Effects of arbuscular mycorrhizal fungi on the growth, photosynthesis and photosynthetic pigments of Leymus chinensis seedlings under salt-alkali stress and nitrogen deposition

Effects of plasma-activated water on germination ‎and initial seedling growth of wheat

In this research, the effect of seed halopriming with plasma activated water (PAW) on wheat germination parameters have been studied. Response surface methodology was used to investigate the effect of three factors including: 1) type of water (distilled water, 0.2 and 0.4 min/mL PAW), 2) priming time (1, 3 and 5 h), and 3) salinity of the priming solution (0, 25 and 50 mmol/L NaCl) on wheat germination parameters. The results revealed that increasing PAW levels up to 0.18 min/mL led to an increase in seed germination percentage, seedling weight (both fresh and dry), seedling length, vigor indexes A and B, and water uptake and decreasing mean germination time. Increasing the level of PAW by more than 0.18 min/mL had a negative effect on these parameters. The fresh and dry weight of the seedlings respectively at the 0.18 and 0.2 min/mL levels of PAW, in all salinity levels, had the highest value. The effect of halopriming on enhancing seedling length was more than other characteristics. The optimum ranges of PAW, salinity and priming time were 0.13 min/mL, 10.3 mmol/L and 120.22 min for germination percentage, 0.18 min/mL, 15 mmol/L and 191.24 min for seedling fresh weight, 0.15 min/mL, 13.84 mmol/L and 221.2 min for seedling dry weight, 0.33 min/mL, 24.36 mmol/L and 152.62 min for mean germination time, 0.11 min/mL, 19.03 mmol/L and 177.77 min for vigor indexes A and 0.1 min/mL, 18.1 mmol/L and 178.99 min for vigor indexes B.

Optimum Nitrogen and Phosphorus Combination Improved Yield and Nutrient Use Efficiency of Sorghum in Saline Soil

Two-year experiments were conducted to assess the responses of yield and nutrient use efficiency of sorghum to nitrogen and phosphorus under saline soils. Three nitrogen rates (0, 180, and 360 N kg ha-1) and three phosphorus rates (0, 60, and 120 P2O5 kg ha-1) were used in this study. Our results showed that nitrogen and phosphorus supply increased SPAD (leaf greenness, 5.0-29.1%), NSC (non-structural carbohydrates, 14.0-41.2%), nutrient accumulation (nitrogen: 14.1-50.0%, phosphorus: 11.8-41.5%, potassium: 13.7-28.2%), biomass (fresh: 10.8-29.3%, dry: 5.0-22.8%), yield (16.6-30.7%), and harvest index (2.0-9.8%) of sorghum at the maturity stage grown in saline soils but significantly decreased nutrient use efficiency. Combined application showed better performance on these attributes than sole nitrogen and sole phosphorus. The highest seed yield (5919 kg ha-1) was recorded at 180 N kg ha-1 and 60 P2O5 kg ha-1 treatment, while the largest value of dry biomass (18,401 kg ha-1) was obtained at 360 N kg ha-1 and 120 P2O5 kg ha-1 treatment. The Pearson analysis showed that seed yield had the highest correlation with aerial potassium accumulation, while dry biomass had the highest correlation with NSC as well as aerial nitrogen accumulation. A treatment of 180 N kg ha-1 and 60 P2O5 kg ha-1 was recommended to be used in sorghum production in saline soils based on harvest index and nutrient use efficiency.

Advances and mechanisms of fungal symbionts in improving the salt tolerance of crops

Soil salinization leads to reduced crop yields and waste of land resources, thereby impacting global food security. To meet the increasing demand for food and simultaneously alleviate pressure on soil resources, the development of sustainable agriculture is imperative. In contrast to physical and chemical methods, bioremediation represents an efficient and environmentally friendly approach. Fungal symbionts have been found to be associated with most plants in natural ecosystems, colonizing and residing within the internal tissues of host plants. Moreover, the potential of fungal symbionts in improving saline-alkaline soil has been widely recognized and confirmed. Numerous reports have documented the effectiveness of arbuscular mycorrhizal fungi in alleviating salt stress in plants. Meanwhile, research on other endophytic fungi for mitigating plant salt stress has emerged in recent years, which contributes to refining mechanisms for enhancing plant salt tolerance. In this review, we summarized various mechanisms by which endophytic fungi enhance plant salt tolerance. We also provided an overview of the challenges and development directions in the field of fungal symbiosis, with the aim of offering a viable strategy for the bioremediation of saline-alkali soils.

Co-application of biochars and Piriformospora indica improved the quality of coastal saline soil and promoted the growth of forage

Soil quality is defined as the ability of soil to maintain the soil environment and the biosphere. Due to the limitation of salt and alkali stress, soil quality can be reduced, which in turn affects agricultural production. Biochar is widely used in saline-alkali land improvement because of its special pore structure and strong ion exchange ability, while Piriformospora indica is widely used in saline-alkali land improvement because it can symbiose with plants and improve plant stress resistance. However, the synergistic effect of combined biochar application and inoculation of P. indica on the quality of saline-alkali soil and plant development is uncertain. Hence, we investigated the combined influences of biochar and P. indica on the soil physicochemical characteristics, as well as the growth and chlorophyll florescence of sorghum-sudangrass hybrids (Sorghum bicolor × Sorghum sudane) in our study. The results indicated that after applying biochar and P. indica together, there was a considerable drop in soil pH, conductivity, Na+, and Cl- concentrations. Meanwhile, the soil organic matter (SOM), available phosphorus (AP), and alkaline hydrolyzable nitrogen (AN) increased by 151.81%, 50.84%, and 103.50%, respectively, when the Bamboo biochar was combined with 120 ml/pot of P. indica. Eventually, sorghum-sudangrass hybrid biomass, transpiration rate, and chlorophyll content increased by 111.69%, 204.98%, and 118.54%, respectively. According to our findings, using P. indica and biochar together can enhance soil quality and plant growth. The results also provide insights to enhance the quality of saline-alkali soils and the role of microorganisms in nutrient cycling.

Overexpression of phosphoenolpyruvate carboxylase kinase gene MsPPCK1 from Medicago sativa L. increased alkali tolerance of alfalfa by enhancing photosynthetic efficiency and promoting nodule development

The phosphoenolpyruvate carboxylase kinase of Medicago sativa L. (MsPPCK1) modulates the phosphorylation status and activity of the C4 pathway phosphoenolpyruvate carboxylase enzyme, which is pivotal for photosynthetic carbon assimilation in plants. This study investigated the role of MsPPCK1 in alfalfa by creating transgenic plants overexpressing MsPPCK1 under the control of the CaMV35S promoter. The enhanced alkali tolerance of transgenic plants indicated an important role of MsPPCK1 gene in regulating plant alkali tolerance. Transgenic plants exhibited heightened antioxidant activity (SOD, POD, and CAT), reduced MDA, H2O2, OFR and REC% content, increased activity of key photosynthetic enzymes (PEPC, PPDK, NADP-ME, and NADP-MDH), and enhanced photosynthetic parameters (Pn, E, Gs, and Ci). Moreover, MsPPCK1 overexpression increased the content of organic acids (oxaloacetic, malic, citric, and succinic acids) in the plants. The upregulation of MsPPCK1 under rhizobial inoculation showcased its other role in nodule development. In transgenic plants, MsDMI2, MsEnod12, and MsNODL4 expression increased, facilitating root nodule development and augmenting plant nodulation. Accelerated root nodule growth positively influences plant growth and yield and enhances alfalfa resistance to alkali stress. This study highlights the pivotal role of MsPPCK1 in fortifying plant alkali stress tolerance and improving yield, underscoring its potential as a key genetic target for developing alkali-tolerant and high-yielding alfalfa varieties.

Effect of salt-alkali stress on seed germination of the halophyte Halostachys caspica

The increasing global phenomenon of soil salinization has prompted heightened interest in the physiological ecology of plant salt and alkali tolerance. Halostachys caspica belonging to Amaranthaceae, an exceptionally salt-tolerant halophyte, is widely distributed in the arid and saline-alkali regions of Xinjiang, in Northwest China. Soil salinization and alkalinization frequently co-occur in nature, but very few studies focus on the interactive effects of various salt and alkali stress on plants. In this study, the impacts on the H. caspica seed germination, germination recovery and seedling growth were investigated under the salt and alkali stress. The results showed that the seed germination percentage was not significantly reduced at low salinity at pH 5.30-9.60, but decreased with elevated salt concentration and pH. Immediately after, salt was removed, ungerminated seeds under high salt concentration treatment exhibited a higher recovery germination percentage, indicating seed germination of H. caspica was inhibited under the condition of high salt-alkali stress. Stepwise regression analysis indicated that, at the same salt concentrations, alkaline salts exerted a more severe inhibition on seed germination, compared to neutral salts. The detrimental effects of salinity or high pH alone were less serious than their combination. Salt concentration, pH value, and their interactions had inhibitory effects on seed germination, with salinity being the decisive factor, while pH played a secondary role in salt-alkali mixed stress.

