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Mucoromycotina fine root endophytes have similar ecological functions as arbuscular mycorrhizal fungi in assisting plant nutrient uptake. The mechanisms enabling their symbiosis with plants remain largely unexplored. The mechanisms of Mucoromycotina fine root endophyte symbioses may overlap with those regulating arbuscular mycorrhizal fungal symbioses or the plant endophytes Colletotrichum tofieldiae and Serendipita indica. Contrasting colonisation mechanisms between Mucoromycotina fine root endophytes and arbuscular mycorrhiza fungi could provide insights into how ancient fungi facilitated the terrestrialisation of land plants. Investigations into mechanisms of symbiosis will benefit from inclusion of Mucoromycotina fine root endophytes as these fungi are more culturable than arbuscular mycorrhizal fungi under laboratory conditions and can be grown in the absence of a plant host. The most studied plant–fungal symbioses to date are the interactions between plants and arbuscular mycorrhizal (AM) fungi of the Glomeromycotina clade. Advancements in phylogenetics and microbial community profiling have distinguished a group of symbiosis-forming fungi that resemble AM fungi as belonging instead to the Mucoromycotina. These enigmatic fungi are now known as Mucoromycotina 'fine root endophytes' and could provide a means to understand the origins of plant–fungal symbioses. Most of our knowledge of the mechanisms of fungal symbiosis comes from investigations using AM fungi. Here, we argue that inclusion of Mucoromycotina fine root endophytes in future studies will expand our understanding of the mechanisms, evolution, and ecology of plant–fungal symbioses. [ABSTRACT FROM AUTHOR]

The existing literature on symbioses involving microorganisms is biased towards describing the larger of the partners, even though it is often the microbial partner that determines fitness. It is possible to address size asymmetries between mutualistic partners through the scale-independent parameters, z and c, of species–area relationships (SARs). Some general questions and gaps in understanding which can be addressed with SARs are the spatial scales where spatial aggregation is observed whether SAR parameters are determined by environmental settings, and formulating null expectations for global diversity of endosymbionts. We highlight how SARs can be used to address key questions in arbuscular mycorrhizal symbioses, such as the relationship between fine-scale diversity of fungal symbionts on roots and plant fitness. Symbioses involving microorganisms prevail in nature and are key to regulating numerous ecosystem processes and in driving evolution. A major concern in understanding the ecology of symbioses involving microorganisms arises in the effectiveness of sampling strategies to capture the contrasting size of organisms involved. In many mutualisms, including mycorrhizas and gut systems, hosts interact simultaneously with multiple smaller sized mutualists, the identity of which determines success for the host. This complicates quantifying the diversity of mutualisms because sampling techniques fail to capture effectively the diversity of each partner. Here we propose the use of species–area relationships (SARs) to explicitly consider the spatial scale of microbial partners in symbioses, which we propose will improve our understanding of the ecology of mutualisms. [ABSTRACT FROM AUTHOR]

• This review states the isolation, culture, characterization and application of OMF. • Major bottlenecks of traditional identification of OMF and its elucidation are discussed. • States the application OMF for bio-hardening and growth promotion of seedlings. • Provides insights for mass cultivation and conservation of orchids. In nature all orchids develop a mutualistic association with specialized group of fungi called orchid mycorrhiza. In natural environment, orchids are exclusively reliant on mycorrhizal fungi for seed germination, establishment, growth and development. In the early developmental stages, all orchids are mycoheterotrophic, and in most cases the association subsists throughout their lifespan. The significance of orchid mycorrhizal fungi (OMF) for seed germination, nourishment, growth promotion, and survival has been established more than a century ago and tremendous advancements were made in recent decades. Till date, understanding the mode of interaction between orchids and mycorrhizal fungi and determining the architecture of interaction networks are major challenges in ecology and evolutionary biology. The development of molecular techniques has empowered us to unscramble the fungal diversity comprised in the symbiosis and has facilitated us to overcome the difficulties associated with the conventional identification of OMF and orchid-fungal interactions. In addition, the application of modern biotechnological approaches resolved many controversial issues of OMF. Recently, OMF are used for biological hardening and growth promotion of in vitro raised seedlings, early flowering and quality improvement of flowers, and diseases and pests management. The aim of this communication is to update and summarize orchid mycorrhizal research including isolation, culture, and characterization of OMF, understanding the mechanisms of orchid-fungus symbiosis, and application of OMF in seed germination, growth promotion, and survival of asymbiotically raised seedlings and conservation of orchids. This appraisal will convey valuable insights to orchidologists engaged in biology, propagation, and conservation of orchids. [ABSTRACT FROM AUTHOR]

• Seed and aerial biomass enhanced in response to vermicompost and mycorrhiza. • Phenolic content increased by moderate drought stress and mycorrhizal inoculation. • Rutin and quercetin increased with moderate drought stress and mycorrhizal inoculation • In 75% FC and mycorrhiza application lowest HPPH IC50 and highest FRAP recorded • In interactions, M and V increased NPK uptake chlorophyll and osmolyte contents. The use of root symbionts and vermicompost as powerful natural tools is advised in stress conditions. To study the effect of vermicompost and mycorrhizal fungi on some phytochemicals and functional traits of buckwheat under drought stress, a greenhouse experiment was conducted. Three levels of drought stress: D0 (100% Field Capacity: FC), D1 (75% FC), and D2 (50% FC), two levels of mycorrhizal inoculation: M0 (without) and M1(with), and two levels of vermicompost V0 (without) and V1 (with) were used. Vermicompost significantly enhanced seed yield and aerial parts biomass. The highest grain yield (4.97 g dry weight per pot) and aerial parts biomass (40.3 g fresh weight per pot) were obtained in D0V1. The use of mycorrhiza was mainly effective on phytochemical parameters. Moderate levels of drought stress (D1: 75% FC) increased total phenols (33.6 mg gallic acid/g dry weight) and flavonoids (38.3 mg rutin/g Dry weight). Rutin content ranged from 16.24 to 32.5 mg/g dry weight that the highest content being in D1V1M0. Phenolic, flavonoid, and rutin content are correlated with higher antioxidant properties. This increase showed that mycorrhiza and vermicompost act as moderators and elicit to produce metabolites. Simultaneous use of M and V increased nitrogen, phosphorus, and potassium uptake. Cluster analysis classified the treatments into three groups with a higher impact of drought stress. According to Principal component analysis (PCA) FWH, Rutin, TFC, TPC, SS, and IC50 were affecting dimensions. The results showed that drought stress up to 75% FC (D1) can be used in buckwheat. [Display omitted]. [ABSTRACT FROM AUTHOR]

