Arbuscular Mycorrhizal Fungus "Rhizophagus irregularis" impacts on physiological and biochemical responses of ryegrass and chickpea plants under beryllium stress

Differential AMF-mediated biochemical responses in sorghum and oat plants under environmental impacts of neodymium nanoparticles

This study investigates the impact of neodymium (Nd) nanoparticle (NdNP) toxicity on the physiological and biochemical responses of sorghum (Sorghum bicolor) and oat (Avena sativa) plants and evaluates the potential mitigating effects of arbuscular mycorrhizal fungi (AMF). Sorghum and oat plants were grown under controlled conditions with and without AMF inoculation, and subjected to NdNPs (500 mg Nd kg-1 soil). Results revealed that Nd nanoparticles significantly reduced biomass in both species, with a 50% decrease in sorghum and a 59% decrease in oats. However, AMF treatment ameliorated these effects, increasing biomass by 69% in oats under Nd nanoparticles toxicity compared to untreated contaminated plants. Soluble sugar metabolism was notably affected; AMF treatment led to significant increases in fructose and sucrose contents in both sorghum (+31% and +23%, respectively) and oat (+25% and +37%, respectively) plants under NdNPs toxicity. Improved sugar metabolism via enhanced activities of sucrose phosphate synthase (+29-54%) and invertase (+39-54%) enzymes resulted in higher proline (+21-81%) and polyamines (+49-52%) levels in AMF-treated plants under NdNPs toxicity, along with alterations in the biosynthesis pathways of amino acids and fatty acids, resulting in better osmoprotection and stress tolerance. Moreover, citrate (+29-55%) and oxalate (+177-312%) levels increased in both plants in response to NdNPs toxicity, which was accompanied by a positive response of isobutyric acid to AMF treatment in stressed plants, which potentially might serve as mechanisms for plants to mitigate NdNPs toxicity. These findings suggest that AMF can significantly mitigate Nd-induced damage and improve plant resilience through enhanced metabolic adjustments, highlighting a potential strategy for managing rare earth element (REE) nanoparticle toxicity in agricultural soils.

Comparative analysis of biodiversity, physiology, and anatomical adaptations in riparian flora exposed to industrial pollution stress

Anthropogenic activities such as industrial pollution of water bodies possess threat to floras leading to extinction and endangerment. This study investigates the impact of industrial pollution on vegetation along River Chenab and its associated drains. Rivers and channels transporting industrial effluents have been determined to be significantly contaminated. The contamination was evidenced by the acidic and alkaline nature of industrial effluents, salinity, total dissolved solids, and the sodium absorption ratio. The research revealed that the pollution in the region severely impacts the native vegetation, resulting in a marked decline in density, frequency, relative density, and relative frequency across 10 sites, including three drain sites and one non-polluted site. Four plant species, Calotropis procera, Eclipta alba, Phyla nodiflora, and Ranunculus sceleratus exhibited tolerance to pollution and were present at all sites during all seasons. Anatomical modifications, such as increased root aerenchyma and vascular bundles, enabled these plants to thrive in polluted environments. The study highlights the importance of these species in phytoremediation and their potential for use in restoring degraded ecosystems.

Inoculation with Micromonospora sp. enhances carbohydrate and amino acid production, strengthening antioxidant metabolism to mitigate heat stress in wheat cultivars

Introduction

Heat stress caused by global warming adversely affects wheat yield through declining most nutritional quality attributes in grains, excluding grain protein content.

Methods

This research investigated the biochemical, physiological, and antioxidant responses of wheat plants under heat stress, focusing on the role of plant growth-promoting bacteria (Micromonospora sp.). Two wheat genotypes were studied: one heat-sensitive and one heat-tolerant, examining their responses to heat stress with and without bacterial inoculation.

Results

Under heat stress, the sensitive cultivar experienced significant reductions in photosynthesis rate, chlorophyll content, and RuBisCO activity (57-61%), while the tolerant cultivar had milder reductions (24-28%). Micromonospora sp. treatment notably improved these parameters in the sensitive cultivar (+48-78%), resulting in a substantial increase in biomass production (+43-53%), which was not seen in the tolerant cultivar. Additionally, oxidative stress markers (H2O2 and MDA) were elevated more in the sensitive cultivar (82% and 90% higher) compared to the tolerant one. Micromonospora sp. treatment effectively reduced these markers in the sensitive cultivar (-28% and -27%). Enhanced activity of antioxidant enzymes and ASC-GSH pathway enzymes was particularly evident in Micromonospora sp.-treated sensitive plants. Carbohydrate metabolism shifted, with increased soluble sugars and significant rises in sucrose content in Micromonospora sp.-treated plants under stress.