Azolla filiculoides extract improved salt tolerance in wheat (Triticum aestivum L.) is associated with prompting osmostasis, antioxidant potential and stress-interrelated genes

The growth and productivity of crop plants are negatively affected by salinity-induced ionic and oxidative stresses. This study aimed to provide insight into the interaction of NaCl-induced salinity with Azolla aqueous extract (AAE) regarding growth, antioxidant balance, and stress-responsive genes expression in wheat seedlings. In a pot experiment, wheat kernels were primed for 21 h with either deionized water or 0.1% AAE. Water-primed seedlings received either tap water, 250 mM NaCl, AAE spray, or AAE spray + NaCl. The AAE-primed seedlings received either tap water or 250 mM NaCl. Salinity lowered growth rate, chlorophyll level, and protein and amino acids pool. However, carotenoids, stress indicators (EL, MDA, and H2O2), osmomodulators (sugars, and proline), antioxidant enzymes (CAT, POD, APX, and PPO), and the expression of some stress-responsive genes (POD, PPO and PAL, PCS, and TLP) were significantly increased. However, administering AAE contributed to increased growth, balanced leaf pigments and assimilation efficacy, diminished stress indicators, rebalanced osmomodulators and antioxidant enzymes, and down-regulation of stress-induced genes in NaCl-stressed plants, with priming surpassing spray in most cases. In conclusion, AAE can be used as a green approach for sustaining regular growth and metabolism and remodelling the physio-chemical status of wheat seedlings thriving in salt-affected soils.

Arbuscular Mycorrhizal Fungi-Mediated Modulation of Physiological, Biochemical, and Secondary Metabolite Responses in Hemp (Cannabis sativa L.) under Salt and Drought Stress

The increasing impact of global climate change has resulted in adversity stresses, like salt and drought, gradually becoming the main factors that limit crop growth. Hemp, which contains numerous medicinal active components and multiple bioactive functions, is widely used in the agricultural, industrial, and medical fields, hence promoting the rapid development of related industries. Arbuscular mycorrhizal fungi (AMF) can establish a symbiotic relationship with 80% of vascular plants. This symbiosis promotes host plant growth, regulates plant physiology and biochemistry, facilitates secondary metabolite synthesis, and enhances resistance to abiotic stresses. However, the effects of salt stress, drought stress, and AMF interaction in hemp are not well understood. In this study, to investigate this, we performed a study where we cultured hemp that was either inoculated or uninoculated with Funneliformis mosseae and determined changes in effective colonization rate, growth, soluble substances, photosynthesis, fluorescence, ions, and secondary metabolites by cultivating hemp under different concentrations of NaCl (0 mM, 100 mM, and 200 mM) and different soil moisture content (45%, 25%, and 15%). The results showed that salt, drought stress, or salt-drought interaction stress all inhibited colonization rate after stress, plant growth, mainly due to ion toxicity and oxidative damage. Inoculation with F. mosseae effectively alleviated plant growth inhibition under 100 mM NaCl salt stress, drought stress, and salt-drought interaction stress conditions. It also improved osmoregulation, photosynthetic properties, fluorescence properties, and ion homeostasis, and promoted the accumulation of secondary metabolites. However, under 200 mM NaCl salt stress conditions, inoculation with F. mosseae negatively affected plant physiology, biochemistry, and secondary metabolite synthesis, although it did alleviate growth inhibition. The results demonstrate that there are different effects of salt-drought interaction stress versus single stress (salt or drought stress) on plant growth physiology. In addition, we provide new insights about the positive effects of AMF on host plants under such stress conditions and the effects of AMF on plants under high salt stress.

Transcriptomic and physiological analyses of Trichoderma citrinoviride HT-1 assisted phytoremediation of Cd contaminated water by Phragmites australis

Plant growth promoting microbe assisted phytoremediation is considered a more effective approach to rehabilitation than the single use of plants, but underlying mechanism is still unclear. In this study, we combined transcriptomic and physiological methods to explore the mechanism of plant growth promoting microbe Trichoderma citrinoviride HT-1 assisted phytoremediation of Cd contaminated water by Phragmites australis. The results show that the strain HT-1 significantly promoted P. australis growth, increased the photosynthetic rate, enhanced antioxidant enzyme activities. The chlorophyll content and the activity of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) were increased by 83.78%, 23.17%, 47.60%, 97.14% and 12.23% on average, and decreased the content of malondialdehyde (MDA) by 31.10%. At the same time, strain HT-1 improved the absorption and transport of Cd in P. australis, and the removal rate of Cd was increased by 7.56% on average. Transcriptome analysis showed that strain HT-1 induced significant up-regulated the expression of genes related to oxidative phosphorylation and ribosome pathways, and these upregulated genes promoted P. australis remediation efficiency and resistance to Cd stress. Our results provide a mechanistic understanding of plant growth promoting microbe assisted phytoremediation under Cd stress.

Warming affects leaf light use efficiency and functional traits in alpine plants: evidence from a 4-year in-situ field experiment

Introduction

Light use efficiency (LUE) is a crucial determinant of plant productivity, while leaf functional traits directly affect ecosystem functions. However, it remains unclear how climate warming affects LUE and leaf functional traits of dominant species in alpine meadows.

Methods

We conducted a 4-year in-situ field warming experiment to investigate the eco-physiological characteristics for a dominant species (Elymus nutans) and a common species (Potentilla anserina) on the Tibetan Plateau. The leaf traits, photosynthesis and fluorescence characteristics were measured, along with the soil physical-chemical properties associated with the two species.

Results and discussions

Experimental warming increased the leaf LUE, maximum photochemical efficiency, non-photochemical quenching, relative water content and specific leaf area for both species. However, there was a decrease in leaf and soil element content. Different species exhibit varying adaptability to warming. Increasing temperature significantly increased the photosynthetic rate, stomatal conductance, transpiration rate, total water content, and specific leaf volume of E. nutans; however, all these traits exhibited an opposite trend in P. anserina. Warming has a direct negative impact on leaf LUE and an indirectly enhances LUE through its effects on leaf traits. The impact of warming on plant photosynthetic capacity is primarily mediated by soil nutrients and leaf traits. These results indicate that the two different species employ distinct adaptive strategies in response to climate change, which are related to their species-specific variations. Such changes can confer an adaptive advantage for plant to cope with environmental change and potentially lead to alterations to ecosystem structure and functioning.

Improvement of Panax notoginseng saponin accumulation triggered by methyl jasmonate under arbuscular mycorrhizal fungi

Panax notoginseng is a highly valued perennial medicinal herb plant in Yunnan Province, China, and the taproots are the main medicinal parts that are rich in active substances of P. notoginseng saponins. The main purpose of this study is to uncover the physiological and molecular mechanism of Panax notoginseng saponin accumulation triggered by methyl jasmonate (MeJA) under arbuscular mycorrhizal fungi (AMF) by determining physiological indices, high-throughput sequencing and correlation analysis. Physiological results showed that the biomass and saponin contents of P. notoginseng, the concentrations of jasmonic acids (JAs) and the key enzyme activities involved in notoginsenoside biosynthesis significantly increased under AMF or MeJA, but the interactive treatment of AMF and MeJA weakened the effect of AMF, suggesting that a high concentration of endogenous JA have inhibitory effect. Transcriptome sequencing results indicated that differential expressed genes (DEGs) involved in notoginsenoside and JA biosynthesis were significantly enriched in response to AMF induction, e.g., upregulated genes of diphosphocytidyl-2-C-methyl-d-erythritol kinases (ISPEs), cytochrome P450 monooxygenases (CYP450s)_and glycosyltransferases (GTs), while treatments AMF-MeJA and salicylhydroxamic acid (SHAM) decreased the abundance of these DEGs. Interestingly, a high correlation presented between any two of saponin contents, key enzyme activities and expression levels of DEGs. Taken together, the inoculation of AMF can improve the growth and saponin accumulation of P. notoginseng by strengthening the activities of key enzymes and the expression levels of encoding genes, in which the JA regulatory pathway is a key link. This study provides references for implementing ecological planting of P. notoginseng, improving saponin accumulation and illustrating the biosynthesis mechanism.

Effects of Funneliformis mosseae on Growth and Photosynthetic Characteristics of Camellia oleifera under Different Nitrogen Forms

Nitrogen fertilizer increases agricultural yields but increases economic costs and causes a series of environmental problems. Arbuscular mycorrhizal fungi (AMF) have the potential to be used as biological fertilizer. However, the influence of nitrogen form on plant growth responsiveness to AMF inoculation is poorly understood. In this study, we investigated the effects of Funneliformis mosseae on growth, root morphology and photosynthetic characteristics of Camellia oleifera under different nitrogen forms during three harvest periods and clarified the most suitable nitrogen form for C. oleifera-AMF symbiosis. The results showed that urea, ammonium and nitrate nitrogen promoted plant growth and photosynthetic capacity, among which urea treatment had the highest value in all three harvests. No significant difference in plant growth parameters was observed between ammonium and nitrate nitrogen treatments in the first two harvests, while the plant height was significantly lower under ammonium nitrogen treatment than nitrate nitrogen treatment in the third harvest. Inoculation with F. mosseae in the presence of indigenous AMF could promote AMF colonization and plant growth at all three harvest times. Inoculation with F. mosseae significantly increased gas exchange parameters, the maximum photochemical efficiency (Fv/Fm) and the actual photochemical efficiency (ΦPSII). Inoculation with AMF increased the photochemical quenching coefficient (qP) better under urea treatment and improved the non-photochemical quenching coefficient (qN) better under ammonium nitrogen treatment. Principal component analysis showed that urea is the most beneficial nitrogen fertilizer for C. oleifera-AMF symbiosis. The results of this study provide a theoretical basis for the combination use of AMF and nitrogen fertilizer in agroforestry.

