The effect of arbuscular mycorrhizal fungi on biological activity and biochemical properties of soil under vetch growing conditions in calcareous soils

Due to soils from arid regions with high lime and low organic matter content, farmers receive low yields along with high costs of agricultural inputs, which causes them to look for a solution. In this context, Arbuscular mycorrhizal fungi (AMF) have great potential to reduce fertilizer use by mediating soil nutrient cycles. However, little is known about studies of AMF inoculum on microbial biomass carbon (C), nitrogen (N), and phosphorus (P) cycling during vetch plant vegetation in calcareous areas. In this study, changes in soil biogeochemical properties related to soil C, N, and P cycling were investigated with five different AMF inoculations under vetch (common Vetch (CV; Vicia sativa L.) and Narbonne Vetch (NV; Vicia narbonensis L.) growing conditions. For the field study, a total of five different mycorrhizae were used in the experiment with the random plots design. AMF inoculation decreased the lime content of the soil, and the highest decrease was observed in NV with Glomus (G.) intraradices + G. constrictum + G. microcarpum inoculation (24.41 %). The highest MBC content was recorded in CV vetch G. intraradices (1176.3 mg C kg-1) and the highest MBN content in NV vetch G. intraradices + G. constrictum + G. microcarpum (1356.9 mg C kg-1). CAT activity of soils was highest in CV vetch G. intraradices (31.43 %) and lowest in NV vetch G. intraradices + G. constrictum + G. microcarpum (72.88 %), urease enzyme activity decreased in all treatments except G. constrictum + Gigaspora sp. and G. mosseae inoculations in CV. The highest DHG activity was detected in GF (15.72 %) AMFs in CV and GI (21.99 %) in NV. APA activity was highest in Glomus constrictum + Gigaspora sp. (23.33 %) in CV and Glomus fasciculatum (10.08 %) in NV. In CV plots, G. intraradices + G. constrictum + G. microcarpum (91.67 %) isolates had the highest and G. intraradices community had the lowest RC% (97.33 %) in mixed mycorrhiza species, while in NV plots G. fasciculatum inoculum had the highest and G. intraradices community had the lowest RC%. This study has important implications for the application of AMF for sustainable agriculture. When the results of the study were evaluated, the most effective AMF isolates in terms of C, N, and P cycles were G. constrictum + G. fasciculatum + Gigaspora sp. in Common vetch variety, and G. intraradices in Narbonne vetch variety.

Keep in touch: the soil-root hydraulic continuum and its role in drought resistance in crops

Drought is a major threat to food security worldwide. Recently, the root-soil interface has emerged as a major site of hydraulic resistance during water stress. Here, we review the impact of soil drying on whole-plant hydraulics and discuss mechanisms by which plants can adapt by modifying the properties of the rhizosphere either directly or through interactions with the soil microbiome.

Co-occurring tree species drive arbuscular mycorrhizal fungi diversity in tropical forest

It is still uncertain whether environment or host plant species is more important in determining AMF diversity; although, plant roots are usually associated with abundant AMF species in different environments. This study explored the effect of plant species and environmental factors on AMF diversity based on three co-occurring tree species (Glochidion coccineum, Schefflera octophylla, and Schima superba) on six elevations of Mt. Jianfengling. A total of 185 OTUs (operational taxonomic units) of AMF were found in the three co-occurring dominant tree species. Of which 109 unique OTUs were identified in the three co-occurring plant species, which accounted for the total number of 58.92%. Forty-five OTUs were shared by the three co-occurring tree species, accounting for a total number of 24.32%. The plant species of Schefflera octophylla was identified as having the highest AMF diversity with the largest number of OTUs of 143. The fungi in the genus of Glomus were the dominant AMF species in the three co-occurring tree species. AMF communities and diversity are quite different, either within different plant species at the same elevation or within the same plant species at different elevations. However, the altitude had no significant effect on the ACE index. Therefore, the results suggest that plant species have a more important effect on AMF diversity and community composition.

Funneliformis mosseae influences leaf decomposition by altering microbial communities under saline-alkali conditions

Recent studies have indicated that arbuscular mycorrhizal fungi (AMF) can influence decomposition of organic materials. However, the underlying mechanisms remain unclear. Here we investigated whether AMF influence the decomposition of leaf litters and change the associated litter bacterial and fungal communities and whether this effect is altered by the level of soil saline-alkali. A pot experiment was conducted using Trifolium repens as host plant without or with AMF (Funneliformis mosseae) and with two levels of soil saline-alkali (0 and 200 mmol/L). Litterbags with different mesh size were used to measure the effect of AMF on decomposition. Our study found that AMF significantly accelerated leaf litter decomposition under both non-saline-alkali and saline-alkali conditions. The composition of bacterial and fungal communities was also altered by AMF independent of soil saline-alkali conditions. For bacterial community, AMF increased the richness but not the diversity and increased the relative abundance of Firmicutes and Nitrospirota. For fungal community, the richness and diversity were higher in AMF than in non-AMF treatment. AMF significantly resulted in a decrease of the relative abundance of Ascomycota but an increase of the relative abundance of Basidiomycota, Chytridiomycota, Mortierellomycota and Rozellomycota. Structural equation modeling (SEM) showed that AMF increased leaf litter decomposition under saline-alkali conditions primarily by affecting bacterial community composition. Together, we show that AMF increase decomposition and alter the bacterial and fungal communities, and that these effects are not modulated by the level of soil saline-alkali.

The role of arbuscular mycorrhizal symbiosis in improving plant water status under drought

Arbuscular mycorrhizal fungi (AMF) have been presumed to ameliorate crop tolerance to drought. Here, we review the role of AMF in maintaining water supply to plants from drying soils and the underlying biophysical mechanisms. We used a soil-plant hydraulic model to illustrate the impact of several AMF mechanisms on plant responses to edaphic drought. The AMF enhance the soil's capability to transport water and extend the effective root length, thereby attenuating the drop in matric potential at the root surface during soil drying. The synthesized evidence and the corresponding simulations demonstrate that symbiosis with AMF postpones the stress onset limit, which is defined as the disproportionality between transpiration rates and leaf water potentials, during soil drying. The symbiosis can thus help crops survive extended intervals of limited water availability. We also provide our perspective on future research needs and call for reconciling the dynamic changes in soil and root hydraulics in order to better understand the role of AMF in plant water relations in the face of climate changes.

Synergistic mechanisms of bioorganic fertilizer and AMF driving rhizosphere bacterial community to improve phytoremediation efficiency of multiple HMs-contaminated saline soil

The addition of Arbuscular mycorrhizal fungi (AMF) or bioorganic fertilizer (BOF) alone has been reported to enhance plant tolerance to heavy metals and salt stress and promote plant growth, while their synergistic effects on plant growth and rhizosphere microorganism are largely unknown. This study explored the effects of AMF (Rhizophagus intraradices), BOF and BOF + RI assisted phytoremediation on heavy metals contaminated saline soil improvement and revealed the microbial mechanism. For this purpose, a pot trial consisting of four treatments (CK, RI, BOF and BOF + RI) was carried out. The results showed that the biomass, nutrient element contents, the accumulation of heavy metals and Na of Astragalus adsurgens and soil properties were most significantly improved by BOF + RI. BOF + RI significantly impacted rhizosphere microbial diversity, abundance and community composition. Chloroflexi and Patescibacteria at the phylum level and Actinomadura, Iamia, and Desulfosporosinus at the genus level were significantly enriched in BOF + RI. Network analysis revealed that BOF + RI significantly changed the keystone and enhanced complexity and interaction. Most of the keystones had roles in promoting plant growth and stress resistance. This study suggested that phytoremediation assisted by BOF and AMF is an attractive approach to ameliorate heavy metals contaminated saline soil.

