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

Physiological Alteration in Sunflower Plants (Helianthus annuus L.) Exposed to High CO2 and Arbuscular Mycorrhizal Fungi

Sunflower plants (Helianthus annuus L.) in a CO2-enriched atmosphere (eCO2) were used herein to examine the developmental and physiological effects of biofertilization with mycorrhizae (Rhizophagus irregularis). The eCO2 environment stimulated colonization using R. irregularis mycorrhizal fungi, as compared to plants grown under ambient CO2 conditions (aCO2). This colonization promotes plant growth due to an increased nutrient content (P, K, Mg, and B), which favors a greater synthesis of photosynthetic pigments. Biofertilized plants (M) under eCO2 conditions have a higher concentration of carbon compounds in their leaves, as compared to non-biofertilized eCO2 plants (NM). The biofertilization (M) of sunflowers with R. irregularis decreased the C/N ratio, as compared to the NM plants, decreasing the hydrogen peroxide content and increasing the antioxidant enzyme activity (catalase and APX). These results suggest that sunflower symbiosis with R. irregularis improves the absorption of N, while also decreasing the plant’s oxidative stress. It may be concluded that biofertilization with mycorrhizae (R. irregularis) may potentially replace the chemical fertilization of sunflower plants (H. annuus L.), resulting in more environmentally friendly agricultural practices. This information is essential to our understanding of the mechanisms influencing the C and N dynamic in future climate change scenarios, in which high CO2 levels are expected.

Comprehensive Assessment of Ameliorative Effects of AMF in Alleviating Abiotic Stress in Tomato Plants

Population growth and food necessity envisaged the dire need for supplementation to a larger community balance in food production. With the advent of the green revolution, agriculture witnessed the insurrection of horticultural fruit crops and field crops in enormous modes. Nevertheless, chemical fertilizer usage foresees soil pollution and fertility loss. Utilization of biocontrol agents and plant growth promotion by microbial colonization enrooted significant restoration benefits. Constant reliability for healthy foods has been emancipated across the globe stressing high nutritive contents among indigenous field crops like tomato (Solanum lycopersicum). However, stress tolerance mechanisms and efficient abatement require deeper insights. The applicability of arbuscular mycorrhizal fungi (AMF) poses as an ultimate strategy to minimize the deleterious consequences of abiotic stress such as salt, drought, temperature and heavy metal stress sustainably. The rational modality employing the application of AMF is one of significant efforts to lessen cell damages under abiotic stress. The novelty of the compilation can be redressed to cohesive literature for combating stress. The literature review will provide agricultural scientists worldwide in providing a rational approach that can have possible implications in not only tomato but also other vegetable crops.

Antioxidant response in arbuscular mycorrhizal fungi inoculated wetland plant under Cr stress

Arbuscular mycorrhizal fungi (AMF) provide a positive effect on antioxidant mechanisms in terrestrial plants under heavy metal stress. This study investigated the effects of AMF on wetland plant (Iris wilsonii) growth and antioxidant response under Cr stress at different water depths. Results showed that AMF inoculated I. wilsonii had higher antioxidant response than non-inoculated controls, with shoot superoxide dismutase (SOD), root SOD, shoot peroxidase (POD), and root POD contents increased by 4.7-39.6%, 7.5-29.5%, 11.2-68.6%, 16.8-50.3%, respectively. Meanwhile, shoot (root) proline, malondialdehyde (MDA) and superoxide anion (O₂^.-) contents in the AMF inoculated I. wilsonii were 10.2-44.3% (2.8-37.2%), 11.5-35.4% (16.9-28.2), and 14.9-30.5% (-0.9-26.3%) lower than those in the non-inoculated controls, respectively. Besides, AMF improved the growth of I. wilsonii with biomass, height, chlorophyll, K, and P contents in the shoots increased by 10.5-32.5%, 17.4-44.9%, 4.7-37.7%, 12.0-30.7%, 13.5-20.6%, respectively. Moreover, the I. wilsonii tolerance to Cr stress was also enhanced under the water depth of 6-3 cm. Therefore, AMF play an important role in wetland plant growth and antioxidant response under Cr stress, and it can improve wetland plants' tolerance to Cr stress at fluctuating water depth.

Enhanced uptake of drip-applied flonicamid by arbuscular mycorrhizal fungi and improved control of cotton aphid

BACKGROUND

Drip application of insecticides has been used for controlling crop pests, but the application doses are usually higher than those used for foliar spray. Arbuscular mycorrhizal fungi (AMF) have been reported to improve root absorption of nutrients from soil, which may also enhance the uptake of drip-applied insecticides, reducing application doses. In this study, greenhouse and field experiments were carried out to determine if AMF could colonize cotton roots, if the colonization could enhance the absorption of drip-applied flonicamid, and if the enhanced uptake could reduce flonicamid application dose, while maintaining control efficacy against cotton aphid.

RESULTS

The applied AMF effectively colonized cotton roots and significantly promoted root growth. Fresh weights of cotton roots inoculated with multiple AMF were 28% greater than those of uninoculated plants. Multiple AMF colonization significantly increased flonicamid concentrations in leaves, which were 44.5-139.7% higher than for non AMF-colonized roots, corresponding to 3.7-31.8% increases in corrected mortalities of cotton aphid compared with uninoculated plants. AMF colonization reduced the application rate of flonicamid and the residue level of flonicamid in soil.

CONCLUSION

Drip application of flonicamid to cotton roots inoculated with AMF represents a new approach to insecticide application. AMF colonization increased flonicamid uptake, improved aphid control efficacy and reduced flonicamid application rates. © 2020 Society of Chemical Industry.

Eco-physiological processes are more sensitive to simulated N deposition in leguminous forbs than non-leguminous forbs in an alpine meadow of the Qinghai-Tibetan Plateau

Increased nitrogen (N) deposition can affect ecosystem processes and thus influence plant eco-physiological processes in grasslands. However, how N deposition affects eco-physiological processes of leguminous and non-leguminous forbs in alpine grasslands is understudied. A long-term field experiment using a range of simulated N deposition rates (0, 8, 24, 40, 56, and 72 kg N ha^-1 year^-1) was established to examine the effects of N deposition on various eco-physiological parameters in leguminous and non-leguminous forbs in an alpine meadow of the Qinghai-Tibetan Plateau. We found that the responses of leguminous and non-leguminous forbs to simulated N deposition varied. Net photosynthetic rate of leguminous and non-leguminous forbs exhibited different response patterns, but chronic increases in simulated N deposition rates may lead to negative effects in both functional groups. Neither functional group responded differently in aboveground biomass under the highest N addition level (72 kg N ha^-1 year^-1) compared to the control. Differences in aboveground biomass of leguminous forbs were observed at intermediate N levels. Short-term simulated N deposition significantly promoted N uptake of both functional groups. In leguminous forbs, simulated N deposition affected net photosynthetic rates (P_N) and aboveground biomass (AGB) mainly via stomatal conductance (gs), water use efficiency (WUE), and plant N uptake. In non-leguminous forbs, simulated N deposition affected P_N and AGB mainly through WUE and plant N uptake. Our findings suggest that leguminous and non-leguminous forbs have differential response mechanisms to N deposition, and compared with non-leguminous forbs, leguminous forbs are more sensitive to continuing increased N deposition. The obvious decline trend in photosynthetic capacity in leguminous forbs is likely to exacerbate the already divergent ecological processes between leguminous and non-leguminous forbs. More importantly, these changes are likely to alter the future composition, function, and stability of alpine meadow ecosystems.