Lipid profiling reveals Leymus Chinensis root insensitivity to Ca limitation

BACKGROUND

Leymus chinensis (L. chinensis) is a perennial native forage grass widely distributed in the steppe of Inner Mongolia as the dominant species. Calcium (Ca) is an essential mineral element important for plant adaptation to the growth environment. Ca limitation was previously shown to strongly inhibit Arabidopsis (Arabidopsis thaliana) seedling growth and disrupt plasma membrane stability and selectivity, increasing fluid-phase-based endocytosis and contents of all major membrane lipids.

RESULTS

In this study, we investigated the significance of Ca for L. chinensis growth and membrane stability relative to Arabidopsis. Our results showed that Ca limitation did not affect L. chinensis seedling growth and endocytosis in roots. Moreover, the plasma membrane maintained high selectivity. The lipid phosphatidylcholine (PC): phosphatidylethanolamine (PE) ratio, an indicator of the membrane stability, was five times higher in L. chinensis than in Arabidopsis. Furthermore, in L. chinensis, Ca limitation did not affect the content of any major lipid types, decreased malondialdehyde (MDA) content, and increased superoxide dismutase (SOD) activity, showing an opposite pattern to that in Arabidopsis. L. chinensis roots accumulated higher contents of PC, phosphatidylinositol (PI), monogalactosyldiacylglycerol (MGDG), phosphatidylglycerol (PG), cardiolipin (CL), digalactosyldiacylglycerol (DGDG), and lysophosphatidylcholine (LPC) but less phosphatidylethanolamine (PE), diacylglycerol (DAG), triacylglycerolv (TAG), phosphatidylserine (PS), lysobisphosphatidic acids (LPAs), lysophosphatidylethanolamine (LPE), and lysophosphatidylserine (LPS) than Arabidopsis roots. Moreover, we detected 31 and 66 unique lipids in L. chinensis and Arabidopsis, respectively.

CONCLUSIONS

This study revealed that L. chinensis roots have unique membrane lipid composition that was not sensitive to Ca limitation, which might contribute to the wider natural distribution of this species.

Arbuscular mycorrhizal fungi alter rhizosphere fungal community characteristics of Acorus calamus to improve Cr resistance

To investigate changes in fungal community characteristics under different Cr(VI) concentration stresses and the advantages of adding arbuscular mycorrhizal fungi (AMF), we used high throughput sequencing to characterize the fungal communities. Cr(VI) stress reduced rhizosphere soil SOM (soil organic matter) content and AMF addition improved this stress phenomenon. There were significant differences in fungal community changes under different Cr(VI) concentrations. The fungal community characteristics changed through inhibition of fungal metabolic ability, as fungal abundance increased after AMF addition, and the fungal diversity increased under high Cr(VI) concentration. The dominant phyla were members of the Ascomycota, Basidiomycota, Mortierellomycota, and Rozellomycota. Dominant groups relevant to Cr resistance were Ascomycota and Basidiomycota fungi. Moreover, Fungal community characteristics were analyzed using high-throughput sequencing of the cytochrome c metabolic pathway, NADH dehydrogenase, and NADH: ubiquinone reductase and all these functions were enhanced after AMF addition. Therefore, Cr(VI) stress significantly affects fungal community structure, while AMF addition could increase its SOM content, and metabolic capacity, and improve fungal community tolerance to Cr stress. This study contributed to the understanding response of rhizosphere fungal community in AMF-assisted wetland phytoremediation under Cr stress.

Revealing the effects and mechanisms of arbuscular mycorrhizal fungi on manganese uptake and detoxification in Rhus chinensis

Arbuscular mycorrhizal fungi (AMF) can alleviate heavy metal phytotoxicity and promote plant growth, while the underlying mechanisms of AMF symbiosis with host plants under manganese (Mn) stress remain elusive. A pot experiment was carried out to investigate the plant growth, micro-structure, Mn accumulation, subcellular distribution, chemical forms, and physiological and biochemical response of Rhus chinensis inoculated with Funneliformis mosseae (FM) under different Mn treatments. The results showed that compared with plants without FM, FM-associated plants exhibited higher growth status, photosynthetic pigments, and photosynthesis under Mn stress. FM-associated plants were able to maintain greater integrity in mesophyll structure, higher thickness of leaf, upper epidermis, and lower epidermis under Mn treatment, and promote leaf growth. Mn accumulation in leaves (258.67-2230.50 mg kg-1), stems (132.67-1160.00 mg kg-1), and roots (360.92-2446.04 mg kg-1) of the seedlings inoculated with FM was higher than non-inoculated ones. FM-associated plants exhibited higher osmotic regulating substances and antioxidant enzymes' activities under Mn exposure, suggesting lower Mn toxicity in FM inoculated seedlings, despite the augment in Mn accumulation. After FM inoculation, Mn concentration (151.04-1211.32 mg kg-1) and percentage (64.41-78.55%) enhanced in the cell wall, whilst the transport of Mn to aerial plant organs decreased. Furthermore, FM symbiosis favored the conversion of Mn from high toxic forms (2.17-15.68% in FEthanol, 11.37-24.52% in Fdeionized water) to inactive forms (28.30-38.15% in FNaCl, 18.07-28.59% in FHAc, 4.41-17.99% in FHCl) with low phytotoxicity. Our study offers a theoretical basis for remediation of the FM- R. chinensis symbiotic system in Mn-contaminated environments.

Role of Arbuscular Mycorrhizal Fungi in Regulating Growth, Enhancing Productivity, and Potentially Influencing Ecosystems under Abiotic and Biotic Stresses

Arbuscular mycorrhizal fungi (AMF) form symbiotic relationships with the roots of nearly all land-dwelling plants, increasing growth and productivity, especially during abiotic stress. AMF improves plant development by improving nutrient acquisition, such as phosphorus, water, and mineral uptake. AMF improves plant tolerance and resilience to abiotic stressors such as drought, salt, and heavy metal toxicity. These benefits come from the arbuscular mycorrhizal interface, which lets fungal and plant partners exchange nutrients, signalling molecules, and protective chemical compounds. Plants' antioxidant defence systems, osmotic adjustment, and hormone regulation are also affected by AMF infestation. These responses promote plant performance, photosynthetic efficiency, and biomass production in abiotic stress conditions. As a result of its positive effects on soil structure, nutrient cycling, and carbon sequestration, AMF contributes to the maintenance of resilient ecosystems. The effects of AMFs on plant growth and ecological stability are species- and environment-specific. AMF's growth-regulating, productivity-enhancing role in abiotic stress alleviation under abiotic stress is reviewed. More research is needed to understand the molecular mechanisms that drive AMF-plant interactions and their responses to abiotic stresses. AMF triggers plants' morphological, physiological, and molecular responses to abiotic stress. Water and nutrient acquisition, plant development, and abiotic stress tolerance are improved by arbuscular mycorrhizal symbiosis. In plants, AMF colonization modulates antioxidant defense mechanisms, osmotic adjustment, and hormonal regulation. These responses promote plant performance, photosynthetic efficiency, and biomass production in abiotic stress circumstances. AMF-mediated effects are also enhanced by essential oils (EOs), superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), hydrogen peroxide (H2O2), malondialdehyde (MDA), and phosphorus (P). Understanding how AMF increases plant adaptation and reduces abiotic stress will help sustain agriculture, ecosystem management, and climate change mitigation. Arbuscular mycorrhizal fungi (AMF) have gained prominence in agriculture due to their multifaceted roles in promoting plant health and productivity. This review delves into how AMF influences plant growth and nutrient absorption, especially under challenging environmental conditions. We further explore the extent to which AMF bolsters plant resilience and growth during stress.

Influence of nitrogen and phosphorus additions on parameters of photosynthesis and chlorophyll fluorescence in Cyclocarya paliurus seedlings

Cyclocarya paliurus has been traditionally used as a functional food in China. A hydroponic experiment was conducted to determine the effects of N and P additions on photosynthesis and chlorophyll fluorescence (ChlF) of C. paliurus seedlings. N and P additions significantly altered photosynthesis and ChlF in the seedlings, but responses of these parameters to the N and P concentrations varied at different developmental stages. The greatest net photosynthetic rate (P N) and actual photochemical efficiency of PSII (ФPSII) occurred in the treatment of 150.0 mg(N) L-1 and 25.0 mg(P) L-1 addition, whereas the highest maximum quantum yield of PSII (Fv/Fm) and water-use efficiency (WUE) were recorded with 150.0 mg(N) L-1 and 15.0 mg(P) L-1 on the 60th day after treatment. Significantly positive correlations of P N with leaf relative chlorophyll content, transpiration rate, WUE, Fv/Fm, and ΦPSII, as well as the ФPSII with the Fv/Fm, were found. Our results indicated that an optimal addition of N and P nutrients depends on their coupling effects on the photosynthetic capacity and PSII photochemistry.

