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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]

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]

Arbuscular mycorrhizal fungi (AMF) function mostly depends on their colonization to roots. However, it has not been systematically clear how arbuscular mycorrhiza (AM) formation is affected by organic contaminants. In this study, a meta-analysis was performed to estimate the effects of three groups of organic contaminants (polycyclic aromatic hydrocarbons (PAHs), crude oil, and pesticide) in soil on mycorrhizal colonization rates (MCRs) from various moderators, such as AMF (genus, species, and inoculation mode), contaminant (level, type, and source), and experimental conditions (plant type, duration, and soil sterilization). Our results showed that all MCRs (total, vesicular, arbuscular and hyphal) significantly decreased under the stresses of three contaminants. Generally, pesticide caused larger decrease in all MCRs than PAHs and crude soil except for vesicular MCRs. Mixed AMF showed larger decrease in the total and vesicular MCRs than single AM fungus, but contrary trends in the arbuscular and hyphal MCRs. Moreover, man-made contaminant seemed to produce larger negative effects on the total, vesicular, and arbuscular MCRs than industry contaminant. The inhibitive effects of three contaminants on the total and vesicular MCRs increased with increasing experimental duration, and were larger in the non-sterilized soil than in the sterilized soil. Hyphal and spore growth were also inhibited by three contaminants in most cases. Hyphal length and spore number of single AM fungus were lower than those of mixed AMF, and pesticide produced larger inhibition on the hyphal length and spore number than PAHs and crude oil. Similar trend was found in the non-sterilized soil relative to the sterilized soil. This study indicated that AM formation and AM structure were negatively affected by three organic contaminants, whereas the inhibitive degrees varied with AMF, organic contaminant and experimental conditions. [Display omitted] • All MCRs were inhibited by three organic contaminants regardless of moderators. • Hyphal length and spore number declined under three contaminants in most cases. • Moderators produced different effects on MCRs under three contaminant stresses. • Pesticide produced the largest negative effects on all MCRs except for vesicle MCR. [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) 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 production of the redox-active signaling molecule, NO, has long been associated with interactions between microbes and their host plants. Emerging evidence now suggests that specific NO signatures and cognate patterns of PHYTOGLOBIN1 (PHYTOGB1) expression, a key regulator of cellular NO homeostasis, may help determine either symbiosis or pathogenicity. [ABSTRACT FROM AUTHOR]

Mycorrhization of nursery plants with arbuscular mycorrhizal fungi (AMF) has become a usual practice in olive nurseries. Mycorrhizal associations increase plant tolerance to biotic and abiotic stresses after transplanting by improving root system structure and development. Nutrient fertilization is also desirable because roots are confined in a limited amount of soil in the nursery containers. Since the olive tree is a species with low phosphorus requirements, and AMF can affect root system development and nutrient uptake, it is of interest to study the possible interaction between both factors. Three different experiments with potted plants growing in a shade house, and one experiment under field conditions, were preformed using young olive plants to explore these questions. Inoculation with Glomus intraradices did not affect the phosphorus level in the plants but reduced shoot growth in plants growing in phosphorus-rich soil. When the substrate was a soil poor in phosphorus, shoot growth of AMF-inoculated plants was similar to the control but root development was greater. Mycorrhization also increased flower number and quality in ‘Arbequina’. Shoot growth also was reduced when a sterilized substrate was used, suggesting that the use of natural soil is preferred. Since no mycorrhization effect was observed when inoculation was performed at the moment of transplanting to the field, inoculation during the nursery-growing period is recommended to improve plant quality for orchard establishment. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizas (AM) are adapted to soils with higher pH, less organic matter and more available nitrogen than ectomycorrhizas (EM). We hypothesise that also climatic factors have a direct role in the relative success of the two types. We tested their colonisation rates after soil freezing. Soil was taken from forest and meadow sites to comprise propagules of both types of mycorrhizal fungi. The soil was sieved (6 mm) and mixed. Soil batches were exposed to +5 °C (control), −12, −25, −48 or −130 °C, time at target temperature was 6 h. Silver birch ( Betula pendula ), grey alder ( Alnus incana ) and white clover ( Trifolium repens ) were sown to these soils and grown in favourable conditions for 11 weeks. EM colonisation in birch and alder was similar in all treatments. Arbuscule formation in alder and clover was not affected, but vesicles, AM fungal hyphae and spores in roots were reduced with decreasing temperature. Soil soluble phosphorus (P) was increased by freezing as were also the foliar concentrations in birch. By contrast, clover had less foliar P in the lowest temperature treatments which may be due to less efficient functioning of AM. To conclude, the development and function of AM were impaired to some extent by very low temperatures, while EM were not affected. The low-temperature tolerance of EM may be another explanation to their predominance in cold climates. [ABSTRACT FROM AUTHOR]

