesis-related genes was facilitated by AM, and this is probably another approach for Zn tolerance. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal (AM) fungi improve plant growth, nutrition, fitness and stress tolerance while AM fungi obtain carbohydrates and lipids from the host. This whole process of mutual benefit requires substantial alterations in the structural and functional aspects of the host root cells. These modifications ultimately culminate in the formation of arbuscules, which are specialized intraradical and highly branched fungal structures. Arbuscule-containing cells undergo massive reprogramming to hosting arbuscule and members of the GRAS transcription factor family have been characterized as AM inducible genes which play a pivotal role in these process. Here, we show a functional analysis for the GRAS transcription factor SCL3/SlGRAS18 in tomato. SlGRAS18 interacts with SlDELLA, a central regulator of AM formation. Silencing of SlGRAS18 positively impacts arbuscule development and the improvement in symbiotic status, favouring flowering and therefore progress in the formation and development of fruits in SlGRAS18 silenced plants which parallel to a discernible pattern of mineral nutrient redistribution in leaves. Our results advance the knowledge of GRAS transcription factors involved in the formation and establishment of AM symbiosis and provide experimental evidence for how specific genetic alterations can lead to more effective AM symbiosis. • The tomato transcription factor SlGRAS18 is a negative regulator of Arbuscular Mycorrhiza (AM). • Tomato SlGRAS18 interacts with SlDELLA, a central regulator of AM formation. • Silencing of SlGRAS18 positively impacts the symbiotic effectiveness. [ABSTRACT FROM AUTHOR]

Background: Evaluation of native soil microbes is a realistic way to develop bio-agents for ecological restoration. Soil alkalinity, which has a high pH, is one of the most common concerns in dry and semi-arid climates. Alkaline soils face problems due to poor physical properties, which affect plant growth and crop production. A pot experiment was carried out to investigate the impact of native mycorrhizal fungi (AMF) on the wheat plant (Triticum aestivum L.) under two levels of alkalinity stress -T1 (37 mM NaHCO3), T2 (74 mM NaHCO3) - at two developmental stages (the vegetative and productive stages). Results: Alkalinity stress significantly inhibited the germination percentage, plant biomass, photosynthetic pigments, and some nutrients (K, N, and P). Mycorrhizal inoculation improved growth parameters and productivity of wheat-stressed plants. However, lipid peroxidation was significantly lowered in mycorrhizal-inoculated plants compared to non-inoculated plants. Catalase and peroxidase were inhibited in wheat leaves and roots by alkalinity, while mycorrhiza promoted the activity of these enzymes. Conclusion: The results of this study demonstrated that alkalinity stress had highly negative effects on some growth parameters of the wheat plant, while AMF inoculation attenuated these detrimental effects of alkalinity stress at two stages by reducing the pH and Na concentration and increasing the availability of P and the productivity of wheat in particular crop yield parameters. [ABSTRACT FROM AUTHOR]

Both plants and their associated arbuscular mycorrhizal (AM) fungi require nitrogen (N) for their metabolism and growth. This can result in both positive and negative effects of AM symbiosis on plant N nutrition. Either way, the demand for and efficiency of uptake of mineral N from the soil by mycorrhizal plants are often higher than those of nonmycorrhizal plants. In consequence, the symbiosis of plants with AM fungi exerts important feedbacks on soil processes in general and N cycling in particular. Here, we investigated the role of the AM symbiosis in N uptake by Andropogon gerardii from an organic source (15N-labeled plant litter) that was provided beyond the direct reach of roots. In addition, we tested if pathways of 15N uptake from litter by mycorrhizal hyphae were affected by amendment with different synthetic nitrification inhibitors (dicyandiamide [DCD], nitrapyrin, or 3,4-dimethylpyrazole phosphate [DMPP]). We observed efficient acquisition of 15N by mycorrhizal plants through the mycorrhizal pathway, independent of nitrification inhibitors. These results were in stark contrast to 15N uptake by nonmycorrhizal plants, which generally took up much less 15N, and the uptake was further suppressed by nitrapyrin or DMPP amendments. Quantitative real-time PCR analyses showed that bacteria involved in the rate-limiting step of nitrification, ammonia oxidation, were suppressed similarly by the presence of AM fungi and by nitrapyrin or DMPP (but not DCD) amendments. On the other hand, abundances of ammonia-oxidizing archaea were not strongly affected by either the AM fungi or the nitrification inhibitors. [ABSTRACT FROM AUTHOR]

Simple Summary: Tomato can interact with arbuscular mycorrhizal fungi (AMF) to form a symbiotic association called arbuscular mycorrhiza. This symbiosis, in addition to providing nutritional benefits to plants, induces a plant defense response against biotic and abiotic stresses locally in the roots, and systemically throughout the entire plant. However, the mechanisms underlying these conferred systemic resistance-induced responses are largely unknown. This work aimed to identify which regulatory molecules could be involved in the response mechanisms elicited during priming. The findings presented here provide valuable information on the molecules that could participate in these responses, with the aim of elucidating the whole mechanism. Arbuscular mycorrhizal symbiosis is an association that provides nutritional benefits to plants. Importantly, it induces a physiological state allowing plants to respond to a subsequent pathogen attack in a more rapid and intense manner. Consequently, mycorrhiza-colonized plants become less susceptible to root and shoot pathogens. This study aimed to identify some of the molecular players and potential mechanisms related to the onset of defense priming by mycorrhiza colonization, as well as miRNAs that may act as regulators of priming genes. The upregulation of cellulose synthases, pectinesterase inhibitors, and xyloglucan endotransglucosylase/hydrolase, as well as the downregulation of a pectinesterase, suggest that the modification and reinforcement of the cell wall may prime the leaves of mycorrhizal plants to react faster and stronger to subsequent pathogen attack. This was confirmed by the findings of miR164a-3p, miR164a-5p, miR171e-5p, and miR397, which target genes and are also related to the biosynthesis or modification of cell wall components. Our findings support the hypothesis that the reinforcement or remodeling of the cell wall and cuticle could participate in the priming mechanism triggered by mycorrhiza colonization, by strengthening the first physical barriers upstream of the pathogen encounter. [ABSTRACT FROM AUTHOR]