Discussion

The higher soluble sugar levels facilitated amino acid synthesis, contributing to biosynthesis of secondary metabolites, including flavonoids, polyphenols, and anthocyanins. This was reflected in increased activity of phenylalanine ammonia-lyase, cinnamate (CA) 4-hydroxylase, and chalcone synthase enzymes, indicating the activation of phenylpropanoid pathways. Overall, the findings suggest that Micromonospora sp. can mitigate heat stress effects by enhancing photosynthetic efficiency, antioxidant defense, and metabolic adaptations in heat-sensitive wheat cultivars.

Optimizing mycorrhizal fungi application for improved nutrient uptake, growth, and disease resistance in cardamom seedlings (Elettaria cardamomum (L.) Maton)

This study evaluated the impact of various doses (5, 10, 15 g) and application sequences (1, 2, or 3 times at monthly intervals) of arbuscular mycorrhizal (AM) fungal inoculum on cardamom seedlings over two years (2020-2021 and 2021-2022). The results indicated that the dosage of AM inoculum had a more substantial effect on the seedlings than the application sequence. A 10 g dose significantly increased shoot length and dry weight, while three applications of 5 g each improved the number of fibrous roots. Although potassium uptake was not affected, phosphorus and calcium uptake were highest with the 10 g dose. Arbuscular mycorrhizal inoculation also enhanced phosphatase activity in the rhizosphere, with 5 g improving acid phosphatase and 10 g improving alkaline phosphatase activity. Disease incidence, including seedling rot was lower with the 10 g dose, and additional sequential applications did not further reduce disease. Structural equation modeling (SEM) revealed that AM colonization positively influenced dry weight through the number of fibrous roots, showing a strong relationship between AM dose, colonization, spore count, and mycorrhizal dependency. This study indicates that applying a 10 g dose of AM fungal inoculum can be particularly beneficial in agroecosystems for improving cardamom seedling growth, nutrient uptake, and disease resistance.

Synergistic Effect of Arbuscular Mycorrhizal Fungi and Germanium on the Growth, Nutritional Quality, and Health-Promoting Activities of Spinacia oleracea L

Arbuscular mycorrhizal fungi (AMF) and the antioxidant germanium (Ge) are promising tools for boosting bioactive compound synthesis and producing healthier foods. However, their combined effect remains unexplored. This study demonstrates the synergistic impact of AMF and Ge on the growth, metabolite accumulation, biological activities, and nutritional qualities of Spinacia oleracea L. (spinach), a globally significant leafy vegetable. Individually, Ge and AMF increased biomass by 68.1% and 22.7%, respectively, while their combined effect led to an 86.3% increase. AMF and Ge also improved proximate composition, with AMF-Ge interaction enhancing crude fiber and mineral content (p < 0.05). Interestingly, AMF enhanced photosynthesis-related parameters (e.g., total chlorophyll) in Ge treated plants, which in turn increased carbohydrate accumulation. This accumulation could provide a route for the biosynthesis of amino acids, organic acids, and fatty acids, as evidenced by increased essential amino acid and organic acid levels. Consistently, the activity of key enzymes involved in amino acids biosynthesis (e.g., glutamine synthase (GS), methionine biosynthase (MS), lysine biosynthase (LS)) showed significant increments. Furthermore, AMF improved fatty acid levels, particularly unsaturated fatty acids in Ge-treated plants compared to the control. In addition, increased phenylalanine provided a precursor for the production of antioxidants (e.g., phenols and flavonoids), through the action of the enzyme phenylalanine ammonia-lyase (PAL), resulting in improved antioxidant activity gains as indicated by FRAP, ABTS, and DPPH assays. This study is the first to show that Ge enhances the beneficial effect of AMF on spinach, improving growth and nutritional quality, with promising implications for agricultural practices.