Aloe vera (Aloe barbadensis Miller) is a perennial drought tolerant medicinal species. This research study investigates the influence of biofertilizers on mycorrhizal fungi colonization, leaf number and width, plant height, offset number, leaf relative elongation rate (RER), leaf dry weight and leaf gel weight, water productivity (WP) for the gel, and aloin content in Aloe vera plants. The experiments were carried out in the warm and dry climate of Bushehr Province, Iran during 2016–2018. Treatments are reported to include irrigation regimes and biofertilizers at four levels. In terms of irrigation regimes, 25%, 50%, 75%, and 100% of water requirement accompanied the following treatments for biofertilizers, phosphorus-solubilizing bacteria (PSB), mycorrhizal fungi (MF), PSB+MF , and control (without any biofertilizers). The PSB includes Pseudomonas putida strain P 13 and Pantoea agglomerans strain P 5, in addition to Glomus mosseae as MF. The biofertilizer benefits (remarkably PSB+MF) on investigated traits were observed in three harvests. The results confirm the positive impacts of biofertilizers on important traits such as offset number (an economical part of Aloe vera planting), water productivity with less water consumption, and root colonization, which is the main reason of increasing the mentioned traits. Considering the minimal difference between 100%, 75% and 50% of water requirement in terms of gel fresh weight and more aloin content in 50% of our experiments, Aloe vera is reported as a high drought tolerant plant which merely requires an acceptable gel yield and aloin content. Moreover, better water productivity and consumption is possible in warm and arid regions by applying 50% of Aloe vera water requirement as well as biofertilizers. [Display omitted] [ABSTRACT FROM AUTHOR]

Traits are inherent properties of organisms, but how are they defined for organismal networks such as mycorrhizal symbioses? Mycorrhizal symbioses are complex and diverse belowground symbioses between plants and fungi that have proved challenging to fit into a unified and coherent trait framework. We propose an inclusive mycorrhizal trait framework that classifies traits as morphological, physiological, and phenological features that have functional implications for the symbiosis. We further classify mycorrhizal traits by location – plant, fungus, or the symbiosis – which highlights new questions in trait-based mycorrhizal ecology designed to charge and challenge the scientific community. This new framework is an opportunity for researchers to interrogate their data to identify novel insights and gaps in our understanding of mycorrhizal symbioses. Applying trait-based approaches to ecological research on mycorrhizal symbioses broadens ecological inferences, but there is no single unified framework to unite disparate language, terminology, and methods across the many multidisciplinary scientists studying mycorrhizas. We propose an inclusive framework for trait-based mycorrhizal ecology aimed to stimulate scientists around the world to collect and use more mycorrhizal trait data, particularly in understudied areas. This would widen our understanding regarding the ecological role of mycorrhizal symbioses at individual, species, community, and ecosystem scales. Analyzing how mycorrhizal symbioses fit within existing trait definitions highlights significant theoretical and empirical knowledge gaps, novel questions, and new research directions to improve our understanding of trait-based mycorrhizal ecology. [ABSTRACT FROM AUTHOR]

Edaphic drought reduces phosphorus (P) diffusivity in soils and arbuscular mycorrhizal fungi (AMF) can compensate for this. We recently showed, along a high-resolution substrate moisture gradient, that AMF effectively deliver P to plants under drought from areas beyond the reach of roots. Here, we investigated how edaphic drought affected the active sites of P exchange between AMF and plants inside the roots using different histochemical stains. Inoculation of dwarf tomato plants (cv. MicroTom) with AMF (Rhizophagus irregularis) slightly increased water retention (decreased the water potential) in substrates, decreased root length, and increased shoot P concentrations compared to non-mycorrhizal plants. Despite their reduced root length, mycorrhizal tomato plants showed a surprisingly congruent physiological drought stress response with their non-mycorrhizal counterparts. However, the activity of alkaline phosphatase (ALP) detected in intraradical fungal structures decreased significantly as soil and xylem water potentials decreased. The decline of ALP activity with increasing drought intensity was accompanied by a reduction of elevated P concentration benefits in shoots of mycorrhizal plants compared to non-mycorrhizal plants. Therefore, we conclude that edaphic drought can restrict the nutritional advantages that plants receive from AMF at the root-fungal interface. This is one of the direct consequences of drought. • Short-term drought hardly showed an effect of colonization of tomato roots by AMF. • Yet, alkaline phosphatase activity in the intraradical hyphae strongly decreased. • Reductions in phosphatase activity correlated with declining shoot phosphorus. • Reduced P transfer from fungus to plant thus seems directly induced by drought. [ABSTRACT FROM AUTHOR]