Biostimulant use in the world is increasing more and more, in this sense, this work was carried out at the Tecomatlan Institute, Puebla, Mexico, to evaluate the influence of the Quitomax® use and the inoculation with two strains of mycorrhizae on the growth and development of tomato plants. Seedlings were produced in a shade house, in trays of 200 cells, filled with a commercial substrate, under same treatments that would later be applied in field conditions, which consisted of a control where seeds were imbibed in water for three hours. The same time was used when mycorrhiza was used, while the two strains of mycorrhizae (Incam4 and Incam11) were applied by coating the seeds, so that six treatments were formed, since both biostimulants were also used in combination. A randomized block design with four replications was used for the distribution of treatments under field conditions. At transplanting, each inoculum was applied to the root system and Quitomax® was applied sprayed to the foliage at seven and 28 days, in the treatments that required it. In the postures, height growth was evaluated every seven days and stem diameter at the transplanting time. Under field conditions, growth and yield variables were evaluated. In the posturing phase, the treatments did not modify stem diameter with respect to the control, and had a greater effect on plant height. Under field conditions, the effect was more marked on yield than on the growth variables evaluated, highlighting the combined action of Quitomax® with the Incam4 strain. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhiza (AM) is a mutualistic symbiotic interaction between plant roots and AM fungi (AMF). This interaction is highly beneficial for plant growth, development and fitness, which has made AM symbiosis the focus of basic and applied research aimed at increasing plant productivity through sustainable agricultural practices. The creation of AM requires host root cells to undergo significant structural and functional modifications. Numerous studies of mycorrhizal plants have shown that extensive transcriptional changes are induced in the host during all stages of colonization. Advances have recently been made in identifying several plant transcription factors (TFs) that play a pivotal role in the transcriptional regulation of AM development, particularly those belonging to the GRAS TF family. There is now sufficient experimental evidence to suggest that GRAS TFs are capable to establish intra and interspecific interactions, forming a transcriptional regulatory complex that controls essential processes in the AM symbiosis. In this minireview, we discuss the integrative role of GRAS TFs in the regulation of the complex genetic re-programming determining AM symbiotic interactions. Particularly, research being done shows the relevance of GRAS TFs in the morphological and developmental changes required for the formation and turnover of arbuscules, the fungal structures where the bidirectional nutrient translocation occurs. [ABSTRACT FROM AUTHOR]

Accelerating global warming and water scarcity and improving water use efficiency are considered essential factors for achieving adequate crop development and productivity. Therefore, the authors targeted the use of arbuscular mycorrhizal fungi (AMF) and Pseudomonas fluorescens (Ps1) for improving growth, productivity, and water use efficiency of broccoli plants (Brassica olercea L. var. italica, cv. Belstar F1) under various irrigation regimes i.e., 50, 75, and 100% of crop evapotranspiration (ETc). Two greenhouse experiments were carried out in clayey soil. The combined inoculation of endomycorrhizae and Ps. fluorescens (Ps1) improved water use efficiency and consequently vegetative growth and yield. Under the applied irrigation regime 75% ETc of broccoli inoculated with both endomycorrhizae and Ps. fluorescens (Ps1) showed higher head weight (616 and 647 gram) than those grown under the irrigation regime 75% ETc combined with endomycorrhizae (568 and 559 gram) during the two seasons, respectively. However, a minimum yield value of 149 and 142 grams per plant was recorded for uninoculated plants grown under 50% irrigation regime during both seasons. In conclusion, the combined inoculation with endomycorrhizae and Ps. fluorescens (Ps1) under irrigation regime 75% ETc was the optimum combination for increasing water stress resistance and broccoli productivity under water scarcity circumstances. [ABSTRACT FROM AUTHOR]

Nickel (Ni) is a fundamental micronutrient in plants but hampers plant growth and metabolism at elevated levels in the soil by inducing oxidative stress. In the recent years, use of polyamines (PAs) and arbuscular mycorrhiza (AM) have gained importance for their roles in enabling plants to withstand Ni toxicity. However, information about their comparative effectiveness in alleviating Ni stress is scanty. Therefore, the current study was designed to evaluate relative impacts of three PAs (Put, Spd, and Spm) and AM (Rhizoglomus intraradices) in reducing Ni uptake, ROS generation, and modulating antioxidant defense machinery in two pigeonpea genotypes (Pusa 2001-tolerant and AL 201-sensitive). Roots of Ni supplied plants accumulated significantly more Ni than the leaves, more in AL 201 than Pusa 2001, which was proportionate to reduced dry weights and enhanced oxidative burst. Although all the three PAs as well as AM inoculations upsurge plant growth by remarkably lowering Ni transport as well as the sequential oxidative burden, AM was most effective, followed by Put, Spd with least positive impact of Spm. The combined applications of AM and Put were able to strengthen antioxidant defense mechanisms, including those of ascorbate-glutathione cycle, most strongly when compared with + Spd + AM and + Spm + AM. Pusa 2001 was more responsive to PAs priming because of its proficiency to develop better effective mycorrhizal symbiosis with R. intraradices when compared with AL201. Hence, the results suggest use of combined applications of PAs (mainly Put) and R. intraradices as an effective strategy for mitigating Ni toxicity in pigeonpea genotypes. [ABSTRACT FROM AUTHOR]

Background and Aims Condensed tannin (CT) is an important compound in plant biological structural defence and for tolerance of herbivory and environmental stress. However, little is known of the role and location of CT within the fine roots of woody plants. To understand the role of CT in fine roots across diverse species of woody dicot, we evaluated the localization of CT that accumulated in root tissue, and examined its relationships with the stele and cortex tissue in cross-sections of roots in 20 tree species forming different microbial symbiotic groups (ectomycorrhiza and arbuscular mycorrhiza). Methods In a cool-temperate forest in Japan, cross-sections of sampled roots in different branching order classes, namely, first order, second to third order, fourth order, and higher than fourth order (higher order), were measured in terms of the length-based ratios of stele diameter and cortex thickness to root diameter. All root samples were then stained with ρ -dimethylaminocinnamaldehyde solution and we determined the ratio of localized CT accumulation area to the root cross-section area (CT ratio). Key Results Stele ratio tended to increase with increasing root order, whereas cortex ratio either remained unchanged or decreased with increasing order in all species. The CT ratio was significantly positively correlated to the stele ratio and negatively correlated to the cortex ratio in second- to fourth-order roots across species during the shift from primary to secondary root growth. Ectomycorrhiza-associated species mostly had a higher stele ratio and lower cortex ratio than arbuscular mycorrhiza-associated species across root orders. Compared with arbuscular mycorrhiza species, there was greater accumulation of CT in response to changes in the root order of ectomycorrhiza species. Conclusions Different development patterns of the stele, cortex and CT accumulation along the transition from root tip to secondary roots could be distinguished between different mycorrhizal associations. The CT in tissues in different mycorrhizal associations could help with root protection in specific branching orders during shifts in stele and cortex development before and during cork layer formation. [ABSTRACT FROM AUTHOR]