Copper mitigates salinity stress by regulating water status, photosynthetic pigments and ion homeostasis and increases the yield of Eggplant (Solanum melongena)

Eggplant (Solanum melongena) is moderately sensitive to salinity. Seed priming and exogenous supplementation are technique that enhances germination, growth, and crop yield by overcoming salt stress. Therefore, this study was designed to understand the role of seed priming and copper (Cu) supplementation in modulating salt tolerance in eggplant. When exposed to salt stress, eggplant seedlings showed significantly higher Na+ content, an increased Na/K ratio, prolonged mean germination time, higher relative water loss, more days to flower bud initiation and first flowering, along with decreased germination rate, growth factors, water content, photosynthetic pigments, ionic contents (K+, Ca2+, Mg2+), and yield. The results demonstrated that the germination rate, final germination percentage, germination index, germination energy, and seed vigor index significantly improved, while the mean germination time decreased in Cu-primed seeds. The results also revealed that Cu supplementations increased seedling traits, leaf water content, photosynthetic pigment contents, ionic contents (K+, Ca2+, and Mg2+), and yield while decreasing the contents of Na+, and Na/K ratio, mean germination time, relative water loss, days to flower bud initiation, and days to 1st flowering under salt stress. Germination of seeds, seedlings growth traits, plant water status, plant pigments, yield, and ionic contents with the NaCl and Cu treatments were found to substantially interact with each other according to both hierarchical clustering and PCA. Overall, Cu seed priming and exogenous supplementation emerged as a promising strategy to enhance salt tolerance and promote germination, growth, and yield by regulating water status, photosynthetic pigments, and ion homeostasis in eggplant seedlings under NaCl stress. These findings provide valuable insights into the mechanisms of Cu-mediated stress alleviation in eggplant, with implications for sustainable crop production in saline environments.

Ethylene is the key phytohormone to enhance arsenic resistance in Arabidopsis thaliana

The toxic metalloid arsenic is prevalent in the environment and poses a threat to nearly all organisms. However, the mechanism by which phytohormones modulate arsenic resistance is not well-understood. Therefore, we analyzed multiple phytohormones based on the results of transcriptome sequencing, content changes, and related mutant growth under arsenic stress. We found that ethylene was the key phytohormone in Arabidopsis thaliana response to arsenic. Further investigation showed the ethylene-overproducing mutant eto1-1 generated less malondialdehyde (MDA), H2O2, and O2•- under arsenic stress compared to wild-type, while the ethylene-insensitive mutant ein2-5 displayed opposite patterns. Compared to wild-type, eto1-1 accumulated a smaller amount of arsenic and a larger amount of non-protein thiols. Additionally, the immediate ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), enhanced resistance to arsenic in wide-type, but not in mutants with impaired detoxification capability (i.e., cad1-3, pad2-1, abcc1abcc2), which confirmed that ethylene regulated arsenic detoxification by enhancing arsenic chelation. ACC also upregulated the expression of gene(s) involved in arsenic detoxification, among which ABCC2 was directly transcriptionally activated by the ethylene master transcription factor ethylene-insensitive 3 (EIN3). Overall, our study shows that ethylene is the key phytohormone to enhance arsenic resistance by reducing arsenic accumulation and promoting arsenic detoxification at both physiological and molecular levels.

Modulation of cherry tomato performances in response to molybdenum biofortification and arbuscular mycorrhizal fungi in a soilless system

Molybdenum (Mo) is a crucial microelement for both, humans and plants. The use of agronomic biofortification techniques can be an alternative method to enhance Mo content in vegetables. Concomitantly, arbuscular mycorrhizal fungi (AMF) application is a valuable strategy to enhance plant performances and overcome plant abiotic distresses such as microelement overdose. The aim of this research was to estimate the direct and/or indirect effects of Mo supply at four doses [0.0, 0.5 (standard dose), 2.0 or 4.0 μmol L-1], alone or combined with AMF inoculation, on plant performances. In particular, plant height and first flower truss emission, productive features (total yield, marketable yield and average marketable fruit weight) and fruit qualitative characteristics (fruit dry matter, soluble solids content, titratable acidity, ascorbic acid, lycopene, polyphenol, nitrogen, copper, iron and molybdenum) of an established cherry tomato genotype cultivated in soilless conditions were investigated. Moreover, proline and malondialdehyde concentrations, as well as Mo hazard quotient (HQ) in response to experimental treatments were determined. A split-plot randomized experimental block design with Mo dosages as plots and +AMF or -AMF as sub-plots was adopted. Data revealed that AMF inoculation enhanced marketable yield (+50.0 %), as well as some qualitative traits, such as fruit soluble solids content (SSC) (+9.9 %), ascorbic acid (+7.3 %), polyphenols (+2.3 %), and lycopene (+2.5 %). Molybdenum application significantly increased SSC, polyphenols, fruit Mo concentration (+29.0 % and +100.0 % in plants biofortified with 2.0 and 4.0 μmol Mo L-1 compared to those fertigated with the standard dose, respectively) and proline, whereas it decreased N (-25.0 % and -41.6 % in plants biofortified with 2.0 and 4.0 μmol Mo L-1 compared to those fertigated with the standard dose, respectively). Interestingly, the application of AMF mitigated the detrimental effect of high Mo dosages (2.0 or 4.0 μmol L-1). A pronounced advance in terms of plant height 45 DAT, fruit lycopene concentration and fruit Fe, Cu and Mo concentrations was observed when AMF treatment and Mo dosages (2.0 or 4.0 μmol Mo L-1) were combined. Plants inoculated or not with AMF showed an improvement in the hazard quotient (HQ) in reaction to Mo application. However, the HQ - for a consumption of 200 g day-1 of biofortified cherry tomato - remained within the safety level for human consumption. This study suggests that Mo-implementation (at 2.0 or 4.0 μmol L-1) combined with AMF inoculation could represent a viable cultivation protocol to enhance yield, produce premium quality tomato fruits and, concomitantly, improve Mo dose in human diet. In the light of our findings, further studies on the interaction between AMF and microelements in other vegetable crops are recommended.