Alternate wetting-drying (AWD) in rice cultivation controls soil redox conditions and consequently nutrient solubility. Under low redox potential, ferric iron reduction leads to bound phosphate (Fe(III)–P) dissolution, but lack of oxygen retards organic phosphorus (P org) mineralization. Microorganisms accelerate P org mineralization as the redox potential increases during drying, but it is not known which P source will be preferentially taken up by microorganisms and plants. Using double 32/33P labeling, we traced for the first time the P released from inorganic (32P) and organic (33P) sources into microbial biomass P (MBP), phospholipids, and plants under continuous flooding (CF) and AWD. The CF rapidly induced reducing conditions that increased Fe–P dissolution and thus P availability. The AWD had no preference for 32P and 33P incorporation into plants. However, the ratios of 32P in roots to 32P in MBP or to 32P in phospholipids in rooted soil were 4–9 times higher than the respective ratios of 33P. Moreover, the ratios of 33P in roots to 33P in MBP or to 33P in phospholipids were always <0.6. Thus, plants and microorganisms were more competitive for P from Fe–P and from P org , respectively. The AWD increased 32P and 33P incorporation into phospholipids in rooted soil by 53–56% as compared to CF. Also, the ratio of 32P in phospholipids to 32P in MBP was 1.4–2.2 times higher under AWD than under CF. Thus, AWD stimulated microorganisms to allocate more P for cell membrane synthesis as compared to CF. Plants were similarly effective to take up P from inorganic and organic sources. Increased root biomass stimulated arbuscular mycorrhizal symbiosis (represented by 16:1ω5c) and thus 33P recovery in roots under AWD. In turn, the acceleration of microbial P turnover and the microbe-specific preference for P org highlight the importance of arbuscular mycorrhiza for plant P uptake under fluctuating water conditions. [Display omitted] • Continuous flooding increased reductive dissolution of Fe–P and thus P availability. • Microbes allocated more P for cell membrane synthesis under alternate wetting-drying. • Microorganisms in a maintenance state allocated more P for cell compound synthesis. • Rice plants were similarly effective to take up P from inorganic and organic sources. [ABSTRACT FROM AUTHOR]

• Habenaria barbertoni and H. epipactidea's mycorrhizal communities were compared. • Orchid species shared mycorrhizae from the orders Cantharellales and Sebacinales. • Mycorrhizae identified in orchids included both overlapping and distinct taxa. • Mycorrhizae from rust lineage Atractiellales were only detected in H. barbertoni. Southern Africa is a biodiversity hotspot for a variety of orchids, including Habenaria. However, we know very little about the orchid mycorrhizae that are associated with these orchids. To bridge this gap, we compared the community of orchid mycorrhizae that are associated with two indigenous Habenaria species, H. barbertoni and H. epipactidea , using a high-throughput sequencing platform. We selected these two orchids because their distribution zones overlap in South Africa. Furthermore, H. barbertoni is endangered, whereas H. epipactidea is not. We hypothesised that the mycorrhizal diversity and composition linked with the roots of these two orchids would overlap, but that some distinct fungal taxa would exist, and these distinct fungi would include unusual taxa. Analyses of the DNA sequence data revealed that the two orchids shared 35 fungal OTUs. Twenty-four and seventeen OTUs were exclusively detected in the roots of H. barbertoni and H. epipactidea , respectively. Mycorrhizal fungi from the rust lineage Atractiellales (Atractiellomycetes, Pucciniomycotina) were only detected in the roots of the endangered H. barbertoni , which represents the first report of these fungi associated with orchids outside of the Andean rainforest. Our findings increase knowledge of the diversity of mycorrhizae associated with indigenous orchids on the African continent. [ABSTRACT FROM AUTHOR]

Most arbuscular mycorrhizal fungi exhibit global distributions but have been studied mostly in a specific region of the globe, mainly covering temperate and boreal habitats, where nitrogen is the most common nutrient limiting primary productivity. Yet, it is relatively common to extrapolate our understanding of temperate and boreal systems to other regions of the globe. While the physiology of mycorrhizal associations is unlikely to differ worldwide, there are good chances that environmental settings interact with the way mycorrhizas function across ecoregions. Here, we first argue that mycorrhizal ecologists should develop region-specific hypotheses. We subsequently identify likely differences in how mycorrhizas function in subtropical regions compared with better-studied temperate and boreal areas. We finally use the subtropical region of China to develop five geographically-focused hypotheses, envisaging that they will trigger the interest of the scientific community worldwide in understudied regions into studying mycorrhizas through a new lens. Expanding the range of hypotheses in mycorrhizal ecology to describe understudied regions of the world, has the potential to confer multifaceted benefits to both science and society. We advocate to do so, and present a roadmap on how to develop such hypotheses. [Display omitted] • We tend to overgeneralize our understanding on mycorrhizas. • Encouraging regional studies on mycorrhizas can bring about multifaceted benefits. • The (sub)tropics pose multiple opportunities to further explore mycorrhiza. • We use the case of subtropical China to develop region specific hypotheses. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal (AM) symbiosis can strengthen plant defense against abiotic stress, such as drought, through multiple mechanisms; however, the specialized chemical defenses induced by AM symbiosis are largely unknown. In a pot experiment, licorice (Glycyrrhiza uralensis Fisch.) inoculated with and without arbuscular mycorrhizal fungus Rhizophagus irregularis Schenck & Smith were grown under well-watered or water deficit conditions. Transcriptomic and metabolomic analyses were combined to investigate licorice root specialized metabolism induced by AM symbiosis under drought stress. Results showed that mycorrhizal plants had few dead leaves, less biomass reduction, and less differentially expressed genes and metabolite features in response to drought compared with nonmycorrhizal plants. Transcriptomic and metabolomic data revealed that mycorrhizal roots generally accumulated lignin regardless of the water regime; however, the expression of genes involved in lignin biosynthesis was significantly downregulated by drought stress in mycorrhizal plants. By contrast, AM inoculation significantly decreased specialized metabolites accumulation, including phenolics and flavonoids under well-watered conditions, whereas these decreases turned to be nonsignificant under drought stress. Moreover, these specific phenolics and flavonoids showed significant drought-induced accumulation pattern in mycorrhizal roots. These results highlight that accumulation of specific root phenolics and flavonoids may support the drought tolerance of mycorrhizal plants. [Display omitted] • Mycorrhizal symbiosis significantly reduced licorice drought damage. • Mycorrhizal symbiosis enhanced plant drought tolerance. • Mycorrhizal symbiosis increased licorice root lignin accumulation. • Mycorrhizal symbiosis facilitated specific phenolic and flavonoid accumulation under drought. [ABSTRACT FROM AUTHOR]