Trifoliate orange seedlings were grown in perspex pots of a split-root system, where one half of the split roots was inoculated with or without arbuscular mycorrhizal fungi (AMF, Acaulospora scrobiculata or Funneliformis mosseae ). Five months after inoculation, the growth performance, leaf, stem and root biomass and photosynthetic rate were generally significantly higher in AM than in non-AM seedlings. Greater root morphological traits were observed in the AM root side than in the non-AM side for the same plant and in AM than in non-AM plants. AM seedlings had significantly higher leaf sucrose and glucose contents and total (leaf + root) glucose and fructose contents as compared to non-AM ones. In the split roots, the AM side displayed substantially higher sucrose, glucose and fructose contents than the non-AM side for the same plant, and in AM than in non-AM plants. These results showed greater C movement into the non-AM side from an AM-colonized plant than from a non-AM-colonized plant. These results conclude that the presence of AM in one side of the split roots benefited C acquisition and root development to another half non-AM side, suggesting functional equilibrium and resource allocation of AM within a root system. [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]

Arundo donax has become one of the most promising species for cellulose paste, biomass, and second-generation biofuel production. Because this species is not able to produce viable seeds, micropropagation is the best method for large scale production. Several studies have demonstrated that arbuscular mycorrhizal fungi (AMF) can improve the acclimatization of micropropagated plantlets, enhancing their growth and survival. In this study, we evaluated the effect of AMF during the acclimatization period of A. donax plantlets and its posterior establishment to the field. Plantlets were inoculated with mycorrhiza-based biofertilizer (AEGIS SYM ® ) that contained Rhizophagus intraradices and Funneliformis mosseae . The inoculum was applied at the time of transplantation of plantlets to 28-cm 3 cell trays filled with commercial nutrient-rich agricultural substrate. The results showed that during acclimatization, mycorrhized plantlets (AM) present higher number of leaves and height increments as compared to non-mycorrhized plantlets (control). Moreover, at the end of the hardening process, AM plantlets presented higher height, number of leaves, biomass, shoot:root ratio and chlorophyll a and b content than control plantlets. After open field establishment, AM plantlets presented greater size, number of stems and survival rate. These results demonstrate that inoculating micropropagated A. donax with AMF enhances its growth and development as well as produces better quality plantlets, which can be very useful for the large-scale production of this energetic crop. [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]

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]

Highlights: [•] We detected two pathways through which glyphosate can affect grassland mycorrhiza. [•] Application on the soil, even at low doses, reduced directly spore viability. [•] Arbuscules were more affected indirectly, when glyphosate was applied to plant tissue. [•] Mycorrhizal root colonization was similarly reduced by both pathways. [•] Glyphosate application affects AMF functionality regardless of the pathway involved. [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]