Drought-Tolerant Bacteria and Arbuscular Mycorrhizal Fungi Mitigate the Detrimental Effects of Drought Stress Induced by Withholding Irrigation at Critical Growth Stages of Soybean (Glycine max, L.)

Considering current global climate change, drought stress is regarded as a major problem negatively impacting the growth of soybeans, particularly at the critical stages R3 (early pod) and R5 (seed development). Microbial inoculation is regarded as an ecologically friendly and low-cost-effective strategy for helping soybean plants withstand drought stress. The present study aimed to isolate newly drought-tolerant bacteria from native soil and evaluated their potential for producing growth-promoting substances as well as understanding how these isolated bacteria along with arbuscular mycorrhizal fungi (AMF) could mitigate drought stress in soybean plants at critical growth stages in a field experiment. In this study, 30 Bradyrhizobium isolates and 30 rhizobacterial isolates were isolated from the soybean nodules and rhizosphere, respectively. Polyethylene glycol (PEG) 6000 was used for evaluating their tolerance to drought, and then the production of growth promotion substances was evaluated under both without/with PEG. The most effective isolates (DTB4 and DTR30) were identified genetically using 16S rRNA gene. A field experiment was conducted to study the impact of inoculation with DTB4 and DTR30 along with AMF (Glomus clarum, Funneliformis mosseae, and Gigaspora margarita) on the growth and yield of drought-stressed soybeans. Our results showed that the bioinoculant applications improved the growth traits (shoot length, root length, leaf area, and dry weight), chlorophyll content, nutrient content (N, P, and K), nodulation, and yield components (pods number, seeds weight, and grain yield) of soybean plants under drought stress (p ≤ 0.05). Moreover, proline contents were decreased due to the bioinoculant applications under drought when compared to uninoculated treatments. As well as the count of bacteria, mycorrhizal colonization indices, and the activity of soil enzymes (dehydrogenase and phosphatase) were enhanced in the soybean rhizosphere under drought stress. This study's findings imply that using a mixture of bioinoculants may help soybean plants withstand drought stress, particularly during critical growth stages, and that soybean growth, productivity, and soil microbial activity were improved under drought stress.

Characterization of arbuscular mycorrhizal fungal species associating with Zea mays

Taxonomic identification of arbuscular mycorrhizal (AM) fungal spores extracted directly from the field is sometimes difficult because spores are often degraded or parasitized by other organisms. Single-spore inoculation of a suitable host plant allows for establishing monosporic cultures of AM fungi. This study aimed to propagate AM fungal spores isolated from maize soil using single spores for morphological characterization. First, trap cultures were established to trigger the sporulation of AM fungal species. Second, trap cultures were established with individual morphotypes by picking up only one spore under a dissecting microscope and transferring it to a small triangle of sterilized filter paper, which was then carefully inoculated below a root from germinated sorghum seeds in each pot and covered with a sterile substrate. All pots were placed in sunbags and maintained in a plant growth room for 120 days. Spores obtained from single spore trap cultures from each treatment, maize after oats (MO), maize after maize (MM), maize after peas (MP), and maize after soybean (MS), were extracted using the sieving method. Healthy spores were selected for morphological analysis. Direct PCR was conducted by crushing spores in RNAlater and applying three sets of primer pairs: ITS1 × ITS4, NS31 × AML2, and SSUmcf and LSUmBr. Nucleotide sequences obtained from Sanger sequencing were aligned on MEGA X. The phylogenetic tree showed that the closest neighbors of the propagated AM fungal species belonged to the genera Claroideoglomus, Funneliformis, Gigaspora, Paraglomus, and Rhizophagus. The morphological characteristics were compared to the descriptive features of described species posted on the INVAM website, and they included Acaulospora cavernata, Diversispora spurca, Funneliformis geosporus, Funneliformis mosseae, Gigaspora clarus, Gigaspora margarita, Glomus macrosporum, Paraglomus occultum, and Rhizophagus intraradices. These findings can provide a great contribution to crop productivity and sustainable management of the agricultural ecosystem. Also, the isolate analyzed could be grouped into efficient promoters of growth and mycorrhization of maize independent of their geographical location.