The use of microbial inoculants, particularly arbuscular mycorrhizal fungi, has great potential for sustainable crop management, which aims to reduce the use of chemical fertilizers and pesticides. However, one of the major challenges of their use in agriculture is the variability of the inoculation effects in the field, partly because of the varying environmental conditions. Light intensity and quality affect plant growth and defense, but little is known about their impacts on the benefits of mycorrhizal symbioses. We tested the effects of five different light intensities on plant nutrition and resistance to the necrotrophic foliar pathogen Botrytis cinerea in mycorrhizal and non-mycorrhizal lettuce plants. Our results evidence that mycorrhiza establishment is strongly influenced by light intensity, both regarding the extension of root colonization and the abundance of fungal vesicles within the roots. Light intensity also had significant effects on plant growth, nutrient content, and resistance to the pathogen. The effect of the mycorrhizal symbiosis on plant growth and nutrient content depended on the light intensity, and mycorrhiza efficiently reduced disease incidence and severity under all light intensities. Thus, mycorrhiza-induced resistance can be uncoupled from mycorrhizal effects on plant nutrition. Therefore, mycorrhizal symbioses can be beneficial by providing biotic stress protection even in the absence of nutritional or growth benefits. [ABSTRACT FROM AUTHOR]

Background and Aims An arbuscular mycorrhiza is a mutualistic symbiosis with plants as carbon providers for fungi. However, achlorophyllous arbuscular mycorrhizal species are known to obtain carbon from fungi, i.e. they are mycoheterotrophic. These species all have the Paris type of arbuscular mycorrhiza. Recently, two chlorophyllous Paris -type species proved to be partially mycoheterotrophic. In this study, we explore the frequency of this condition and its association with Paris -type arbuscular mycorrhiza. Methods We searched for evidence of mycoheterotrophy in all currently published 13C, 2H and 15N stable isotope abundance patterns suited for calculations of enrichment factors, i.e. isotopic differences between neighbouring Paris - and Arum -type species. We found suitable data for 135 plant species classified into the two arbuscular mycorrhizal morphotypes. Key Results About half of the chlorophyllous Paris -type species tested were significantly enriched in 13C and often also enriched in 2H and 15N, compared with co-occurring Arum -type species. Based on a two-source linear mixing model, the carbon gain from the fungal source ranged between 7 and 93 % with ferns > horsetails > seed plants. The seed plants represented 13 families, many without a previous record of mycoheterotrophy. The 13C-enriched chlorophyllous Paris -type species were exclusively herbaceous perennials, with a majority of them thriving on shady forest ground. Conclusions Significant carbon acquisition from fungi appears quite common and widespread among Paris -type species, this arbuscular mycorrhizal morphotype probably being a pre-condition for developing varying degrees of mycoheterotrophy. [ABSTRACT FROM AUTHOR]

Summary: D14 and KAI2 receptors enable plants to distinguish between strigolactones (SLs) and karrikins (KARs), respectively, in order to trigger appropriate environmental and developmental responses. Both receptors are related to the regulation of arbuscular mycorrhiza (AM) formation and are members of the RsbQ‐like family of α,β‐hydrolases. DLK2 proteins, whose function remains unknown, constitute a third clade from the RsbQ‐like protein family. We investigated whether the tomato SlDLK2 is a new regulatory component in the AM symbiosis.Genetic approaches were conducted to analyze SlDLK2 expression and to understand SlDLK2 function in AM symbiosis.We show that SlDLK2 expression in roots is AM‐dependent and is associated with cells containing arbuscules. SlDLK2 ectopic expression arrests arbuscule branching and downregulates AM‐responsive genes, even in the absence of symbiosis; while the opposite effect was observed upon SlDLK2 silencing. Moreover, SlDLK2 overexpression in Medicago truncatula roots showed the same altered phenotype observed in tomato roots. Interestingly, SlDLK2 interacts with DELLA, a protein that regulates arbuscule formation/degradation in AM roots.We propose that SlDLK2 is a new component of the complex plant‐mediated mechanism regulating the life cycle of arbuscules in AM symbiosis. [ABSTRACT FROM AUTHOR]

To overcome phosphorus (P) deficiency, about 80% of plant species establish symbiosis with arbuscular mycorrhizal fungi (AMF), which in return constitute a major sink of photosynthates. Information on whether plant carbon (C) allocation towards AMF increases with declining availability of the P source is limited. We offered orthophosphate (OP), apatite (AP), or phytic acid (PA) as the only P source available to arbuscular mycorrhiza (AM) (Solanum lycopersicum x Rhizophagus irregularis) in a mesocosm experiment, where the fungi had exclusive access to each P source. After exposure, we determined P contents in the plant, related these to the overall C budget of the system, including the organic C (OC) contents, the respired CO2, the phospholipid fatty acid (PLFA) 16:1ω5c (extraradical mycelium), and the neutral fatty acid (NLFA) 16:1ω5c (energy storage) at the fungal compartment. Arbuscular mycorrhizal (AM) plants incorporated P derived from the three P sources through the mycorrhizal pathway, but did this with differing C-P trading costs. The mobilization of PA and AP by the AM plant entailed larger mycelium infrastructure and significantly larger respiratory losses of CO2, in comparison with the utilization of the readily soluble OP. Our study thus suggests that AM plants invest larger C amounts into their fungal partners at lower P availability. This larger C flux to the AM fungi might also lead to larger soil organic C contents, in the course of forming larger AM biomass under P-limiting conditions. [ABSTRACT FROM AUTHOR]