Abstract: Arbuscular mycorrhizal fungi (AMF) have great potential as biocontrol organisms against the root–knot nematode Meloidogyne incognita which causes severe gall formation in plants, but knowledge about the underlying molecular mechanisms involved in the biocontrol of nematodes is scarce. In the present study, suppression subtractive hybridization (SSH) was used to investigate plant genes that are specifically up-regulated in tomato roots (Solanum lycopersicum cv. Marmande) pre-colonized by the AMF Glomus mosseae (BEG 12) and 12 days after soil inoculation with M. incognita juveniles. Nematode infection was significantly lower in the mycorrhizal roots as compared to the non-mycorrhizal roots, and identified genes were classified mainly in the categories of defense, signal transduction and protein synthesis and modification. The higher expression of a selection of defense-related plant genes specifically in the biocontrol interaction compared to in plants that were only mycorrhizal or only nematode-infected was confirmed, which pleads for the existence of mycorrhiza-induced priming of plant defense responses. In conclusion, by focusing on up-regulated gene expression in the biocontrol interaction between mycorrhizal tomato and M. incognita, new insights were found into the molecular mechanisms underlying the mycorrhiza-induced resistance against root–knot nematodes. In particular, the involvement of the phenylpropanoid pathway and reactive oxygen species (ROS) metabolism could explain the reduced root–knot nematode infection in mycorrhizal tomato roots, processes that have also been reported to play a pivotal role in plant resistance to nematodes. [Copyright &y& Elsevier]

Abstract: White lupin (Lupinus albus L.), a non-host plant for arbuscular mycorrhizal (AM) fungi in the typically mycotrophic family Fabaceae, has been investigated for root metabolites that inhibit hyphal development in AM fungi. Four known pyranoisoflavones, licoisoflavone B (1), sophoraisoflavone A (2), alpinumisoflavone (3) and 3′-hydroxy-4′-O-methylalpinumisoflavone (4), together with three previously unknown pyranoisoflavones, lupindipyranoisoflavone A (5), 10′-hydroxylicoisoflavone B (6) and 10′-hydroxysophoraisoflavone A (7) were isolated from the root exudates of white lupin as an inhibitor of germ tube growth in the AM fungus Gigaspora margarita. Pyranoisoflavones 1, 2 and 3 strongly inhibited germ tube growth at 0.63, 1.25 and 0.63μg/disc, respectively. The remaining compounds 4–7 were either moderate or weak inhibitors that inhibited germ tube growth at concentrations higher than 10μg/disc. Licoisoflavone B (1) and sophoraisoflavone A (2) completely inhibited hyphal branching induced by a lupin strigolactone, orobanchyl acetate, in G. margarita at 0.16 and 0.63μg/disc, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Greenhouse gas mitigation options include the production of carbonized materials and their addition to soils for longer term storage. Hydrothermal carbonization (HTC) is a novel way to produce carbonized materials. The goal here was to test if HTC material, in our case derived from beet root chips, has adverse effects on plant growth or that of root associated symbionts such as arbuscular mycorrhizal fungi. We carried out several studies, and found that increasing concentrations of HTC material could be deleterious for plant growth of Taraxacum, starting at 10vol% additions. Conversely, root colonization of the fungal symbiont was stimulated at an addition of 20vol%. Soil pH changes occurring during the study could be traced to microbial reduction reactions, and these led to a pH increase of the medium despite the quite acidic nature of the HTC material itself. In separate assays, we showed that spore germination of the AM fungus Glomus intraradices was stimulated by the HTC material, suggesting that direct effects on the fungi are likely in addition to those mediated by the host plant. A third experiment with a different plant species (Trifolium repens) confirmed the major conclusions, and showed also neutral to stimulatory effect on nodulation. Our results suggest that HTC materials should be carefully tested and optimized to reduce negative effects on plant growth before applications in the field are undertaken, particularly at high addition rates. [Copyright &y& Elsevier]