Application of AtMYB75 as a reporter gene in the study of symbiosis between tomato and Funneliformis mosseae

Composite plants containing transgenic hairy roots produced with Agrobacterium rhizogenes-mediated transformation have become an important method to study the interaction between plants and arbuscular mycorrhizal fungi (AMF). Not all hairy roots induced by A. rhizogenes are transgenic, however, which leads to requirement of a binary vector to carry a reporter gene to distinguish transgenic roots from non-transformed hairy roots. The beta-glucuronidase gene (GUS) and fluorescent protein gene often are used as reporter markers in the process of hairy root transformation, but they require expensive chemical reagents or imaging equipment. Alternatively, AtMYB75, an R2R3 MYB transcription factor from Arabidopsis thaliana, recently has been used as a reporter gene in hairy root transformation in some leguminous plants and can cause anthocyanin accumulation in transgenic hairy roots. Whether AtMYB75 can be used as a reporter gene in the hairy roots of tomato and if the anthocyanins accumulating in the roots will affect AMF colonization, however, are still unknown. In this study, the one-step cutting method was used for tomato hairy root transformation by A.rhizogenes. It is faster and has a higher transformation efficiency than the conventional method. AtMYB75 was used as a reporter gene in tomato hairy root transformation. The results showed that the overexpression of AtMYB75 caused anthocyanin accumulation in the transformed hairy roots. Anthocyanin accumulation in the transgenic hairy roots did not affect their colonization by the arbuscular mycorrhizal fungus, Funneliformis mosseae strain BGC NM04A, and there was no difference in the expression of the AMF colonization marker gene SlPT4 in AtMYB75 transgenic roots and wild-type roots. Hence, AtMYB75 can be used as a reporter gene in tomato hairy root transformation and in the study of symbiosis between tomato and AMF.

Rhizophagus irregularis improves Hg tolerance of Medicago truncatula by upregulating the Zn transporter genes ZIP2 and ZIP6

Mercury (Hg) pollution of soils is a critical environmental problem. To rehabilitate Hg contaminated soils, arbuscular mycorrhizal (AM) fungi-based phytoremediation may be supportive, yet the functional potential of AM fungi in response to Hg exposure is unclear. In a greenhouse experiment, we assessed the response of Medicago truncatula (Hg tolerance index (TI), Hg partitioning) to different Hg concentrations [0 (Hg0), 25 (Hg25), 50 (Hg50) µg g^-1] in treatments with (AM) and without (NM) inoculation of Rhizophagus irregularis. Additionally, zinc (Zn) uptake and the expression of two Zn transporter genes (ZIP2, ZIP6) were examined because Zn is an essential element for plants and shares the same outer electronic configuration as Hg, implying potential competition for the same transporters. The results showed that AM plants had a higher TI than NM plants. Plant roots were identified as dominant Hg reservoirs. AM inoculation reduced the root Hg concentration under Hg50 compared to the NM treatment. There was an interaction between Hg treatment and AM inoculation on Hg stem concentration, i.e., at Hg25, AM inoculation decreased the Hg translocation from roots to stems, while Hg translocation was increased at Hg50 compared to the NM treatment. Zn acquisition was improved by R. irregularis. The negative relationship between Hg and Zn concentrations in the roots of AM and NM plants implied potential competition for the same transporters, although the expression of Zn transporters was upregulated by AM inoculation at all Hg levels. In conclusion, this baseline study demonstrated that R. irregularis may play an important role in Hg tolerance of M. truncatula, suggesting its potential for Hg-contaminated phytoremediation.

Plant-soil interactions in the native range of two congeneric species with contrasting invasive success

The aim of this study was to compare plant-soil interactions in the native range of two congeneric European species differing in their invasive success in the world: a globally invasive Cirsium vulgare and non-invasive C. oleraceum. We assessed changes in soil nutrients and soil biota following soil conditioning by each species and compared performance of plants grown in self-conditioned and unconditioned soil, from which all, some or no biota was excluded. The invasive species depleted more nutrients than the non-invasive species and coped better with altered nutrient levels. The invasive species had higher seedling establishment which benefited from the presence of unconditioned biota transferred by soil filtrate. Biomass of both species increased in soil with self-conditioned soil filtrate and decreased in soil with self-conditioned whole-soil inoculum compared to unconditioned filtrate and inoculum. However, the increase was smaller and the decrease greater for the invasive species. The invasive species allocated less biomass to roots when associated with harmful biota, reducing negative effects of the biota on its performance. The results show that in the native range the invasive species is more limited by self-conditioned pathogens and benefits more from unconditioned mutualists and thus may benefit more from loss of effectively specialized soil biota in a secondary range. Our study highlights the utility of detailed plant-soil feedback research in species native range for understanding factors regulating species performance in their native range and pinpointing the types of biota involved in their regulation.

Comprehensive analysis reveals the underlying mechanism of arbuscular mycorrhizal fungi in kenaf cadmium stress alleviation

Soil Cadmium (Cd) contamination has become a severe environmental problem around the world. Kenaf has great potential for utilization and phytoremediation of soil contaminated with heavy metal. Arbuscular mycorrhizal fungi (AMF) can help plants alleviate Cd stress, but the underlying mechanism remains completely unknown. In this study, kenaf was inoculated or not inoculated with AMF at cadmium concentrations of 10 mg kg^-1 and 50 mg kg^-1 from the seedling stage to the vigorous growth stage. The results showed that AMF symbionts improved nutrient transport efficiency and significantly improved plant growth. Additionally, AMF colonization increased cell wall polysaccharide content which help to bind Cd in the cell wall and reduced the transport of Cd to aboveground plant tissues. The increase in soil pH (6.9), total balcomycin and easily extractable balcomycin content facilitated the chelation of metal by mycorrhizal fungi and reduced the biological effectiveness of Cd. Furthermore, AMF upregulated the expression levels of key kenaf genes, such as Hc.GH3.1, Hc.AKR, and Hc.PHR1, which plays an important role in enhancing kenaf Cd tolerance. Our findings systematically revealed the mechanisms by which AMF responds to Cd stress in kenaf, inoculation of AMF with kenaf could be used to enhance the removal of Cd from soil pollution in mining areas by phytoremediation.

Modeling geographic distribution of arbuscular mycorrhizal fungi from molecular evidence in soils of Argentinean Puna using a maximum entropy approach

The biogeographic region of Argentinean Puna mainly extends at elevations higher than 3,000 m within the Andean Plateau and hosts diverse ecological communities highly adapted to extreme aridity and low temperatures. Soils of Puna are typically poorly evolved and geomorphology is shaped by drainage networks, resulting in highly vegetated endorheic basins and hypersaline basins known as salar or salt flats. Local communities rely on soil fertility for agricultural practices and on pastures for livestock rearing. From this perspective, investigating the scarcely explored microbiological diversity of these soils as indicators of ecosystems functioning might help to predict the fragility of these harsh environments. In this study we collected soil samples from 28 points, following a nested design within three different macro-habitats, i.e., Puna grassland, hypersaline salar and family-run crop fields. Total fungi and arbuscular mycorrhizal fungi (AMF) occurrence were analyzed using eDNA sequencing. In addition, the significance of soil salinity and organic matter content as significant predictors of AMF occurrence, was assessed through Generalized Linear Mixed Modeling. We also investigated whether intensive grazing by cattle and lama in Puna grasslands may reduce the presence of AMF in these highly disturbed soils, driving or not major ecological changes, but no consistent results were found, suggesting that more specific experiments and further investigations may address the question more specifically. Finally, to predict the suitability for AMF in the different macro-habitats, Species Distribution Modeling (SDM) was performed within an environmental coherent area comprising both the phytogeographic regions of Puna and Altoandino. We modeled AMF distribution with a maximum entropy approach, including bioclimatic and edaphic predictors and obtaining maps of environmental suitability for AMF within the predicted areas. To assess the impact of farming on AMF occurrence, we set a new series of models excluding the cultivated Chaupi Rodeo samples. Overall, SDM predicted a lower suitability for AMF in hypersaline salar areas, while grassland habitats and a wider temperature seasonality range appear to be factors significantly related to AMF enrichment, suggesting a main role of seasonal dynamics in shaping AMF communities. The highest abundance of AMF was observed in Vicia faba crop fields, while potato fields yielded a very low AMF occurrence. The models excluding the cultivated Chaupi Rodeo samples highlighted that if these cultivated areas had theoretically remained unmanaged habitats of Puna and Altoandino, then large-scale soil features and local bioclimatic constraints would likely support a lower suitability for AMF. Using SDM we evidenced the influence of bioclimatic, edaphic and anthropic predictors in shaping AMF occurrence and highlighted the relevance of considering human activities to accurately predict AMF distribution.