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The role of mutualisms in mediating temporal stability in an ecosystem has been debated extensively. Here, we focus on how a ubiquitous mutualism, arbuscular mycorrhiza, influences temporal stability of a key ecosystem process, ecosystem respiration. We discriminated between two forms of temporal stability, temporal variability and resilience, and hypothesized that excluding arbuscular mycorrhiza would be detrimental for both of them. We analyzed a set of 10 parallel manipulation experiments to assess how excluding arbuscular mycorrhiza modulates temporal stability compared to other common experimental factors. We quantified the temporal variability of ecosystem respiration and the resilience to experimental perturbations (i.e., pulses, stresses, and a disturbance) following manipulations of mycorrhizal state. We observed lower temporal variability in the absence of arbuscular mycorrhiza in discord to our main hypothesis. Manipulating arbuscular mycorrhiza had a stronger impact on temporal variability than the pulse (application of urea), the stress (addition of salt), and a disturbance (experimental defoliation) but weaker than excluding primary producers or comparing across different plant species. Resilience to experimental perturbations declined in non‐mycorrhizal microcosms. We present an empirical study on how mutualisms impact temporal stability. Arbuscular mycorrhiza differentially alters temporal variability and resilience, highlighting that generalizing across different forms of temporal stability could be misleading. [ABSTRACT FROM AUTHOR]

The impacts of climate change on worldwide crop production become increasingly severe. Thus, sustainable enhancements of agricultural production are needed. The present study investigated the effects of drought and arbuscular mycorrhizal fungi on wheat plants (Triticum aestivum) and their interaction with aphids. Considering predicted climate change scenarios, wheat plants were exposed to well‐watered conditions, continuous drought (CD), or pulsed (PD) drought and plants were grown without (NM) or with mycorrhizal (AM) fungi. Ear biomass and harvest index were evaluated when grains were produced. Moreover, drought‐ and mycorrhiza‐induced changes in the amino acid composition of leaf phloem exudates were studied and the population growth and survival of Sitobion avenae aphids on those plants measured. Wheat plants responded differently toward the irrigation treatments. Under drought stress, ear biomass was reduced, while AM resulted in an enhanced harvest index. In phloem exudates especially, relative concentrations of the osmoprotectant proline were modulated by drought. Aphid population size was influenced by the interaction of drought and mycorrhiza treatment. This study emphasizes the pronounced influence of irrigation frequency on plant performance and indicates positive contributions of AM that may be relevant for agriculture. [ABSTRACT FROM AUTHOR]

The negative effects of the current agricultural practices include erosion, acidification, loss of soil organic matter (dehumification), loss of soil structure, soil contamination by risky elements, reduction of biological diversity and land use for non-agricultural purposes. All these effects are a huge risk to the further development of soil quality from an agronomic point of view and its resilience to projected climate change. Organic matter has a crucial role in it. Relatively significant correlations with the quality or the health of soil parameters and the soil organic matter or some fraction of the soil organic matter have been found. In particular, Ctot, Cox, humic and fulvic acids, the C/N ratio, and glomalin. Our work was focused on glomalin, a glycoprotein produced by the hyphae and spores of arbuscular mycorrhizal fungi (AMF), which we classify as Glomeromycota. Arbuscular mycorrhiza, and its molecular pathways, is not a well understood phenomenon. It appears that many proteins are involved in the arbuscular mycorrhiza from which glomalin is probably one of the most significant. This protein is also responsible for the unique chemical and physical properties of soils and has an ecological and economical relevance in this sense and it is a real product of the mycorrhiza. Glomalin is very resistant to destruction (recalcitrant) and difficult to dissolve in water. Its extraction requires specific conditions: high temperature (121°C) and a citrate buffer with a neutral or alkaline pH. Due to these properties, glomalin (or its fractions) are very stable compounds that protect the soil aggregate surface. In this review, the actual literature has been researched and the importance of glomalin is discussed. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhiza (AM) is a widespread symbiosis between plant roots and fungi of the Glomeromycotina , which improves nutrient uptake by plants. The molecular mechanisms underlying development and function of the symbiosis are subject to increasing research activity. Since AM occurs in the soil, most studies targeting a molecular understanding of AM development and function, use solid substrates for co-cultivating plants and AM fungi. However, for some experiments very clean roots, highly controlled nutrient conditions or applications of defined concentrations of signaling molecules (such as hormones) or other small chemicals (such as synthetic inhibitors or signaling agonists) are needed. To this end, hydroponics has been widely used in research on mechanisms of plant nutrition and some hydroponic systems were developed for AM fungal spore amplification. Here, we present a hydroponics set-up, which can be successfully utilized for experimental root colonization assays. We established a "tip-wick" system based on pipette tips and rock wool wicks for co-cultivation of AM fungi with small model plants such as Lotus japonicus. A larger "Falcon-wick" system using Falcon tubes and rockwool wicks was developed for larger model plants such as rice. The hydroponic system can also be employed for growing L. japonicus hairy roots after transformation by Agrobacterium rhizogenes , thus circumventing the laborious cultivation on agar medium-containing Petri dishes during hairy root development. The tip-wick and Falcon-wick systems are easy to use and can be built with low cost, conventional and reusable lab plastic ware and a simple aquarium pump. [ABSTRACT FROM AUTHOR]

Strigolactones (SLs) are plant-derived signaling molecules that stimulate the hyphal branching of arbuscular mycorrhizal fungi (AMF), and consequently promote symbiotic interaction between the fungus and the plant. Currently, our knowledge on the molecular mechanism of SL transport is restricted to the Solanaceae family. In the Solanaceae family, SL translocation toward the rhizosphere occurs through the exodermis via hypodermal passage cells and involves a member of the G subfamily, of the ATP-binding cassette (ABC) membrane transporters. Most Fabaceae species, including those that are agriculturally important, have a different root anatomy compared to most angiosperm plants (i.e., lacking an exodermis). Thus, we have investigated how SL transport occurs in the model legume Medicago truncatula. Here, we show that overexpression of a SL transporter from petunia (PaPDR1) enhances AMF colonization rates in M. truncatula. This result demonstrates the importance of ABCG proteins for the translocation of orobanchol-type molecules to facilitate arbuscular mycorrhiza, regardless of root anatomy and phylogenetic relationships. Moreover, our research has led to the identification of Medicago ABCG59, a close homologue of Petunia PDR1, that exhibits root specific expression and is up-regulated by phosphate starvation as well as in the presence of rac -GR24, a synthetic SL. Its promoter is active in cortical cells, root tips, and the meristematic zone of nodules. The mtabcg59 loss-of-function mutant displayed a reduced level of mycorrhization compared to the WT plants but had no impact on the number of nodules after Sinorhizobium meliloti inoculation. The reduced mycorrhization indicates that less SLs are secreted by the mutant plants, which is in line with the observation that mtabcg59 exudates exhibit a reduced stimulatory effect on the germination of the parasitic plant Phelipanche ramosa compared to the corresponding wild type. [ABSTRACT FROM AUTHOR]