Abstract: Thirty actinomycete strains were isolated from the rhizosphere of field-grown plants (Trifolium repens L.) and identified by microscopic characteristics, biochemical tests and molecular techniques. The 16S rDNA sequence analysis showed that most of the isolates belong to the Streptomyces genus. These thirty isolates were tested for their capabilities of solubilizing/mineralizing sparingly phosphate sources, N2-fixation and/or siderophore production, typical traits of the so-called Plant Growth Promoting Rhizobacteria (PGPR). Phosphate solubilizing ability was widely exhibited by the isolated. All of them produced acid phosphatase and thirteen of them alkaline phosphatase. Ten strains grew in N-free media. Almost all strains produced siderophores, however the production level was in general very low and only the strain Thermobifida MCR24 released considerable amounts of this metabolite. Streptomyces MCR9, Thermobifida MCR24 and Streptomyces MCR26 were selected to test their interactions with arbuscular mycorrhizal (AM) fungi because they produced the highest plant growth beneficial effects among ten isolates preselected as promissory PGPR. The inoculation of AM fungi improved early establishment of MCR9 in clover rhizosphere, and the late establishment of MCR24. The three actinomycete strains improved AM mycelial growth in absence of the test plant, and MCR9 and MCR26 also stimulate AM fungal spore germination. Inoculation of clover plants with either of the selected actinomycetes enhanced plant growth and N acquisition. Co-inoculation of actinomycetes and Glomus mosseae produced synergic benefits on plant growth and MCR9 and MCR24 also on P acquisition. The three selected actinomycetes improve AM formation by clover plants and Glomus mosseae. [Copyright &y& Elsevier]

Summary: Soil biota such as earthworms, arbuscular mycorrhizal fungi (AMF) and plant roots are known to play a major role in engineering the belowground part of the terrestrial ecosystems, thus strongly influencing the water budget and quality on earth. However, the effect of soil organisms and their interactions on the numerous soil physical properties to be considered are still poorly understood. Shrinkage analysis allows quantifying a large spectrum of soil properties in a single experiment, with small standard errors. The objectives of the present study were, therefore, to assess the ability of the method to quantify changes in soil properties as induced by single or combined effects of leek roots (Allium porrum), AMF (Glomus intraradices) and earthworms (Allolobophora chlorotica). The study was performed on homogenised soil microcosms and the experiments lasted 35weeks. The volume of the root network and the external fungal hyphae was measured at the end, and undisturbed soil cores were collected. Shrinkage analysis allowed calculating the changes in soil hydro-structural stability, soil plasma and structural pore volumes, soil bulk density and plant available water, and structural pore size distributions. Data analysis revealed different impacts of the experimented soil biota on the soil physical properties. At any water content, the presence of A. chlorotica resulted in a decrease of the specific bulk volume and the hydro-structural stability around 25%, and in a significant increase in the bulk soil density. These changes went with a decrease of the structural pore volumes at any pore size, a disappearing of the thinnest structural pores, a decrease in plant available water, and a hardening of the plasma. On the contrary, leek roots decreased the bulk soil density up to 1.23gcm−3 despite an initial bulk density of 1.15gcm−3. This increase in volume was accompanied with a enhanced hydro-structural stability, a larger structural pore volume at any pore size, smaller structural pore radii and an increase in plant available water. Interestingly, a synergistic effect of leek roots and AMF in the absence of the earthworms was highlighted, and this synergistic effect was not observed in presence of earthworms. The structural pore volume generated by root and AMF growth was several orders of magnitude larger than the volume of the organisms. Root exudates as well as other AMF secretion have served as carbon source for bacteria that in turn would enhance soil aggregation and porosity, thus supporting the idea of a self-organization of the soil–plant–microbe complex previously described. [Copyright &y& Elsevier]