Investigation of the potential role of fusicoccin, a fungal phytotoxin, in mitigating salt stress in onion roots

Fusicoccin is a diterpene glycoside that plays an important role in the regulation of plant growth and development. Fusicoccin produced by Fusicoccum amydali fungus is known to affect plant growth positively with external applications due to its potential to stimulate the tolerance system of plants under stress conditions. In this study, it was aimed to reduce the negative effects of salt (0.15 M NaCl) stress on the germination and growth of onion (Allium cepa L.) bulbs by external fusicoccin (3 µM) application. For this purpose, the germination percentage, root length, root number, fresh weight, mitotic activity, micronucleus frequency, chromosomal abnormality, antioxidant enzyme activity, osmolyte accumulation, cell membrane damage and root anatomical structure were investigated in the current study. Salt stress caused a statistically significant difference (p < 0.05) in all examined parameters. External application of fusicoccin to onion bulbs germinated under salt stress conditions was found to be promising as a plant growth promoter and mitosis stimulator. In addition, fusicoccin application alleviated the harmful effects of salt stress on the chromosome structure and root anatomical structure and protected the cells from the cytotoxic and genotoxic effects of salt. Moreover, this application contributed to the fight against reactive oxygen species of onion plant and increased salt tolerance by regulating the accumulation of osmolyte substances such as proline and antioxidant enzymes such as superoxide dismutase and catalase, and by minimizing cell membrane damage in root cells. In conclusion, this study showed that exogenous application of 3 µM fusicoccin reduced the damage caused by oxidative stress in onion bulbs and served for healthy germination and growth.

Moderate nitrogen application improved salt tolerance by enhancing photosynthesis, antioxidants, and osmotic adjustment in rapeseed (Brassica napus L.)

Salt stress is a major adverse environmental factor limiting plant growth. Nitrogen (N) application is an effective strategy to alleviate the negative effects of salt stress on plants. To improve the knowledge of the mechanism of N application on alleviating salt stress on rapeseed seedlings, a pot experiment was conducted with four N application treatments (0, 0.1, 0.2, and 0.3 g N kg^-1 soil, referred to as N0, N1, N2, and N3, respectively) and exposed to non-salt stress (0 g NaCl kg^-1 soil, referred to as S0) and salt stress (3 g NaCl kg^-1 soil, referred to as S1) conditions. The results indicated that in comparison with non-salt stress, salt stress increased the Na content (236.53%) and reactive oxygen species (ROS) production such as hydrogen peroxide (H₂O₂) (30.26%), resulting in cell membrane lipid peroxidation characterized by an increased content of malondialdehyde (MDA) (122.32%) and suppressed photosynthetic rate (15.59%), finally leading to inhibited plant growth such as shorter plant height, thinner root neck, lower leaf area, and decreased dry weight. N application improved the plant growth, and the improvement by N application under salt stress was stronger than that under non-salt stress, suggesting that rapeseed seedlings exposed to salt stress are more sensitive to N application and require N to support their growth. Moreover, seedlings exposed to salt stress under N application showed lower ROS accumulation; increased photosynthesis; higher antioxidants such as catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR), and ascorbic acid (AsA); and greater accumulation of osmotic substances including soluble protein, soluble sugar, and proline, as compared with seedlings without N application. In particular, the best improvement by N application under salt stress occurred at the N2 level, while too high N application could weaken the improvement due to inhibited N metabolism. In summary, this study suggests that moderate N application can improve photosynthesis, antioxidants, and osmoregulation to alleviate the adverse effects of salt stress in rapeseed seedlings.

Insights into the genomic evolution and the alkali tolerance mechanisms of Agaricus sinodeliciosus by comparative genomic and transcriptomic analyses

Agaricus sinodeliciosus is a rare wild edible mushroom from northwest China, and grows naturally in mild saline-alkali soil, which is also unusual in mushrooms. A. sinodeliciosus represents a potential model organism for explaining saline-alkali tolerance mechanisms and revealing related physiological processes in mushrooms. Here, we provide a high-quality genome of A. sinodeliciosus. Comparative genomic analyses reveal A. sinodeliciosus has numerous changes to its genome organization after a solitary evolutionary history under saline-alkali environments, such as gene family contraction, retrotransposon expansion and rapid evolution of adaptative genes. Our saline and alkali tolerance tests show that mycelium growth and fruit body formation of this species are effected by mild alkalinity. Transcriptomic analyses reveal that genes involved in carbon and nitrogen utilization, cell stability and fruit body formation of A. sinodeliciosus could be activated under mildly alkaline conditions. In particular, the 'starch and sucrose metabolism', 'biosynthesis of amino acids' and 'phenylpropanoid biosynthesis' pathways are important for mildly alkaline tolerance of A. sinodeliciosus. Like plants and arbuscular mycorrhizal fungi, in the rot fungus A. sinodeliciosus, the biosynthesis of intracellular small molecules could be enhanced to counter osmotic and oxidative stresses caused by mild alkalinity, and the biosynthesis of monolignol could be suppressed to increase cell wall infiltrates under mildly alkaline conditions. This research provides an understanding of the genomic evolution and mechanisms of A. sinodeliciosus in tolerance to saline-alkali environments. The A. sinodeliciosus genome constitutes a valuable resource for evolutionary and ecological studies of Agaricus.

Modulation of NaCl-induced osmotic, cytogenetic, oxidative and anatomic damages by coronatine treatment in onion (Allium cepa L.)

Coronatine (COR), a bacterial phytotoxin produced by Pseudomonas syringae, plays important roles in many plant growth processes. Onion bulbs were divided four groups to investigate the effects of COR against sodium chloride (NaCl) stress exposure in Allium cepa L. root tips. While control group bulbs were soaked in tap water medium, treatment group bulbs were grown in 0.15 M NaCl, 0.01 µM COR and 0.01 µM COR + 0.15 M NaCl medium, respectively. NaCl stress seriously inhibited the germination, root lenght, root number and fresh weight of the bulbs. It significantly decreased the mitotic index (MI), whereas dramatically increased the micronucleus (MN) frequency and chromosomal aberrations (CAs). Moreover, in order to determine the level of lipid peroxidation occurring in the cell membrane, malondialdehyde (MDA) content was measured and it was determined that it was at the highest level in the group germinated in NaCl medium alone. Similarly, it was revealed that the superoxide dismutase (SOD), catalase (CAT) and free proline contents in the group germinated in NaCl medium alone were higher than the other groups. On the other hand, NaCl stress caused significant injuries such as epidermis/cortex cell damage, MN formation in epidermis/cortex cells, flattened cells nuclei, unclear vascular tissue, cortex cell wall thickening, accumulation of certain chemical compounds in cortex cells and necrotic areas in the anatomical structure of bulb roots. However, exogenous COR application significantly alleviated the negative effects of NaCl stress on bulb germination and growth, antioxidant defense system, cytogenetic and anatomical structure. Thus, it has been proven that COR can be used as a protective agent against the harmful effects of NaCl on onion.

Label-free quantitative proteomics of arbuscular mycorrhizal Elaeagnus angustifolia seedlings provides insights into salt-stress tolerance mechanisms

INTRODUCTION

Soil salinization has become one of the most serious environmental issues globally. Excessive accumulation of soluble salts will adversely affect the survival, growth, and reproduction of plants. Elaeagnus angustifolia L., commonly known as oleaster or Russian olive, has the characteristics of tolerance to drought and salt. Arbuscular mycorrhizal (AM) fungi are considered to be bio-ameliorator of saline soils that can enhance the salt tolerance of the host plants. However, there is little information on the root proteomics of AM plants under salt stress.

METHODS

In this study, a label-free quantitative proteomics method was employed to identify the differentially abundant proteins in AM E. angustifolia seedlings under salt stress.

RESULTS

The results showed that a total of 170 proteins were significantly differentially regulated in E.angustifolia seedlings after AMF inoculation under salt stress. Mycorrhizal symbiosis helps the host plant E. angustifolia to respond positively to salt stress and enhances its salt tolerance by regulating the activities of some key proteins related to amino acid metabolism, lipid metabolism, and glutathione metabolism in root tissues.

CONCLUSION

Aspartate aminotransferase, dehydratase-enolase-phosphatase 1 (DEP1), phospholipases D, diacylglycerol kinase, glycerol-3-phosphate O-acyltransferases, and gamma-glutamyl transpeptidases may play important roles in mitigating the detrimental effect of salt stress on mycorrhizal E. angustifolia . In conclusion, these findings provide new insights into the salt-stress tolerance mechanisms of AM E. angustifolia seedlings and also clarify the role of AM fungi in the molecular regulation network of E. angustifolia under salt stress.

Nitrogen application alleviates salt stress by enhancing osmotic balance, ROS scavenging, and photosynthesis of rapeseed seedlings (Brassica napus)

Nitrogen application could alleviate salt stress on crops, but the specific physiological mechanism is still unclear. Therefore, in this study, a pot experiment was conducted to explore the effects of different application rates of nitrogen (0, 0.15, 0.30, and 0.45 g·kg^-1) on the growth parameters, osmotic adjustment, reactive oxygen species scavenging, and photosynthesis of rapeseed seedlings planted in the soils with different concentrations of sodium chloride (1.5, 3.5, 5.5, and 7.5 g·kg^-1). The results showed that nitrogen could alleviate the inhibition of salt on rapeseed growth, and improve the antioxidant enzyme activities and the contents of non-enzymatic substances, K⁺, soluble protein (SP), soluble sugar (SS), and proline. Besides, there was a significant correlation between the indexes of active oxygen scavenging system, osmoregulation system, and photosynthesis. Therefore, applying appropriate amount of nitrogen can promote the growth and development of rapeseed seedlings under salt stress, accelerate the scavenging of reactive oxygen species, maintain osmotic balance, and promote photosynthesis. This study will improve our understanding on the mechanism by which nitrogen application alleviates salt stress to crops.