The hidden power of secondary metabolites in plant-fungi interactions and sustainable phytoremediation

The global environment is dominated by various small exotic substances, known as secondary metabolites, produced by plants and microorganisms. Plants and fungi are particularly plentiful sources of these molecules, whose physiological functions, in many cases, remain a mystery. Fungal secondary metabolites (SM) are a diverse group of substances that exhibit a wide range of chemical properties and generally fall into one of four main family groups: Terpenoids, polyketides, non-ribosomal peptides, or a combination of the latter two. They are incredibly varied in their functions and are often related to the increased fitness of the respective fungus in its environment, often competing with other microbes or interacting with plant species. Several of these metabolites have essential roles in the biological control of plant diseases by various beneficial microorganisms used for crop protection and biofertilization worldwide. Besides direct toxic effects against phytopathogens, natural metabolites can promote root and shoot development and/or disease resistance by activating host systemic defenses. The ability of these microorganisms to synthesize and store biologically active metabolites that are a potent source of novel natural compounds beneficial for agriculture is becoming a top priority for SM fungi research. In this review, we will discuss fungal-plant secondary metabolites with antifungal properties and the role of signaling molecules in induced and acquired systemic resistance activities. Additionally, fungal secondary metabolites mimic plant promotion molecules such as auxins, gibberellins, and abscisic acid, which modulate plant growth under biotic stress. Moreover, we will present a new trend regarding phytoremediation applications using fungal secondary metabolites to achieve sustainable food production and microbial diversity in an eco-friendly environment.

Effect of arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) on microorganism of phenanthrene and pyrene contaminated soils

A pot experiment was performed to investigate the effect of phytoremediation (CK, using tall fescue), fungi remediation (GV, using Glomus versiforme), bacterial remediation (PS, using Pseudomonas fluorescens Ps2-6), and microbial-phytoremediation (GVPS, using three species) on removing polycyclic aromatic hydrocarbons (PAHs) and the microbial diversity in soils. Inoculation with G. versiforme and P. fluorescens could increase the biomass of tall fescue and the accumulation of phenanthrene (PHE) and pyrene (PYR) in plants. Among them, the highest PHE and PYR removal efficiencies and highest biomass of tall fescue were observed in the GVPS treatment and the microbial diversity in contaminated soil was changed, the result revealed that Proteobacteria and Ascomycota were the dominant bacterial phylum and fungal phylum in all treatments, while more Proteobacteria were detected in GVPS treatment. At the genus level, the abundance of Sphingomonas (3.17%), Pseudomonas (2.05%), and Fusarium (8.65%) treated with GVPS increased compared with other treatments. These pieces of evidence contribute to a better understanding of the mechanisms involved in the combined microbial-phytoremediation strategies for PAHs-contaminated soils, especially the effects of microbial-phytoremediation on rhizosphere microbial diversity.

Arbuscular mycorrhizas increased tomato biomass and nutrition but did not affect local soil P availability or 16S bacterial community in the field

While interest in arbuscular mycorrhizal (AM) fungal effects on soil phosphorus (P) have recently increased, field experiments on this topic are lacking. While microcosm studies provided valuable insights, the lack of field studies represents a knowledge gap. Here, we present a field study in which we grew a mycorrhiza-defective tomato (Solanum lycopersicum L.) genotype (named rmc) and its mycorrhizal wild-type progenitor (named 76R) with and without additional fertiliser, using a drip-irrigation system to examine the impacts of the AM symbiosis on soil P availability and plant growth and nutrition. AM effects on fruit biomass and nutrients, soil nutrient availability, soil moisture and the soil bacterial community were examined. At the time of harvest, the AM tomato plants without fertiliser had the same early season fruit biomass and fruit nutrient concentrations as plants that received fertiliser. The presence of roots reduced the concentration of available soil P, ammonium and soil moisture in the top 10 cm soil layer. Arbuscular mycorrhizas did not significantly affect soil P availability, soil moisture, or 16S bacterial community composition. These findings suggest an indirect role for AM fungi in tomato production but not necessarily a direct role in determining soil physicochemical traits, during the one season that this experiment was conducted. While longer-term field studies may be required in the future, the present study provides new insights into impacts of AM fungi on P availability and uptake in a field soil system.

Cooperation between arbuscular mycorrhizal fungi and plant growth-promoting bacteria and their effects on plant growth and soil quality

The roles of arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) in improving nutrition uptake and soil quality have been well documented. However, few studies have explored their effects on root morphology and soil properties. In this study, we inoculated Elymus nutans Griseb with AMF and/or PGPR in order to explore their effects on plant growth, soil physicochemical properties, and soil enzyme activities. The results showed that AMF and/or PGPR inoculation significantly enhanced aboveground and belowground vegetation biomass. Both single and dual inoculations were beneficial for plant root length, surface area, root branches, stem diameter, height, and the ratio of shoot to root, but decreased root volume and root average diameter. Soil total nitrogen, alkaline phosphatase, and urease activities showed significant growth, and soil electrical conductivity and pH significantly declined under the inoculation treatments. Specific root length showed a negative correlation with belowground biomass, but a positive correlation with root length and root branches. These results indicated that AMF and PGPR had synergetic effects on root morphology, soil nutrient availability, and plant growth.

Quercetin and 1-methyl-2-oxindole mimic root signaling that promotes spore germination and mycelial growth of Gigaspora margarita

Arbuscular mycorrhizal fungi (AMF) are obligate biotrophs, and the difficulty of growing them in asymbiotic or monoxenic (AMF + root) conditions limits research and their large-scale production as biofertilizer. We hypothesized that a combination of flavanols and strigolactones can mimic complex root signaling during the presymbiotic stages of AMF. We evaluated the germination, mycelial growth, branching, and auxiliary cell clusters formation by Gigaspora margarita during the presymbiotic stage in the presence (or absence) of transformed Cichorium intybus roots in basal culture medium enriched with glucose, a flavonol (quercetin or biochanin A) and a strigolactone analogue (1-Methyl-2-oxindole or indole propionic acid). With quercetin (5 µM), methyl oxindole (2.5 nM), and glucose (8.2 g/L) in the absence of roots, the presymbiotic mycelium of G. margarita grew without cytoplasmic retraction and produced auxiliary cells over 71 days similar to presymbiotic mycelium in the presence of roots but without glucose, strigolactones, and flavonols. Our results indicate that glucose and a specific combination of certain concentrations of a flavonol and a strigolactone might be used in asymbiotic or monoxenic liquid or semisolid cultures to stimulate AMF inoculant bioprocesses.

