Arbuscular mycorrhizas enhance nutrient uptake in different wheat genotypes at high salinity levels under field and greenhouse conditions

Effect of Claroideoglomus etunicatum and Indole-3-acetic Acid on Growth and Biochemical Properties of Vetiver Grass (Vetiveria zizanioides) Under Salinity Stress

Salinity represents a major environmental factor limiting plant growth and productivity. In order to better understand the effects of arbuscular mycorrhizal fungus Claroideoglomus etunicatum and Indole-3-acetic acid (IAA) on the growth and chemical composition of vetiver grass (Vetiveria zizanioides) under salt stress, a factorial experiment was conducted in a completely randomized design with three replications. The experiment included four NaCl levels (0, 8, 16, and 24 decisiemens per meter (dS/m)) and four levels of treatments (no amendment application, application of IAA, application of C. etunicatum, and interaction of IAA and C. etunicatum) with three replications. The results of the experiment showed that the addition of sodium chloride increased the concentration of proline and the activities of catalase, peroxidase, and superoxide dismutase enzymes. The application of the growth regulator (IAA) and C. etunicatum significantly increased the fresh and dry weight (101%) of shoots, dry weight of roots, and the concentration of macro- and micro-elements in shoots under salinity condition (99.82% phosphorus; 9.79% Iron). The application of mycorrhiza and auxin significantly reduced the concentration of proline and the activities of catalase, peroxidase, and superoxide dismutase enzymes. In general, the addition of IAA and C. etunicatum to roots under salt stress conditions can improve growth and increase the concentration of some nutrients in vetiver shoots.

Brassinosteroids mediate arbuscular mycorrhizal symbiosis through multiple potential pathways and partial identification in tomato

Currently, little is known regarding the specific processes through which brassinosteroids (BR) affect arbuscular mycorrhizal (AM) symbiosis. Understanding this relationship is vital for advancing plant physiology and agricultural applications. In this study, we aimed to elucidate the regulatory mechanisms of BR in AM symbiosis. According to the log2 fold change-value and adjP-value, we integrated the common differentially expressed genes (DEGs) in maize (Zea mays L.) treated with BR and AM, Arabidopsis (Arabidopsis thaliana) mutants deficient in BR receptors, and tomato (Solanum lycopersicum) plants inoculated with AM fungi. In addition, we characterized the symbiotic performance of tomato plants with BR receptor defects and overexpression. The results indicated that the common differential genes induced by BR and AM were involved in metabolic processes, such as cell wall modification, cytoskeleton remodeling, auxin and ethylene signaling, photosynthesis, mineral nutrient transport, and stress defense. Specifically, these include the BR1 gene, which modifies the cell wall. However, the fungal colonization rate of BR receptor-deficient tomato plants was significantly reduced, and the total phosphorus concentration was increased. Conversely, the performance of the overexpressing tomato transformation plants demonstrated a significant contrast. Additionally, the mild rescue of mycorrhizal attenuation in mutants treated with exogenous BR suggests the possibility of direct feedback from BR synthesis to AM. Notably, the cell wall modification gene (SlBR1) and calcium spike gene (SlIPD3) were induced by both BR and AM, suggesting that BR may influence cell penetration during the early stages of AM colonization. Synthesis: Our results demonstrated that BR positively regulates AM symbiosis through multiple pathways. These findings pave the way for future research, including isolation of the individual contributions of each pathway to this complex process and exploration of possible agricultural applications.

Role of mycorrhizas and root exudates in plant uptake of soil nutrients (calcium, iron, magnesium, and potassium): has the puzzle been completely solved?

Anthropogenic global change is driving an increase in the frequency and intensity of drought and flood events, along with associated imbalances and limitation of several soil nutrients. In the context of an increasing human population, these impacts represent a global-scale challenge for biodiversity conservation and sustainable crop production to ensure food security. Plants have evolved strategies to enhance uptake of soil nutrients under environmental stress conditions; for example, symbioses with fungi (mycorrhization) in the rhizosphere and the release of exudates from roots. Although crop cultivation is managed for the effects of limited availability of nitrogen (N) and phosphorus (P), there is increasing evidence for limitation of plant growth and fitness because of the low availability of other soil nutrients such as the metals potassium (K), calcium (Ca), magnesium (Mg), and iron (Fe), which may become increasingly limiting for plant productivity under global change. The roles of mycorrhizas and plant exudates on N and P uptake have been studied intensively; however, our understanding of the effects on metal nutrients is less clear and still inconsistent. Here, we review the literature on the role of mycorrhizas and root exudates in plant uptake of key nutrients (N, P, K, Ca, Mg, and Fe) in the context of potential nutrient deficiencies in crop and non-crop terrestrial ecosystems, and identify knowledge gaps for future research to improve nutrient-uptake capacity in food crop plants.