Abstract: The effects of an arbuscular mycorrhizal (AM) fungus (Glomus etunicatum) on atrazine dissipation, soil phosphatase and dehydrogenase activities and soil microbial community structure were investigated. A compartmented side-arm (‘cross-pot’) system was used for plant cultivation. Maize was cultivated in the main root compartment and atrazine-contaminated soil was added to the side-arms and between them 650 or 37μm nylon mesh was inserted which allowed mycorrhizal roots or extraradical mycelium to access atrazine in soil in the side-arms. Mycorrhizal roots and extraradical mycelium increased the degradation of atrazine in soil and modified the soil enzyme activities and total soil phospholipid fatty acids (PLFAs). Atrazine declined more and there was greater stimulation of phosphatase and dehydrogenase activities and total PLFAs in soil in the extraradical mycelium compartment than in the mycorrhizal root compartment when the atrazine addition rate to soil was 5.0mg kg−1. Mycelium had a more important influence than mycorrhizal roots on atrazine degradation. However, when the atrazine addition rate was 50.0mg kg−1, atrazine declined more in the mycorrhizal root compartment than in the extraradical mycelium compartment, perhaps due to inhibition of bacterial activity and higher toxicity to AM mycelium by atrazine at higher concentration. Soil PLFA profiles indicated that the AM fungus exerted a pronounced effect on soil microbial community structure. [Copyright &y& Elsevier]

Abstract: The present study was undertaken to investigate whether the behaviour in vitro of Lunularia cruciata grown with Glomus intraradices and G. proliferum, on SRV medium with 29.2mm sucrose satisfies the requirements of Koch'' postulates for mutualistic symbiosis. Hyphae emerging from mycothallus were able to grow over a two-compartment Petri dish barrier and capture and translocate phosphorus into the host liverwort. Thus, there were increases in plant dry weight, higher AM fungi spore production, and higher plant total phosphorus content. Moreover, this colonization of L. cruciata reproduces typical symptoms generally associated with mycorrhizae. These results showed that mycothalli of L. cruciata have available functionalities generally associated with mycorrhizal symbiosis in higher plants; however, the energy/photosynthetic carbon requirements to maintain a mutualistic symbiosis may be a limiting factor in vivo. Features here discussed indicate that, at least in tested experimental conditions, the endophytic association of L. cruciata with both G. intraradices and G. proliferum is a parasitic/opportunistic partnership rather than a mutualistic symbiosis. [Copyright &y& Elsevier]

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]

• AMF improved the biomass, nutritional status and oxidative balance of stressed pistachio rootstocks. • AMF decreased the accumulation of Na+ and Cl− in leaves and Na+ in roots of pistachio rootstocks grown under salinity. • The response of the pistachio rootstocks to drought and salinity stresses was different and depends on the stress. • Sarakhs under drought stress, and Badami-Riz–e-Zarand and UCB1 under salinity stress behaved as the most tolerant cultivars. Environmentally-friendly management techniques such as arbuscular mycorrhizal fungi (AMF) strategies are urgently required to improve plant nutrition and overcome abiotic stress. In this study, we evaluated the influence of symbiotic AMF on four pistachio rootstocks subjected to drought (100 % as the control, and 80 %, 60 %, and 40 % of field capacity as the treatments) and salinity (0.91 as the control, and 7.57, 16.12, and 24.63 dS/m using NaCl as the treatments) stress for 60 days in two separate experiments. Under both drought and salinity stress conditions, the root and shoot dry weights of the pistachio rootstocks markedly increased in the AMF-inoculated plants (+M). The accumulation of minerals in the leaves and roots of (+M) plants was significantly higher than in the non-inoculated plants (-M). AMF improved the nutritional status (N, P, Mg2+, and Ca2+) of the genotypes under both stress conditions. Mycorrhizal association significantly decreased Na+ and Cl− concentrations in the leaves and roots of the pistachio rootstocks under salinity stress. In (+M) plants under drought stress, hydrogen peroxide (H 2 O 2) and methylglyoxal (MG) concentrations in leaf and root tissues and malondialdehyde (MDA) in the roots, and under salinity stress, the H 2 O 2 and MG concentrations in the leaves and MDA in both tissues were lower than those in the (-M) plants. The Sarakhs rootstock under salinity stress accumulated lower minerals (N, P, K+, and Ca2+) and more antioxidants than the other rootstocks, which could be due to its higher sensitivity to this stress. Both stresses reduced the chlorophyll concentration and increased the oxidant content and electrolyte leakage from the roots and leaves of the rootstocks. Sarakhs rootstock under drought stress and Badami-Riz–e-Zarand and UCB1 rootstocks under salinity stress behaved better in terms of mineral absorption. Thus, they were more tolerant of drought and salinity stress, respectively. Based on these findings, the association of mycorrhizal fungi and pistachio rootstocks is a sustainable strategy for increasing biomass, mineral, and Chl contents, and decreasing oxidant content, thereby enhancing the stress tolerance of plants. [ABSTRACT FROM AUTHOR]