Boosting Sustainable Agriculture by Arbuscular Mycorrhiza under Stress Condition: Mechanism and Future Prospective

Global agriculture is frequently subjected to stresses from increased salt content, drought, heavy metals, and other factors, which limit plant growth and production, deteriorate soil health, and constitute a severe danger to global food security. Development of environmentally acceptable mitigation techniques against stresses and restrictions on the use of chemical fertilizers in agricultural fields is essential. Therefore, eco-friendly practises must be kept to prevent the detrimental impacts of stress on agricultural regions. The advanced metabolic machinery needed to handle this issue is not now existent in plants to deal against the stresses. Research has shown that the key role and mechanisms of arbuscular mycorrhiza fungi (AMF) to enhance plant nutrient uptake, immobilisation and translocation of heavy metals, and plant growth-promoting attributes may be suitable agents for plant growth under diversed stressed condition. The successful symbiosis and the functional relationship between the plant and AMF may build the protective regulatory mechansm against the key challenge in particular stress. AMF's compatibility with hyperaccumulator plants has also been supported by studies on gene regulation and theoretical arguments. In order to address this account, the present review included reducing the impacts of biotic and abiotic stress through AMF, the mechanisms of AMF to improve the host plant's capacity to endure stress, and the strategies employed by AM fungus to support plant survival in stressful conditions.

Epichloë endophytes improved Leymus chinensis tolerance to both neutral and alkali salt stresses

Symbiotic relationships with microbes may influence how plants respond to environmental change. In the present study, we tested the hypothesis that symbiosis with the endophytes promoted salt tolerance of the native grass. In the field pot experiment we compared the performance of endophyte-infected (E+) and endophyte-uninfected (E-) Leymus chinensis, a dominant species native to the Inner Mongolia steppe, under altered neutral and alkaline salt stresses. The results showed that under both neutral and alkaline salt stresses, endophyte infection significantly increased plant height, leaf length and fibrous root biomass. Under neutral salt stress, endophyte infection decreased Na⁺ content and Na⁺/K⁺ ratio (p=0.066) in the leaf sheath while increased Ca²⁺ and Mg²⁺ content in the rhizome. Under alkali salt stress, endophyte infection tended to increase K⁺ content in the fibrous root, enhance Mg²⁺ content in the fibrous root while reduce Na⁺/K⁺ ratio in the leaf blade in the 100 mmol/L alkali salt treatment. Although endophyte-infected L. chinensis cannot accumulate Na⁺ high enough to be halophytes, the observed growth promotion and stress tolerance give endophyte/plant associations the potential to be a model for endophyte-assisted phytoremediation of saline-alkaline soils.

The efficiency of arbuscular mycorrhiza in increasing tolerance of Triticum aestivum L. to alkaline stress

BACKGROUND

Evaluation of native soil microbes is a realistic way to develop bio-agents for ecological restoration. Soil alkalinity, which has a high pH, is one of the most common concerns in dry and semi-arid climates. Alkaline soils face problems due to poor physical properties, which affect plant growth and crop production. A pot experiment was carried out to investigate the impact of native mycorrhizal fungi (AMF) on the wheat plant (Triticum aestivum L.) under two levels of alkalinity stress -T1 (37 mM NaHCO3), T2 (74 mM NaHCO3) - at two developmental stages (the vegetative and productive stages).

RESULTS

Alkalinity stress significantly inhibited the germination percentage, plant biomass, photosynthetic pigments, and some nutrients (K, N, and P). Mycorrhizal inoculation improved growth parameters and productivity of wheat-stressed plants. However, lipid peroxidation was significantly lowered in mycorrhizal-inoculated plants compared to non-inoculated plants. Catalase and peroxidase were inhibited in wheat leaves and roots by alkalinity, while mycorrhiza promoted the activity of these enzymes.

CONCLUSION

The results of this study demonstrated that alkalinity stress had highly negative effects on some growth parameters of the wheat plant, while AMF inoculation attenuated these detrimental effects of alkalinity stress at two stages by reducing the pH and Na concentration and increasing the availability of P and the productivity of wheat in particular crop yield parameters.

Dual Inoculation of Plant Growth-Promoting Bacillus endophyticus and Funneliformis mosseae Improves Plant Growth and Soil Properties in Ginger

Co-inoculation with beneficial microbes has been suggested as a useful practice for the enhancement of plant growth, nutrient uptake, and soil nutrients. For the first time in Uzbekistan the role of plant-growth-promoting Bacillus endophyticus IGPEB 33 and arbuscular mycorrhizal fungi (AMF) on plant growth, the physiological properties of ginger (Zingiber officinale), and soil enzymatic activities was studied. Moreover, the coinoculation of B. endophyticus IGPEB 33 and AMF treatment significantly increased the plant height by 81%, leaf number by 70%, leaf length by 82%, and leaf width by 40% compared to the control. B. endophyticus IGPEB 33 individually increased plant height significantly by 51%, leaf number by 56%, leaf length by 67%, and leaf width by 27% as compared to the control treatment. Compared to the control, B. endophyticus IGPEB 33 and AMF individually significantly increased chlorophyll a by 81-58%, chlorophyll b by 68-37%, total chlorophyll by 74-53%, and carotenoid content by 67-55%. However, combination of B. endophyticus IGPEB 33 and AMF significantly increased chlorophyll a by 86%, chlorophyll b by 72%, total chlorophyll by 82%, and carotenoid content by 83% compared to the control. Additionally, plant-growth-promoting B. endophyticus IGPEB 33 and AMF inoculation improved soil nutrients and soil enzyme activities compared to the all treatments. Co-inoculation with plant-growth-promoting B. endophyticus and AMF could be an alternative for the production of ginger that is more beneficial to soil nutrient deficiencies. We suggest that a combination of plant-growth-promoting B. endophyticus and AMF inoculation could be a more sustainable and eco-friendly approach in a nutrient-deficient soil.

Impact of an arbuscular mycorrhizal fungal inoculum and exogenous methyl jasmonate on the performance of tall fescue under saline-alkali condition

Hormonal regulation and symbiotic relationships provide benefits for plants to overcome stress conditions. The aim of this study was to elucidate the effects of arbuscular mycorrhizal fungal (AMF) inoculum, methyl jasmonate (MeJA), and saline-alkali effects on the growth and physiology of tall fescue (Festuca elata "Crossfire II"). Treatments included AMF-inoculation, and non-AMF inoculation, four MeJA application concentrations (0, 50, 100, and 200 mg/L), and two saline-alkali levels (0 and 200 mmol/L). The results showed that AMF inoculation significantly enhanced saline-alkali resistance of the plants, and the beneficial effects were increased by MeJA at a concentration of 50 mg/L (50 MeJA) and decreased by MeJA at a concentration both of 100 (100 MeJA) and 200 mg/L (200 MeJA). AMF inoculation plants when treated with 50 MeJA accumulated significantly more biomass, had greater proline and total phenolic concentration, and lower malondialdehyde (MDA) concentration than plants only treated either with AMF or 50 MeJA. However, no significant differences in growth or physiological characteristics were observed between AMF and non-AMF plants when treated either with 100 or 200 MeJA. All of these results suggest that the interaction between a certain concentration of MeJA and AMF can significantly increase saline-alkali resistance of the tall fescue by regulating the biomass, proline, total phenolic, and MDA. Our findings provide new information on the effect of biological and chemical priming treatments on plant performance under saline-alkali stress.

Prospective of mycorrhiza and Beauvaria bassiana silica nanoparticles on Gossypium hirsutum L. plants as biocontrol agent against cotton leafworm, Spodoptera littoralis

BACKGROUND

Plant-herbivorous insects are a severe danger to the world's agricultural production of various crops. Insecticides used indiscriminately resulted in habitat destruction due to their high toxicity, as well as disease resistance. In this respect, the development of a sustainable approach to supreme crop production with the least damage is a crucially prerequisite. As a result, the current study was carried out to understand the potential effect of arbuscular mycorrhizal (AM) fungi along with Beauvaria bassiana silica nanoparticles (Si NPs) as a new approach to increase cotton (Gossypium hirsutum L. Merr.) defense against an insect herbivore, Spodoptera littoralis. AM and non-AM cotton plants were infested with S. littoralis and then sprayed with a biopesticide [B. bassiana Si NPs] or a chemical insecticide (Chlorpyrifos).

RESULTS

The gas chromatography-mass spectrometry (GC-MS) analysis of B. bassiana Si NPs fungal extract showed that the major constituents identified were Oleyl alcohol, trifluoroacetate, 11-Dodecen-1-AL and 13-Octadecenal, (Z)-(CAS). Besides, results revealed a highly significant decrease in growth parameters in S. littoralis infested plants, however, with AM fungal inoculation a substantial improvement in growth traits and biochemical parameters such as protein and carbohydrates contents was observed. In addition, stimulation in proline and antioxidant enzymes activity and a decrease in malondialdehyde content were observed after AM inoculation.

CONCLUSION

AM fungi mitigate the harmful effects of herbivorous insects by strengthening the cotton plant's health via enhancing both morphological and biochemical traits that can partially or completely replace the application of chemical insecticides.