The pleiotropic role of Salinicoccus bacteria in enhancing ROS homeostasis and detoxification metabolism in soybean and oat to cope with pollution of triclosan

Triclosan has been extensively used as a preservative in cosmetics and personal care products. However, its accumulation represents a real environmental threat. Thus, its phytotoxic impact needs more consideration. Our study was conducted to highlight the phytotoxic effect of triclosan on the growth, ROS homeostasis, and detoxification metabolism of two different plant species i.e., legumes (Glycine max) and grass (Avena sativa). Moreover, we investigated the potentiality of plant growth-promoting bacteria (ST-PGPB) in mitigating the phytotoxic effect of triclosan. Triclosan induced biomass (fresh and dry weights) reduction in both plants, but to a higher extent in oats. This decline was associated with a noticeable increment in the oxidative damage (e.g., MDA and H2O2) and detoxification metabolites such as metallothionein (MTC), phytochelatins (PCs), and glutathione-S-transferase (GST). This elevation was associated with a remarkable reduction in both enzymatic and non-enzymatic antioxidants. On the other hand, the bioactive strain of ST-PGPB, Salinicoccus sp. JzA1 significantly alleviated the harmful effect of triclosan on both soybean and oat plants by enhancing their biomass, photosynthesis, as well as levels of minerals (K, Ca, P, Mn, and Zn). In parallel, a striking quenching in oxidative damage and an obvious improvement in non-enzymatic (polyphenols, tocopherols, flavonoids) and enzymatic antioxidants were observed. Furthermore, Salinicoccus sp. JzA1 augmented the detoxification metabolism by enhancing the levels of phytochelatins, metallothionein, and glutathione-S-transferase (GST) activity in a species-specific manner which is more apparent in soybean rather than in oat plants. To this end, stress mitigating impact of Salinicoccus sp. JzA1 provides a basis to improve the resilience of crop species under cosmetics and personal care products toxicity.

Enhancing alfalfa photosynthetic performance through arbuscular mycorrhizal fungi inoculation across varied phosphorus application levels

This study evaluated the effects of arbuscular mycorrhizal fungi inoculation on the growth and photosynthetic performance of alfalfa under different phosphorus application levels. This experiment adopts two-factors completely random design, and sets four levels of fungi application: single inoculation with Funneliformis mosseae (Fm, T1), single inoculation with Glomus etunicatum (Ge, T2) and mixed inoculation with Funneliformis mosseae × Glomus etunicatum (Fm×Ge, T3) and treatment uninfected fungus (CK, T0). Four phosphorus application levels were set under the fungi application level: P2O5 0 (P0), 50 (P1), 100 (P2) and 150 (P3) mg·kg-1. There were 16 treatments for fungus phosphorus interaction. The strain was placed 5 cm below the surface of the flowerpot soil, and the phosphate fertilizer was dissolved in water and applied at one time. The results showed that the intercellular CO2 concentration (Ci) of alfalfa decreased at first and then increased with the increase of phosphorus application, except for light use efficiency (LUE) and leaf instantaneous water use efficiency (WUE), other indicators showed the opposite trend. The effect of mixed inoculation (T3) was significantly better than that of non-inoculation (T0) (p < 0.05). Pearson correlation analysis showed that Ci was significantly negatively correlated with alfalfa leaf transpiration rate (Tr) and WUE (p < 0.05), and was extremely significantly negatively correlated with other indicators (p < 0.01). The other indexes were positively correlated (p < 0.05). This may be mainly because the factors affecting plant photosynthesis are non-stomatal factors. Through the comprehensive analysis of membership function, the indexes of alfalfa under different treatments were comprehensively ranked, and the top three were: T3P2>T3P1>T1P2. Therefore, when the phosphorus treatment was 100 mg·kg-1, the mixed inoculation of Funneliformis mosseae and Glomus etunicatum had the best effect, which was conducive to improving the photosynthetic efficiency of alfalfa, increasing the dry matter yield, and improving the economic benefits of local alfalfa in Xinjiang. In future studies, the anatomical structure and photosynthetic performance of alfalfa leaves and stems should be combined to clarify the synergistic mechanism of the anatomical structure and photosynthetic performance of alfalfa.