This study aimed to assess the effectiveness of plant growth-promoting rhizobacteria (PGPR; Pseudomonas strain So_08) and arbuscular mycorrhizal fungi (AMF; Rhizoglomus irregulare BEG72 and Funneliformis mosseae BEG234) in mitigating the detrimental effects of cadmium (Cd) and zinc (Zn) stress in tomato plants. Plant biomass, root morphology, leaf relative water content, membrane stability, photosynthetic performance, chlorophyll content, and heavy metals (HMs) accumulation were determined. Furthermore, an ionomic profile was conducted to investigate whether microbial inoculants affected the uptake and allocation of macro- and micronutrients. Metabolomics with pathway analysis of both roots and leaves was performed to unravel the mechanisms underlying the differential responses to HMs stress. The findings revealed that the levels of HMs did not significantly affect plant growth parameters; however, they affected membrane stability, photosynthetic performance, nutrient allocation, and chlorophyll content. Cadmium was mainly accumulated in roots, whilst Zn exhibited accumulation in various plant organs. Our findings demonstrate the beneficial effects of PGPR and AMF in mitigating Cd and Zn stress in tomato plants. The microbial inoculations improved physiological parameters and induced differential accumulation of macro- and micronutrients, modulating nutrient uptake balance. These results provide insights into the mechanisms underlying the plant-microbe interactions and highlight the differential modulation of the biosynthetic pathways of secondary metabolites related to oxidative stress response, membrane lipids stability, and phytohormone crosstalk. [Display omitted] • Microbial biostimulants are proposed to mitigate heavy metal stress in tomato. • A tripartite interaction between tomato, microbes and heavy metals was reported. • Such interaction was found to impact mineral nutrients uptake and allocation. • Photosynthetic performance and the oxidative status were modulated. • Metabolomics unravelled unique signatures to this multifactorial response. [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]

Arbuscular mycorrhizal fungi (AMF) play a vital role in mediating rhizosphere interactions and plant growth, especially in resource-constrained soils. However, few studies have documented the effects of AMF on plant–plant interaction patterns and resource use efficiency along stress gradients. In this study, a growth environment-controlled experiment was carried out to evaluate the effects of AMF inoculation on maize-grass pea intercropping along three phosphorus (P) and two water gradients. The data indicated that soil water and P availability determined the plant interspecific interaction pattern, and that interaction was strongly mediated by AMF inoculation. Grass pea and maize were mutually facilitated under low P and water conditions and transitioned to a new pattern, i.e., that maize was facilitated but grass pea was neutral role or facilitator with increasing resource availability. The facilitative effect was particularly significant under P- and water-deficient conditions. Moreover, the transition of the plant–plant interaction pattern was mechanically driven by improving rhizospheric phosphatase activities by 5.08–20.02 %, rhizospheric acidification and enhanced microbial activities under resource deficit conditions. Critically, AMF inoculation was observed to significantly improve rhizospheric soil P availability and microbial biomass (p < 0.05); however, it enhanced the complementary utilization of P and water and weakened interspecific competition under high-resource conditions. Therefore, AMF inoculation positively transformed the plant–plant interaction pattern along resource gradients for higher P, nitrogen and water use efficiency. This study validates the context-dependent interspecific interaction and the role of AMF in optimizing resource use in a nutrient-impoverished intercropping system. Illustrating the effect of AMF inoculation on plant growth and plant–plant interaction in maize-grass pea intercropping system. [Display omitted] • Plant diversity increased rhizosphere microbial activity and phosphatase secretion. • AMF inoculation enhanced facilitation intensity with increasing stress conditions. • AMF lowered interspecific competition intensity for higher resource use efficiency. [ABSTRACT FROM AUTHOR]

• Arbuscular mycorrhizal symbiosis lowers walnut rootstock dependency on Pi supply. • Symbiosis improves sapling development and quality under low Pi fertilization. • Arbuscular mycorrhizal benefits are rootstock-dependent. • Symbiotic growth gains are observed after acclimatization and post-acclimatization. The English walnut (Juglans regia L.) is the main species cultivated for the production of edible nuts. In vitro micropropagation of walnut explants, necessary for mass propagation of high-quality walnut rootstocks, needs an ex vitro acclimatization phase followed by a post -acclimatization growth in greenhouse when plantlets become photoautotrophic. However, poor survival and slow growth rates are common difficulties encountered in nurseries when establishing micropropagated walnut saplings. Walnut exhibits dependency on symbiotic soil-borne arbuscular mycorrhizal fungi for better soil nutrient acquisition and development due to a coarse root architecture that limits soil inorganic phosphate (Pi) uptake. In the context of rootstock production, the objective of this study was to investigate for the first time the effect of the arbuscular mycorrhizal fungus Rhizophagus irregularis on the growth, quality, and Pi nutrition of seven in vitro grown walnut rootstocks of economic interest (RG2, RG6, R17, RX1, VLACH, VX211, and WIP3). For this purpose, inoculation was performed before both acclimatization and post -acclimatization of rootstocks under two contrasting Pi fertilization regimes. Two months after inoculation, we analysed mycorrhizal growth, phosphate and quality responses in the four conditions tested by measuring plant height, root length, root surface, branch number, collar, biomass dry weight, Pi content, and quality (Dickson's index). The results indicated that Pi fertilization impacted root colonization parameters only in a few cases. Irrespective of root colonization parameters and developmental stages, mycorrhizal growth depression after inoculation with R. irregularis was generally observed with increasing Pi availability in the substrate. Principal component analysis showed that mycorrhizal dependency, growth and quality responses were positively correlated to each other under the lowest Pi fertilization regime tested, both at the acclimatization and post -acclimatization stages. We also found that mycorrhizal benefits in terms of growth, quality and Pi nutrition, were rootstock-dependent, indicating that walnut dependency for Pi nutrition varies between cultivars. [ABSTRACT FROM AUTHOR]