The biological and biochemical composition of wheat (Triticum aestivum) as affected by the bio and organic fertilizers

Microorganisms and organic compounds (humic and fulvic acid) offer viable alternatives to insecticides and mineral fertilizers. Even though many studies have shown the effects of biofertilizers and organic substances separately, little information is available on plant responses to the combined application of these bio-stimulants, even though these biological inputs have a high potential for simultaneous action. A two-year (2020/21-2021/22) field experiment was conducted to investigate the impact of organic and biofertilizers application on the growth, yield, and biochemical attributes of wheat (cv. Misr-1). Pre-planting, wheat seeds were inoculated with two biofertilizers including Mycorrhizae, and Azotobacter, and their combination (MIX), and control (un-inoculation) were considered the main plot factor. The subplot factor contained the foliar sprays of humic acid, fulvic acid, and control (no spray). The results revealed that the seed inoculation with mycorrhizae and azotobacter in combination with foliar-applied humic acid markedly (p ≤ 0.05) affected the growth, yield, and seed biochemical composition of wheat. Combination of mycorrhiza and azotobacter significantly (p ≤ 0.05) increased) plant height (100 cm), crop growth rate (18.69 g), number of spikelets per spike (22), biological yield (13.4 ton ha-1), grain yield (5.56 ton ha-1), straw yield (8.21 ton ha-1),), nitrogen (2.07%), phosphorous (0.91%), potassium (1.64%), protein content (12.76%), starch (51.81%), and gluten content (30.90%) compared to control. Among organic fertilizers, humic acid caused the maximum increase in plant height (93 cm), crop growth rate ( 15 g day-1 m-2),1000 grain weight (51 g), biological yield ( 11ton ha-1), grain yield (4.5 ton ha-1), protein content (11%), chlorophyll content (46 SPAD), and gluten (29.45%) as compared to all other treatments. The foliar application of humic acid combined with the mycorrhizae or azotobacter seed inoculation was efficient to induce wheat vegetative growth development, as well as yield and its components.

Plant Growth Promoting Rhizobacteria, Arbuscular Mycorrhizal Fungi and Their Synergistic Interactions to Counteract the Negative Effects of Saline Soil on Agriculture: Key Macromolecules and Mechanisms

Soil saltiness is a noteworthy issue as it results in loss of profitability and development of agrarian harvests and decline in soil health. Microorganisms associated with plants contribute to their growth promotion and salinity tolerance by employing a multitude of macromolecules and pathways. Plant growth promoting rhizobacteria (PGPR) have an immediate impact on improving profitability based on higher crop yield. Some PGPR produce 1-aminocyclopropane-1-carboxylic (ACC) deaminase (EC 4.1.99.4), which controls ethylene production by diverting ACC into α-ketobutyrate and ammonia. ACC deaminase enhances germination rate and growth parameters of root and shoot in different harvests with and without salt stress. Arbuscular mycorrhizal fungi (AMF) show a symbiotic relationship with plants, which helps in efficient uptake of mineral nutrients and water by the plants and also provide protection to the plants against pathogens and various abiotic stresses. The dual inoculation of PGPR and AMF enhances nutrient uptake and productivity of several crops compared to a single inoculation in both normal and stressed environments. Positively interacting PGPR + AMF combination is an efficient and cost-effective recipe for improving plant tolerance against salinity stress, which can be an extremely useful approach for sustainable agriculture.