Responses of ajowan (Trachyspermum ammi L.) to exogenous salicylic acid and iron oxide nanoparticles under salt stress

This research with a factorial arrangement was undertaken to investigate physiological responses of ajowan plants to foliar treatment of salicylic acid (1 mM) and nano-Fe₂O₃ (3 mM) under various salinity levels (0, 4, 8, 12 dS m^-1 NaCl, respectively). Rising salinity enhanced sodium and endogenous SA contents, soluble sugars, protein, glycine betaine, proline, antioxidant enzymes activities, ROS generation, and lipid peroxidation, while reduced potassium and iron contents, membrane stability index, leaf water content, leaf pigments, root and shoot biomasses, and seed yield. Application of particularly SA and SA+nano-Fe₂O₃ alleviated salt toxicity via enhancing K⁺ uptake, K⁺/Na⁺ ratio, Fe content, endogenous level of SA, the activities of antioxidant enzymes (superoxide dismutase, catalase, peroxidase, and polyphenol oxidase), and most of the osmolytes. These changes were resulted in improving membrane stability index, leaf water content, leaf pigments, root and shoot growth, and finally seed yield of plants under moderate and severe salinities. Therefore, these treatments can additively enhance salt tolerance and physiological performance of ajowan through increasing antioxidant capacity, osmolytes, and photosynthetic pigments. Graphical Abstract .

Transcriptomic Study for Identification of Major Nitrogen Stress Responsive Genes in Australian Bread Wheat Cultivars

High nitrogen use efficiency (NUE) in bread wheat is pivotal to sustain high productivity. Knowledge about the physiological and transcriptomic changes that regulate NUE, in particular how plants cope with nitrogen (N) stress during flowering and the grain filling period, is crucial in achieving high NUE. Nitrogen response is differentially manifested in different tissues and shows significant genetic variability. A comparative transcriptome study was carried out using RNA-seq analysis to investigate the effect of nitrogen levels on gene expression at 0 days post anthesis (0 DPA) and 10 DPA in second leaf and grain tissues of three Australian wheat (Triticum aestivum) varieties that were known to have varying NUEs. A total of 12,344 differentially expressed genes (DEGs) were identified under nitrogen stress where down-regulated DEGs were predominantly associated with carbohydrate metabolic process, photosynthesis, light-harvesting, and defense response, whereas the up-regulated DEGs were associated with nucleotide metabolism, proteolysis, and transmembrane transport under nitrogen stress. Protein–protein interaction and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways analysis further revealed that highly interacted down-regulated DEGs were involved in light-harvesting and photosynthesis, and up-regulated DEGs were mostly involved in steroid biosynthesis under N stress. The common down-regulated genes across the cultivars included photosystem II 10 kDa polypeptide family proteins, plant protein 1589 of uncharacterized protein function, etc., whereas common up-regulated genes included glutamate carboxypeptidase 2, placenta-specific8 (PLAC8) family protein, and a sulfate transporter. On the other hand, high NUE cultivar Mace responded to nitrogen stress by down-regulation of a stress-related gene annotated as beta-1,3-endoglucanase and pathogenesis-related protein (PR-4, PR-1) and up-regulation of MYB/SANT domain-containing RADIALIS (RAD)-like transcription factors. The medium NUE cultivar Spitfire and low NUE cultivar Volcani demonstrated strong down-regulation of Photosystem II 10 kDa polypeptide family protein and predominant up-regulation of 11S globulin seed storage protein 2 and protein transport protein Sec61 subunit gamma. In grain tissue, most of the DEGs were related to nitrogen metabolism and proteolysis. The DEGs with high abundance in high NUE cultivar can be good candidates to develop nitrogen stress-tolerant variety with improved NUE.

NaCl Improves Suaeda salsa Aniline Tolerance in Wastewater

Halophytes have been studied as a model for morphological traits of adaptation to saline environments. However, little information has been given on plant growth, chlorophyll fluorescence responses, and change of ion content in halophytes grown in an aniline–salinity coexistent environment. This study hypothesized that aniline could induce alterations in plant growth, chlorophyll fluorescence, and ion content in Suaeda salsa, but salinity could promote the tolerance of halophytes to aniline. A 6 (aniline) × 3 (NaCl) factorial experiment (for a total of 18 treatments) was conducted to test the above hypothesis. After 30 d of cultivation, roots and shoots were harvested separately to analyze the effects of salinity on the seedling growth under aniline stress. Biomass accumulation was inhibited by aniline treatment, and the inhibition was significantly alleviated by 200 mM NaCl. The change in chlorophyll fluorescence in leaves with aniline stress was moderated by the addition of NaCl. The removal efficiency of aniline was significantly enhanced by moderate salinity. Aniline stress decreased the accumulation of Mg2+, but various concentrations of NaCl increased the accumulation of Mg2+, especially with 200 mM NaCl in both roots and shoots. Both aniline and salinity decreased the content of Ca2+. There was a negative correlation between the K+ and NaCl concentrations and between the Cl− and aniline concentrations. Our results indicated that Suaeda salsa may be suitable for the remediation of salinity and aniline-enriched wastewater.

Synergistic effects between arbuscular mycorrhizal fungi and rhizobium isolated from As-contaminated soils on the As-phytoremediation capacity of the tropical woody legume Anadenanthera peregrina

The synergistic relationship between arbuscular mycorrhizal fungi and plant species may play a key role in phytoremediation of arsenic(As)-contaminated soils. By using modified Leonard jars, we investigated both the distinct and integrative roles of arbuscular mycorrhizal fungi (AMF-Acaulospora scrobiculata) and rhizobia (BH-ICB-A8) isolated from As-contaminated soil on the capacity of Anadenanthera peregrina to reclaim arsenate [As(V)] from soil. AMF inoculation greatly increased plant phosphorous nutrition, as reflected in greater growth, and increased As-concentrations in the roots and shoots. While rhizobia inoculation alone increased nitrogen nutrition it did not promote plant growth or As-uptake. Rhizobia and AMF inoculation together had synergistic effects, however, increasing both the growth and the As-phytoremediation capacity of A. peregrina. Joint inoculation with rhizobia and AMF should therefore be considered a potential technique for rehabilitating As-contaminated areas using A. peregrina.