Nickel (Ni) is an essential micronutrient but considered toxic for plant growth when present in excess in the soil. Polyamines (PAs) and arbuscular mycorrhiza (AM) play key roles in alleviating metal toxicity in plants. Present study compared the roles of AM and PAs in improving rhizobial symbiosis, ureide, and trehalose (Tre) metabolism under Ni stress in Cajanus cajan (pigeon pea) genotypes (Pusa 2001, AL 201). The results documented significant negative impacts of Ni on plant biomass, especially roots, more in AL 201 than Pusa 2001. Symbiotic efficiency with Rhizobium and AM declined under Ni stress, resulting in reduced AM colonization, N2 fixation, and ureide biosynthesis. This decline was proportionate to increased Ni uptake in roots and nodules. Put-reduced Ni uptake improved plant growth and functional efficiency of nodules and ureides synthesis, with higher positive effects than other PAs. However, AM inoculations were most effective in enhancing nodulation, nitrogen fixing potential, and Tre synthesis under Ni toxicity. Combined applications of AM with respective PAs, especially +Put+AM, were highly beneficial in alleviating Ni-induced nodule senescence by arresting leghemoglobin degradation and improving functional efficiency of nodules by boosting Tre metabolism, especially in Pusa 2001. The study suggested use of Put along with AM as a promising approach in imparting Ni tolerance to pigeon pea plants. [ABSTRACT FROM AUTHOR]

Under the field conditions crop plants interact with diverse microorganisms. These include beneficial (symbiotic) and phytopathogenic microorganisms, which jointly affect growth and productivity of the plants. In last decades, production of potato (Solanum tuberosum L.) suffers from increased incidence of potato virus Y (PVY), which is one of most important potato pests. Arbuscular mycorrhizal fungi (AMF) are common symbionts of potato, however the impact of mycorrhizal symbiosis on the progression of PVY-induced disease is scarcely known. Therefore, in the present study we investigated the effect of joint PVY infection and mycorrhizal colonization by Rhizophagus irregularis on growth traits of the host potato plant (cv. Pirol). The tested PVY isolate belonged to N-Wilga strain group, which is considered to be predominant in Europe and many other parts of the world. The viral particles were concentrated in the leaves, but decreased the root growth. Furthermore, the infection with PVY evoked prolonged oxidative stress reflected by increased level of endogenous H2O2. AMF alleviated oxidative stress in PVY-infected host plants by a substantial decrease in the level of shoot- and root-derived H2O2, but still caused asymptomatic growth depression. It was assumed that mycorrhizal symbiosis of potato might mask infection by PVY in field observations. [ABSTRACT FROM AUTHOR]

Aims: This study assessed intraspecific variation in morphological traits of the fine root branch orders of Cryptomeria japonica, and identified variation in the diameter of the first three-order roots among species types with mycorrhiza, and the diameter of first-order roots at the family level. Methods: Diameter, length, and specific root length of branch order roots (up to the fourth-order) were measured in intact fine root systems collected in four C. japonica stands. Relationships between soil chemical properties and morphological traits of the first- to fourth-order roots were investigated. The diameter of roots of 52 tree species reported in previous studies was compared at species types with mycorrhiza and at family level. Results: The diameter of first-order roots in C. japonica varied by 1.2 times among stands. Negative correlations between soil NH4+ content and specific root length of the second- and third-order roots were observed in C. japonica. The diameter of first- and second-order roots forming arbuscular mycorrhiza in coniferous trees were significantly higher than those of roots forming ectomycorrhiza in coniferous and broadleaf trees. The diameter of first-order roots in Cupressaceae were significantly larger than those of Pinaceae, Sapindaceae, Betulaceae, and Fagaceae. Conclusions: Clarifying intraspecific variation in morphological traits of C. japonica lower-order roots may contribute to understanding their responses to different site conditions such as soil inorganic nitrogen contents. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal (AM) participate in fungi-plant symbiotic relationships and mediate the acquisition of soil-borne nutrients by host plants. However, little is known about how AM colonization affects the homeostasis of iron (Fe) and zinc (Zn) in the host plant. Here, we assessed the performance of mycorrhizal growth, oxidative defense, nutrient accumulation, and key gene responses in AM-colonized tobacco (Nicotiana tabacum L.) under different nutrient stress. The total mycorrhizal frequency of AM fungi on tobacco roots reached 86 % and 75 % under low and high phosphorus (P) treatments, respectively. Under Fe/Zn stress, AM alleviated the inhibition of tobacco biomass accumulation, decreased the content of lipid peroxides, and upregulated enzymatic antioxidant capability. In AM-colonized tobacco, Fe/Zn accumulation was increased under deficient conditions and decreased under surplus conditions. Tobacco uptake of P, Fe, and Zn was impaired by excess nutrient concentrations and improved at low concentrations, and this phenomenon was supported by AM colonization. Fe/Zn deficiency upregulated genes related to Fe/Zn uptake, and Fe/Zn excess upregulated genes related to heavy metal efflux, with AM colonization further promoting these upregulations. Notely, we found a possible crosstalk node, Yellow Stripe-Like 7 (NtYSL7), in the AM and Fe/Zn homeostasis regulatory network. NtYSL7 has a plasma membrane-localized oligopeptide transporter domain. NtYSL7 is strongly induced by AM colonization, deficiency of Fe, and surplus Zn, and interacts with many Fe/Zn transporters. AM assists host plants in maintaining Fe/Zn homeostasis by improving nutrient accumulation, redox homeostasis, and transport mechanisms, and NtYSL7 is likely important within the crosstalk network of AM, Fe, and Zn nutrient homeostasis. [Display omitted] • AM helps tobacco uphold Fe and Zn balance via nutrient buildup, defensive oxidation, and transport processes. • AM alleviates the antagonism of tobacco P, Fe and Zn. • Involvement of YSL7 in regulating tobacco Fe and Zn transport mechanisms mediated by AM. [ABSTRACT FROM AUTHOR]