Effect of Pisolithus tinctorious on Physiological and Hormonal Traits in Cistus Plants to Water Deficit: Relationships among Water Status, Photosynthetic Activity and Plant Quality

Cistus species can form ectomycorrhizae and arbuscular mycorrhizal fungus that can bring benefits when plants are under water stress conditions. However, the application of some ectomycorrhizae on the water uptake under drought through physiological traits and hormonal regulation is less known. The experiment was performed during three months in a growth chamber with Cistus albidus plants in which the combined effect of the ectomycorrhiza Pisolithus tinctorious inoculation and two irrigation treatments (control and water-stressed plants) were applied. Irrigation absence caused significant decrease in aerial growth and tended to decrease soil water potential at the root surface, leading to a decrease in leaf water potential. Under these conditions, the abscisic acid and salicylic acid content increased while the precursor of ethylene decreased. Although the mycorrhization percentages were not high, the inoculation of P. tinctorious improved the water status and slightly cushioned the rise in leaf temperature of water-stressed plants. The ectomycorrhiza decreased the scopoletin values in leaves of plants subjected to deficit irrigation, indicating that inoculated plants had been able to synthesize defense mechanisms. Therefore, Pisolithus tinctorious alleviated some of the harmful effects of water scarcity in Cistus plants, being its use a sustainable option in gardening or restoration projects.

Insights Into Microbially Induced Salt Tolerance and Endurance Mechanisms (STEM) in Plants

Salt stress threatens the achievement of sustainable global food security goals by inducing secondary stresses, such as osmotic, ionic, and oxidative stress, that are detrimental to plant growth and productivity. Various studies have reported the beneficial roles of microbes in ameliorating salt stress in plants. This review emphasizes salt tolerance and endurance mechanisms (STEM) in microbially inoculated (MI) plants that ensure plant growth and survival. Well-established STEM have been documented in MI plants and include conglomeration of osmolytes, antioxidant barricading, recuperating nutritional status, and ionic homeostasis. This is achieved via involvement of P solubilization, siderophore production, nitrogen fixation, selective ion absorption, volatile organic compound production, exopolysaccharide production, modifications to plant physiological processes (photosynthesis, transpiration, and stomatal conductance), and molecular alterations to alter various biochemical and physiological processes. Salt tolerance and endurance mechanism in MI plants ensures plant growth by improving nutrient uptake and maintaining ionic homeostasis, promoting superior water use efficiency and osmoprotection, enhancing photosynthetic efficiency, preserving cell ultrastructure, and reinforcing antioxidant metabolism. Molecular research in MI plants under salt stress conditions has found variations in the expression profiles of genes such as HKT1, NHX, and SOS1 (ion transporters), PIPs and TIPs (aquaporins), RBCS, RBCL (RuBisCo subunits), Lipoxygenase2 [jasmonic acid (JA) signaling], ABA (abscisic acid)-responsive gene, and APX, CAT, and POD (involved in antioxidant defense). Proteomic analysis in arbuscular mycorrhizal fungi-inoculated plants revealed upregulated expression of signal transduction proteins, including Ca2+ transporter ATPase, calcium-dependent protein kinase, calmodulin, and energy-related proteins (NADH dehydrogenase, iron-sulfur protein NADH dehydrogenase, cytochrome C oxidase, and ATP synthase). Future research should focus on the role of stress hormones, such as JA, salicylic acid, and brassinosteroids, in salt-stressed MI plants and how MI affects the cell wall, secondary metabolism, and signal transduction in host plants.

Do halophytes and glycophytes differ in their interactions with arbuscular mycorrhizal fungi under salt stress? A meta-analysis

BACKGROUND

Halophytes are better than glycophytes at employing mechanisms to avoid salt injury, but both types of plants can undergo damage due to high soil salinity. Arbuscular mycorrhizal fungi (AMF) can mitigate the damage from salt stress in both halophytes and glycophytes by enhancing salt tolerance and improving energy efficiency. However, variations in mycorrhizal symbiotic efficiency between halophytes and glycophytes were still poorly understood. Therefore, we evaluated the magnitude of AMF effects on plant growth and determined the mechanisms that regulate the growth response of halophytes and glycophytes by performing a meta-analysis of 916 studies (from 182 publications).

RESULTS

Arbuscular mycorrhizal fungi significantly enhance biomass accumulation, osmolytes synthesis (soluble sugar and soluble protein), nutrients acquisition (nitrogen, phosphorus, and potassium ion), antioxidant enzyme activities (superoxide dismutase and catalase), and photosynthetic capacity (chlorophyll and carotenoid contents, photosynthetic rate, stomatal conductance, and transpiration rate). AMF also substantially decreased sodium ion acquisition and malondialdehyde levels in both halophytes and glycophytes under salt stress conditions. Mycorrhizal halophytes deploy inorganic ions (potassium and calcium ions) and limited organic osmolytes (proline and soluble sugar) to achieve energy-efficient osmotic adjustment and further promote biomass accumulation. Mycorrhizal glycophytes depend on the combined actions of soluble sugar accumulation, nutrients acquisition, sodium ion exclusion, superoxide dismutase elevation, and chlorophyll synthesis to achieve biomass accumulation.