Interactive effects of exogenous melatonin and Rhizophagus intraradices on saline-alkaline stress tolerance in Leymus chinensis

Melatonin, a ubiquitous molecule found in almost all organisms, is considered an important regulator in plant growth. However, little is known about the interactive effect of melatonin and arbuscular mycorrhizal (AM) fungi on plant resistance against soil salinity and alkalinity. To fill in such a gap in knowledge, we conducted three experiments to explore (1) whether exogenous melatonin and an AM fungus had interactive effects on plant response to saline-alkaline stress, (2) whether the influence of melatonin on mycorrhizal plant stress tolerance was attributable to effect on the AM fungus, and (3) whether the effect of melatonin application was due to changes in soil salinity and alkalinity. We found interactive effects between melatonin and the AM fungus on alleviating ROS burst, decreasing malondialdehyde content and protecting Leymus chinensis photosynthetic activity through activation of antioxidant enzyme and gene expression (superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase) in plant shoots and roots. Our results showed that exogenous melatonin promoted spore germination and hyphal length of the AM fungus under Petri-dish conditions. However, exogenous melatonin application did not exhibit significant effects on soil salinity and alkalinity. This study provides an insight into the beneficial effects of exogenous melatonin on saline-alkaline stress tolerance in mycorrhizal L. chinensis through regulating antioxidant systems, protecting photosynthetic activity, and promoting associated AM fungal growth without changing soil salinity and alkalinity. It also reveals potential applications of exogenous melatonin and AM fungi for the restoration of saline-alkaline degraded grassland.

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

BACKGROUND

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

RESULTS

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

CONCLUSIONS

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

Metabolomics Analysis Reveals the Alkali Tolerance Mechanism in Puccinellia tenuiflora Plants Inoculated with Arbuscular Mycorrhizal Fungi

Soil alkalization is a major environmental threat that affects plant distribution and yield in northeastern China. Puccinellia tenuiflora is an alkali-tolerant grass species that is used for salt-alkali grassland restoration. However, little is known about the molecular mechanisms by which arbuscular mycorrhizal fungi (AMF) enhance P. tenuiflora responses to alkali stress. Here, metabolite profiling in P. tenuiflora seedlings with or without arbuscular mycorrhizal fungi (AMF) under alkali stress was conducted using liquid chromatography combined with time-of-flight mass spectrometry (LC/TOF-MS). The results showed that AMF colonization increased seedling biomass under alkali stress. In addition, principal component analysis (PCA) and orthogonal projections to latent structures discriminant analysis (OPLS-DA) demonstrated that non-AM and AM seedlings showed different responses under alkali stress. A heat map analysis showed that the levels of 88 metabolites were significantly changed in non-AM seedlings, but those of only 31 metabolites were significantly changed in AM seedlings. Moreover, the levels of a total of 62 metabolites were significantly changed in P. tenuiflora seedlings after AMF inoculation. The results suggested that AMF inoculation significantly increased amino acid, organic acid, flavonoid and sterol contents to improve osmotic adjustment and maintain cell membrane stability under alkali stress. P. tenuiflora seedlings after AMF inoculation produced more plant hormones (salicylic acid and abscisic acid) than the non-AM seedlings, probably to enhance the antioxidant system and facilitate ion balance under stress conditions. In conclusion, these findings provide new insights into the metabolic mechanisms of P. tenuiflora seedlings with arbuscular mycorrhizal fungi under alkali conditions and clarify the role of AM in the molecular regulation of this species under alkali stress.

Effect of Arbuscular Mycorrhizal Fungi (AMF) and Plant Growth-Promoting Bacteria (PGPR) Inoculations on Elaeagnus angustifolia L. in Saline Soil

Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) are considered highly-efficient agents for conferring salt tolerance in host plants and improving soil fertility in rhizosphere. However, information about the inoculation of beneficial microbes on halophytes in arid and semi-arid regions remains inadequate. The objective of this study was to evaluate the influence of AMF (Glomus mosseae) inoculation, alone or in combination with PGPR (Bacillus amyloliquefaciens), on biomass accumulation, morphological characteristics, photosynthetic capacity, and rhizospheric soil enzyme activities of Elaeagnus angustifolia L., a typical halophyte in the northwest of China. The results indicate that, for one-year-old seedlings of Elaeagnus angustifolia L., AMF significantly promoted biomass accumulation in aboveground organs, increased the numbers of leaves and branches, and improved the leaf areas, stem diameters and plant height. AMF-mediated morphological characteristics of aboveground organs favored light interception and absorption and maximized the capacities for photosynthesis, transpiration, carbon dioxide assimilation and gas exchange of Elaeagnus angustifolia L. seedlings in saline soil. AMF also promoted root growth, modified root architecture, and enhanced soil enzyme activities. Elaeagnus angustifolia L. was more responsive to specific inoculation by AMF than by a combination of AMF and PGPR or by solely PGPR in saline soils. Therefore, we suggest that G. mosseae can be used in saline soil to enhance Elaeagnus angustifolia L. seedlings growth and improve soil nutrient uptake. This represents a biological technique to aid in restoration of saline-degraded areas.

Arbuscular Mycorrhizal Fungi Mediate Drought Tolerance and Recovery in Two Contrasting Carob (Ceratonia siliqua L.) Ecotypes by Regulating Stomatal, Water Relations, and (In)Organic Adjustments

Irregular precipitation and drought caused an increase in tree mortality rates in multiple forest biomes with alterations in both ecosystem services and carbon balance. Carob (Ceratonia siliqua) growth and production in arid and semi-arid ecosystems are likely affected by climate change-induced droughts. Understanding the physiological responses of drought-induced early-stage tree death and strategies to enhance drought tolerance and optimize growth will help tree improvement programs. Mycorrhizal inoculation has a pronounced impact on plant growth, water absorption, mineral nutrition, and protection from abiotic stresses. However, a better understanding of these complex interconnected cellular processes and arbuscular mycorrhizal fungi (AMF)-mediated mechanisms regulating drought tolerance in plants will enhance its potential application as an efficient approach for bio-amelioration of stresses. The objectives of this work were to elucidate the different effects of autochthone AMF on inorganic solute and water content uptakes, organic adjustments (sugar and proteins content), leaf gas exchange (stomatal conductance and efficiency of photosystems I and II), and oxidative damage of two contrasting ecotypes of carob seedlings: coastal (southern ecotype (SE)) and in-land (northern ecotype (NE)) under control (C), drought (by cessation of irrigation for 15 days (15D)), and recovery (R) conditions. Our findings showed that AMF promoted growth, nutrient content, and physiological and biochemical parameters in plants of both ecotypes during C, 15D, and R conditions. After four days of recovery, stomatal conductance (gs), the maximum photochemical efficiency of PSII (Fv/Fm), water content, and plant uptake of mineral nutrients (P, K, Na, and Ca) were significantly higher in shoots of mycorrhizal (AM) than non-mycorrhizal (NM) control plants. Consequently, AMF reduced to a greater degree the accumulation of hydrogen peroxide (H2O2) and oxidative damage to lipid (malondialdehyde (MDA)) content in AM than NM plants in NE and SE, after recovery. Altogether, our findings suggest that AMF can play a role in drought resistance of carob trees at an early stage by increasing the inorganic solutes (P, K, Na, and Ca), water content uptake, organic solutes (soluble sugars and protein content), stomatal conductance, and defense response against oxidative damage during re-watering after drought stress.