The study aimed at investigating Arbuscular Mycorrhiza (AM) mediated metabolic changes in two genotypes of mungbean (Vigna radiata) differing in their salt tolerance in presence of salt stress (100 mM NaCl). Colonisation by Claroideoglomus etunicatum resulted in higher growth, photosynthetic efficiency, total protein content, and lower levels of stress markers, indicating alleviation of stress in mungbean plants. AM differentially upregulated the components of Tricarboxylic acid (TCA) cycle in salt tolerant (ST) and salt sensitive (SS) genotypes that could be correlated to AM-mediated moderation in nutrient uptake. Under salt stress, while maximum increase in the activity of α-ketoglutarate dehydrogenase (65%) was observed in mycorrhizal (M)-ST; the increase in isocitrate dehydrogenase (79%) and fumarase (133%) activities was maximum in M-SS plants over their non-mycorrhizal (NM) counterparts. Apart from TCA, AM also affected gamma-aminobutyric acid (GABA) and glyoxylate pathways. Activities of enzymes implicated in GABA shunt increased in both the genotypes under stress resulting in increase in GABA concentration (46%). Notably, glyoxylate pathway was induced by AM in SS only, wherein M-SS exhibited significantly higher isocitrate lyase (49%) and malate synthase (104%) activities, reflected in higher malic acid concentration (84%), than NM under stress. The results suggest that AM moderates the central carbon metabolism and strategizes towards boosting the formation of stress-alleviating metabolites such as GABA and malic acid, especially in SS, bypassing the steps catalysed by salt-sensitive enzymes in TCA cycle. The study, therefore, advances the understanding on mechanisms by which AM ameliorates salt stress. [Display omitted] • Report on differential effects of AMF in salt tolerant (ST) and salt sensitive (SS) mungbean genotypes. • AMF enhances TCA cycle enzyme activities on account of moderation in nutrient uptake. • AMF induces glyoxylate cycle and GABA shunt in SS genotype, while only GABA shunt is induced in ST. • Higher Na ion accumulation by SS shunts isocitrate towards glyoxylate cycle, evading the salt-sensitive steps of TCA. [ABSTRACT FROM AUTHOR]

• Feremycorrhiza means 'nearly mycorrhiza'. • Feremycorrhiza has mycorrhiza-like effects on plant growth and nutrition. • Austroboletus occidentalis has ectomycorrhizal traits and lineage. • A. occidentalis has limited saprotrophic capacity similar to ectomycorrhizal fungi. • A. occidentalis genome lacks invertase genes similar to ectomycorrhizal fungi. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) form symbioses with most plants, potentially improving their growth and nutrient assimilation activities. Cysteine (Cys) and methionine (Met) are nitrogen (N)- and sulphur (S)-containing amino acids. Compared with phosphate and N, limited attention has been paid to the role of AMF in low molecular weight organic S acquisition. To explore the uptake and relative contributions of organic and inorganic N and S to plants, and the role of AMF in S uptake, a pot study was conducted based on 14C, 35S, 13C, and 15N quad labelling (6-h labelling test after adding the labelled solution to the soil–plant system) using a mutant tomato genotype with highly decreased AMF symbiosis capacity. Tomato roots can uptake limited amounts of added Met and Cys (<1.77%) within 6 h, as indicated by the 14C and 13C labelling results, and most of them were utilised by soil microorganisms. After uptake for 6 h, 10.0–14.8% of N and 1.4–6.1% of S derived from added Cys and Met were utilised by plants, mainly in inorganic N and S forms derived from Cys and Met decomposition. Met and Cys could be important S sources (Met: 3.0–9.8%, Cys: 8.8–22.0%) for plants, however have negligible roles in N nutrition (∼1%), as most N uptake by plants was derived from soil inorganic N. The tomato uptake of inorganic S derived from Cys decomposition was much higher than that derived from Met, as higher ratios of S-Cys were released as SO 4 2− from microorganisms during the 6-h testing periods. Even with the artificial addition of AMF, most of the added Met and Cys were utilised by Gram-negative bacteria, as indicated by 13C-PLFA biomarkers. AMF reduced host plant uptake of organic N and S, but stimulated plant N uptake from Met and Cys, which was mainly inorganic N following mineralisation. AMF not only utilise organic carbon from host plants but also capture soil organic matter to satisfy their energy demands. In the spaces where both root and AMF occur, AMF colonisation decreased tomato 35S uptake from Cys, Met, and SO 4 2− by 24.6%, 20.6%, and 11.0% within the 6-h uptake period, respectively, when compared with that in the mutant genotype with reduced colonisation capacity; in contrast, AMF colonisation increased 35S-Cys uptake by 118.7% from areas that roots could not reach. Overall, AMF enhanced host plant N uptake but reduced organic N uptake under competition with plant roots for S in the rhizosphere, but stimulated plant S uptake by extraradical mycelia, based on this short-term pulse-chase test. • Limited Met and Cys was absorbed by tomato under competition with microorganisms. • Inorganic S uptake by tomato from Cys decomposition higher than that from Met. • Met and Cys could be key S sources for plants, with negligible roles in N nutrition. • AMF reduce plant organic N/S uptake but stimulate plant N uptake from Met and Cys. • AMF colonisation increased 35S-Cys uptake from areas roots could not reach. [ABSTRACT FROM AUTHOR]