Because of light constraints, it is expected that latitude exerts a strong influence on reciprocal exchange of resources between mycorrhizal plants and fungi, and this could have consequences on the responsiveness of plants to mycorrhizal fungi. To assess environmental filtering due to AM fungi with regards to latitude, we synthesized data from a common garden experiment on comparative mycorrhizal responsiveness of North American annual and perennial herbaceous plants (Wilson & Hartnett, [31]) with plant distribution data for the specific plants from USDA ([28]; Notes S3). When we analysed annual and perennial plants separately, we found a significant relationship only for perennials (Kendall tau was -0.32 - P = 0.004, whereas for annuals the Kendall tau was 0.03 - P = 0.87). Negative feedback within a mutualism: host-specific growth of mycorrhizal fungi reduces plant benefit. [Extracted from the article]

Arbuscular mycorrhiza (AM) has been proven having important roles to support plant growth in a variety of environmental and land constraints. The present study aimed at elucidating the potential of AM propagules obtained from rhizosphere of elephant grass from 7 (seven) soil types in around area of Solo city and Semarang city, the province of Jawa Tengah, Indonesia, to be screened as a biofertilizer. The first step, exploration and analysis of rhizospheric soil of elephant grass from drylands of Alfisol Jumantono, Histosol Ambarawa, Oxisol Tuntang, Andisol Tengaran, Inceptisol Delanggu, Vertisol Jatikuwung and Entisol Pracimantoro for the existence of AM which consisted of spore density and diversity. The second step, pot cultural experiment was conducted for comparing the infectivity and effectivity of AM spores from 7 (seven) soil types in the same media of zeolite and using maize as host. Based on the results of exploration in natural conditions, the rhizospheric soil of elephant grass from Alfisol Jumantono (AJ) and Entisol Pracimantoro (EP) were categorized having low spore density, and based on the pot cultural experiment using zeolite, these two inoculums of AJ and EP also showed low AM infectivity, but resulted in the highest AM effectivity on plant growth as indicated by the highest plant biomass. Based on the result of exploration in natural conditions, the rhizospheric soil from Andisol Tengaran (ATe) indicated the highest spore density (450 spores/100 g soil), however based on the pot culture experiment the inoculum ATe showed the lowest AM effectivity on plant dry weight. The inoculum sources from EP and AJ showed the highest value of mycorrhizal dependency (MD) and growth response (GR), whereas the inoculum of ATe showed the lowest MD and GR in zeolite pot culture. The continued examinations for the functional capability of AM in target conditions are needed for obtaining effective AM biofertilizer. [ABSTRACT FROM AUTHOR]

Sorghum is an important crop grown worldwide for feed and fibre. Like most plants, it has the capacity to benefit from symbioses with arbuscular mycorrhizal (AM) fungi, and its diverse genotypes likely vary in their responses. Currently, the genetic basis of mycorrhiza‐responsiveness is largely unknown. Here, we investigated transcriptional and physiological responses of sorghum accessions, founders of a bioenergy nested association mapping panel, for their responses to four species of AM fungi. Transcriptome comparisons across four accessions identified mycorrhiza‐inducible genes; stringent filtering criteria revealed 278 genes that show mycorrhiza‐inducible expression independent of genotype and 55 genes whose expression varies with genotype. The latter suggests variation in phosphate transport and defence across these accessions. The mycorrhiza growth and nutrient responses of 18 sorghum accessions varied tremendously, ranging from mycorrhiza‐dependent to negatively mycorrhiza‐responsive. Additionally, accessions varied in the number of AM fungi to which they showed positive responses, from one to several fungal species. Mycorrhiza growth and phosphorus responses were positively correlated, whereas expression of two mycorrhiza‐inducible phosphate transporters, SbPT8 and SbPT9, correlated negatively with mycorrhizal growth responses. AM fungi improve growth and mineral nutrition of sorghum, and the substantial variation between lines provides the potential to map loci influencing mycorrhiza responses. Here, we investigated sorghum bioenergy accessions for their physiological and transcriptional responses to four diverse species of arbuscular mycorrhizal fungi. Variation in mycorrhiza‐induced growth and nutritional responses was observed, and this set of lines shows diversity in both mycorrhiza responsiveness and dependence. Additionally, four sorghum mycorrhizal root transcriptomes were generated which enabled the identification of conserved and variable arbuscular mycorrhiza‐regulated sorghum genes. Genetically diverse sorghum lines show variation in their growth, nutrition, and transcriptional responses to several arbuscular mycorrhizal fungi. [ABSTRACT FROM AUTHOR]

Under fertilization levels specific to intensive farming, the impact of compensation of soil nutritional value by arbuscular mycorrhiza (AM) might be limited. Therefore, the question arises whether modern crop varieties, selected for high NPK assimilation rate, are able to gain symbiotic benefits under other challenging field conditions, such as drought. Accordingly, in this study we aimed to evaluate the contribution of Rhizophagus irregularis to the drought response of a stay-green corn hybrid in pot cultures equally fertilized until silking, compared to non-mycorrhizal (NM) counterparts. The highest tested fertilization regime not detrimental to the long-term vitality of intraradical hyphae reached the levels recommended for field cultivation of silage corn, except phosphorus application restricted to 60%. Under normal watering, mycorrhiza increased leaf nitrogen and phosphorus acquisition but only in cultures supplied with low NPK levels. At high fertilization levels, only the older leaves retained AM dependency, whereas for other leaf positions the AM-NM differences were leveled out. The similar size and nutritional status of highly fertilized AM and NM cultures, used in this study, eliminated fungal benefits before and during the 2-week drought progression. Nevertheless, mycorrhizal contribution became evident at the time of renewed watering, when AM plants showed much faster reversal of drought-induced leaf senescence symptoms: impaired photosynthesis and nitrogen management. Our results suggest that mycorrhiza can alter drought-induced senescence even in stay-green mutants. Moreover, this effect was apparently not mediated by AM-improved growth but triggered by activation of fungal transport at the time of recovery. Interestingly, the fungal protective potential was shown to be preserved at the expense of lowering AM vesicle number. It can be interpreted as engagement of hyphal nutritional resources targeted to maintain the symbiotic relationship despite the reduced vitality of the host. Finally, we compared the productivity of AM and NM cultures subjected to short-term drought at silking time and further fertilized with moderate or high NPK doses until the grain-filling stage. The yield and nutritive value of green forage showed that alleviation of drought-induced senescence by AM was not sufficient to have a significant positive effect on the final productivity compared to NM plants. [ABSTRACT FROM AUTHOR]