Alleviation of Salt Stress in Upland Rice (Oryza sativa L. ssp. indica cv. Leum Pua) Using Arbuscular Mycorrhizal Fungi Inoculation

Arbuscular mycorrhizal fungi (AMF) symbionts not only promote the growth of host plant but also alleviate abiotic stresses. This study aimed to investigate the putative role of AMF in salt stress regulation of upland pigmented rice cv. Leum Pua (LP) comparing with Pokkali salt tolerant (positive check). In general, LP is a variety of glutinous rice that contains anthocyanin pigment in the black pericarp, due to which it possesses high antioxidant activities compared to non-pigmented rice. Pot experiment was conducted to evaluate the impact of inoculated AMF, Glomus etunicatum (GE), Glomus geosporum (GG), and Glomus mosseae (GM) strains, in the LP plantlets subjected to 0 (control) or 150 mM NaCl (salt stress) for 2 weeks in comparison with Pokkali (a salt tolerant rice cultivar), which was maintained as a positive check. Root colonization percentage under NaCl conditions ranged from 23 to 30%. Na⁺ content in the flag leaf tissues was increased to 18-35 mg g^-1 DW after exposure to 150 mM NaCl for 14 days in both inoculated and un-inoculated LP plants, whereas Na:K ratio was very low in cv. Pokkali. Interestingly, sucrose content in the flag leaf tissues of un-inoculated LP plants under salt stress was increased significantly by 50 folds over the control as an indicator of salt stress response, whereas it was unchanged in all AMF treatments. Fructose and free proline in GE inoculated plants under salt stress were accumulated over control by 5.75 and 13.59 folds, respectively, for osmotic adjustment of the cell, thereby maintaining the structure and functions of chlorophyll pigments, F_v/F_m, Φ_PSII, and stomatal function. Shoot height, flag leaf length, number of panicles, panicle length, panicle weight, and 100-grain weight in GE inoculated plants of cv. LP under salt stress were maintained similar to cv. Pokkali. Interestingly, cyanidin-3-glucoside (C3G) and peonidin-3-glucoside (P3G) in the pericarp of cv. LP were regulated by GE inoculation under salt stress conditions. In summary, AMF-inoculation in rice crop is a successful alternative approach to reduce salt toxicity, maintain the yield attributes, and regulate anthocyanins enrichment in the pericarp of grains.

Arbuscular mycorrhizal fungi effect growth and photosynthesis of Phragmites australis (Cav.) Trin ex. Steudel under copper stress

Arbuscular mycorrhizal fungi (AMF) is an effective way to remove heavy metals' inhibition on plants, however, few relevant research attempts have been made to determine the contribution of AMF to the physiological and biochemical changes related to the enhanced copper tolerance of Phragmites australis under metal-stressed conditions. In this study, the effects of AMF inoculation on P. australis under different concentrations of copper stress were investigated according to the changes in the parameters related to growth and development, and photosynthetic charateristics. Then, differentially expressed proteins (DEPs) were evaluated by the Isobaric Tag for Relative and Absolute Quantification (iTRAQ) system, which could accurately quantify the DEPs by measuring peak intensities of reporter ions in tandem mass spectrometry (MS/MS) spectra. It was found that AMF inoculation may relieve the photosynthesis inhibition caused by copper stress on P. australis and thus promote growth. Proteomic analysis results showed that under copper stress, the inoculation of R. irregularis resulted in a total of 459 differently-expressed proteins (200 up-regulated and 259 down-regulated) in root buds. In addition, the photosynthetic changes caused by AMF inoculation mainly involve the up-regulated expression of transmembrane protein-pigment complexes CP43 (photosystem II) and FNR (ferredoxin-NADP+ oxidoreductase related to photosynthetic electron transport). These results indicate that AMF could effectively improve the growth and physiological activity of P. australis under copper stress, and thus provides a new direction and instructive evidence for determining the mechanisms by which AMF inoculation enhances the copper tolerance of plants.

Seed germination and early seedling growth of six wetland plant species in saline-alkaline environment

This study focused on the effect of saline and alkaline stress on six typical wetland plant species during seed germination and early seedling growth stages. Based on the indicators of germination, seedling growth and ionic absorption in seedlings, relatively saline and alkaline tolerant plant species were selected and tolerance mechanism was discussed. Results showed that the existence of saline and alkaline stress inhibited the capacity of germination and early seedling growth of most tested plant species to varying degrees, therein effects of saline-alkaline stress were greater than saline stress. Based on the results of principal component analysis (PCA), germination percentage, K⁺ content, plant height, Na⁺ content and Na⁺/K⁺ ratios can be selected as representative indicators for saline and alkaline tolerance evaluation during seed germination and early seedling growth stages. Among tested species, Juncus effusus and Vetiveria zizanioides exhibited relatively higher saline and alkaline tolerant capacity during their seed germination and early seedling growth. Additionally, both species increase K⁺ accumulation and retain lower Na⁺/K⁺ ratios, which might be their tolerance mechanisms at ion level. In conclusion, V. zizaniodes and J. effusus were recommended as potential plant species for restoring degraded saline-alkaline wetlands and/or establishing constructed wetlands for treating saline wastewater.

Role of Arbuscular Mycorrhizal Fungi in Plant Growth Regulation: Implications in Abiotic Stress Tolerance

Abiotic stresses hamper plant growth and productivity. Climate change and agricultural malpractices like excessive use of fertilizers and pesticides have aggravated the effects of abiotic stresses on crop productivity and degraded the ecosystem. There is an urgent need for environment-friendly management techniques such as the use of arbuscular mycorrhizal fungi (AMF) for enhancing crop productivity. AMF are commonly known as bio-fertilizers. Moreover, it is widely believed that the inoculation of AMF provides tolerance to host plants against various stressful situations like heat, salinity, drought, metals, and extreme temperatures. AMF may both assist host plants in the up-regulation of tolerance mechanisms and prevent the down-regulation of key metabolic pathways. AMF, being natural root symbionts, provide essential plant inorganic nutrients to host plants, thereby improving growth and yield under unstressed and stressed regimes. The role of AMF as a bio-fertilizer can potentially strengthen plants' adaptability to changing environment. Thus, further research focusing on the AMF-mediated promotion of crop quality and productivity is needed. The present review provides a comprehensive up-to-date knowledge on AMF and their influence on host plants at various growth stages, their advantages and applications, and consequently the importance of the relationships of different plant nutrients with AMF.