The restoration of degraded areas in mined land has not always achieved the desired success. Biological tools such as the use of arbuscular mycorrhizal fungi (AMF) are needed to increase and accelerate the restoration effectiveness of natural processes and ecosystem services in restored degraded areas. AMF can increase water and nutrient uptake by the host plants, therefore decreasing plant stress and improving habitat development in mined areas under restoration. We conducted a global meta-analysis from 193 independent outcomes to understand the overall effect of employing AMF as a restoration tool and to evaluate sources of variation on the effects of AMF inoculation on plant development in areas degraded by mining. Our results emphasize the great potential of the use of AMF to stimulate plant growth in the restoration of mined areas with stronger effects if associated with the utilization of organic matter and other soil microorganisms. Although AMF studies are concentrated in temperate regions, AMF inoculum promoted greater plant development on mined substrates regardless of the region and fungi type or origin. Inoculation also improved plant growth in materials of difficult restoration, such as overburden and tailings, but the AMF effects depended upon the exploited mineral type. Further investment in long-term field studies on the effects of AMF inoculation on plant survival, reproduction, fitness, and related ecological processes is essential to further consolidate the use of AMF on the restoration of mined areas. • Arbuscular mycorrhiza fungi is an efficient tool for restoration of mined areas. • Mycorrhiza fungi effects depended on the exploited mineral type. • Arbuscular mycorrhiza fungi improve plant growth on substrates from tailings. • Symbiotic microorganism addition enhances mycorrhizal effect on plant growth. [ABSTRACT FROM AUTHOR]

• Arbuscular mycorrhizal fungi (AMF) increased litter decomposition by stimulating saprotrophs in nutrient poor soils. • AMF inoculation amplified hotspot areas of enzyme activities in the rhizosphere by 13%-400%. • The importance of AMF to plant growth was greater in nutrient poor soils than in nutrient rich soils. Plants acquire and recycle nutrients from soil organic matter, and these dynamics depend on a highly diverse array of microorganisms in the rhizosphere. Although functions of many microbial groups have been identified, how different groups interact to affect biogeochemical processes is still poorly understood. We investigated the interactive effects of saprotrophs and arbuscular mycorrhizal fungi (AMF) on Medicago sativa litter decomposition and spatial distribution of enzyme activity in the rhizosphere in nutrient poor and rich soils, using compartmented microcosms designed for zymography. In nutrient poor soils, co-inoculation of saprotrophic bacteria (Alcaligenes faecalis) or fungi (Phanerochaete chrysosporium) with AMF (Rhizophagus irregularis) resulted in faster litter decomposition and greater hotspot areas of enzymes in the rhizosphere compared to mono-inoculations. These positive effects were stronger in the interaction of AMF with saprotrophic bacteria than that with saprotrophic fungi. The synergy of saprotrophic bacteria with AMF for litter decomposition and enzymatic hotspot formation was weaker in nutrient rich soils than that in nutrient poor soils. In contrast, in nutrient rich soils, co-inoculation of saprotrophic fungi with AMF reduced litter decomposition. A partial least squares path modeling (PLS-PM) analysis indicated that faster litter decomposition and larger enzymatic hotspots increased overall plant growth. These findings suggest the existence of important synergistic relationships between these two microbial guilds for plant growth in nutrient poor soils. Specifically, AMF accelerated litter mineralization by increasing saprotrophic biomass and enzyme activities (i.e., nitrate reductase, urease and cellulase). At the same time, saprotrophs increased AMF colonization rate, which increased the hotspot areas of enzyme activities. These hotspots, in turn, broadened the nutrient mobilization zone around the roots - in the rhizosphere. Consequently, the synergistic interactions between saprotrophs and AMF for litter decomposition and the formation of enzymatic hotspots may be an important mechanism for promoting plant fitness under low soil nutrient availability. [ABSTRACT FROM AUTHOR]

• Application of silicon and mycorrhizal inoculum mitigate drought stress in licorice. • Amino acid profile of Glycyrrhiza glabra root were changed by applied treatments. • Irrigation at 100% of field capacity with applying silicon, showed maximum proline. • Histidine and lysine were highest by 80% irrigation, silicon and fungi inoculation. • Silicon at 300 ppm and mycorrhizal inoculation enhance tolerance to drought stress. Abiotic stresses usually trigger plant responses that entail several changes in the metabolism of amino acids. The Glycyrrhiza glabra rhizomes activate integrative biochemical networks in response to water deficit conditions, mycorrhiza inoculation, and silicon application. In the present study, irrigation was performed to make the soil reach 5 different levels of 20, 40, 60, 80, and 100% of field capacity (control). Silicon application was used at 300 ppm concentration solute in irrigation water for half of treatments. The Claroiedoglomus etunicatum is used as mycorrhizal inoculum. After 2 months, the amino acid profile of treated plants (from acidic root extracts) was analyzed by Liquid Chromatography–tandem mass spectrometry (LC-MS/MS). Results were indicated that amino acids changed as a result of water deficiency, silicon nutrition, and mycorrhiza inoculation. As proline accumulation can be one of the indicator responses to drought stress, in this study, 100% irrigation with applying silicon, without mycorrhiza inoculation showed increased levels in proline (83.09 mg.g−1 dry biomass), while minimum proline (18.27 mg.g−1 dry biomass) was observed by 40% irrigation with mycorrhiza inoculation, without applying silicon. Maximum values of histidine (23.19 mg.g−1 dry biomass) and lysine (36.29 mg.g−1 dry biomass) were observed by application of 80% field capacity water irrigation with silicon solution and fungi inoculation. Minimum histidine and valine were in the treatment of 100% field capacity irrigation without silicon and inoculation (3.15 and 6.64 mg.g−1 dry biomass, respectively). As minimum amino acids were almost observed in treatments that were not achieved silicon and mycorrhiza, so results of this study showed that silicon at 300 ppm and licorice root inoculation by C. etunicatum effectively can change amino acid profile and protein quality under drought stress. Comprehensive results were achieved with a detailed understanding of how drought stress can trigger plant responses via relevant mechanisms, therefore enabling the use of mineral nutrition, such as silicon, and biofertilizers, including mycorrhiza, in crop enhancements. [ABSTRACT FROM AUTHOR]