Effects of arbuscular mycorrhizal fungi on frond antimony enrichment, morphology, and proteomics in Pteris cretica var. nervosa during antimony phytoremediation

Pteris cretica var. nervosa is a dominant fern species found in antimony (Sb) mining areas, capable of forming symbiosis with arbuscular mycorrhizal fungi (AMF), especially with those members of the Glomus genus. Despite this fern's relevance and the potential contribution of mycorrhizal symbiosis to phytoremediation, the AMF's impact on P. var. nervosa phytoremediation of Sb remains unknown. Here, we exposed P. var. nervosa to different concentrations of Sb for 6 months. Our results showed that Sb reduced shoot biomass, enlarged the root/shoot ratio, and disrupted the fronds' intracellular structure. AMF inoculation, however, was able to moderate these phenotypic changes and increased the accumulation level of Sb in plants. From a proteomics analysis of this plant's fronds, a total of 283 proteins were identified. Notably, those proteins with catalytic function, carbon fixing and ATP metabolic function were highly enriched. K-means clustering demonstrated protein-changing patterns involved in multiple metabolic pathways during exposure to Sb. Further, these patterns can be moderated by AMF inoculation. Pearson correlations were used to assess the plant biomarkers-soil Sb relationships; This revealed a strong correlation between ribosome alteration and the root/shoot ratio when inoculated with AMF, and a positive correlation between photosynthesis proteins and chlorophyll (SPAD value). Our results indicate AMF could moderate the fronds impairment by maintaining the sufficient protein levels for ribosomal functioning, photosynthesis activity and to counter ROS production. We demonstrate the effective use of AMF associated with P. cretica var. nervosa for Sb phytoremediation and the potential of applying proteomics to better understand the mechanism behind this symbiotic plant physiological response.

Mycorrhiza and Iron Tailings Synergistically Enhance Maize Resistance to Arsenic on Medium Arsenic-Polluted Soils Through Increasing Phosphorus and Iron Uptake

Agricultural arsenic (As, CAS. No. 7440-38-2) over the issue of pollution has been related to people's livelihood, security and moderate use of As contaminated soil is an important aspect of contaminated soil remediation. In this potted plant experiment, synergistic effects of arbuscular mycorrhizal fungi (AMF) Funneliformis mosseae and iron (Fe, CAS. No. 7439-89-6) oxides on plant growth and phosphorus (P, CAS. No. 7723-14-0), As and Fe uptake by maize (Zea mays L.) were studied on simulating medium As-polluted soils in greenhouse. Different amounts (0, 5, 10, 20, 40 g kg^- 1) of iron tailings (IT) were added. The results showed that IT20 and IT40 addition significantly increased mycorrhizal infection rate, plant biomass, root length and P, Fe uptake under FM treatment; IT40 addition decreased As concentration in roots. In addition, FM inoculation increased biomass, root length and P uptake by shoots, but decreased Fe and As concentration in shoots. Therefore, the combined FM inoculation and IT40 addition promoted maize growth and decreased As concentration in shoots by decreasing As absorption efficiency, increasing P and Fe uptake and P/As ratio.

Ancient lineages of arbuscular mycorrhizal fungi provide little plant benefit

Almost all land plants form symbiotic associations with arbuscular mycorrhizal fungi (AMF). Individual plants usually are colonized by a wide range of phylogenetically diverse AMF species. The impact that different AMF taxa have on plant growth is only partly understood. We screened 44 AMF isolates for their effect on growth promotion and nutrient uptake of leek plants (Allium porrum), including isolates that have not been tested previously. In particular, we aimed to test weather AMF lineages with an ancient evolutionary age differ from relatively recent lineages in their effects on leek plants. The AMF isolates that were tested covered 18 species from all five AMF orders, eight families, and 13 genera. The experiment was conducted in a greenhouse. A soil-sand mixture was used as substrate for the leek plants. Plant growth response to inoculation with AMF varied from - 19 to 232% and depended on isolate, species, and family identity. Species from the ancient families Archaeosporaceae and Paraglomeraceae tended to be less beneficial, in terms of stimulation plant growth and nutrient uptake, than species of Glomeraceae, Entrophosporaceae, and Diversisporaceae, which are considered phylogenetically more recent than those ancient families. Root colonization levels also depended on AMF family. This study indicates that plant benefit in the symbiosis between plants and AMF is linked to fungal identity and phylogeny and it shows that there are large differences in effectiveness of different AMF.

Co-inoculation with arbuscular mycorrhizal fungi differing in carbon sink strength induces a synergistic effect in plant growth

Arbuscular mycorrhizal (AM) fungi play a key role in determining ecosystem functionality. Understanding how diversity in the fungal community affects plant productivity is therefore an important question in ecology. Current research has focused on understanding the role of functional complementarity in the fungal community when the host plant faces multiple stress factors. Fewer studies, however, have investigated how variation in traits affecting nutrient exchange can impact the plant growth dynamics, even in the absence of environmental stressors. Combining experimental data and a mathematical model based on ordinary differential equations, we investigate the role played by carbon sink strength on plant productivity. We simulate and measure plant growth over time when the plant is associated with two fungal isolates with different carbon sink strength, and when the plant is in pairwise association with each of the isolates alone. Overall, our theoretical as well as our experimental results show that co-inoculation with fungi with different carbon sink strength can induce positive non-additive effects (or synergistic effects) in plant productivity. Fungi with high carbon sink strength are able to quickly establish a fungal community and increase the nutrient supply to the plant, with a consequent positive impact on plant growth rate. On the other side, fungi with low carbon sink strength inflict lower carbon costs to the host plant, and support maximal plant productivity once plant biomass is large. As AM fungi are widely used as organic fertilizers worldwide, our findings have important implications for restoration ecology and agricultural management.

Arbuscular mycorrhizal fungi alter microbiome structure of rhizosphere soil to enhance maize tolerance to La

Rhizosphere microbes are essential partners for plant stress tolerance. Recent studies indicate that arbuscular mycorrhizal fungi (AMF) can facilitate the revegetation of soils contaminated by heavy metals though interacting with rhizosphere microbiome. However, it is unclear how AMF affect rhizosphere microbiome to improve the growth of plant under rare earth elements (REEs) stress. AMF (Claroideoglomus etunicatum) was inoculated to maize grown in soils spiked with Lanthanum (0 mg kg^-1, La0; 10 mg kg^-1, La10; 100 mg kg^-1, La100; 500 mg kg^-1, La500). Plant biomass, nutrient uptake, REE uptake and rhizosphere bacterial and fungal community were evaluated. The results indicated that La100 and La500 decreased significantly root colonization rates and nutrition uptake (K, P, Ca and Mg content). La500 decreased significantly α-diversity indexes of bacterial and fungal community. AMF enhanced significantly the shoot and root fresh and dry weight of maize in all La treatments (except for the root fresh and dry weight of La0 and La10 treatment). For La100 and La500 treatments, AMF increased significantly nutrition uptake (K, P, Ca and Mg content) in shoot of maize by 27.40-441.77%. For La500 treatment, AMF decreased significantly shoot La concentration by 51.53% in maize, but increased significantly root La concentration by 30.45%. In addition, AMF decreased bacterial and fungal Shannon index in La0 treatment, but increased bacterial Shannon index in La500 treatment. Both AMF and La500 affected significantly the bacterial and fungal community composition, and AMF led to more influence than La. AMF promoted the enrichment of bacteria, including Planomicrobium, Lysobacter, Saccharothrix, Agrococcus, Microbacterium, Streptomyces, Penicillium and other unclassified genus, and fungi (Penicillium) in La500, which showed the function for promoting plant growth and tolerance of heavy metal. The study revealed that AMF can regulate the rhizosphere bacterial and fungal composition and foster certain beneficial microbes to enhance the tolerance of maize under La stress. Phytoremediation assisted by AMF is an attractive approach to ameliorate REEs-contaminated soils.