Effects of simulated N deposition on photosynthesis and productivity of key plants from different functional groups of alpine meadow on Qinghai-Tibetan plateau

Nitrogen (N) deposition may alter physiological process of plants in grassland ecosystem. However, little is known about the response mechanism of individual plants in alpine regions to N deposition. We conducted a field experiment, and three treatments including 0 kg Nha^-1year^-1 (CK), 8 kgNha^-1year^-1 (Low N), and 72 kg N ha^-1 year^-1 (High N) were established to simulate N deposition in alpine meadow of Qinghai-Tibetan plateau. Our objectives were to determine the influence of N deposition on photosynthesis of different functional types of herbage species in alpine meadow, and finally characterize the links of plant productivity and photosynthesis with soil nutrients. The results showed that responses of alpine plants were species-specific under N deposition. Compared with grass species Agropyron cristatum and forb species Thalictrum aquilegifolium, the sedge species Carex melanantha was much more sensitive to N deposition; a lower N load (8 kgNha^-1year^-1) can cause a negative effect on its photosynthesis and productivity. Additionally, N deposition can promote plant N uptake and significantly decreased the C (carbon)/N (nitrogen) ratio. Compared with CK and low N deposition, high N deposition inhibited the photosynthesis and growth of the forb species Thalictrum aquilegifolium and sedge species Carex melanantha. In all three functional types of herbage species, the grass species A. cristatum tended to show a much higher photosynthetic capacity and better growth potential; thus, suggesting that grass species A. cristatum will be a more adaptative alpine plants under N deposition. Our findings suggested that plant photosynthetic responses to N deposition were species-specific, low N deposition was not beneficial for all the herbage species, and N deposition may change plant composition by the differential photosynthetic responses among species in alpine grassland. Plant composition shift to grass-dorminant in alpine regions might be attributed to a much higher photosynthetic potential and N use efficiency of grass species.

Comparison of PAH content, potential risk in vegetation, and bare soil near Daqing oil well and evaluating the effects of soil properties on PAHs

As the largest oil field in China, Daqing oil field has been developed in the past six decades. The objectives of this study were to measure the levels of polycyclic aromatic hydrocarbons (PAHs) and assess their ecological risk of PAHs in vegetation soil and bare soil near oil well in Daqing and surrounding soil. Ten sites were selected from two types of soil in grassland: vegetation soil (VS, n = 5) and bare soil (BS, n = 5). The mean concentration of 16 PAHs (∑₁₆ PAHs) was 2240.2 μg/kg. The mean concentrations of eight carcinogenic PAHs (∑_8c PAHs) was 1312.3 μg/kg which accounts for 59% of ∑₁₆ PAHs. The sampling sites had higher proportions of high weight molecular ringed PAHs with higher proportions of benzo (a) pyren (BaP) and benzo (k) fluoranthene (BkF). The main source of PAHs was petroleum, coal/biomass combustion, and vehicular emission in these sampling sites. According to Canadian soil quality guidelines, 60% sites had a significant risk to human health. Moreover, 50% sites had high ecological risk and 30% sites were close to this critical value. Notably, PAH levels were significantly higher in VS than BS; moreover, VS had higher organic matter (OM) content, soil dehydrogenase (sDHA) activity, and lower pH and salt content. A structural equation model was established to explore the effects of soil properties on PAH concentration in VS. The result revealed that OM and sDHA were meaningful to enhance the adsorption and biological fixation of PAHs. This study will provide basic information on PAH level and potential application for phytoremediation.

Arbuscular Mycorrhizal Fungi Trigger Transcriptional Expression of Flavonoid and Chlorogenic Acid Biosynthetic Pathways Genes in Tomato against Tomato Mosaic Virus

Tomato mosaic disease, caused by Tomato Mosaic Virus (ToMV), is one of the most destructive diseases which results in serious crop losses. Research investigations dealing with the biocontrol activity of arbuscular mycorrhizal fungi (AMF) against this viral disease are limited. In this study, the biocontrol activity of AMF on tomato plants infected with ToMV was evaluated in the greenhouse. In addition, their impacts on the transcriptional expression levels of thirteen genes controlling the phenylpropanoid, flavonoid and chlorogenic acid biosynthetic pathways were also investigated using quantitative real-time PCR. Transcriptional expressions of the majority of the studied genes were up-regulated by mycorrhizal colonization in the presence of ToMV, particularly PAL1 and HQT, suggesting their pathogen-dependent inducing effect. Under greenhouse conditions, a significant reduction in the disease severity and incidence, as well as the viral accumulation level was observed as a response to the mycorrhizal colonization of the infected plants. Moreover, the evaluated growth parameters, photosynthetic pigments, and flavonoid content were significantly enhanced by AMF colonization. The obtained results demonstrated the protective role of AMF in triggering the plant immunity against ToMV in a pathogen-dependent manner. Beside their protective and growth-promotion activities, AMF are characterized by low-cost and environment-friendly properties which support their possible use for control of tomato mosaic disease.

Salt-adaptive strategies in oil seed crop Ricinus communis early seedlings (cotyledon vs. true leaf) revealed from proteomics analysis

Soil salinity is a major abiotic stress affecting crop growth and productivity. Ricinus communis has good salt tolerance and is also an important oilseed crop throughout the world. Early seedling stage (such as cotyledon expansion stage) is the most vulnerable period for plant under stresses. However, little information exist concerning the physiological and molecular mechanisms of Ricinus communis seedlings and the role play by cotyledons and true leaf under salt stress. In the present study, biomass, photosynthesis, chlorophyll fluorescence, inorganic ions and organic solutes contents were measured, and two dimensional gel electrophoresis-based proteomic technology was employed to identify the differentially abundant proteins in the salt-treated Ricinus communis cotyledons and true leaves. The results showed that salt stress reduced growth and photosynthesis in the seedlings. With increasing salinity, the Na⁺ content increased and K⁺ content decreased in both cotyledons and leaves, but the true leaves had lower Na⁺ and higher K⁺ contents. Soluble sugars and proline are the primary organic solutes to cope with osmotic stress. In addition, proteomic analysis revealed 30 and 42 differentially accumulated protein spots in castor cotyledon and true leaf under salt stress, respectively. Most of the identified proteins were involved in carbohydrate and energy metabolism, photosynthesis, genetic information process, reactive oxygen species metabolism, amino acid metabolism and cell structure. The physiological and proteomic results highlighted that cotyledons accumulated a large number of Na⁺ and provided more energy to help true leaves cope with salt stress. The true leaves saved carbon structures to synthesize osmotic substances, and the enhancement of chlorophyll synthesis and electron transfer in true leaves could also maintain photosynthesis under salt stress. These findings provide new insights into different physiological mechanisms in cotyledon and true leaf of Ricinus communis response to salt stress during early seedling stage.