Tools for accurate measurements of microbial biomass/abundance are imperative in soil ecology. This perspective was prompted by a lack of consistency in how the neutral lipid fatty acid (NLFA) and phospholipid fatty acid (PLFA) 16:1ω5 are used to estimate arbuscular mycorrhizal (AM) fungal abundance, which we argue can lead to erroneous conclusions within studies and complicate among-study comparisons. We show that more than half of all studies published to date use PLFA 16:1ω5 to quantify AM fungal biomass without proper controls. This is problematic because AM fungi cannot be separated from the bacterial contribution to this fatty acid signature. We provide a set of recommendations for future research and specifically urge researchers to extract and analyze NLFA 16:1ω5 for more accurate and sensitive assessments of AM fungal biomass as this can be done without doubling effort. • Large number of studies have used PLFA 16:1ω5 as AM fungal indicator. • The use of PLFA 16:1ω5 without proper non-mycorrhizal controls is problematic as it can also reflect bacterial biomass. • We urge researchers to use NLFA 16:1ω5 to estimate AM fungal biomass as this can be done without doubling effort. [ABSTRACT FROM AUTHOR]

Denitrification by microorganisms in soil regulates ecosystem nitrogen availability and cycling. Although arbuscular mycorrhiza fungi (AMF) are best known as the key connectors between plant and microorganisms in below-ground soil, however, less knowledge is available about the interactive effects of AMF and vegetation community traits on soil denitrifiers. In this study, we manipulated experimental pots with or without AMF inoculation (AMF+ and AMF− treatments) under three plant richness levels and 27 different plant community compositions. Our results provided evidence that inoculation of AMF significantly increased the abundances of nirS -, nirK - and nosZ -type denitrifiers as revealed by quantitative PCR (qPCR), which inferred a positive role of AMF in N-cycling microorganisms. Plant community traits, including richness, community composition, biomass and species, were less important in influencing the abundances of soil denitrifiers, and no significant interactive effect was detected between AMF inoculation and plant richness or plant community compositions, indicating a weak direct relationship between plants and soil denitrifiers. Our study provided comprehensive insights into the roles of AMF-plant associate bio-system in driving the variation of soil denitrifiers. • AMF inoculation increased abundances of nirK , nirS and nosZ genes. • Plant traits were less important in influencing the abundances of soil denitrifiers. • The effect of AMF on denitrifiers' abundances was related with plant compositions. [ABSTRACT FROM AUTHOR]

The formation of a common mycorrhizal network among roots of different plant species growing close to each other can influence plant community dynamics, regulating plant relationships through the differential transfer of nutrients from one plant to another. However, knowledge of the mechanisms that regulate this process is poor. Here we quantify the contribution of arbuscular mycorrhizae to the transfer of N among heterospecific plants growing adjacent to each other and examine whether the differential transfer of N within the plant community via mycorrhizae can alter competitive relationships among plant species. Plants of four species (wheat, pea, flax, and chicory) were grown in four-compartment pots (one species per compartment) under three conditions: no belowground interaction permitted among the compartments (Clo-sys); belowground interaction limited to soil microorganisms (including arbuscular mycorrhizal [AM] fungi) and soil solution (Res-sys); and belowground interaction permitted, so the crossing of roots, soil microorganisms, and soil solution was allowed (Ope-sys). Each condition was tested in both the absence (−myc) and presence (+myc) of AM symbiosis. The transfer of N from pea to the three non-legume companion species (assessed via direct 15N labelling) was greater in Ope-sys than Res-sys for wheat and chicory but not for flax. In general, N transfer was greater in +myc than –myc in all species. In wheat the positive effects of AM symbiosis on N transfer were pronounced in Ope-sys but not in Res-sys, whereas in flax and chicory mycorrhization had similar effects in both Ope-sys and Res-sys. In Res-sys and in the absence of AM symbiosis, wheat intercepted about 50% of the total N transferred from pea, chicory about 40%, and flax about 10%. Mycorrhization altered these ratios, reducing the proportion of N transferred to wheat while increasing the proportion transferred to the other two species (especially to chicory), thus favouring the weakest components of the mixture. Similar effects of AM symbiosis were observed in Ope-sys. Our study shows that AM symbiosis affects the distribution of N and as a consequence the competitive relationships among adjacent plants of different species. • Arbuscular mycorrhizae increased N-transfer from the legume to the neighbouring plants • AM symbiosis differentially affected the distribution of N to the neighbouring plants • N-transfer was mostly due to the uptake of N released from the legume into the substrate • AM symbiosis differentially affected the growth of the associated plant species • CMNs altered the competitive relationships among associated plant species [ABSTRACT FROM AUTHOR]