Arbuscular mycorrhizal colonization rate of an exotic plant, Galinsoga quadriradiata, in mountain ranges changes with altitude

Arbuscular mycorrhizal fungi (AMF) are suggested to be important for invasions by many exotic plants. However, it is not yet known how associations between AMF and invasive plant populations change in mountains ranges and how changed associations affect further expansion of different populations in new habitats. We conducted a field survey to detect AMF colonization rate of the invasive Galinsoga quadriradiata along an elevational gradient ranging from 223 to 1947 masl in the Qinling and Bashan Mountains, China. Additionally, a greenhouse experiment was conducted to compare plant growth performance among five elevational populations. In the field, total plant mass and seed production, as well as root AMF colonization rate, significantly decreased with elevation. When populations were grown in a novel soil environment in the greenhouse, the high-altitude populations achieved higher seed and total mass at lower AMF colonization rate than the low-altitude populations. Moreover, high AMF association was related to high intraspecific competition within low-altitude populations and limited seed production. Our results revealed that the associations between AMF and G. quadriradiata decrease with altitude in mountain ranges, and this may indicate that differentiation of association between AMF and elevational populations occurs during range expansion of G. quadriradiata. The results of the greenhouse experiment suggest that the high-altitude populations are more aggressive than the low-altitude populations in a non-stressful environment.

High-throughput sequencing analysis of the rhizosphere arbuscular mycorrhizal fungi (AMF) community composition associated with Ferula sinkiangensis

BACKGROUND

Ferula sinkiangensis is an increasingly endangered medicinal plant. Arbuscular mycorrhiza fungi (AMF) are symbiotic microorganisms that live in the soil wherein they enhance nutrient uptake, stress resistance, and pathogen defense in host plants. While such AMF have the potential to contribute to the cultivation of Ferula sinkiangensis, the composition of AMF communities associated with Ferula sinkiangensis and the relationship between these fungi and other pertinent abiotic factors still remains to be clarified.

RESULTS

Herein, we collected rhizosphere and surrounding soil samples at a range of depths (0-20, 20-40, and 40-60 cm) and a range of slope positions (bottom, middle, top). These samples were then subjected to analyses of soil physicochemical properties and high-throughput sequencing (Illumina MiSeq). We determined that Glomus and Diversispora species were highly enriched in all samples. We further found that AMF diversity and richness varied significantly as a function of slope position, with this variation primarily being tied to differences in relative Glomus and Diversispora abundance. In contrast, no significant relationship was observed between soil depth and overall AMF composition, although some AMF species were found to be sensitive to soil depth. Many factors significantly affected AMF community composition, including organic matter content, total nitrogen, total potassium, ammonium nitrogen, nitrate nitrogen, available potassium, total dissolvable salt levels, pH, soil water content, and slope position. We further determined that Shannon diversity index values in these communities were positively correlated with total phosphorus, nitrate-nitrogen levels, and pH values (P < 0.05), whereas total phosphorus, total dissolvable salt levels, and pH were positively correlated with Chao1 values (P < 0.05).

CONCLUSION

In summary, our data revealed that Glomus and Diversispora are key AMF genera found within Ferula sinkiangensis rhizosphere soil. These fungi are closely associated with specific environmental and soil physicochemical properties, and these soil sample properties also differed significantly as a function of slope position (P < 0.05). Together, our results provide new insights regarding the relationship between AMF species and Ferula sinkiangensis, offering a theoretical basis for further studies of their development.

Promises and potential of in situ nano-phytoremediation strategy to mycorrhizo-remediate heavy metal contaminated soils using non-food bioenergy crops (Vetiver zizinoides & Cannabis sativa)

Heavy metals (HMs) in soil, air, and water environments effect human health. These HMs cannot be degraded in soil and they can only be transformed from one state to another. Food and energy resources such as coal, oil, petrol, etc. are gradually diminishing due to ever increasing demand and consumption, world faces crisis. There is an urgent need to address these problems by reclaiming the waste/polluted land for food and energy production. Various physicochemical remediation strategies are being proposed, developed, and tested but they are all very costly and only applicable to small contaminated sites. During the past two decades or so, plant-based phytoremediation technology is rapidly evolving as a promising new tool to address the issue with the potential to remediate HM contaminated soils in a sustainable manner. Plants, labeled as phyto-tolerant or phyto-accumulators, surviving on such contaminated soils reduce the toxicity by preventing their translocation or destroying the contaminants by sequestration by synthesizing thiol-containing HM-binding proteins (nano-molecules) and peptides (phytochelators or PCs) which modulate internal levels of metal concentration between deficient and toxic levels. But such plants are very slow growing, producing small biomass, and the process taking a long time to effectively remediate such soils. To overcome limitations of using such plants, plants capable of high biomass production and tolerating multiple HMs, such as non-food bioenergy crops (Vetiver and Hamp), are required. This plant-based remediation strategy can further be enhanced with the use of both plants and rhizosphere microbes like arbuscular mycorrhizal fungi (AMF) and plant growth-promoting bacteria. The combination of three components, i.e. high biomass producing plant, soil, and its rhizosphere harboring plant growth-promoting rhizobial (PGPR) microbiota, particularly AMF, will further improve the process of nano-phytoremediation of HM contaminated soils. This mini review focuses on how phytoremediation, nanotechnology, AMF and PGPR technologies can be merged together to form an integrated nano-mycorrhizo-phytoremediation (NMPR) strategy which synergistically achieve the goal of remediation of soil contaminants and improve the phytoremediation performance of bioenergy plants grown on HM polluted soils. This review also identifies the urgent need to conduct field-scale application of this strategy and use it as potential tool for reestablishing plant cover and population diversity during restoration of derelict land post-industrial/mining activities.

High-Throughput DNA Sequence-Based Analysis of AMF Communities

Arbuscular mycorrhizal fungi (AMF) are obligate symbionts of most land plants. They have great ecological and economic impacts as they support plant nutrition and water supply, soil structure, and plant resistance to pathogens. Investigating AMF presence and distribution at small and large scales is critical. Therefore, research requires standard protocols to be easily implemented. In this chapter, we describe a workflow for AMF identification by high-throughput sequencing through Illumina MiSeq platform of two DNA target regions: small subunit (SSU) and internal transcribed spacer (ITS). The protocol can apply to both soil and root AMF communities.

Distribution of arbuscular mycorrhizal fungi (AMF) in Terceira and São Miguel Islands (Azores)

BACKGROUND

The data, presented here, come from samples collected during three research projects which aimed to assess the impact of land-use type on Arbuscular Mycorrhizal Fungi (AMF) diversity and community composition in pastures of Terceira Island (Azores, Macaronesia, Portugal) and also in the native forest of two Azorean Islands (Terceira and São Miguel; Azores, Macaronesia, Portugal). Both projects contributed to improving the knowledge of AMF community structure at both local and regional scales.

NEW INFORMATION

Little is known on the AMF communities from Azores islands and this study reports the first survey in two Azorean Islands (Terceira and São Miguel). A total of 18,733 glomeromycotan spores were classified at the species level from 244 field soil samples collected in three different habitat types - native forests (dominated by Juniperus brevifolia and Picconia azorica), semi-natural and intensively-managed pastures. Thirty-seven distinct spore morphotypes, representing ten glomeromycotan families, were detected. Species of the family Acaulosporaceae dominated the samples, with 13 species (38% of the taxa), followed by Glomeraceae (6 spp.), Diversisporaceae (4 spp.), Archaeosporaceae (3 spp.), Claroideoglomeraceae (3 spp.), Gigasporaceae (3 spp.), Ambisporaceae and Paraglomeraceae, both with the same number of AMF species (2 spp.), Sacculosporaceae (1 sp.) and Entrophospora (family insertae sedis). Members of the family Acaulosporaceae occurred almost exclusively in the native forests especially associated with the Picconia azorica rhizosphere, while members of Gigasporaceae family showed a high tendency to occupy the semi-natural pastures and the native forests of Picconia azorica. Members of Glomeraceae family were broadly distributed by all types of habitat which confirm the high ecological plasticity of this AMF family to occupy the more diverse habitats.