Mitigation of Salinity Stress in Plants by Arbuscular Mycorrhizal Symbiosis: Current Understanding and New Challenges

Modern agriculture is facing twin challenge of ensuring global food security and executing it in a sustainable manner. However, the rapidly expanding salinity stress in cultivable areas poses a major peril to crop yield. Among various biotechnological techniques being used to reduce the negative effects of salinity, the use of arbuscular mycorrhizal fungi (AMF) is considered to be an efficient approach for bio-amelioration of salinity stress. AMF deploy an array of biochemical and physiological mechanisms that act in a concerted manner to provide more salinity tolerance to the host plant. Some of the well-known mechanisms include improved nutrient uptake and maintenance of ionic homeostasis, superior water use efficiency and osmoprotection, enhanced photosynthetic efficiency, preservation of cell ultrastructure, and reinforced antioxidant metabolism. Molecular studies in past one decade have further elucidated the processes involved in amelioration of salt stress in mycorrhizal plants. The participating AMF induce expression of genes involved in Na+ extrusion to the soil solution, K+ acquisition (by phloem loading and unloading) and release into the xylem, therefore maintaining favorable Na+:K+ ratio. Colonization by AMF differentially affects expression of plasma membrane and tonoplast aquaporins (PIPs and TIPs), which consequently improves water status of the plant. Formation of AM (arbuscular mycorrhiza) surges the capacity of plant to mend photosystem-II (PSII) and boosts quantum efficiency of PSII under salt stress conditions by mounting the transcript levels of chloroplast genes encoding antenna proteins involved in transfer of excitation energy. Furthermore, AM-induced interplay of phytohormones, including strigolactones, abscisic acid, gibberellic acid, salicylic acid, and jasmonic acid have also been associated with the salt tolerance mechanism. This review comprehensively covers major research advances on physiological, biochemical, and molecular mechanisms implicated in AM-induced salt stress tolerance in plants. The review identifies the challenges involved in the application of AM in alleviation of salt stress in plants in order to improve crop productivity.

Effects of β-cyclodextrin on phytoremediation of soil co-contaminated with Cd and BDE-209 by arbuscular mycorrhizal amaranth

Pot experiments were conducted to investigate the effects of a series of β-cyclodextrin (β-CD) on phytoremediation of soil co-contaminated with Cd and BDE-209 by amaranth (Amaranthus hypochondriacus L.) inoculated with arbuscular mycorrhizal fungus (AMF) - Rhizophagus intraradices. Results showed that the combination of mycorrhizal amaranth and 0.4% β-CD (RI+β_0.4) significantly enhanced Cd concentrations and contents in shoots, total PBDEs concentration in roots, and BDE-209 dissipation in soil. Moreover, the RI+β_0.4 treatment exerted the highest removal efficiency of both Cd and BDE-209. On the contrary, the xylem area, shoot Cd and BDE-209 concentrations and contents, and removal efficiency of Cd were markedly reduced in mycorrhizal amaranth with 0.8% or 1.2% β-CD treatments (RI+β_0.8, RI+β_1.2), compared with single inoculation treatment. The well-organized chloroplast and well-defined root anatomical structure were also observed in the treatment of RI+β_0.4. Positive correlation was found between shoot biomass and chlorophyll concentrations. Shoot Cd or BDE-209 concentrations were positively correlated with xylem areas. In conclusion, mycorrhizal amaranth added with 0.4% β-CD could be used for the decontamination of soil polluted with mixture of Cd and BDE-209 due to the higher chlorophyll concentration and the larger xylem area.

Transcriptome analysis reveals the impact of arbuscular mycorrhizal symbiosis on Sesbania cannabina expose to high salinity

Arbuscular mycorrhiza can improve the salt-tolerance of host plant. A systematic study of mycorrhizal plant responses to salt stress may provide insights into the acquired salt tolerance. Here, the transcriptional profiles of mycorrhizal Sesbania cannabina shoot and root under saline stress were obtained by RNA-Seq. Using weighted gene coexpression network analysis and pairwise comparisons, we identified coexpressed modules, networks and hub genes in mycorrhizal S. cannabina in response to salt stress. In total, 10,371 DEGs were parsed into five coexpression gene modules. One module was positively correlated with both salt treatment and arbuscular mycorrhizal (AM) inoculation, and associated with photosynthesis and ROS scavenging in both enzymatic and nonenzymatic pathways. The hub genes in the module were mostly transcription factors including WRKY, MYB, ETHYLENE RESPONSE FACTOR, and TCP members involved in the circadian clock and might represent central regulatory components of acquired salinity tolerance in AM S. cannabina. The expression patterns of 12 genes involved in photosynthesis, oxidation-reduction processes, and several transcription factors revealed by qRT-PCR confirmed the RNA-Seq data. This large-scale assessment of Sesbania genomic resources will help in exploring the molecular mechanisms underlying plant–AM fungi interaction in salt stress responses.

Proteomics Analysis of E. angustifolia Seedlings Inoculated with Arbuscular Mycorrhizal Fungi under Salt Stress

To reveal the mechanism of salinity stress alleviation by arbuscular mycorrhizal fungi (AMF), we investigated the growth parameter, soluble sugar, soluble protein, and protein abundance pattern of E. angustifolia seedlings that were cultured under salinity stress (300 mmol/L NaCl) and inoculated by Rhizophagus irregularis (RI). Furthermore, a label-free quantitative proteomics approach was used to reveal the stress-responsive proteins in the leaves of E. angustifolia. The result indicates that the abundance of 75 proteins in the leaves was significantly influenced when E. angustifolia was inoculated with AMF, which were mainly involved in the metabolism, signal transduction, and reactive oxygen species (ROS) scavenging. Furthermore, we identified chorismate mutase, elongation factor mitochondrial, peptidyl-prolyl cis-trans isomerase, calcium-dependent kinase, glutathione S-transferase, glutathione peroxidase, NADH dehydrogenase, alkaline neutral invertase, peroxidase, and other proteins closely related to the salt tolerance process. The proteomic results indicated that E. angustifolia seedlings inoculated with AMF increased the secondary metabolism level of phenylpropane metabolism, enhanced the signal transduction of Ca²⁺ and ROS scavenging ability, promoted the biosynthesis of protein, accelerated the protein folding, and inhibited the degradation of protein under salt stress. Moreover, AMF enhanced the synthesis of ATP and provided sufficient energy for plant cell activity. This study implied that symbiosis of halophytes and AMF has potential as an application for the improvement of saline-alkali soils.