Microbial Diversity and Adaptation under Salt-Affected Soils: A Review

The salinization of soil is responsible for the reduction in the growth and development of plants. As the global population increases day by day, there is a decrease in the cultivation of farmland due to the salinization of soil, which threatens food security. Salt-affected soils occur all over the world, especially in arid and semi-arid regions. The total area of global salt-affected soil is 1 billion ha, and in India, an area of nearly 6.74 million ha−1 is salt-stressed, out of which 2.95 million ha−1 are saline soil (including coastal) and 3.78 million ha−1 are alkali soil. The rectification and management of salt-stressed soils require specific approaches for sustainable crop production. Remediating salt-affected soil by chemical, physical and biological methods with available resources is recommended for agricultural purposes. Bioremediation is an eco-friendly approach compared to chemical and physical methods. The role of microorganisms has been documented by many workers for the bioremediation of such problematic soils. Halophilic Bacteria, Arbuscular mycorrhizal fungi, Cyanobacteria, plant growth-promoting rhizobacteria and microbial inoculation have been found to be effective for plant growth promotion under salt-stress conditions. The microbial mediated approaches can be adopted for the mitigation of salt-affected soil and help increase crop productivity. A microbial product consisting of beneficial halophiles maintains and enhances the soil health and the yield of the crop in salt-affected soil. This review will focus on the remediation of salt-affected soil by using microorganisms and their mechanisms in the soil and interaction with the plants.

Arbuscular Mycorrhizal Fungi Symbiosis to Enhance Plant–Soil Interaction

Arbuscular mycorrhizal fungi (AMF) form a symbiotic relationship with plants; a symbiotic relationship is one in which both partners benefit from each other. Fungi benefit plants by improving uptake of water and nutrients, especially phosphorous, while plants provide 10–20% of their photosynthates to fungus. AMF tend to make associations with 85% of plant families and play a significant role in the sustainability of an ecosystem. Plants’ growth and productivity are negatively affected by various biotic and abiotic stresses. AMF proved to enhance plants’ tolerance against various stresses, such as drought, salinity, high temperature, and heavy metals. There are some obstacles impeding the beneficial formation of AMF communities, such as heavy tillage practices, high fertilizer rates, unchecked pesticide application, and monocultures. Keeping in view the stress-extenuation potential of AMF, the present review sheds light on their role in reducing erosion, nutrient leaching, and tolerance to abiotic stresses. In addition, recent advances in commercial production of AMF are discussed.

Leaf Carbon Exchange of Two Dominant Plant Species Impacted by Water and Nitrogen Application in a Semi-Arid Temperate Steppe

Photosynthetic characteristics are widely used as indicators of plant responses to global environmental changes such as precipitation change and nitrogen (N) deposition increase. How different plant species respond physiologically to the future precipitation change combined with increasing N availability is largely unclear. A field experiment was conducted to study responses in seasonal and interannual leaf carbon (C) exchange of two dominant plant species, Leymus chinensis and Stipa grandis, to additional water (either as spring snow or as summer water) and N application in a semi-arid temperate steppe of China. Our results showed that spring snow and summer water addition both increased the maximum photosynthetic rate (A_max) of two dominant species. Such effect was likely caused by raised light saturation point, the maximum apparent quantum yield, stomatal conductance, and transpiration rate. The N application combined with spring snow or summer water addition both enhanced A_max of S. grandis in both experimental years, whereas N application only increased A_max of L. chinensis combined with summer water addition. Their responses were attributed to a concurrent increase in leaf N concentration (N_leaf) and decrease in leaf phosphorus (P) concentration (P_leaf), indicating that N_leaf and P_leaf affect photosynthetic characteristics to regulate leaf C exchange. Our results suggest that differentiated responses among different species in photosynthetic characteristics may lead to changes in ecosystem structure and functioning under increasing precipitation and N deposition.

Arbuscular Mycorrhizal Fungi Induced Plant Resistance against Fusarium Wilt in Jasmonate Biosynthesis Defective Mutant and Wild Type of Tomato

Arbuscular mycorrhizal (AM) fungi can form mutual symbiotic associations with most terrestrial plants and improve the resistance of host plants against pathogens. However, the bioprotection provided by AM fungi can depend on the host–fungus combinations. In this study, we unraveled the effects of pre-inoculation with AM fungus Rhizophagus irregularis on plant resistance against the hemibiotrophic fungal pathogen Fusarium oxysporum in jasmonate (JA) biosynthesis mutant tomato, suppressor of prosystemin-mediated responses8 (spr8) and the wild type Castlemart (CM). Results showed that R. irregularis colonization in CM plants significantly decreased the disease index, which was not observed in spr8 plants, suggesting that the disease protection of AM fungi was a plant-genotype-specific trait. Inoculation with R. irregularis significantly increased the shoot dry weight of CM plants when infected with F. oxysporum, with increased plant P content and net photosynthetic rate. Induced expression of the JA synthesis genes, including allene oxide cyclase gene (AOC) and lipoxygenase D gene (LOXD), and increased activities of polyphenol oxidase (PPO) and phenylalanine ammonia lyase (PAL) were recorded in mycorrhizal CM plants infected with F. oxysporum, but not in spr8 plants. Thus, mycorrhiza-induced resistance (MIR) to fungal pathogen in tomato was highly relevant to the JA signaling pathway.

Effect of silicon application with mycorrhizal inoculation on Brassica juncea cultivated under water stress

Brassica juncea L. is a significant member of the Brassicaceae family, also known as Indian mustard. Water is a limiting factor in the successful production of this crop. Here, we tested the effect of water shortage in B. juncea plants supplemented with or without the application of silicon and arbuscular mycorrhizal fungi in total 8 different treatments compared under open filed conditions using a randomised complete block design (RCBD). The treatments under control conditions were control (C, T1); C+Silicon (Si, T2); C+My (Mycorrhiza; T3); and C+Si+My (T4). In contrast, treatments under stress conditions were S (Stress; T5); S+Si (T6); S+My (T7) and S+Si+My (T8), respectively. In total, we evaluated 16 traits, including plant response to stress by evaluating peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) activity. The fresh weight (g) increased only 7.47 percent with mycorrhiza (C+My) and 22.39 percent with silicon (C+Si) but increased 291.08 percent with both mycorrhiza and silicon (C+Si+My). Using mycorrhiza (S+My) or silicon (S+Si) alone produced a significant increase of 53.16 percent and 55.84 percent in fresh weight, respectively, while using both mycorrhiza and silicon (S+Si+My) together produced a dramatic increase of 380.71 percent under stress conditions. Superoxidase dismutase concentration (Ug⁻¹ FW) was found to be increased by 29.48 percent, 6.71 percent, and 22.63 percent after applying C+My, C+Si and C+Si+My, but treatment under stress revealed some contrasting trends, with an increase of 11.21 percent and 19.77 percent for S+My, S+Si+My, but a decrease of 13.15 percent for S+Si. Finally, in the presence of stress, carotenoid content (mg/g FW) increased by 58.06 percent, 54.83 percent, 183.87 percent with C+My, and 23.81 percent with S+My and S+Si+My, but decreased by 22.22 percent with S+Si. Silicon application proved to be more effective than AMF treatment with Rhizophagus irregularis, and the best results were obtained with the combination of Si and AMF. This work will help to suggest the measures to overcome the water stress in B. juncea.

Effects of 5-Year Nitrogen Addition on Species Composition and Diversity of an Alpine Steppe Plant Community on Qinghai-Tibetan Plateau

The N deposition rate is notably increased in China, especially in the Qinghai-Tibetan Plateau (QTP). How plants respond to the projected N deposition on the alpine steppe is still in debate. In this study, to investigate the effects of N deposition on the plant community of the alpine steppe, we simulated N deposition at six different N addition rate levels (0, 8, 24, 40, 56, 72 kg N ha⁻¹ y⁻¹) from 2015 to 2019. Species composition and diversity were investigated as the assessment indices. The results showed that the importance value of grasses significantly increased with the increase of the N addition rate, while that of forbs significantly decreased. A high N addition rate (72 kg N ha⁻¹ y⁻¹) induced species composition change, making Leymus secalinus become the most dominant species within the entire plant community. Compared with the control (without N addition), species richness, Shannon–Weiner diversity, Simpson dominance and Pielou Evenness were significantly reduced under a high N addition rate. The changes of plant diversity in the alpine steppe were closely correlated with dynamics of soil nutrients, especially total carbon (TC), total phosphorus (TP) and ammonia nitrogen (NH₄-N). Our findings suggested that a high N deposition rate (72 kg N ha⁻¹ y⁻¹) could significantly change plant composition and reduce the diversity of the alpine steppe, though they were less affected by low N deposition rates at present. With the increase of the N deposition rate, plant composition and diversity of the alpine steppe may be negatively affected in the future. In addition, Leymus secalinus is more competitive than other species with an N deposition rate increase. Soil C, soil P and soil NH⁴-N variation induced by N deposition might play a key role in regulating changes in plant composition and diversity in the alpine steppe. In addition, longer term field investigation needs to be carried out to testify to this phenomenon with the increase of N deposition in the future.