Holobiont chronobiology: mycorrhiza may be a key to linking aboveground and underground rhythms

Circadian clocks are nearly ubiquitous timing mechanisms that can orchestrate rhythmic behavior and gene expression in a wide range of organisms. Clock mechanisms are becoming well understood in fungal, animal, and plant model systems, yet many of these organisms are surrounded by a complex and diverse microbiota which should be taken into account when examining their biology. Of particular interest are the symbiotic relationships between organisms that have coevolved over time, forming a unit called a holobiont. Several studies have now shown linkages between the circadian rhythms of symbiotic partners. Interrelated regulation of holobiont circadian rhythms seems thus important to coordinate shifts in activity over the day for all the partners. Therefore, we suggest that the classical view of "chronobiological individuals" should include "a holobiont" rather than an organism. Unfortunately, mechanisms that may regulate interspecies temporal acclimation and the evolution of the circadian clock in holobionts are far from being understood. For the plant holobiont, our understanding is particularly limited. In this case, the holobiont encompasses two different ecosystems, one above and the other below the ground, with the two potentially receiving timing information from different synchronizing signals (Zeitgebers). The arbuscular mycorrhizal (AM) symbiosis, formed by plant roots and fungi, is one of the oldest and most widespread associations between organisms. By mediating the nutritional flux between the plant and the many microbes in the soil, AM symbiosis constitutes the backbone of the plant holobiont. Even though the importance of the AM symbiosis has been well recognized in agricultural and environmental sciences, its circadian chronobiology remains almost completely unknown. We have begun to study the circadian clock of arbuscular mycorrhizal fungi, and we compile and here discuss the available information on the subject. We propose that analyzing the interrelated temporal organization of the AM symbiosis and determining its underlying mechanisms will advance our understanding of the role and coordination of circadian clocks in holobionts in general.

Mycorrhizae Alter Constitutive and Herbivore-Induced Volatile Emissions by Milkweeds

Plants use volatile organic compounds (VOCs) to cue natural enemies to their herbivore prey on plants. Simultaneously, herbivores utilize volatile cues to identify appropriate hosts. Despite extensive efforts to understand sources of variation in plant communication by VOCs, we lack an understanding of how ubiquitous belowground mutualists, such as arbuscular mycorrhizal fungi (AMF), influence plant VOC emissions. In a full factorial experiment, we subjected plants of two milkweed (Asclepias) species under three levels of AMF availability to damage by aphids (Aphis nerii). We then measured plant headspace volatiles and chemical defenses (cardenolides) and compared these to VOCs emitted and cardenolides produced by plants without herbivores. We found that AMF have plant species-specific effects on constitutive and aphid-induced VOC emissions. High AMF availability increased emissions of total VOCs, two green leaf volatiles (3-hexenyl acetate and hexyl acetate), and methyl salicylate in A. curassavica, but did not affect emissions in A. incarnata. In contrast, aphids consistently increased emissions of 6-methyl-5-hepten-2-one and benzeneacetaldehyde in both species, independent of AMF availability. Both high AMF availability and aphids alone suppressed emissions of individual terpenes. However, aphid damage on plants under high AMF availability increased, or did not affect, emissions of those terpenes. Lastly, aphid feeding suppressed cardenolide concentrations only in A. curassavica, and AMF did not affect cardenolides in either plant species. Our findings suggest that by altering milkweed VOC profiles, AMF may affect both herbivore performance and natural enemy attraction.

Seasonal variation in winter wheat field soil arbuscular mycorrhizal fungus communities after non-mycorrhizal crop cultivation

Intensive farming practices that implement deep and frequent tillage, high input inorganic fertilization, cultivation with non-host species, and pesticide use are widely reported to be detrimental for arbuscular mycorrhizal fungi (AMF), which are one of the most important plant biofertilizers. The effect of the reduction of agricultural input on AMF community dynamics following conversion from conventional non-mycorrhizal to lower input mycorrhizal crop cultivation has not yet been fully elucidated. We investigated the effect of the reduction of agricultural input, rotation, and season on AMF communities in winter wheat field soil after conversion from long-term (more than 20 years) non-mycorrhizal (sugar beet) crop cultivation. We described AMF communities from bulk soil samples by specifically targeting the 18S ribosomal gene using a combination of AMF specific primers and 454 pyrosequencing. No effect was found after 3 years' reduction of agricultural input, and only marginal effects were due to rotation with specific crops preceding winter wheat. Instead, season and year of sampling had the most appreciable influence on the AMF community. We suggest that, after conversion from long-term non-mycorrhizal to mycorrhizal crop cultivation, AMF diversity is low if compared to similar agroecosystems. Seasonal and successional dynamics play an important role as determinants of community structure.

Expression of putative circadian clock components in the arbuscular mycorrhizal fungus Rhizoglomus irregulare

Arbuscular mycorrhizal fungi (AMF) are obligatory plant symbionts that live underground, so few studies have examined their response to light. Responses to blue light by other fungi can be mediated by White Collar-1 (WC-1) and WC-2 proteins. These wc genes, together with the frequency gene (frq), also form part of the endogenous circadian clock. The clock mechanism has never been studied in AMF, although circadian growth of their hyphae in the field has been reported. Using both genomic and transcriptomic data, we have found homologs of wc-1, wc-2, and frq and related circadian clock genes in the arbuscular mycorrhizal fungus Rhizoglomus irregulare (synonym Rhizophagus irregularis). Gene expression of wc-1, wc-2, and frq was analyzed using RT-qPCR on RNA extracted from germinating spores and from fungal material cultivated in vitro with transformed carrot roots. We found that all three core clock genes were expressed in both pre- and post-mycorrhizal stages of R. irregulare growth. Similar to the model fungus Neurospora crassa, the core circadian oscillator gene frq was induced by brief light stimulation. The presence of circadian clock and output genes in R. irregulare opens the door to the study of circadian clocks in the fungal partner of plant-AMF symbiosis. Our finding also provides new insight into the evolution of the circadian frq gene in fungi.

Plant growth and arbuscular mycorrhizae development in oil sands processing by-products

Soil pollutants such as hydrocarbons can induce toxic effects in plants and associated arbuscular mycorrhizal fungi (AMF). This study was conducted to evaluate if the legume Lotus corniculatus and the grass Elymus trachycaulus and arbuscular mycorrhizal fungi could grow in two oil sands processing by-products after bitumen extraction from the oil sands in northern Alberta, Canada. Substrate treatments were coarse tailings sand (CTS), a mix of dry mature fine tailings (MFT) with CTS (1:1) and Pleistocene sandy soil (hydrocarbon free); microbial treatments were without AMF, with AMF and AMF plus soil bacteria isolated from oil sands reclamation sites. Plant biomass, root morphology, leaf water content, shoot tissue phosphorus content and mycorrhizal colonization were evaluated. Both plant species had reduced growth in CTS and tailings mix relative to sandy soil. AMF frequency and intensity in roots of E. trachycaulus was not influenced by soil hydrocarbons; however, it decreased significantly over time in roots of L. corniculatus without bacteria in CTS. Mycorrhizal inoculation alone did not significantly improve plant growth in CTS and tailings mix; however, inoculation with mycorrhizae plus bacteria led to a significantly positive response of both plant species in CTS. Thus, combined inoculation with selected mycorrhizae and bacteria led to synergistic effects. Such combinations may be used in future to improve plant growth in reclamation of CTS and tailings mix.