The effects of microbial fertilizers application on growth, yield and some biochemical changes in the leaves and seeds of guar (Cyamopsis tetragonoloba L.)

Guar (Cyamopsis tetragonoloba L.) is a summer legume that is becoming a crucial industrial crop because of its high gum and protein content. Thus far, the combined effects of arbuscular mycorrhizal fungi (AMF) and Bradyrhizobium on the yield and chemical composition of guar plants are not well studied. Therefore, the current investigation was designed to estimate the individual as well as the combined effects of AMF and Bradyrhizobium on plant growth, yield and nutritional quality of seeds and leaves of guar. AMF and/or Bradyrhizobium inoculation improved chemical composition of guar seeds and its morpho-physiological (plant height, fresh weight, dry weight, and yield production) traits. In addition to increased guar growth and yield production, the inoculation of AMF and/or Bradyrhizobium increased guar leaf and seed minerals, fiber, lipids, crude protein and ash contents. At primary metabolites, there were increases in sugar levels including raffinose stachyose, verbascose and galactomannan. These increases in sugar provided a route for organic acids, amino acids and fatty acids production. Interestingly, there was an increase in essential amino acids and unsaturated fatty acids. At the bioactive secondary metabolite levels, biofertilizers improved phenols and flavonoids levels and anthocyanin and polyamines biosynthesis. In line with these increases, precursors of anthocyanin (phenylalanine, p-coumaric acid, and cinnamic acid) and the levels of polyamines (diaminopropane, putrescine, cadaverine, spermidine, spermine, and agmatine) were increased. Overall, for the first time, our study shed the light on how AMF and Bradyrhizobium improved guar yield and metabolism. Our findings suggested that the combined inoculation of AMF and Bradyrhizobium is an innovative approach to improve guar growth, yield production and yield quality.

Arbuscular mycorrhizal fungi as an effective approach to enhance the growth and metabolism of soybean plants under thallium (TI) toxicity

Thallium (TI) is a toxic metal that can trigger harmful impacts on growth and metabolism of plants. Utilizing arbuscular mycorrhizal fungi (AMF) proves to be an effective strategy for alleviating heavy metal toxicity in plants. To this end, AMF were applied to mitigate TI toxic effects on the growth, primary and secondary metabolism of soybean plants. Here, TI stress inhibited the growth and photosynthetic parameters of soybean plants. It also increased the oxidative damage as demonstrated by increased levels of oxidative markers, (MDA and lipoxygenase (LOX) activity). However, AMF could mitigate the reduction in growth and photosynthesis induced by TI, as well as the induction of oxidative damage. To overcome TI toxicity, AMF increased the levels and metabolism of osmolytes such as proline in soybean plants. This was in line with the increased activities of key enzymes that involved in proline biosynthesis (e.g., P5CS (pyrroline-5-carboxylate synthetase), P5CR (pyrroline-5-carboxylate reductase) and OAT (ornithine aminotransferase) under the AMF and/or TI treatments. Furthermore, soybean plants could benefit from the synergism between AMF and TI to enhance the contents of individual (e.g., spermine and spermidine) and total polyamines as well as their metabolic enzymes (e.g., arginine decarboxylase and ornithine decarboxylase). Overall, the combined application of AMF emerges as a viable approach for alleviating TI toxicity in soybean plants.

Elevated CO2 differentially attenuates beryllium-induced oxidative stress in oat and alfalfa

Elevated CO2 (eCO2 ) is one of the climate changes that may benefit plant growth under emerging soil contaminants such as heavy metals. In this regard, the morpho-physiological mechanisms underlying the mitigating impact of eCO2 on beryllium (Be) phytotoxicity are poorly known. Hence, we investigated eCO2 and Be interactive effects on the growth and metabolism of two species from different groups: cereal (oat) and legume (alfalfa). Be stress significantly reduced the growth and photosynthetic attributes in both species, but alfalfa was more susceptible to Be toxicity. Be stress induced reactive oxygen species (ROS) accumulation by increasing photorespiration, subsequently resulting in increased lipid and protein oxidation. However, the growth inhibition and oxidative stress induced by Be stress were mitigated by eCO2 . This could be explained, at least partially, by the increase in organic acids (e.g., citric acid) released into the soil, which subsequently reduced Be uptake. Additionally, eCO2 reduced cellular oxidative damage by reducing photorespiration, which was more significant in alfalfa plants. Furthermore, eCO2 improved the redox status and detoxification processes, including phytochelatins, total glutathione and metallothioneins levels, and glutathione-S-transferase activity in both species, but to a greater extend in alfalfa. In this context, eCO2 also stimulated anthocyanin biosynthesis by accumulating its precursors (phenylalanine, coumaric acid, cinnamic acid, and naringenin) and key biosynthetic enzymes (phenylalanine ammonia-lyase, cinnamate hydroxylase, and coumarate:CoA ligase) mainly in alfalfa plants. Overall, this study explored the mechanistic approach by which eCO2 alleviates the harmful effects of Be. Alfalfa was more sensitive to Be stress than oats; however, the alleviating impact of eCO2 on Be stress was more pronounced in alfalfa.