Ice-core based assessment of nitrogen deposition in the central Tibetan Plateau over the last millennium

Atmospheric nitrogen deposition is a unique source of bioavailable nitrogen for ecosystems in remote regions, and has vital impacts on ecological processes. Understanding variations of atmospheric nitrogen deposition in these regions remains challenging due to a lack of observations. Ice cores contain records of nitrogen species of nitrate (NO₃^-) and ammonium (NH₄⁺), hence provide valuable long-term data to study past variations of atmospheric nitrogen deposition. In this study, we present an annually resolved record of NH₄⁺ and NO₃^- over the past millennium, derived from the Zangser Kangri (ZK) ice core in the central Tibetan Plateau. The concentration peaks of NH₄⁺ and NO₃^- coincide with those of Ca²⁺ (a dust tracer), indicating that variation of nitrogen species in the ZK ice core is largely driven by dust activities. An EOF analysis for all chemical species (Cl^-, SO₄^2-, NO₃^-, Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺) reveals significant but separate loadings of NH₄⁺ and NO₃^- on EOF 2, suggesting an additional source of nitrogen, likely from biogenic emissions of terrestrial ecosystems. Over the past millennium, the EOF 2 series has relatively high values around 1300 CE and 1600 CE, and has increased significantly since the Industrial Revolution. These variations are likely driven by temperature-dependent biogenic emissions on the Tibetan Plateau. Analyses of seasonal air mass backward trajectories and wind fields find that the chemical concentrations in the ZK ice core are mostly influenced by the westerly, but South Asia summer monsoon plays an important role in the transport of nitrogen species generated from biogenic emissions. This is further confirmed by the significant correlation between EOF 2 series and the South Asian summer monsoon index. This study provides new insight into the preindustrial sources, natural variabilities and major drivers of nitrogen deposition on the Tibetan Plateau.

Arbuscular Mycorrhizal Fungi Contribute to Phosphorous Uptake and Allocation Strategies of Solidago canadensis in a Phosphorous-Deficient Environment

Arbuscular mycorrhizal fungi (AMF) can facilitate the uptake of limiting or inaccessible nutrients by plants. However, the importance of AMF for invasive plants under phosphorus (P) limitation is poorly well understood because of the presence of non-focal microorganisms, such as endophytes or rhizosphere bacteria. In this study, we investigated how an invasive clonal plant Solidago canadensis benefits from the AMF Glomus intraradices by using a completely sterile culturing system, which is composed of aseptic seedlings, a pure AMF strain, and a sterile growth environment. We found that the colonization rate, abundance, and spore production of AMF in the insoluble P treatment was more than twice as much as in the available P treatment. Plant above-ground growth was enhanced almost 50% by AMF in the insoluble P treatment. Importantly, AMF were able to facilitate P acquisition by the plant in insoluble P conditions, allowing plants to have lower investment into below-ground biomass and higher benefit/return for above-ground biomass. This study demonstrated the important contribution that AMF make to plants in phosphate-deficient environments eliminating interference from non-focal microorganisms. Our results also suggest that interaction with AMF could contribute to the invasiveness of clonal plant S. canadensis in a resource-deficient environment.

Arbuscular mycorrhizal fungi improve the growth and performance in the seedlings of Leymus chinensis under alkali and drought stresses

Alkali and drought stresses are increasing severe environmental problems throughout the world, especially in the Songnen grassland of northern China. Leymus chinensis is the dominant grass species in the Songnen grassland of northern China and the most promising species for grassland restoration. Arbuscular mycorrhizal fungi (AMF) can colonize 80% of vascular plants, which can enhance the growth of host plants and provide extrinsic protection against abiotic stresses. However, little is known about the interaction effect of alkali and drought stresses on plant-AM symbionts. Here, seedlings of Leymus chinensis inoculated with or without mycorrhizae were cultivated in soil with 0, 100 or 200 mM NaHCO₃ under 0, 5 or 10% (w/v) PEG treatment, and the changes in growth, osmotic adjustment substances and ions were measured. The results showed that the interaction of alkali and drought stresses caused greater seedling growth inhibition than either single alkali or drought stress due to ion toxicity and oxidative damage. Mycorrhizae could alleviate the growth inhibition of seedlings under alkali or drought stress. The interaction of alkali and drought stresses did not affect the alleviating effect of mycorrhizae on seedling growth but improved the osmotic regulation ability and ionic balance of the seedlings. Our results clearly show different effects of the interaction of alkali and drought stresses versus a single stress (alkali or drought) on plant development and provide new insights into the positive effect of arbuscular mycorrhizal fungi on host plants under such stress conditions.

Foliar Application of Salicylic Acid Improves Salt Tolerance of Sorghum (Sorghum bicolor (L.) Moench)

It has been reported that around the world, approximately 19.5% of all irrigated land and 2.1% of dry land is affected by salt stress, and these percentages continue to increase. Sorghum is the fifth most important cereal in the world and therefore research on its salt tolerance is of global importance. In our research, we focused on foliar application of salicylic acid (SA) on salt-stressed sorghum. We performed a pot experiment with two salt levels (0 and 100 mM sodium chloride NaCl) and five SA concentrations (0, 50, 100, 150 and 200 mg/L). Our results suggest that in saline conditions foliar application of SA induced an adaptive response to salinity by inducing proline accumulation as well as antioxidant enzymes activities and enhanced the protection of the photosynthetic machinery, maintained photosynthesis activities, and improved the growth of sorghum plants. These alleviation effects were depended on applied SA concentration. Under saline condition 150 mg/L, SA was the most effective for relieving the adverse effect of salt stress. Under non-saline conditions 100 mg/L SA was the best for improving sorghum growth and dry matter production. Our results demonstrated that foliar SA application is effective in improving sorghum growth under salinity.

Role of Combined Inoculation with Arbuscular Mycorrhizal Fungi, as a Sustainable Tool, for Stimulating the Growth, Physiological Processes, and Flowering Performance of Lavender

Arbuscular mycorrhizal fungi (AMF) are essential soil microorganisms for terrestrial ecosystems and form beneficial symbioses with the root systems of most agricultural plants. The purpose of this paper was to examine the effect of the community of six AMF on the growth, physiological response, and flowering performance in organic potted lavender culture. The mixture of AMF containing Rhizophagus irregularis, Claroideoglomus claroideum, Funneliformis mosseae, Funneliformis geosporum, Claroideoglomus etunicatum, and Glomus microaggregatum was added in a pot with peat, volcanic rock, and coconut bark. We analyzed the fresh shoot biomass, root biomass, total plant biomass, leaf area, flowering performance, photosynthesis rate, and photosynthetic pigment content. Pearson’s correlation coefficient was performed to get a better understanding of the relationships between the studied variables. The total plant biomass was more pronounced in plants with AMF-S20g (212.01 g plant−1) and AMF-S30g (220.25 g plant−1) than with AMF-S10g (201.96 g plant−1) or in untreated plants (180.87 g plant−1). A statistically significant increase for Chl a, Chl b, and Car was found for AMF-S20g and AMF-S30. Our findings suggest that the AMF mixture application in a growing substrate with peat, coconut bark, and volcanic rock improved plant growth, physiological processes, and ornamental value in mycorrhizal lavender plants. This environmentally friendly agricultural practice could be used for the sustainable production of lavender.

Indigenous Microorganisms Offset Arbuscular Mycorrhizal Fungi-Induced Plant Growth and Nutrient Acquisition Through Negatively Modulating the Genes of Phosphorus Transport and Nitrogen Assimilation

Arbuscular mycorrhizal (AM) fungi that promote plant growth and nutrient acquisition are essential for nutrient-deficient karst areas, while they inevitably regulate host plants jointly with indigenous microorganisms in natural soil. However, how indigenous microorganisms regulate AM-induced benefits on plant growth and nutrient acquisition remains unclear. In this study, the Bidens tripartita as the common plant species in the karst region was cultivated into three soil substrates treated by AM fungi inoculation (AMF), AM fungi inoculation combining with indigenous microorganisms (AMI), and the control without AM fungi and indigenous microorganisms (CK). The plant biomass and concentration of nitrogen (N) and phosphorus (P) were measured, and the transcriptomic analysis was carried out using root tissues. The results showed that AM fungi significantly enhanced the plant biomass, N, and P accumulation with the reduction of plants' N/P ratio; however, the indigenous microorganisms offset the AM-induced benefits in biomass and N and P acquisition. In addition, there are 819 genes in differentially expressed genes (DEGs) of AMF vs. AMI ∩ AMF vs. CK, meaning that AM fungi induced these genes that were simultaneously regulated by indigenous microorganisms. Furthermore, the enrichment analysis suggested that these genes were significantly associated with the metabolic processes of organophosphate, P, sulfur, N, and arginine biosynthesis. Notably, 34 and 17 genes of DEGs were related to P and N metabolism, respectively. Moreover, the indigenous microorganisms significantly downregulated these DEGs, especially those encoding the PHO1 P transporters and the glnA, glutamate dehydrogenase 2 (GDH2), and urease as key enzymes in N assimilation; however, the indigenous microorganisms significantly upregulated genes encoding PHO84 inducing cellular response to phosphate (Pi) starvation. These regulations indicated that indigenous microorganisms restrained the N and P metabolism induced by AM fungi. In conclusion, we suggested that indigenous microorganisms offset nutrient benefits of AM fungi for host plants through regulating these genes related to P transport and N assimilation.