Interactive effects of single, binary and trinary trace metals (lead, zinc and copper) on the physiological responses of Kandelia obovata seedlings

Heavy metals are considered important environmental contaminants, and their mixture toxicity on plants has complex mutual interactions. The interactive effects of heavy metals on growth, photosynthetic parameters, lipid peroxidation and compatible osmolytes were studied in Kandelia obovata grown for 5 months in sediment treated with combinations of lead (Pb), zinc (Zn) and copper (Cu). The results showed no significant reduction of biomass under heavy metal stresses, except for decreased root biomass under higher Pb + Cu treatment, indicating high tolerance of K. obovata to heavy metal stress. Only the photosynthetic parameters, including net photosynthetic rate (P_n), stomatal conductance (G_s) and transpiration rate (T_r), decreased with increasing concentration of treatments (except for Pb + Cu and Pb + Zn + Cu). Trinary treatment (Pb + Zn + Cu) increased biomass and the photosynthetic parameters when compared to the external addition of binary metals. In the roots, biomass and soluble sugar content were lower under binary than trinary treatments, indicating that the combination of Zn and Cu exhibited improved effects of alleviating toxicity than each of them alone in Pb-containing combined treatments. In the leaves, Zn-containing combined treatments significantly decreased malondialdehyde (MDA), soluble sugar and proline content in low concentration, while Pb + Cu treatments significantly increased these parameters (P < 0.05). The correlation analysis showed that leaf MDA and proline content were negatively correlated with Zn concentration (P < 0.05). Zn could alleviate the effects of combined heavy metal stress, and Pb + Cu treatment showed synergistic effects in leaves. The positive correlations between MDA content and the osmotic parameters showed that osmotic stress and lipid membranes oxidation exist simultaneously under multiple heavy metal stresses. Therefore, biomass, T_r, leaf MDA, leaf proline content and soluble sugar content could indicate metal mixture toxicity to mangrove seedlings.

Physiological Adaptive Strategies of Oil Seed Crop Ricinus communis Early Seedlings (Cotyledon vs. True Leaf) Under Salt and Alkali Stresses: From the Growth, Photosynthesis and Chlorophyll Fluorescence

Ricinus communis is an important energy crop and is considered as one of the most potential plants for salt-alkali soil improvement in Northeast China. Early seedling stage (such as the cotyledon expansion stage) is always a vulnerable stage but plays a vital role in plant establishment, especially under stress conditions. However, little information exists concerning the function of cotyledon and the relationship between cotyledon and true leaf in the adaptation to salt stress and alkali stress of this species. Here, Ricinus communis seedlings were treated with varying (40, 80 and 120 mM) salinity (NaCl) and alkalinity (NaHCO3), growth, photosynthesis, and chlorophyll fluorescence of cotyledons and true leaves were measured. The results showed that the biomass, photosynthetic parameters, and the qp value of both cotyledons and true leaves decreased with increasing salt-alkali stress, and the decrease in biomass, g s and Tr, of true leaves were much greater than that of cotyledons. Salt-alkali stress only reduced photosynthetic pigments and ΦPSII in cotyledons, but did not affect those in true leaves. Additionally, the Fv/Fm and NPQ between cotyledons and true leaves showed different trends in salinity and alkalinity. The results suggested that alkali stress could cause much more damage to the castor bean seedlings, and different physiological responses and adaptive strategies are found in cotyledons and true leaves under salt-alkali stress. This study will help us develop a better understanding of the adaptation mechanisms of cotyledon and true leaf during early seedling stage of castor bean plant, and also provide new insights into the function of cotyledon in Ricinus communis under salt-alkali stress conditions.

Mitigation of Salinity Stress in Plants by Arbuscular Mycorrhizal Symbiosis: Current Understanding and New Challenges

Modern agriculture is facing twin challenge of ensuring global food security and executing it in a sustainable manner. However, the rapidly expanding salinity stress in cultivable areas poses a major peril to crop yield. Among various biotechnological techniques being used to reduce the negative effects of salinity, the use of arbuscular mycorrhizal fungi (AMF) is considered to be an efficient approach for bio-amelioration of salinity stress. AMF deploy an array of biochemical and physiological mechanisms that act in a concerted manner to provide more salinity tolerance to the host plant. Some of the well-known mechanisms include improved nutrient uptake and maintenance of ionic homeostasis, superior water use efficiency and osmoprotection, enhanced photosynthetic efficiency, preservation of cell ultrastructure, and reinforced antioxidant metabolism. Molecular studies in past one decade have further elucidated the processes involved in amelioration of salt stress in mycorrhizal plants. The participating AMF induce expression of genes involved in Na⁺ extrusion to the soil solution, K⁺ acquisition (by phloem loading and unloading) and release into the xylem, therefore maintaining favorable Na⁺:K⁺ ratio. Colonization by AMF differentially affects expression of plasma membrane and tonoplast aquaporins (PIPs and TIPs), which consequently improves water status of the plant. Formation of AM (arbuscular mycorrhiza) surges the capacity of plant to mend photosystem-II (PSII) and boosts quantum efficiency of PSII under salt stress conditions by mounting the transcript levels of chloroplast genes encoding antenna proteins involved in transfer of excitation energy. Furthermore, AM-induced interplay of phytohormones, including strigolactones, abscisic acid, gibberellic acid, salicylic acid, and jasmonic acid have also been associated with the salt tolerance mechanism. This review comprehensively covers major research advances on physiological, biochemical, and molecular mechanisms implicated in AM-induced salt stress tolerance in plants. The review identifies the challenges involved in the application of AM in alleviation of salt stress in plants in order to improve crop productivity.

Ecological stoichiometry-based study of the influence of soil saline-alkali stress on nutrient homeostasis in L. chinensis

Soil salinization is a major cause of land degradation and hinders the effective utilization of agricultural land resources. Leymus chinensis (L. chinensis), as a dominant species with wide ecological amplitude, plays an important role in improving saline-alkali grasslands and indicating the degree of salinization. In this study, a sand culture experiment (nitrogen and phosphorus addition accompanied by saline-alkali stress) was designed to investigate the impact of different saline-alkali environments on the ecological stoichiometric homeostasis of L. chinensis with the aim of elucidating the saline-alkali resistance mechanisms. The results showed that the homeostasis indexes of N, P and N:P in the aboveground part of L. chinensis were generally higher than those in the belowground part under different saline-alkali conditions. Furthermore, the homeostasis index of N (H_N) was greater than that of P (H_P) in the aboveground part, whereas H_N was less than H_P in the belowground part. This indicates that the growth aboveground of L. chinensis was mainly dependent on N, whereas the growth belowground was mainly affected by P. The homeostasis index of the aboveground organs was 4.45-12.93 under pH 7-9.8. In contrast, H_N and H_N:P(+N) in the belowground organs did not conform to a homeostasis model when pH > 9.1. Consequently, when L. chinensis is subjected to high saline-alkali stress, the homeostasis reaction of the roots is more sensitive than that of the aboveground organs.