Irrigation and weed control alter soil microbiology and nutrient availability in North Carolina Sandhill peach orchards

Orchard management practices such as weed control and irrigation are primarily aimed at maximizing fruit yields and economic profits. However, the impact of these practices on soil fertility and soil microbiology is often overlooked. We conducted a two-factor experimental manipulation of weed control by herbicide and trickle irrigation in a nutrient-poor peach (Prunus persica L. cv. Contender) orchard near Jackson Springs, North Carolina. After three and eight years of treatments, an array of soil fertility parameters were examined, including soil pH, soil N, P and cation nutrients, microbial biomass and respiration, N mineralization, and presence of arbuscular mycorrhizal fungi (AMF). Three general trends emerged: 1) irrigation significantly increased soil microbial biomass and activity, 2) infection rate of mycorrhizal fungi within roots were significantly higher under irrigation than non-irrigation treatments, but no significant difference in the AMF community composition was detected among treatments, 3) weed control through herbicides reduced soil organic matter, microbial biomass and activity, and mineral nutrients, but had no significant impacts on root mycorrhizal infection and AMF communities. Weed-control treatments directly decreased availability of soil nutrients in year 8, especially soil extractable inorganic N. Weed control also appears to have altered the soil nutrients via changes in soil microbes and altered net N mineralization via changes in soil microbial biomass and activity. These results indicate that long-term weed control using herbicides reduces soil fertility through reducing organic C inputs, nutrient retention and soil microbes. Together, these findings highlight the need for alternative practices such as winter legume cover cropping that maintain and/or enhance organic inputs to sustain the soil fertility.

The growth and phosphorus acquisition of invasive plants Rudbeckia laciniata and Solidago gigantea are enhanced by arbuscular mycorrhizal fungi

While a number of recent studies have revealed that arbuscular mycorrhizal fungi (AMF) can mediate invasive plant success, the influence of these symbionts on the most successful and high-impact invaders is largely unexplored. Two perennial herbs of this category of invasive plants, Rudbeckia laciniata and Solidago gigantea (Asteraceae), were thus tested in a pot experiment to determine whether AMF influence their growth, the concentration of phosphorus in biomass, and photosynthesis. The following treatments, including three common AMF species, were prepared on soils representative of two habitats that are frequently invaded by both plants, namely fallow and river valley: (1) control-soil without AMF, (2) Rhizophagus irregularis, (3) Funneliformis mosseae, and (4) Claroideoglomus claroideum. The invaders were strongly dependent on AMF for their growth. The mycorrhizal dependency of R. laciniata was 88 and 63 % and of S. gigantea 90 and 82 % for valley and fallow soils, respectively. The fungi also increased P concentration in their biomass. However, we found different effects of the fungal species in the stimulation of plant growth and P acquisition, with R. irregularis and C. claroideum being the most and least effective symbionts, respectively. None of AMF species had an impact on the photosynthetic performance indexes of both plants. Our findings indicate that AMF have a direct effect on the early stages of R. laciniata and S. gigantea growth. The magnitude of the response of both plant species to AMF was dependent on the fungal and soil identities. Therefore, the presence of particular AMF species in a site may determine the success of their invasion.

DNA-Based Characterization and Identification of Arbuscular Mycorrhizal Fungi Species

Arbuscular mycorrhizal fungi (AMF) are obligate symbionts of most land plants. They have great ecological and economic importance as they can improve plant nutrition, plant water supply, soil structure, and plant resistance to pathogens. We describe two approaches for the DNA-based characterization and identification of AMF, which both can be used for single fungal spores, soil, or roots samples and resolve closely related AMF species: (a) Sanger sequencing of a 1.5 kb extended rDNA-barcode from clone libraries, e.g., to characterize AMF isolates, and (b) high throughput 454 GS-FLX+ pyrosequencing of a 0.8 kb rDNA fragment, e.g., for in-field monitoring.

Metal toxicity differently affects the Iris pseudacorus-arbuscular mycorrhiza fungi symbiosis in terrestrial and semi-aquatic habitats

Phytoremediation offers an environmental friendly alternative to conventional cleanup techniques. In this study, mycorrhizal fungi isolated from the roots of Mentha longifolia grown in the basin of the Centuria River (S Poland) were used. Iris pseudacorus was grown in substratum from an industrial waste, enriched in Pb, Fe, Zn, and Cd in a terrestrial and water-logged habitat. Plant yield and photosynthetic performance was the highest in the aquatic environment; however, the presence of toxic metals (TM) negatively affected photosystem II (PSII) photochemistry as shown by the JIP test. Fungi colonization and Cd accumulation within plant tissues was decreased. In the terrestrial habitat, neither arbuscular mycorrhizal fungi (AMF) nor metal toxicity affected plant growth, although metal uptake, Cd in particular, as well as photosynthesis were affected. Inoculated plants accumulated significantly more Cd, and photosynthesis was downregulated. The results presented in this study clearly indicate that the I. pseudacorus-AMF symbiosis adapts itself to the presence of toxic metals in the environment, optimizing resource supply, energy fluxes, and possibly stress tolerance mechanisms. Plant/AMF consortia grown in terrestrial and water-logged habitats utilize different strategies to cope with metal toxicity. The use of AMF in improving the phytoremediation potential of I. pseudacorus needs, however, further research.

Effect of combined microbes on plant tolerance to Zn-Pb contaminations

The presence and composition of soil microbial communities has been shown to have a large impact on plant-plant interactions and consequently plant diversity and composition. The goal of the present study was to evaluate impact of arbuscular mycorrhizal fungi (AMF) and nitrogen-fixing bacteria, which constitutes an essential link between the soil and the plant's roots. A greenhouse pot experiment was conducted to evaluate the feasibility of using selected microbes to improve Hieracium pilosella and Medicago sativa growth on Zn-Pb-rich site. Results of studies revealed that biomass, the dry mass of shoots and roots, increased significantly when plants were inoculated with mycorrhizal fungi and nitrogen-fixing bacteria. The addition of Azospirillum sp. and Nostoc edaphicum without mycorrhiza suppressed plant growth. Single bacterial inoculation alone does not have a positive effect on M. sativa growth, while co-inoculation with AMF improved plant growth. Plant vitality (expressed by the performance index) was improved by the addition of microbes. However, our results indicated that even dry heat sterilization of the substratum created imbalanced relationships between soil-plant and plants and associated microorganisms. The studies indicated that AMF and N2-fixers can improve revegetation of heavy metal-rich industrial sites, if the selection of interacting symbionts is properly conducted.

The influence of arbuscular mycorrhizal fungi inoculation on yam (Dioscorea spp.) tuber weights and secondary metabolite content

Arbuscular mycorrhizal fungi (AMF) are widely distributed in nature. They live in the roots of higher plants, in a symbiotic relationship. In this study, five commercial species of yams (Dioscorea spp.) were inoculated with six species of AMF, Glomus clarum, G. etunicatum, G. fasciculatum, Gigaspora sp., G. mosseae, and Acaulospora sp., in field cultivation conditions to investigate the influence of AMF inoculation on tuber weights and secondary metabolite content in yam tubers. The results showed that mycorrhizae formation rates ranged from 63.33% to 90%. G. etunicatum inoculation treatment increased the tube weights of the five species of yam tubers by 39%, 35%, 20%, 56%, and 40% for Tainung 1, Tainung 2, Ercih, Zihyuxieshu, and Tainung 5, respectively. The content of secondary metabolites, such as polyphenols, flavonoids, and anthocyanin, was significantly increased by the AMF treatment in tuber flesh and peel of all the tested yam species. Specifically, the maximums exchange of secondary metabolite contents increased to 40%, 42%, and 106% for polyphenols, flavonoids, and anthocyanin, respectively, in the tuber fresh. This study revealed that different species of yam had varying degrees of affinity with various AMF species; selecting effective AMF species is necessary to facilitate yam growth and improve the quality and quantity of yam tubers.