Elucidating the Mechanisms Underlying Enhanced Drought Tolerance in Plants Mediated by Arbuscular Mycorrhizal Fungi

Plants are often subjected to various environmental stresses during their life cycle, among which drought stress is perhaps the most significant abiotic stress limiting plant growth and development. Arbuscular mycorrhizal (AM) fungi, a group of beneficial soil fungi, can enhance the adaptability and tolerance of their host plants to drought stress after infecting plant roots and establishing a symbiotic association with their host plant. Therefore, AM fungi represent an eco-friendly strategy in sustainable agricultural systems. There is still a need, however, to better understand the complex mechanisms underlying AM fungi-mediated enhancement of plant drought tolerance to ensure their effective use. AM fungi establish well-developed, extraradical hyphae on root surfaces, and function in water absorption and the uptake and transfer of nutrients into host cells. Thus, they participate in the physiology of host plants through the function of specific genes encoded in their genome. AM fungi also modulate morphological adaptations and various physiological processes in host plants, that help to mitigate drought-induced injury and enhance drought tolerance. Several AM-specific host genes have been identified and reported to be responsible for conferring enhanced drought tolerance. This review provides an overview of the effect of drought stress on the diversity and activity of AM fungi, the symbiotic relationship that exists between AM fungi and host plants under drought stress conditions, elucidates the morphological, physiological, and molecular mechanisms underlying AM fungi-mediated enhanced drought tolerance in plants, and provides an outlook for future research.

Role of arbuscular mycorrhizal fungi as an underground saviuor for protecting plants from abiotic stresses

To increase food production, prevalent agricultural malpractices such as intensive use of fertilizers and pesticides have led to degradation of the ecosystem. In this situation, there is a need to encourage eco-friendly and sustainable methods for improving crop production under ever increasing abiotic stress conditions. One such method can be through use of arbuscular mycorrhizal fungi (AMF or AM fungi). Soil microorganisms such as AMF serve as a link between plants and the soil resources. AMF represent a key functional group of soil microbiota that is fundamental for soil fertility, crop productivity, yield, quality and ecosystem resilience. AMF potentially increases bioavailability of water as well as various micro- and macro- nutrients which enhances production of plant photosynthates. In plants, inoculation with AMF led to increased photochemical efficiency ultimately resulting in enhanced plant growth. In this review we have summarized amelioration of drought or water scarcity, salt stress, increasing temperature or high temperature and heavy metal stresses etc. in crop plants by AMF through its effects on various physiological and biochemical processes including photosynthesis. The review also highlights AMF induced tolerance and adaptive mechanisms which protect crops from stresses. We conclude the review with a discussion of unseen issues and suggestions for future researches.

Nitrogen absorption efficiency and mechanism in Arbuscular mycorrhizal fungi - Canna indica symbiosis

Arbuscular mycorrhizal fungi (AMF) and its symbiosis with Canna indica on nitrogen (N) absorption was investigated for the remediation of contaminated soil. Canna indica plants with rhizome and leaf integrity intact were collected in spring and autumn seasons. To maintain the ideal nutrient composition, Hoagland concentrated nutrient solution was diluted with deionized water and additional nutrient solution was added periodically. Treated root samples were observed with an optical microscope and the number of hyphae and intersections as well as inoculation status were examined. High-throughput sequencing experiment was conducted to quantify AMF inoculation. Alpha diversity study was used to characterize abundance and diversity of the symbiosis. Hydroponic experiments were conducted to explore the absorption effectiveness of AMF-Canna symbiosis under different NH₄⁺-N and NO₃^--N combinations. Hyphal colonization rate was only about 5.66 ± 1.08% in seedling stage in spring, but enhanced in the adult stage in autumn (53.89 ± 1.43%). Results revealed that AMF had no significant impact on NO₃^--N absorption by Canna roots, however, absorption of NH₄⁺-N was improved by 63% under low concentration. Results revealed that when NH₄⁺-N and NO₃^--N were applied combinedly in a 1:1 ratio, their respective absorption rates were enhanced to 99.63% and 99.50%. Compared with the case of NH₄⁺-N as N source alone, synergistic effect of NH₄⁺-N and NO₃^--N significantly changed the absorption of NH₄⁺-N by C. indica, but its correlation with AMF inoculation was still not significant. Current findings could enhance understanding for effective N uptake and resource recovery.

The Role of Plant-Associated Bacteria, Fungi, and Viruses in Drought Stress Mitigation

Drought stress is an alarming constraint to plant growth, development, and productivity worldwide. However, plant-associated bacteria, fungi, and viruses can enhance stress resistance and cope with the negative impacts of drought through the induction of various mechanisms, which involve plant biochemical and physiological changes. These mechanisms include osmotic adjustment, antioxidant enzyme enhancement, modification in phytohormonal levels, biofilm production, increased water and nutrient uptake as well as increased gas exchange and water use efficiency. Production of microbial volatile organic compounds (mVOCs) and induction of stress-responsive genes by microbes also play a crucial role in the acquisition of drought tolerance. This review offers a unique exploration of the role of plant-associated microorganisms-plant growth promoting rhizobacteria and mycorrhizae, viruses, and their interactions-in the plant microbiome (or phytobiome) as a whole and their modes of action that mitigate plant drought stress.

Responses of soil N2 O emissions and their abiotic and biotic drivers to altered rainfall regimes and co-occurring wet N deposition in a semi-arid grassland

Global change factors such as changed rainfall regimes and nitrogen (N) deposition contribute to increases in the emission of the greenhouse gas nitrous oxide (N₂ O) from the soil. In previous research, N deposition has often been simulated by using a single or a series of N addition events over the course of a year, but wet N deposition actually co-occurs with rainfall. How soil N₂ O emissions respond to altered rainfall amount and frequency, wet N deposition, and their interactions is still not fully understood. We designed a three-factor, fully factorial experiment with factors of rainfall amounts (ambient, -30%) rainfall frequency (ambient, ±50%) and wet N deposition (with/without) co-occurring with rainfall in semi-arid grassland mesocosms, and measured N₂ O emissions and their possible biotic and abiotic drivers. Across all treatments, reduced rainfall amount and N deposition increased soil N₂ O emissions by 35% and 28%, respectively. A significant interactive effect was observed between rainfall amount and N deposition, and to a lesser extent between rainfall frequency and N deposition. Without N deposition, reduced rainfall amount and altered rainfall frequency indirectly affected soil N₂ O emissions by changing the abundance of nirK and soil net N mineralization, and the changes in nirK abundance were indirectly driven by soil N availability rather than directly by soil moisture. With N deposition, both the abundance of nirK and the level of soil water-filled pore space contributed to changes in N₂ O emissions in response to altered rainfall regimes, and the changes in the abundance of nirK were indirectly driven by plant N uptake and nitrifier (ammonia-oxidizing bacteria) abundance. Our results imply that unlike wetter grassland ecosystems, reduced precipitation may increase N₂ O emissions, and N deposition may only slightly increase N₂ O emissions in arid and semi-arid N-limited ecosystems that are dominated by grasses with high soil N uptake capacity.

The Alkali Tolerance of Broomcorn Millet (Panicum miliaceum L.) at the Germination and Seedling Stage: The Case of 296 Broomcorn Millet Genotypes

Broomcorn millet (BM), one of the earliest domesticated cereal crops originating in northern China, can tolerate extreme conditions, such as drought and high temperatures, which are prevalent in saline-alkali, arid, and barren landscapes. However, its adaptive mechanism to alkali stress is yet to be comprehensively understood. In this study, 80 and 40 mM standard alkali stress concentrations were used to, respectively, evaluate the alkali tolerance at the germination and seedling stages of 296 BM genotypes. Principal component analysis (PCA), Pearson's correlation analysis, and F-value comprehensive analysis were performed on the germination parameters (germination potential, germination index, germination rate, vigor index, root length/weight, sprout length/weight, and alkali damage rate). Based on their respective F-values, the BM genotypes were divided into five categories ranging from highly alkali resistant to alkali sensitive. To study the response of seedlings to alkaline stress, we investigated the phenotypic parameters (plant height, green leaf area, biomass, and root structure) of 111 genotypes from the above five categories. Combining the parameters of alkali tolerance at the germination and seedling stages, these 111 genotypes were further subdivided into three groups with different alkali tolerances. Variations in physiological responses of the different alkali-tolerant genotypes were further investigated for antioxidant enzyme activity, soluble substances, malondialdehyde (MDA) content, electrolyte leakage rate, and leaf structure. Compared with alkali-sensitive genotypes, alkali-tolerant genotypes had high antioxidant enzyme activity and soluble osmolyte content, low MDA content and electrolyte leakage rate, and a more complete stomata structure. Taken together, this study provides a comprehensive and reliable method for evaluating alkali tolerance and will contribute to the improvement and restoration of saline-alkaline soils by BM.

Contribution of strigolactone in plant physiology, hormonal interaction and abiotic stresses

Strigolactones (SLs) are carotenoid-derived molecules, which regulate various developmental and adaptation processes in plants. These are engaged in different aspects of growth such as development of root, leaf senescence, shoot branching, etc. Plants grown under nutrient-deficient conditions enhance SL production that facilitates root architecture and symbiosis of arbuscular mycorrhizal fungi, as a result increases nutrient uptake. The crosstalk of SLs with other phytohormones such as auxin, abscisic acid, cytokinin and gibberellins, in response to abiotic stresses indicates that SLs actively contribute to the regulatory systems of plant stress adaptation. In response to different environmental circumstances such as salinity, drought, heat, cold, heavy metals and nutrient deprivation, these SLs get accumulated in plant tissues. Strigolactones regulate multiple hormonal responsive pathways, which aids plants to surmount stressful environmental constraints as well as reduce negative impact on overall productivity of crops. The external application of SL analog GR24 for its higher bioaccumulation can be one of the possible approaches for establishing various abiotic stress tolerances in plants.