An important factor controlling tree species diversity is conspecific density dependence (CDD). Adult trees associated with arbuscular mycorrhiza (AM) and ectomycorrhiza (ECM) can exhibit negative and positive CDD effects on conspecific recruitment, respectively. However, the extent to which these mycorrhizal associations affect spatial distributions of individual trees and their relative abundances within forests through CDD remains uncertain. We analysed changes in spatial correlations between adults and conspecific juveniles at different growth stages of five hardwood species in a 6-ha plot of an old-growth forest using a point pattern analysis. The clump sizes of large individuals were also evaluated using the Iδ index (a measure of individual dispersion) in 24 species. In two AM-associated species, juveniles were distributed at greater distances with increasing size or were always distributed at a distance from adults, resulting in small clumps of adults. In contrast, juveniles of two ECM-associated species were distributed close to adults during early or late growth stage, resulting in large clumps of adults. Juveniles of an ECM-associated species disappeared with increasing size, probably due to shade intolerance. In 24 tree species with large numbers of individuals within a plot, the relative basal area was related to both mycorrhizal type and maximum diameter, suggesting that the relative abundance of a species is largely related to its mycorrhizal associations and maximum plant size. This study strongly demonstrated that mycorrhizal associations play an important role in determining the spatial distribution patterns and community structure of tree species through CDD. [ABSTRACT FROM AUTHOR]

Soil replant disease is the main bottleneck interfering with tree growth of peach in soils with poor traits. A potted study was conducted to evaluate the effects of inoculation with an arbuscular mycorrhizal fungus (AMF), Acauloapora scrobiculata, on plant growth, mineral nutrients, soil enzyme activities, soil microbial populations, and root exudate compositions of peach (Prunus persica L. Batsch) seedlings grown in replant soil and non-replant soil. After 15 weeks in AMF inoculation, replant soil heavily inhibited root mycorrhizal colonization. In replant soil, AMF inoculation significantly increased shoot biomass and root phosphorus, potassium, calcium, copper, zinc, iron, and boron concentrations. Mycorrhizal peach seedlings showed a higher number of soil bacteria and total microbes but a lower number of soil fungi under replant conditions, as well higher soil urease and acid phosphatase activity and lower soil sucrase and catalase activity. Greater soil aggregate stability was observed in mycorrhiza-inoculated replant soil than in non-mycorrhizal soil due to the increase of water-stable aggregates in 2–4 mm and 1–2 mm size. In addition, a total of 92 substances were identified in root exudates, and the mycorrhizosphere had considerably more root exudate compositions. AMF inoculation had a significantly inhibitive effect on the relative abundance of allelochemical substances, including benzoic acid, benzaldehyde, diisooctyl phthalate, phenols, and sterols, while there was an increase in diphenyl-ethanedione and à-(benzoyloxy)-benzeneacetonitrile in replanted peach. It was concluded that AMF inoculation could partly mitigate soil replant disease of peach through modulating soil microbe balance, improving soil aggregate stability, and changing root exudate compositions. [ABSTRACT FROM AUTHOR]

Arsenic (As) is the most hazardous soil contaminant, which inactivates metabolic enzymes and restrains plant growth. To withstand As stress conditions, use of some alleviative tools, such as arbuscular mycorrhizal (AM) fungi and silicon (Si), has gained importance. Therefore, the present study evaluated comparative and interactive effects of Si and arbuscular mycorrhiza-Rhizophagus irregularis on phytotoxicity of arsenate (As V) and arsenite (As III) on plant growth, ROS generation, and antioxidant defense responses in pigeonpea genotypes (Tolerant-Pusa 2002; Sensitive-Pusa 991). Roots of As III treated plants accumulated significantly higher total As than As V supplemented plants, more in Pusa 991 than Pusa 2002, which corresponded to proportionately decreased plant growth, root to biomass ratio, and oxidative burst. Although Si nutrition and AM inoculations improved plant growth by significantly reducing As uptake and the resultant oxidative burst, AM was relatively more efficient in upregulating enzymatic and non-enzymatic antioxidant defense responses as well as ascorbate–glutathione pathway when compared with Si. Pusa 2002 was more receptive to Si nourishment due to its ability to establish more efficient mycorrhizal symbiosis, which led to higher Si uptake and lower As concentrations. Moreover, +Si+AM bestowed better metalloid resistance by further reducing ROS and strengthening antioxidants. Results demonstrated that the genotype with more efficient AM symbiosis in As-contaminated soils could accrue higher benefits of Si fertilization in terms of metalloid tolerance in pigeonpea. [ABSTRACT FROM AUTHOR]

THE GOAL of the present investigation was to assess the effect of phosphorus levels and arbuscular mycorrhizal inoculation on growth, yield related traits, productivity and phosphorus uptake by wheat. Two field experiments were conducted using a split plot design with 3 replications in 2016/2017 and 2017/2018 winter seasons. Five levels of P-fertilization (0%, 25%, 50%, 75% and 100% of the recommended dose) were randomizly arranged in main plots and the two treatments of mycorrhizal inoculation "without inoculation (M0) and with inoculation (M1)" were plotted in the sub plots. The results showed that, the yield related traits (number of grains spike-1, number of spikes m-2 and 1000-grain weight) significantly higher with 100% P level in both seasons. Arbuscular mycorrhizal inoculation gave the highest yield related traits in both seasons. Increment levels of phosphorus increased the grain, straw yield and harvest index significantly up to 100% P level of wheat crop. Increasing level of P application (0 to 100% P level) and inoculation with arbuscular mycorrhiza significantly increased P concentration in grains and uptake of P in wheat in both seasons. The combined application of 100% P level with arbuscular mycorrhizal inoculation recorded significantly higher phosphorus uptake in both seasons. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal (AM) fungi can form symbiotic association with the roots of plants that acquire carbon (C) exclusively from the host plants and supply nitrogen (N) to the plants. In this study, our objective was to investigate the effects of the AM fungus on plant growth, C and N partitioning and accumulation of Glycine max L. grown under water stress in pot experiment. Soybean seedlings were inoculated or not inoculated with the AM fungus, and were exposed to three irrigation treatments including full irrigation, deficit irrigation and partial root-zone drying irrigation (PRD). The 15N isotope labeling was used to trace soybean N accumulation. Results showed that water stress significantly decreased plant dry weight. Compared with non-AM fungus, AM fungus increased root N and 15N concentration, and decreased stem, leaf and pod N and 15N concentrations under PRD. AM colonization decreased C and N partitioning into stem and leaf, and increased C and N partitioning into root under PRD. AM plants had greater C accumulation and N use efficiency than non-AM plants. It was concluded that AM symbiosis plays an important role in C and N dynamics of soybean grown under water stress. [ABSTRACT FROM AUTHOR]