• Arbuscular mycorrhiza (AM) responsiveness describes the ability of plants to respond to AM with growth or yield differences. • AM responsiveness depends on the plant-fungal genotype combination and on environmental conditions. • The first genetic polymorphism determining quantitative root colonization by AM fungi was identified in rice CERK1. • A new study provides the first estimate of the impact of arbuscular mycorrhiza on maize yield in the field. • Natural variation genetics promises to uncover loci that enable breeding of crops with optimized AM response. Arbuscular mycorrhiza (AM) is an ancient, widespread symbiosis between most land plants and fungi of the Glomeromycotina, which receives increasing interest for agricultural application because it can promote plant growth and yield. The ability of plants to react to AM with changes in morphology and/or performance in terms of yield is called 'AM responsiveness'. Its amplitude depends on the plant- fungal genotype combination and the abiotic and biotic environment. A molecular understanding of AM responsiveness is key for enabling rational application of AM in agriculture, for example through targeted breeding of AM-optimised crops. However, the genetic and mechanistic underpinnings of AM responsiveness variation remain still unknown. Here, we review current knowledge on AM responsiveness, with a focus on agricultural crops, and speculate on mechanisms that may contribute to the variation in AM response. [ABSTRACT FROM AUTHOR]

• Arbuscular mycorrhiza increased essential oil concentration in Ocimum tenuiflorum L. • Eugenol, β-elemene, and β-caryophyllene are major constituents of the essential oil. • Concentration of major compounds was higher in essential oil of mycorrhizal plants. • Mycorrhiza boosted the antioxidant potential of leaves. • The industrial and therapeutic features were improved in the mycorrhizal plants. The increasing interest and demand of Ocimum tenuiflorum L. and its products in different industrial sectors necessitate appropriate cultural practices for cultivation of the plant with increased herbage and essential oil yield. Studies on O. tenuiflorum in relation to arbuscular mycorrhiza are restricted to evaluation of diversity of the mycorrhizal fungi in its rhizosphere or assessment of the ability of different species to colonize its roots. Hence, the present study aimed to assess the effect of arbuscular mycorrhizal fungus (Rhizophagus intraradices) inoculation on the pharmaceutically desired parameters of two high yielding genotypes of O. tenuiflorum. Colonization by R. intraradices fungus resulted in significant increase in the leaf biomass and concentration of essential oil in both the genotypes. Formation of arbuscular mycorrhiza resulted in up to 59.01 % and 86.95 % increase in essential oil concentration in mycorrhizal genotype A and B plants, respectively, in comparison with control. The characterization of essential oils by Gas Chromatography-Mass Spectrometry showed significant effect of arbuscular mycorrhiza on their chemical profile. A total of 23 and 37 compounds were identified in essential oils of control genotype A and B, respectively, while 21 and 34 compounds were detected in essential oils of their respective mycorrhizal counterparts. Concentration of eugenol (a valued phenylpropanoid), and other medicinally important terpenoids (β-elemene, β-caryophyllene, germacrene A, and germacrene D) increased in essential oils of mycorrhizal plants.While genotype and mycorrhizal interaction significantly influenced biomass and essential oil concentration in leaves, the effect of R. intraradices on concentration of eugenol, β-elemene, and β-caryophyllene did not vary between the two genotypes. Additionally, principal component analysis also highlighted that the volatiles common in the essential oil of the four treatments contributed significantly to the variation in the essential oil composition. Phenol, flavonoid, and polyphenol contents in the leaves were also enhanced on formation of arbuscular mycorrhiza. The study also aimed to evaluate the ability of leaves (fresh and processed) to scavenge reactive oxygen and nitrogen species. Arbuscular mycorrhiza augmented the antioxidant capacity of fresh and processed leaves of both the genotypes. Thus, findings of the study demonstrate that R. intraradices inoculation enhances productivity of O. tenuiflorum and also improves the quality of the products. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal (AM) plants and fungi associate with lower soil organic matter, higher pH, lower phosphorus and higher nitrogen than ectomycorrhizal (EM) ones. However, soil conditions correlate with climatic factors, and we suggest that temperature and humidity have also direct roles in the success of mycorrhiza types. The hypothesis here is that EM perform better at low temperatures than AM, and AM resist drought better than EM. Narrowleaf cottonwood (Populus angustifolia E. James) forms both AM and EM. We grew seedlings in soil at 14, 20 and 26 °C in factorial combinations with adequate watering and a cyclic mild drought for 4 and 7 weeks. As hypothesized, the percent of EM root tips was largest at 14 °C, while the proportional root length with AM was largest at the two higher temperatures. However, unlike expectations, drought increased EM formation slightly, while the AM colonization was lower in the dry treatment. Plant growth was reduced more by low temperature than drought. Root branching was more prominent at low temperature and root length and mass growth at higher temperatures. Soil nutrient availability did not provide a direct explanation to the results, as both soluble soil N and P were the same in 14 and 20 °C, while the change in mycorrhiza colonization took place between these temperatures. Differences in root morphology (root branching vs length) may affect the proportions of the mycorrhiza types at different temperature regimes. The most likely explanation to the differential colonization is that temperature affects AM and EM fungi in a different way. In nature, temperature and humidity regimes are tightly correlated, and temperature as such may be a stronger determinant for the success of mycorrhiza types than has been previously considered. The poorer performance of AM in low-temperature and drought conditions may reflect stress avoidance rather than stress tolerance by AM fungi. • Arbuscular mycorrhiza (AM) may resist drought better than ectomycorrhiza (EM). • EM may resist low temperature better than AM. • Drought reduced AM formation but not EM in dual-mycorrhizal Populus angustifolia. • More EM formed at 14 than at 20 and 26 °C, and more AM at 20 and 26 than at 14 °C. • Temperature may be a more important determinant for mycorrhiza than thought before. [ABSTRACT FROM AUTHOR]

• Arbuscular mycorrhizal symbiosis promoted a higher concentration of valerenic acid. • Moderated salinity induced valerenic acid production. • Symbiosis improved the growth of valerian plants under salinity stress. • Arbuscular mycorrhizal symbiosis improved ion homeostasis in shoots. • The efficiency of arbuscular mycorrhizal symbiosis was type-dependent. Valerian (Valeriana officinalis L.), which is considered as a medicinal plant, is commonly used in traditional medicine. This study aimed to evaluate the effect of arbuscular mycorrhizal (AM) fungi association under moderate and high salinity stress on growth and physio-biochemical traits of V. officinalis. The bio-ameliorative efficiency of two AM species, Rhizophagus intraradices and Funneliformis mosseae was also compared. The mycorrhizal inoculation generally increased the salt tolerance of plant and positively affected plant growth, P, K+, Mg2+ concentration and the ratios of total chlorophyll: carotenoids, K+: Na+, Ca2+: Na+, and Mg2+: Na+ in shoots compared with those of the non-mycorrhizal plants under saline condition. Moreover, the presence of AM symbiosis mitigated the salinity-induced increase in shoot Na+ concentration, shoot proline, and oxidative damage to membranes. AM fungi considerably promoted root proline and total soluble sugars and total phenolics in shoots and roots versus non-mycorrhizal V. officinalis. Moderate salinity stress increased valerenic acid production, which was more pronounced in F. mosseae inoculated plants. The outcome of the symbiosis was associated with the AM species used, and F. mosseae was more efficient than R. intraradices in the alleviation of salinity stress. This study suggests the potential use of mycorrhizal technology as a practical biotechnological approach to enhance growth and augment bioactive compounds production of V. officinalis in salt-affected soils. [ABSTRACT FROM AUTHOR]