Root-inhabiting fungi in alien plant species in relation to invasion status and soil chemical properties

In order to recognize interactions between alien vascular plants and soil microorganisms and thus better understand the mechanisms of plant invasions, we examined the mycorrhizal status, arbuscular mycorrhizal fungi (AMF) colonization rate, arbuscular mycorrhiza (AM) morphology and presence of fungal root endophytes in 37 non-native species in Central Europe. We also studied the AMF diversity and chemical properties of soils from under these species. The plant and soil materials were collected in southern Poland. We found that 35 of the species formed AM and their mycorrhizal status depended on species identity. Thirty-three taxa had AM of Arum-type alone. Lycopersicon esculentum showed intermediate AM morphology and Eragrostis albensis developed both Arum and Paris. The mycelia of dark septate endophytes (DSE) were observed in 32 of the species, while sporangia of Olpidium spp. were found in the roots of 10. Thirteen common and worldwide occurring AMF species as well as three unidentified spore morphotypes were isolated from trap cultures established with the soils from under the plant species. Claroideoglomus claroideum, Funneliformis mosseae and Septoglomus constrictum were found the most frequently. The presence of root-inhabiting fungi and the intensity of their colonization were not correlated with soil chemical properties, plant invasion status, their local abundance and habitat type. No relationships were also found between the presence of AMF, DSE and Olpidium spp. These suggest that other edaphic conditions, plant and fungal species identity or the abundance of these fungi in soils might have an impact on the occurrence and intensity of fungal root colonization in the plants under study.

Increased photosynthetic acclimation in alfalfa associated with arbuscular mycorrhizal fungi (AMF) and cultivated in greenhouse under elevated CO2

Medicago sativa L. (alfalfa) can exhibit photosynthetic down-regulation when grown in greenhouse conditions under elevated atmospheric CO2. This forage legume can establish a double symbiosis with nitrogen fixing bacteria and arbuscular mycorrhizal fungi (AMF), which may increase the carbon sink effect of roots. Our aim was to assess whether the association of alfalfa with AMF can avoid, diminish or delay the photosynthetic acclimation observed in previous studies performed with nodulated plants. The results, however, showed that mycorrhizal (M) alfalfa at the end of their vegetative period had lower carbon (C) discrimination than non-mycorrhizal (NM) controls, indicating photosynthetic acclimation under ECO2 in plants associated with AMF. Decreased C discrimination was due to the acclimation of conductance, since the amount of Rubisco and the expression of genes codifying both large and small subunits of Rubisco were similar or slightly higher in M than in NM plants. Moreover, M alfalfa accumulated a greater amount of soluble sugars in leaves than NM plants, thus favoring a down-regulation effect on photosynthetic rates. The enhanced contents of sugars in leaves coincided with a reduced percentage of arbuscules in roots, suggesting decreased sink of carbohydrates from shoots to roots in M plants. The shorter life cycle of alfalfa associated with AMF in comparison with the NM controls may also be related to the accelerated photosynthetic acclimation in M plants. Further research is needed to clarify to what extent this behavior could be extrapolated to alfalfa cultivated in the field and subjected to periodic cutting of shoots under climatic change scenarios.

Risk management tools and the case study Brassica napus: evaluating possible effects of genetically modified plants on soil microbial diversity

The cultivation of GMPs in Europe raises many questions about the environmental risks, in particular about their ecological impact on non-target organisms and on soil properties. The aim of a multidisciplinary group engaged in a LIFE+project (MAN-GMP-ITA) was to validate and improve an existing environmental risk assessment (ERA) methodology on GMPs within the European legislative framework on GMOs. Given the impossibility of evaluating GMO impact directly, as GMPs are banned in Italy, GMPs have not been used at any stage of the project. The project thus specifically focused on the conditions for the implementation of ERA in different areas of Italy, with an emphasis on some sensitive and protected areas located in the North, Centre, and South of the country, in order to lay the necessary baseline for evaluating the possible effects of a GMP on soil communities. Our sub-group carried out soil analyses in order to obtain soil health and fertility indicators to be used as baselines in the ERA model. Using various methods of chemical, biochemical, functional and genetic analysis, our study assessed the changes in diversity and functionality of bacterial populations, and arbuscular mycorrhizal fungi. The results show that plant identity and growth, soil characteristics, and field site climatic parameters are key factors in contributing to variation in microbial community structure and diversity, thus validating our methodological approach. Our project has come to the conclusion that the uneven composition and biological-agronomical quality of soils need to be taken into consideration in a risk analysis within the framework of ERA for the release of genetically modified plants.

The arbuscular mycorrhizal Rhizophagus irregularis activates storage lipid biosynthesis to cope with the benzo[a]pyrene oxidative stress

The phytoremediation assisted by arbuscular mycorrhizal fungi (AMF) could constitute an ecological and economic method to restore polycyclic aromatic hydrocarbon (PAH) polluted soils. Unfortunately, little is known about the PAH impact on the beneficial symbiotic AMF. Using radiolabelling experiments, our work aims to understand how benzo[a]pyrene (B[a]P), a representative of high molecular weight PAH, acts on the AMF lipid metabolism. Our results showed decreases in the sterol precursors as well as in total phospholipid quantities, in link with the [1-(14)C]acetate incorporation decreases in these lipids. Interestingly, a concomitant increase of [1-(14)C]acetate incorporation by 29.5% into phosphatidylcholine with its content decrease in Rhizophagus irregularis extraradical mycelium was observed, suggesting a membrane regeneration. A second concomitant increase (estimated to 69%) of [1-(14)C]acetate incorporation into triacylglycerols (TAG) with the content decrease was also observed. This suggests a fungal TAG biosynthesis activation probably to offset the decrease in storage lipid content when the fungus was grown under B[a]P pollution. In addition, our findings showed that lipase activity was induced by more than 3 fold in the presence of B[a]P in comparison to the control indicating that the drop in TAG content could be a consequence of their active degradation. Taken together, our data suggest the involvement of the fungal TAG metabolism to cope B[a]P toxicity through two means: (i) by providing carbon skeletons and energy necessary for membrane regeneration and/or for B[a]P translocation and degradation as well as (ii) by activating the phosphatidic acid and hexose metabolisms which may be involved in cellular stress defence.

Differences in the arbuscular mycorrhizal fungi-improved rice resistance to low temperature at two N levels: aspects of N and C metabolism on the plant side

We performed an experiment to determine how N and C metabolism is involved in the low-temperature tolerance of mycorrhizal rice (Oryza sativa) at different N levels and examined the possible signaling molecules involved in the stress response of mycorrhizal rice. Pot cultures were performed, and mycorrhizal rice growth was evaluated based on treatments at two temperatures (15 °C and 25 °C) and two N levels (20 mg pot(-1) and 50 mg pot(-1)). The arbuscular mycorrhizal fungi (AMF) colonization of rice resulted in different responses of the plants to low and high N levels. The mycorrhizal rice with the low N supplementation had more positive feedback from the symbiotic AMF, as indicated by accelerated N and C metabolism of rice possibly involving jasmonic acid (JA) and the up-regulation of enzyme activities for N and C metabolism. Furthermore, the response of the mycorrhizal rice plants to low temperature was associated with P uptake and nitric oxide (NO).

Arbuscular mycorrhizal fungi influence decomposition of, but not plant nutrient capture from, glycine patches in soil

•  The contribution of different arbuscular mycorrhizal fungi (AMF) to nutrient capture from an organic patch, and the subsequent impact on root proliferation was investigated. •  Organic patches were created with glycine labelled with ¹⁵ N and ¹³ C. This allowed decomposition (as ¹³ CO₂ release) and uptake of nutrients (as ¹³ C and ¹⁵ N enrichments in the plant tissues) to be followed. Changes in root responses were followed in situ by the use of minirhizotrons and compared to responses in control (H₂ O) patches. •  Although there were differences in internal colonization and external mycelium production among the three AMF tested, none of the fungi responded to the presence of the glycine patch, and N and C capture was no different to uncolonized controls. However, the presence of glycine affected the manner in which colonized roots responded, particularly below the patch. The presence of AMF affected the decomposition of glycine. •  Root responses to the presence of N-rich patches appear more important than AMF responses.