Impact of Water Shortage on Soil and Plant Attributes in the Presence of Arbuscular Mycorrhizal Fungi from a Harsh Environment

Arbuscular mycorrhizal fungi (AMF) play a crucial role in plant health due to their ability to improve tolerance to biotic and abiotic stresses. Our aim was to evaluate the effectiveness of a pool of native AMF from a harsh environment on plant performance and changes in soil attributes under different levels of drought. An experiment using maize was established, varying the soil water content to simulate severe drought (30% of the water-holding capacity [WHC]), moderate (50% of the WHC) and no drought (80% of the WHC, control treatment). Soil and plant attributes were measured (enzyme activity, microbial biomass, AMF root colonisation and plant biomass and nutrient uptake). There was a two-fold increase in plant biomass under moderate drought when compared to no drought treatment, but there was no difference in nutrient uptake. Under severe drought, there were the highest enzyme activities related to phosphorus (P) cycling and P microbial biomass, indicating higher P microbial immobilization. The increase in AMF root colonisation was observed in plants under moderate and no drought. Our findings demonstrated that the better use of the AMF inoculum varied according to drought levels, with better performance under moderate drought due to the increase in plant biomass.

Response of Sagebrush Steppe Grass Species to AMF Inoculum Sources and Biochar

The sagebrush steppe has presented increasing levels of degradation. The addition of arbuscular mycorrhizal fungi (AMF) and biochar have been suggested to restore ecosystems. However, little is known about their effects on sagebrush steppe plants. We tested three sources of AMF inoculum: soil from a disturbed site (Inoculum A), soil from an undisturbed site (Inoculum B), and commercial inoculum (Inoculum C), all with and without biochar, to test if they could mediate growth of Pseudoroegneria spicata (native perennial), Taeniatherum caput-medusae (early seral; exotic annual) and Ventenata dubia (early seral; exotic annual) under greenhouse conditions. We measured AMF colonization and biomass. We hypothesized that the plant species would be differently affected by the inoculum types. The colonization of T. caput-medusae and V. dubia was greatest when inoculated with Inoculum A (38.8% and 19.6%). In contrast, the colonization of P. spicata was greatest with Inoculum B and Inoculum C (32.1% and 32.2). Biochar decreased biomass production but increased colonization with Inoculum A for P. spicata and V. dubia and with Inoculum C for T. caput-medusae. This study reveals the response of early and late seral sagebrush steppe grass species to contrasting sources of AMF and suggests that late seral plant species respond better to late seral inocula.

Beryllium contamination and its risk management in terrestrial and aquatic environmental settings

Beryllium (Be) is a relatively rare element and occurs naturally in the Earth's crust, in coal, and in various minerals. Beryllium is used as an alloy with other metals in aerospace, electronics and mechanical industries. The major emission sources to the atmosphere are the combustion of coal and fossil fuels and the incineration of municipal solid waste. In soils and natural waters, the majority of Be is sorbed to soil particles and sediments. The majority of contamination occurs through atmospheric deposition of Be on aboveground plant parts. Beryllium and its compounds are toxic to humans and are grouped as carcinogens. The general public is exposed to Be through inhalation of air and the consumption of Be-contaminated food and drinking water. Immobilization of Be in soil and groundwater using organic and inorganic amendments reduces the bioavailability and mobility of Be, thereby limiting the transfer into the food chain. Mobilization of Be in soil using chelating agents facilitates their removal through soil washing and plant uptake. This review provides an overview of the current understanding of the sources, geochemistry, health hazards, remediation practices, and current regulatory mandates of Be contamination in complex environmental settings, including soil and aquatic ecosystems.