CONCLUSIONS

Arbuscular mycorrhizal fungi inoculation is complementary to plant function under salt stress conditions, not only facilitating energy acquisition but also redistributing energy from stress defence to growth. Glycophytes are more dependent on AMF symbiosis than halophytes under salt stress conditions.

Towards a Sustainable Agriculture: Strategies Involving Phytoprotectants against Salt Stress

Salinity is one of the main constraints for agriculture productivity worldwide. This important abiotic stress has worsened in the last 20 years due to the increase in water demands in arid and semi-arid areas. In this context, increasing tolerance of crop plants to salt stress is needed to guarantee future food supply to a growing population. This review compiles knowledge on the use of phytoprotectants of microbial origin (arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria), osmoprotectants, melatonin, phytohormones and antioxidant metabolism-related compounds as alleviators of salt stress in numerous plant species. Phytoprotectants are discussed in detail, including their nature, applicability, and role in the plant in terms of physiological and phenotype effects. As a result, increased crop yield and crop quality can be achieved, which in turn positively impact food security. Herein, efforts from academic and industrial sectors should focus on defining the treatment conditions and plant-phytoprotectant associations providing higher benefits.

A Review of Studies from the Last Twenty Years on Plant–Arbuscular Mycorrhizal Fungi Associations and Their Uses for Wheat Crops

The aim of this work was to summarize the most recent research focused on the study of plant–arbuscular mycorrhizal fungi (AMF) symbiosis, both in a generic context and in the specific context of wheat cultivation. Taking into account the last 20 years, the most significant studies on the main plant advantages taken from this association are reviewed herein. Positive advances that have been reported stem from the mutualistic relationship between the plant and the mycorrhizal fungus, revealing better performance for the host in terms of nutrient uptake and protection from salinity, lack of water, and excess phytotoxic elements. Mycorrhiza studies and the recent progress in research in this sector have shown a possible solution for environmental sustainability: AMF represent a valid alternative to overcome the loss of biological fertility of soils, reduce chemical inputs, and alleviate the effects of biotic and abiotic stress.

Biogeochemical distribution of Pb and Zn forms in two calcareous soils affected by mycorrhizal symbiosis and alfalfa rhizosphere

Using of arbuscular mycorrhizal fungi (AMF) has emerged as a new technique to alleviate the toxic metals stress through changing their chemical behavior. The present work was conducted as a factorial arrangement based on a completely randomized design to study the inoculation effects of Glomus intraradices, Glomus mosseae and Glomus etunicatum, on Pb and Zn fractions in the rhizosphere of alfalfa by using rhizobox technique in two agricultural soils with different Zn and Pb concentrations [with low (LH) and high (HH) concentration levels]. The results showed that AMF colonization promoted plant growth and lowered the shoot and root Pb and shoot Zn concentrations in the studied soils compared to uninoculated treatments. Mycorrhizal colonization significantly increased the Ca(NO₃)₂- extractable Zn and ORG-Zn (respectively 500 and 59.6% more than the uninoculated treatment) and decreased the OXI-Zn (20.32% less than the none inoculated treatment) in the HH soil. By contrast, mycorrhizae slightly increased the CARB, OXI and ORG-Zn forms in the LH soil compared to the uninoculation condition. In the AMF- treated HH soil, an increase was recorded in the Ca(NO₃)₂- extractable Pb, EXCH-Pb and CARB-Pb (respectively, 17.65, 3.09 and 14.22% compared to the none inoculated treatment) and a decrease in the OXI and ORG-Pb forms (respectively, 28.79 and 13.51% compared to the uninoculated treatment). A reverse status was observed for Pb changes in the LH soil. Depending on the contamination level, the mycorrhizal inoculation differentially affected the Pb and Zn fractions at different distances from the root surface. In the LH soil, at <5 mm distance (i.e. rhizospheric soil), the mycorrhizal inoculation decreased the CARB (about 17.99%) and OXI -Zn (about 29.63%) forms compared to bulk soil (i.e. > 5 mm distance) while ORG-Zn was increased up to 48.63%. However, Ca(NO₃)₂- extractable, CARB and ORG-Pb was increased in rhizosphere soil (respectively, 89.33, 3.84 and 6.14%) and OXI-Pb was decreased up to 10.36% compared to the bulk soil. In the HH soil, mycorrhizal inoculation increased the CARB and OXI-Zn (respectively, 1.76 and 5.71%) and OXI-Pb fractions (11.56%) compared to the <5 mm distances. Whereas, it reduced the Ca(NO₃)₂- extractable, EXCH, and ORG-Zn (Respectively, 52.70, 19.19 and 30.16%) and Ca(NO₃)₂- extractable, CARB and ORG-Pb (respectively, 47.18, 3.70 and 5.79%). These results revealed that depending on the soil contamination level and nature of the element, AMF colonization affects biogeochemical fractions of the metals and their accumulation in the plant tissues.