Assessing the effect of extra nitrogen on Kandelia obovata growth under cadmium stress using high-resolution thermal infrared remote sensing and the three-temperature model

Mangrove forests provide many ecological services and are among the most productive intertidal ecosystems on earth. Currently, these forests frequently face significant heavy metal pollution as well as eutrophication. The present study assessed the response of Kandelia obovata Sheue, H.Y. Liu & J. Yong to combined NH4+-N addition and Cd stress based on a three-temperature (3T) model using high-resolution thermal infrared remote sensing. The results show that leaf surface temperature (Tc) and the plant transpiration transfer coefficient (hat) became larger with increasing NH4+-N concentrations in the same Cd treatment, especially under high NH4+-N (50 and 100 mg·L-1) and Cd stress. The thermal bioindicators, growth responses and photosynthetic parameters changed in a consistent fashion, indicating that combined high NH4+-N addition and Cd stress led to stomatal closure, reduced the cooling effect of transpiration, and increased Tc and hat values. Furthermore, appropriate NH4+-N supply reduced stomatal conductance (gs) and the transpiration rate (Tr), which were increased by Cd stress, and then maintained Tc and hat at normal levels. The normalised hat helped to reduce the influence of environmental variation during the diagnosis of mangrove plant health. This indicated that the 3T model with high-resolution thermal infrared remote sensing provides an effective technique for determining the health status of mangrove plants under stress.

Effects of arbuscular mycorrhizal fungi on Leymus chinensis seedlings under salt–alkali stress and nitrogen deposition conditions: from osmotic adjustment and ion balance

Nitrogen deposition and soil salinization–alkalization have become major environmental problems throughout the world. Leymus chinensis is the dominant, and considered the most valuable, species for grassland restoration in the Northeast of China. However, little information exists concerning the role of arbuscular mycorrhizal fungi (AMF) in the adaptation of seedlings to the interactive effects of nitrogen and salt–alkali stress, especially from the perspective of osmotic adjustment and ion balance. Experiments were conducted in a greenhouse and Leymus chinensis seedlings were cultivated with NaCl/NaHCO₃ under two nitrogen treatments (different concentrations of NH₄⁺/NO₃⁻). Root colonization, seedling growth, ion content, and solute accumulation were measured. The results showed that the colonization rate and the dry weights of the seedlings were both decreased with the increasing salt–alkali concentration, and were much lower under alkali stress. Both of the nitrogen treatments decreased the colonization rate and dry weights compared with those of the AM seedlings, especially under the N2 (more NH₄⁺–N content) treatment. The Na⁺ content increased but the K⁺ content decreased under salt–alkali stress, and more markedly under alkali stress. AMF colonization decreased the Na⁺ content and increased the K⁺ content to some extent. In addition, the nitrogen treatments had a negative effect on the two ions in the AM seedlings. Under salt stress, the seedlings accumulated abundant Cl⁻ to maintain osmotic and ionic balance, but alkali stress inhibited the absorption of anions and the seedlings accumulated organic acids in order to resist the imbalance of both osmosis and ions, whether under the AM or nitrogen treatments. In addition, proline accumulation is thought to be a typical adaptive feature in both AM and non-AM plants under nitrogen and salt–alkali stress. Our results suggest that the salt–alkali tolerance of Leymus chinensis seedlings is enhanced by association with arbuscular mycorrhizal fungi, and the seedlings can adapt to the nitrogen and salt–alkali conditions by adjusting their osmotic adjustment and ion balance. Excessive nitrogen partly decreased the salt–alkali tolerance of the Leymus chinensis seedlings.

We evaluated the contribution of arbuscular mycorrhizal fungi to the growth, ion content, and solute accumulation of Leymus chinensis seedlings under salt–alkali stress and nitrogen deposition.

How can salicylic acid and jasmonic acid mitigate salt toxicity in soybean plants?

This research was undertaken to assess the impact of 1mM salicylic acid (SA) and 0.5mM jasmonic acid (JA) on alleviation of oxidative, ionic and osmotic stresses of different levels of salinity (0, 4, 7, 10 dS m-1 NaCl, respectively). Salinity increased the contents of glycine betaine, proline, soluble sugars, proteins and the activities of peroxidase, catalase, superoxide dismutase, ascorbate peroxidase, and the amount of malondialdehyde and sodium ion of soybean leaves, but decreased the leaf water content, membrane stability index, potassium and calcium ions, chlorophylls content, chlorophyll stability index, plant biomass and seed yield. Foliar spray of JA reduced Na+ entry to the cells, while enhancing the glycine betaine and soluble proteins content, antioxidant enzymes activity, membrane stability index and leaf water content. This treatment had no effect on potassium and the calcium ions content, chlorophyll contents, chlorophyll stability index, soluble sugars, plant biomass and seed yield. In contrast, SA enriched the leaf cells with potassium and calcium ions under different levels of salt stress and increased glycine betaine, soluble sugars, proteins, antioxidant enzymes, leaf water content, membrane stability index, chlorophyll content and chlorophyll stability index, but reduced proline content. These superiorities of SA treatment led to considerable improvement in plant biomass (10%) and seed yield (17%) of soybean.

Temporal variations in physiological responses of Kandelia obovata seedlings exposed to multiple heavy metals

A study was conducted to quantify temporal variations in physiological responses of Kandelia obovata under multiple heavy metal stress. The results showed that plant growth was not significantly affected by multiple heavy metal stress during the 120-days experiment. At the start, levels of net photosynthetic rate (P_n), stomatal conductance (G_s) and transpiration rate (T_r) showed effects of "low-promotion, high-inhibition", but P_n and G_s reduced with increasing heavy metal stress at the end. Temporary lipid oxidation was shown by high levels of malondialdehyde (MDA) under high heavy metal stress at the start but was unaffected at the end of the experiment. MDA negatively correlated with biomass and photosynthetic parameters and acted as a sensitive indicator. Proline also shared similar trend and indicated its temporary role in osmotic adjustment. Negative correlations between osmotic adjustment matter and photosynthetic parameters further confirmed the significant role of osmotic adjustment under heavy metal stress.