Phytate is considered a poorly available plant P source but proved to be useful for particular soil bacteria strains. In soil-free conditions, it has been shown that bacteria locked up the mineralized phosphorus from phytate whereas bacterial grazers like nematodes were able to deliver P to plants. Here, we aimed to determine if the interactions between phytate-mineralizing bacteria, bacterial grazer nematodes, and mycorrhizal fungi could increase plant P acquisition from phytate in high P-adsorbing soils. Pinus pinaster was grown in a Cambisol supplemented with phytate. Plants, whether associated or not associated with the ectomycorrhizal fungus Hebeloma cylindrosporum, were either inoculated or not inoculated with the phytase-releasing bacteria Bacillus subtilis and the bacterial-feeding nematode Rhabditis sp. After 100 days, the dual inoculation of bacteria and nematodes significantly increased net plant P accumulation. We observed that, on average, mycorrhizal plants accumulated more P in their shoots than non-mycorrhizal plants. However, the highest plant P acquisition efficiency was found when the three soil organisms were present in the P. pinaster rhizosphere. We conclude that, in a highly inorganic P-fixing soil, plant P acquisition from phytate strongly depends on the grazing of phytate-mineralizing bacteria. Our results confirm the importance of the soil microbial loop to improve plant P nutrition from phytate, which should be considered a route to improve the utilization of this source of poorly available P by plants. • In contrast to trees and ectomycorrhizal fungi, bacteria can mineralize phytate. • We used a high P-sorbing cambisol amended with phytate to study plant P acquisition. • We studied bacteria-grazer nematodes-ectomycorrhizal fungi interactions on plant P. • The ectomycorrhizal fungus and bacteria increased plant P use from phytate. • Non mycorrhizal plants depend on bacterial grazing to get P from soil phytate. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) represent an important route for plant carbon (C) inputs into the soil. Nonetheless, the C input via AMF as well as its impact on soil organic matter (SOM) stabilization and C sequestration remains largely unknown. A mycorrhizal wild type progenitor (MYC) and its mycorrhiza defective mutant (reduced mycorrhizal colonization: rmc) of tomato were continuously labeled with 13CO 2 to trace root C inputs into the soil and quantify rhizosphere priming effects (RPE) as affected by AMF symbiosis and N fertilization. Mycorrhizal abundance and 13C incorporation into shoots, roots, soil and CO 2 were measured at 8, 12 and 16 weeks after transplanting. AMF symbiosis decreased the relative C allocation (% of total assimilated C) to roots, in turn increased the net rhizodeposition. Positive RPE was recorded for both MYC and rmc plants, ranging from 16–71% and 25–101% of the unplanted control, respectively. Although net rhizodeposition was higher for MYC than rmc plants 16 weeks after transplanting, the RPE was comparatively lower. This indicated a higher potential for C sequestration by plants colonized with AMF (MYC) because the reduced nutrient availability restricts the activity of free-living decomposers. Although N fertilization decreased the relative C allocation to roots, rhizosphere and bulk soil, it had no effect on the absolute amount of rhizodeposition to the soil. The RPE and N-cycling enzyme activities decreased by N fertilization 8 and 12 weeks after transplanting, suggesting a lower microbial N demand from SOM mining. The positive relationship between enzyme activities involved in C cycling, microbial biomass C and SOM decomposition underlines the microbial activation hypothesis, which explains the RPE. We therefore concluded that AMF symbiosis and N fertilization increase C sequestration in soil not only by increasing root C inputs, but also by lowering native SOM decomposition and RPE. • Arbuscular mycorrhizal fungi (AMF) reduced rhizosphere priming effect (RPE). • N fertilization lowered the magnitude of RPE by decreasing enzymes. • The net rhizodeposition induced by AMF was dependent on N availability. [ABSTRACT FROM AUTHOR]