Arbuscular Mycorrhizal Symbiosis Modulates Antioxidant Response and Ion Distribution in Salt-Stressed Elaeagnus angustifolia Seedlings

Elaeagnus angustifolia L. is a drought-resistant species. Arbuscular mycorrhizal symbiosis is considered to be a bio-ameliorator of saline soils that can improve salinity tolerance in plants. The present study investigated the effects of inoculation with the arbuscular mycorrhizal fungus Rhizophagus irregularis on the biomass, antioxidant enzyme activities, and root, stem, and leaf ion accumulation of E. angustifolia seedlings grown during salt stress conditions. Salt-stressed mycorrhizal seedlings produced greater root, stem, and leaf biomass than the uninoculated stressed seedlings. In addition, the seedlings colonized by R. irregularis showed notably higher activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) in the leaves of the mycorrhizal seedlings in response to salinity compared to those of the non-mycorrhizal seedlings. Mycorrhizal seedlings not only significantly increased their ability to acquire K⁺, Ca²⁺, and Mg²⁺, but also maintained higher K⁺:Na⁺ ratios in the leaves and lower Ca²⁺:Mg²⁺ ratios than non-mycorrhizal seedlings during salt stress. These results suggest that the salt tolerance of E. angustifolia seedlings could be enhanced by R. irregularis. The arbuscular mycorrhizal symbiosis could be a promising method to restore and utilize salt-alkaline land in northern China.

Arbuscular mycorrhiza effects on plant performance under osmotic stress

At present, drought and soil salinity are among the most severe environmental stresses that affect the growth of plants through marked reduction of water uptake which lowers water potential, leading to osmotic stress. In general, osmotic stress causes a series of morphological, physiological, biochemical, and molecular changes that affect plant performance. Several studies have found that diverse types of soil microorganisms improve plant growth, especially when plants are under stressful conditions. Most important are the arbuscular mycorrhizal fungi (AMF) which form arbuscular mycorrhizas (AM) with approximately 80% of plant species and are present in almost all terrestrial ecosystems. Beyond the well-known role of AM in improving plant nutrient uptake, the contributions of AM to plants coping with osmotic stress merit analysis. With this review, we describe the principal direct and indirect mechanisms by which AM modify plant responses to osmotic stress, highlighting the role of AM in photosynthetic activity, water use efficiency, osmoprotectant production, antioxidant activities, and gene expression. We also discuss the potential for using AMF to improve plant performance under osmotic stress conditions and the lines of research needed to optimize AM use in plant production.

Genetics of mycorrhizal symbiosis in winter wheat (Triticum aestivum)

Bread wheat (Triticum aestivum) is a major staple food and therefore of prime importance for feeding the Earth's growing population. Mycorrhiza is known to improve plant growth, but although extensive knowledge concerning the interaction between mycorrhizal fungi and plants is available, genotypic differences concerning the ability of wheat to form mycorrhizal symbiosis and quantitative trait loci (QTLs) involved in mycorrhization are largely unknown. Therefore, a diverse set of 94 bread wheat genotypes was evaluated with regard to root colonization by arbuscular mycorrhizal fungi. In order to identify genomic regions involved in mycorrhization, these genotypes were analyzed using the wheat 90k iSelect chip, resulting in 17 823 polymorphic mapped markers, which were used in a genome-wide association study. Significant genotypic differences (P < 0.0001) were detected in the ability to form symbiosis and 30 significant markers associated with root colonization, representing six QTL regions, were detected on chromosomes 3A, 4A and 7A, and candidate genes located in these QTL regions were proposed. The results reported here provide key insights into the genetics of root colonization by mycorrhizal fungi in wheat.