Mycorrhizal inoculation in the plant causing increase in growth and production of phytochemicals is well reported, however little information is available related to the effect of mycorrhiza on morphological and biochemical properties of the medicinal plants like Ashwagandha. The present study is an attempt on diversity analysis in Withania somnifera with an aim to ascertain the nature and extent of genetic diversity present among different accessions in presence of mycorrhiza. The major biochemical constituents of Ashwaganda roots are with nolides which are well known for its medicinal properties. Mycorrhizal associations confer benefits like better nutrition acquisition, enhanced growth, defense enhancement and improved abiotic and biotic stress tolerance in plants. The present investigation was undertaken to assess genetic diversity among five different accessions of W. somnifera using morphological and biochemical markers and the effect of mycorrrhizal inoculation on these marker. The present study concluded that presence of mycorrhiza was effective on plant growth and phytochemical constituents more than non-treated plants. Amongst five selected germplasms IC 283662, JA 134, RAS 23, MPAS 6 and MWS 205 of W. somnifera, JA 134 showed best response in pretext of the selected morphological and biochemical features in presence of mycorrhiza. [ABSTRACT FROM AUTHOR]

The perennial woody plants of citrus are one of the most important fruit crops in the world and largely depends on arbuscular mycorrhizal symbiosis (AMS) to obtain essential nutrients from soil. However, the molecular aspects of AMS in citrus and perennial woody plants in general have largely been understudied. We used RNA-sequencing to identify differentially expressed genes in roots of Poncirus trifoliata upon mycorrhization by the AM fungus Glomus versiforme and evaluated their conservation by comparative transcriptome analyses with four herbaceous model plants. We identified 282 differentially expressed genes in P. trifoliata, including orthologs of 21 genes with characterized roles in AMS and 83 genes that are considered to be conserved in AM-host plants. Comparative transcriptome analysis revealed a 'core set' of 156 genes from P. trifoliata whose orthologous genes from at least three of the five species also exhibited similar transcriptional changes during AMS. Functional analysis of one of these conserved AM-induced genes, a 3-keto-acyl-ACP reductase (FatG) involved in fatty acid biosynthesis, confirmed its involvement in AMS in Medicago truncatula. Our results identify a core transcriptional program for AMS that is largely conserved between P. trifoliata and other plants. The comparative transcriptomics approach adds to previous phylogenomics studies to identify conserved genes required for AMS. [ABSTRACT FROM AUTHOR]

Abstract: Association of plants with arbuscular mycorrhizal (AM) fungi may act as either an equalizing or a stabilizing mechanism of coexistence, but the effect of the symbiosis likely depends on the responsiveness to fungi of plant species within a community, rather than simply as a binary metric based on presence or absence of AM fungi. Here, we test the hypothesis that communities consisting of plants that are unresponsive to mycorrhiza, or that differ widely in their response to mycorrhiza, would exhibit larger differences in their niche and fitness resulting to weaker plant–plant competition. We took two complementary approaches to test our hypotheses: first, we reanalysed data from the classic “BIODEPTH” grassland biodiversity manipulation experiment to assess niche and relative fitness differences of plant communities solely comprising species considered to be either obligate or facultative symbiotrophs. Second, we assembled replicate synthetic plant communities comprising all 70 possible four‐species mixtures from a pool of eight species in the presence of an AM fungus to assess pairwise competition coefficients and infer coexistence potential. The species were characteristic of pastures, had an identical CSR survival strategy, and in nature differ in their extent of colonization by AM fungi. We separately established monocultures to estimate competition coefficients and assess plant responsiveness to mycorrhiza. Analysis of data from BIODEPTH showed that plant communities comprising solely species with obligate associations with AM fungi had greater niche and fitness differences compared with communities comprising species without obligate associations with AM fungi. In the manipulation experiment, we found that plants that depended on AM fungi competed more strongly than plants with little dependence on AM fungi. The weakest competition was between AM‐responsive and AM‐unresponsive plant species. Coexistence was more likely in pairwise combinations in which at least one of the plant species responded negatively to mycorrhiza. Synthesis. We directly quantified variation in niche and fitness differences between plant species due to interaction with AM fungi. Integrating this knowledge into explicit competition models in plant community ecology could greatly enhance our ability to predict coexistence in nature. [ABSTRACT FROM AUTHOR]

Summary: Arbuscular mycorrhiza (AM) fungi establish symbiotic interactions with plants, providing the host plant with minerals, i.e. phosphate, in exchange for organic carbon. Arbuscular mycorrhiza fungi of the order Glomerales produce vesicles which store lipids as an energy and carbon source. Acyl‐acyl carrier protein (ACP) thioesterases (Fat) are essential components of the plant plastid‐localized fatty acid synthase and determine the chain length of de novo synthesized fatty acids. In addition to the ubiquitous FatA and FatB thioesterases, AM‐competent plants contain an additional, AM‐specific, FatM gene. Here, we characterize FatM from Lotus japonicus by phenotypically analyzing fatm mutant lines and by studying the biochemical function of the recombinant FatM protein. Reduced shoot phosphate content in fatm indicates compromised symbiotic phosphate uptake due to reduced arbuscule branching, and the fungus shows reduced lipid accumulation accompanied by the occurrence of smaller and less frequent vesicles. Lipid profiling reveals a decrease in mycorrhiza‐specific phospholipid forms, AM fungal signature fatty acids (e.g. 16:1ω5, 18:1ω7 and 20:3) and storage lipids. Recombinant FatM shows preference for palmitoyl (16:0)‐ACP, indicating that large amounts of 16:0 fatty acid are exported from the plastids of arbuscule‐containing cells. Stable isotope labeling with [13C2]acetate showed reduced incorporation into mycorrhiza‐specific fatty acids in the fatm mutant. Therefore, colonized cells reprogram plastidial de novo fatty acid synthesis towards the production of extra amounts of 16:0, which is in agreement with previous results that fatty acid‐containing lipids are transported from the plant to the fungus. [ABSTRACT FROM AUTHOR]