Metabolomics reveals arbuscular mycorrhizal fungi-mediated tolerance of walnut to soil drought

BACKGROUND

Arbuscular mycorrhizal fungi (AMF) have a positive effect on drought tolerance of plants after establishing reciprocal resymbiosis with roots, while the underlying mechanism is not deciphered. Metabolomics can explain the mechanism of plant response to environmental stress by analyzing the changes of all small molecular weight metabolites. The purpose of this study was to use Ultra High Performance Liquid Chromatography Q Exactive Mass Spectrometer to analyze changes in root metabolites of walnut (Juglans regia) after inoculation with an arbuscular mycorrhizal fungus Diversispora spurca under well-watered (WW) and drought stress (DS).

RESULTS

Sixty days of soil drought significantly inhibited root mycorrhizal colonization rate, shoot and root biomass production, and leaf water potential in walnut, while AMF inoculation significantly increased biomass production and leaf water potential, accompanied by a higher increase magnitude under DS versus under WW. A total of 3278 metabolites were identified. Under WW, AMF inoculation up-regulated 172 metabolites and down-regulated 61 metabolites, along with no changes in 1104 metabolites. However, under DS, AMF inoculation up-regulated 49 metabolites and down-regulated 116 metabolites, coupled with no changes in 1172 metabolites. Among them, juglone (a quinone found in walnuts) as the first ranked differential metabolite was up-regulated by AMF under WW but not under DS; 2,3,5-trihydroxy-5-7-dimethoxyflavanone as the first ranked differential metabolite was increased by AMF under DS but not under WW. The KEGG annotation showed a large number of metabolic pathways triggered by AMF, accompanied by different metabolic pathways under WW and DS. Among them, oxidative phosphorylation and phenylalanine metabolism and biosynthesis were triggered by AMF in response to WW and DS, where N-acetyl-L-phenylalanine was induced by AMF to increase under DS, while decreasing under WW.

CONCLUSION

This study provides new insights into the metabolic mechanisms of mycorrhiza-enhanced drought tolerance in walnuts.

What Are the Effects of Moso Bamboo Expansion into Japanese Cedar on Arbuscular Mycorrhizal Fungi: Altering the Community Composition Rather than the Diversity

The unbridled expansion of moso bamboo (Phyllostachys edulis) occurs throughout the world and has a series of consequences. However, the effect of bamboo expansion on arbuscular mycorrhizal fungi (AMF) is still poorly understood. We assessed the changes in the AMF community during bamboo expansion into Japanese cedar (Cryptomeria japonica) forests by analyzing AMF in three forest types-Japanese cedar (JC), bamboo-cedar mixed (BC) and moso bamboo (MB)-using 454 pyrosequencing technology. We found that the AMF community composition differed significantly among forest types. The relative abundance of Glomerales decreased from 74.0% in JC to 61.8% in BC and 42.5% in MB, whereas the relative abundance of Rhizophagus increased from 24.9% in JC to 35.9% in BC and 56.7% in MB. Further analysis showed that soil characteristics explained only 19.2% of the AMF community variation among forest types. Hence, vegetation is presumably the main driver of the alteration of the AMF community. The α diversity of AMF was similar between JC and MB, although it was higher in BC. Overall, this research sheds more light on AMF community dynamics during moso bamboo expansion. Our results highlight that the consequences of bamboo expansion in monoculture forests differ from those in mixed forests.

Regulation mechanism of plant response to heavy metal stress mediated by endophytic fungi

Endophytic fungi exist widely in plants and play an important role in the growth and adaptation of plants. They could be used in phytoremediation techniques against heavy metal contaminated soil since beneficial microbial symbionts can endow plants with resistance to external heavy metal stresses. This review summarized the regulation mechanism of plant response to heavy metal stress mediated by endophytic fungi. Potential endophytic fungi in enhancing plant's adaption to heavy metal stresses include arbuscular mycorrhizal fungi, dark septate endophytic fungi, plant growth promoting endophytic fungi. The mechanisms involve coevolution strategy, immune regulation and detoxification transport to improve the ability of plants to adapt to heavy metal stress. They can increase the synthesis of host hormones and maintaining the balance of endogenous hormones, strengthen osmotic regulation, regulate carbon and nitrogen metabolism, and increase immune activity, antioxidant enzyme and glutathione activity. They also help to improve the detoxification transport and heavy metal emission capacity of the host by significantly producing iron carrier, metallothionein and 1-aminocyclopropane-1-carboxylic acid deaminase. The combination of endophytic fungi and hyperaccumulation plants provides a promising technology for the ecological restoration of heavy metal contaminated soil. Endophytic fungi reserves further development on enhancing host plant's adaptability to heavy metal stresses.