Influence of arbuscular mycorrhizal fungi and treated wastewater on water relations and leaf structure alterations of Viburnum tinus L. plants during both saline and recovery periods

Nowadays, irrigation with low quality water is becoming an alternative to satisfy the needs of crops. However, some plant species have to deal with high salinity of reclaimed water, by adapting their physiological behaviour during both saline and recovery periods and developing morphological changes in their leaves. The application of arbuscular mycorrhizal fungi (AMF) could also be a suitable option to mitigate the negative effects of this kind of water, although the effectiveness of plant-AMF association is influenced by many factors. In this work, during forty weeks, the combined effect of Glomus iranicum var. tenuihypharum and two types of water: control, C, EC<0.9 dS m(-1) and reclaimed water, RW (with EC: 4 dS m(-1) during a first saline period and EC: 6 dS m(-1) during a second saline period) was evaluated for laurustinus plants (Viburnum tinus L.) transplanted in soil. This was followed by a recovery period of eight weeks, when all the plants were irrigated in the control irrigation conditions. Seasonal and daily changes in stem water potential (Ψstem), stomatal conductance (gs), photosynthesis (Pn) and leaf internal CO2 concentration (Ci) of laurustinus plants were evaluated. Leaf structure alterations, nutrient imbalance, height and leaf hydraulic conductivity (Kleaf) were also determined. Due to the high difficulty of absorbing water from the soil, RW plants showed a high volumetric water content (θv) in soil. The stem water potential and the stomatal conductance (gs) values were reduced in RW plants throughout the second saline period. These decreases were also found during the day. Leaf Ca(2+)/Na(+) and K(+)/Na(+) ratios diminished in RW plants respect to the C plants due to the Na(+) accumulation, although height and chlorophyll content values did not show statistical differences. Leaves from RW plants showed a significantly thicker mesophyll than Control leaves as a consequence of high EC. The area of palisade parenchyma (PP) increased while the area of spongy parenchyma (SP) decreased in RW leaves with respect to the C leaves. These structural changes could be considered as a strategy to maximize photosynthesis potential in saline conditions. Mycorrhizal inoculation improved the water status of both C and RW plants by increasing their Ψstem and gs values. As regards leaf structure, AMF showed an opposite effect to salinity for PP and SP. At the end of the recovery period, hardly any statistical differences of physiological parameters were found between treatments, although a tendency to improve them was observed in inoculated plants. In any case, the leaf structural changes and the great reduction in Kleaf observed at Ψleaf below -1.5 MPa would constitute an important mechanism for laurustinus plants to reduce the water loses produced by salinity.

Protective effects of Glomus iranicum var. tenuihypharum on soil and Viburnum tinus plants irrigated with treated wastewater under field conditions

Currently, irrigation using recycled water is increasing, especially in semiarid environments, but a potential problem of using reclaimed wastewater is its elevated salt levels. The application of arbuscular mycorrhizal fungi (AMF) could be a suitable option to mitigate the negative effects produced by the salinity. In this work, the combined effect of Glomus iranicum var. tenuihypharum and two types of water: Control, C, with EC <0.9 dS m(-1) and reclaimed water (wastewater previously treated in a sewage treatment plant) with EC 4 dS m(-1) during a first saline period (11 weeks) and with EC 6 dS m(-1) during a second saline period (25 weeks), was evaluated for laurustinus (Viburnum tinus) plants under field conditions. This plant is a popular shrub very used for gardening. Chemical properties of soil as well as physiological behavior, leaf nutrition, and esthetic value of plants were evaluated. Due to the high salinity from wastewater at 6 dS m(-1), laurustinus plants decreased their stem water potential values and, to a lesser extent, the stomatal conductance. Also, the visual quality of the plants was diminished. The inoculated AMF satisfactorily colonized the laurustinus roots and enhanced the structure of the soil by increasing the glomalin and carbon contents. Furthermore, G. iranicum var. tenuihypharum inoculation decreased Na and Cl content, stimulated flowering and improved the stem water potential of the plants irrigated with both types of reclaimed water. The AMF also had a positive effect as a consequence of stimulation of plant physiological parameters, such as the stem water potential and stomatal conductance. Effective AMF associations that avoid excessive salinity could provide wastewater reuse options, especially when the plants grow in soils.