• Mycorrhizal colonization rates exceeded 50% in two biofilter plants. • Mycorrhizae doubled root biomass and length of F. nodosa in biofilters. • Nutrient and cd removal was 10% higher in columns with mycorrhizal plants. • Mycorrhizal inoculation did not affect plant tolerance to water stress. Mycorrhizae can improve plant growth and drought tolerance by enhancing plant uptake of nutrients and water, which are important targets for biofilters, a common stormwater treatment system. This study evaluated the role of mycorrhizal inoculation on plant growth, photosynthetic efficiency and pollutant removal in two Australian plant species grown in stormwater biofilters. During the establishment period and column study, Ficinia nodosa showed over 80% mycorrhizal colonization, leading to a doubling of shoot and root biomass compared to the control, while Carex appressa showed less than 26% mycorrhizal colonization and no effect on shoot and root biomass. Columns planted with mycorrhizal-inoculated F. nodosa had 5% higher removal of total phosphorus and 10% higher removal of total nitrogen (Figure 5), phosphate (Figure 6), and cadmium (Table 3). Mycorrhizal colonization did not appear to affect plant stress during drought as indicated by similar photosynthetic efficiencies within species. Our results indicate that mycorrhizal inoculation can be highly successful in biofilters while increasing plant growth and nutrient removal, opening opportunities to further study the role of mycorrhizae in enhancing plant drought tolerance and pollutant removal in existing biofiltration systems. [ABSTRACT FROM AUTHOR]

• Effects of mycorrhizas, climate, and soil on root traits and function were studied. • EM plants consumed more carbon for constructing root tissue structures than AM plants. • The interactions of MAT-SRL and MAT-RNC on Rr were positive and negative, respectively. Root respiration is a critical function of root carbon cycling and accounts for a major component of the global carbon budget. However, the insufficient understanding of the global scaling relationships between root traits and respiration rate (R r) impedes the accurate prediction of carbon effluxes from roots. Here, we analyzed a dataset of 138 species to unravel and quantify the effects of mycorrhizal type, climate, soil, and phylogenetic structure of species on fine root trait-function relationships. Four commonly measured traits were included: root nitrogen content (RNC), specific root length (SRL), root diameter, and root tissue density. We found that mycorrhizal type and climate affected the relationships between fine root traits and R r. Specifically, the slopes of SRL-R r and RNC-R r relationships for ectomycorrhizal (EM) plants were significantly greater than those for arbuscular mycorrhizal (AM) plants, irrespective of the phylogenetic conservatism or plant growth forms. This finding suggested that EM plants consumed more carbon than AM plants for constructing root tissue structures. In a warmer environment, the SRL-R r relationship was stronger while the RNC-R r relationship was weaker, possibly because R r was limited by enzyme activity at low temperature and by substrate supply at high temperature. Our results highlighted the importance of mycorrhizas in influencing the root trait-function relationships. Thus, incorporating mycorrhizal types into trait-based terrestrial biosphere models may help to more accurately predict the future carbon-climate change feedback. [ABSTRACT FROM AUTHOR]

The identity and diversity of arbuscular mycorrhizal (AM) fungal symbionts strongly affect the functioning of mycorrhiza, but little is still known about the functional relevance of the individual taxa abundances within AM fungal communities. We hypothesized that proportions of AM fungal taxa influence mycorrhizal benefits to the host, and that a community with spontaneously established ratios of AM fungal species is more beneficial than communities with artificially manipulated ratios. Medic (Medicago truncatula) was inoculated with synthetic AM fungal communities composed of five fungal species in different proportions, and a 'functionally optimized' community generated by previous co-cultivation of the five AM fungi. The composition of the communities was monitored along with the host plant responses to mycorrhiza in three sequential harvests. Most of the artificial AM fungal communities differed compositionally and functionally from the presumably 'functionally optimized' community, which indeed promoted plant growth to the greatest extent. The higher ability to promote plant growth was partly explained by higher intraradical fungal biomass, but functional differences between the communities were also related to the abundances of certain AM fungal species. Thus, the experiment demonstrated functional relevance of species' abundances within AM fungal communities. The observed 'functional optimization' of the AM fungal community is discussed in context with the host plant's and AM fungal species' traits. • Species ratios in mycorrhizal fungal communities influence mycorrhiza functioning. • A spontaneously established mycorrhizal community induced the highest plant benefits. • Manipulation of the fungal species abundances mostly decreased plant benefits. • Fungal species traits explain the differences in the functioning of the communities. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) greatly facilitate uptake of phosphorus (P) by most plant species. Whether or how this changes if water becomes limiting remained little explored. Medicago truncatula plants were grown in previously sterilized cultivation substrate and inoculated or not with AMF isolate Rhizophagus irregularis 'PH5' (M or NM, respectively) in two-compartment rhizoboxes. The compartments were separated or not with root-excluding meshes. A 15-step soil moisture gradient (maintained over 5 weeks) spanned generous water supply through strong water deficiency. Two radioisotopes (33P and 32P) were injected into the plant and distant compartments, respectively, to distinguish cumulative and immediate-term plant P uptake from either of the compartments at each moisture level. M plants were larger than NM plants at high and medium moisture levels and accumulated markedly more P throughout the whole gradient. The immediate-term P uptake did not differ between M and NM plants at high moisture, but at medium and low moistures, M plants acquired significantly more 33P than NM plants, even after accounting for differences in root biomass. Increased immediate-term P uptake by M plants grown under medium and low substrate moistures was probably due to complementary effect of direct hyphal uptake and indirect alterations of substrate hydraulic properties by AMF. This research illustrates that AMF remain functional part of plants even under severe drought stress and thus they should be considered when plant functioning under water deficiency is to be fully understood. • Medicago truncatula plants were inoculated or not with Rhizophagus irregularis. • Mycorrhizal phosphorus uptake was quantified under 15-step moisture gradient. • Radioisotopes enabled to distinguish cumulative and immediate-term phosphorus uptake. • Mycorrhiza increased cumulative phosphorus uptake throughout the whole gradient. • Mycorrhiza increased immediate-term phosphorus uptake at medium and low moistures. [ABSTRACT FROM AUTHOR]