Evidence that arbuscular mycorrhizal and phosphate-solubilizing fungi alleviate NaCl stress in the halophyte Kosteletzkya virginica: nutrient uptake and ion distribution within root tissues

The effects of an arbuscular mycorrhizal (AM) fungus, Glomus mosseae, and a phosphate-solubilizing microorganism (PSM), Mortierella sp., and their interactions, on nutrient (N, P and K) uptake and the ionic composition of different root tissues of the halophyte Kosteletzkya virginica (L.), cultured with or without NaCl, were evaluated. Plant biomass, AM colonization and PSM populations were also assessed. Salt stress adversely affected plant nutrient acquisition, especially root P and K, resulting in an important reduction in shoot dry biomass. Inoculation of the AM fungus or/and PSM strongly promoted AM colonization, PSM populations, plant dry biomass, root/shoot dry weight ratio and nutrient uptake by K. virginica, regardless of salinity level. Ion accumulation in root tissues was inhibited by salt stress. However, dual inoculation of the AM fungus and PSM significantly enhanced ion (e.g., Na(+), Cl(-), K(+), Ca(2+), Mg(2+)) accumulation in different root tissues, and maintained lower Na(+)/K(+) and Ca(2+)/Mg(2+) ratios and a higher Na(+)/Ca(2+) ratio, compared to non-inoculated plants under 100 mM NaCl conditions. Correlation coefficient analysis demonstrated that plant (shoot or root) dry biomass correlated positively with plant nutrient uptake and ion (e.g., Na(+), K(+), Mg(2+) and Cl(-)) concentrations of different root tissues, and correlated negatively with Na(+)/K(+) ratios in the epidermis and cortex. Simultaneously, root/shoot dry weight ratio correlated positively with Na(+)/Ca(2+) ratios in most root tissues. These findings suggest that combined AM fungus and PSM inoculation alleviates the deleterious effects of salt on plant growth by enabling greater nutrient (e.g., P, N and K) absorption, higher accumulation of Na(+), K(+), Mg(2+) and Cl(-) in different root tissues, and maintenance of lower root Na(+)/K(+) and higher Na(+)/Ca(2+) ratios when salinity is within acceptable limits.

Current developments in arbuscular mycorrhizal fungi research and its role in salinity stress alleviation: a biotechnological perspective

Arbuscular mycorrhizal fungi (AMF) form widespread symbiotic associations with 80% of known land plants. They play a major role in plant nutrition, growth, water absorption, nutrient cycling and protection from pathogens, and as a result, contribute to ecosystem processes. Salinity stress conditions undoubtedly limit plant productivity and, therefore, the role of AMF as a biological tool for improving plant salt stress tolerance, is gaining economic importance worldwide. However, this approach requires a better understanding of how plants and AMF intimately interact with each other in saline environments and how this interaction leads to physiological changes in plants. This knowledge is important to develop sustainable strategies for successful utilization of AMF to improve plant health under a variety of stress conditions. Recent advances in the field of molecular biology, "omics" technology and advanced microscopy can provide new insight about these mechanisms of interaction between AMF and plants, as well as other microbes. This review mainly discusses the effect of salinity on AMF and plants, and role of AMF in alleviation of salinity stress including insight on methods for AMF identification. The focus remains on latest advancements in mycorrhizal research that can potentially offer an integrative understanding of the role of AMF in salinity tolerance and sustainable crop production.

Arbuscular mycorrhizal fungi native from a Mediterranean saline area enhance maize tolerance to salinity through improved ion homeostasis

Soil salinity restricts plant growth and productivity. Na(+) represents the major ion causing toxicity because it competes with K(+) for binding sites at the plasma membrane. Inoculation with arbuscular mycorrhizal fungi (AMF) can alleviate salt stress in the host plant through several mechanisms. These may include ion selection during the fungal uptake of nutrients from the soil or during transfer to the host plant. AM benefits could be enhanced when native AMF isolates are used. Thus, we investigated whether native AMF isolated from an area with problems of salinity and desertification can help maize plants to overcome the negative effects of salinity stress better than non-AM plants or plants inoculated with non-native AMF. Results showed that plants inoculated with two out the three native AMF had the highest shoot dry biomass at all salinity levels. Plants inoculated with the three native AMF showed significant increase of K(+) and reduced Na(+) accumulation as compared to non-mycorrhizal plants, concomitantly with higher K(+) /Na(+) ratios in their tissues. For the first time, these effects have been correlated with regulation of ZmAKT2, ZmSOS1 and ZmSKOR genes expression in the roots of maize, contributing to K(+) and Na(+) homeostasis in plants colonized by native AMF.