Arbuscular Mycorrhizal Plants Research Articles

Arbuscular Mycorrhizal Symbiosis Improves Ex Vitro Acclimatization of Sugarcane Plantlets (Saccharum spp.) under Drought Stress Conditions.

The symbiotic associations between arbuscular mycorrhizal fungi (AMF) and plants can induce drought stress tolerance. In this study, we evaluated the effect of Glomus intraradices, a mycorrhizal fungus, on the ex vitro development and survival of sugarcane plantlets subjected to drought stress during the acclimatization stage of micropropagation. In vitro obtained sugarcane plantlets (Saccharum spp. cv Mex 69-290) were inoculated with different doses of G. intraradices (0, 100, and 200 spores per plantlet) during greenhouse acclimatization. Sixty days after inoculation, plantlets were temporarily subjected to drought stress. We evaluated the survival rate, total chlorophyll, total protein, carotenoids, proline, betaine glycine, soluble phenolic content, and antioxidant capacity every 3 days for 12 days. Symbiotic interaction was characterized by microscopy. Our results showed that the survival rate of inoculated plants was higher in 45% than the treatment without mycorrhizae. Total chlorophyll, protein, proline, betaine glycine content, and antioxidant capacity were increased in AMF inoculated plants. The soluble phenolic content was higher in non-inoculated plants than the treatment with mycorrhizae during the drought stress period. Microscopy showed the symbiotic relationship between plant and AMF. The early inoculation of 100 spores of G. intraradices per sugarcane plantlet during the acclimatization stage could represent a preconditioning advantage before transplanting into the field and establishing basic seedbeds.

Arbuscular mycorrhiza and plant growth promoting endophytes facilitates accumulation of saponin under moderate drought stress

ObjectiveParis polyphylla var. yunnanensis, one of the important medicinal plant resources in Yunnan, China, usually takes 6–8 years to be harvested. Therefore, it is urgent to find a method that can not only shorten its growth years, but also improve its quality. In this study, we examined the effects of a combination treatment of arbuscular mycorrhizal fungi (AMF) and plant growth-promoting endophytes (PGPE) and drought stress on the accumulation of saponins in it. MethodsP. polyphylla var. yunnanensis was infected with a mixture of AMF and PGPE under drought stress. The content of saponins, as well as morphological, physiological, and biochemical indicators, were all measured. The UGTs gene related to saponin synthesis was obtained from transcriptome data by homologous comparison, which were used for RT-PCR and phylogenetic analysis. ResultsRegardless of water, AMF treatment could infect the roots of P. polyphylla var. yunnanensis, however double inoculation with AMF and PGPE (AMF + PGPE) would reduce the infection rate of AMF. Plant height, aboveground and underground fresh weight did not differ significantly between the single inoculation AMF and the double inoculation treatment under different water conditions, but the inoculation treatment significantly increased the plant height of P. polyphylla var. yunnanensis compared to the non-inoculation treatment. Single inoculation with AMF considerably increased the net photosynthetic rate, stomatal conductance, and transpiration rate of P. polyphylla var. yunnanensis leaves under various water conditions, but double inoculation with AMF + PGPE greatly increased the intercellular CO2 concentration and chlorophyll fluorescence parameter (Fv/Fm). Under diverse water treatments, single inoculation AMF had the highest proline content, whereas double inoculation AMF + PGPE may greatly improve the amount of abscisic acid (ABA) and indoleacetic acid (IAA) compared to normal water under moderate drought. Double inoculation AMF + PGPE treatment improved the proportion of N, P, and K in the rhizome of P. polyphylla var. yunnanensis under various water conditions. Under moderate drought stress, AMF + PGPE significantly enhanced the contents of P. polyphylla var. yunnanensis saponins I, II, VII, and total saponins as compared to normal water circumstances. Farnesyl diphosphate synthase (FPPS), Geranyl pyrophosphate synthase (GPPS), Cycloartenol synthase (CAS), and Squalene epoxidase (SE1) were the genes that were significantly up-regulated at the same time. The amount of saponins was favorably linked with the expression of CAS, GPPS, and SE1. Saponin VI content and glycosyl transferase (UGT) 010922 gene expression were found to be substantially associated, as was saponin II content and UGT010935 gene expression. ConclusionUnder moderate drought, AMF + PGPE was more conducive to the increase of hormone content, nutrient absorption, and total saponin content in P. polyphylla var. yunnanensis, and AMF + PGPE could up regulate the expression of key genes and UGTs genes in one or more steroidal saponin synthesis pathways to varying degrees, thereby stimulating the synthesis and accumulation of steroidal saponins in the rhizome of P. polyphylla var. yunnanensis. The combination of AMF and PGPE inoculation, as well as adequate soil drought, reduced the buildup of saponins in P. polyphylla var. yunnanensis and increased its quality.

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

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

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

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. 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. 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. 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.

Belowground crop responses to root herbivory are associated with the community structure of native arbuscular mycorrhizal fungi

There is growing interest in managing arbuscular mycorrhizal (AM) fungi in agriculture to support plant production. These fungi can support crop growth and nutrient uptake, but also affect plant-herbivore interactions. While our understanding of how AM fungi affect plant responses to herbivory advances, it is less clear how different naturally-occurring (native) fungal communities differentially influence crop responses to root-feeding insects.To explore this, plants (Sorghum bicolor) were grown in a glasshouse experiment without AM fungi (‘no AM fungi’) or with one of three natural soil inocula sourced either from a sclerophyll forest (‘forest inoculum’), a cropped field (‘field inoculum’), or a field in fallow (‘fallow inoculum’), while half the plants were subjected to a root herbivore (Dermolepida albohirtum). We assessed the effects of soil inoculum and root herbivory on root-colonising AM fungal diversity, plant growth, and nutrient content.Root herbivory did not affect AM fungal diversity or composition. Plants grown with the field or fallow inocula were both dominated by the genera Glomus and Claroideoglomus. These plants exhibited reduced biomass in response to inoculation, but were not impacted by root herbivory. In contrast, plants with the forest inoculum had AM fungal communities dominated by Paraglomus and Ambispora. When subjected to root herbivory, the forest inoculated plants and plants without AM fungi exhibited reductions of 44 % and 61 % in root biomass, and reductions of 65 % and 59 % in root phosphorus, respectively.Our study shows inoculation-driven plant responses to root herbivory that were associated with the community structure of their root-colonising AM fungi. Results suggest associations with communities dominated by Claroideoglomus and Glomus may mitigate the impacts of a root-feeding insect. More exploration of how natural assemblages of AM fungi mediate plant-herbivore interactions is needed if we are to effectively manage soil fungi in agriculture.

Proteomics as a tool to decipher plant responses in arbuscular mycorrhizal interactions: a meta-analysis.

The beneficial symbiosis between plants and arbuscular mycorrhizal (AM) fungi leads to a deep reprogramming of plant metabolism, involving the regulation of several molecular mechanisms, many of which are poorly characterized. In this regard, proteomics is a powerful tool to explore changes related to plant-microbe interactions. This study provides a comprehensive proteomic meta-analysis conducted on AM-modulated proteins at local (roots) and systemic (shoots/leaves) level. The analysis was implemented by an in-depth study of root membrane-associated proteins and by a comparison with a transcriptome meta-analysis. A total of 4262 differentially abundant proteins were retrieved and, to identify the most relevant AM-regulated processes, a range of bioinformatic studies were conducted, including functional enrichment and protein-protein interaction network analysis. In addition to several protein transporters which are present in higher amounts in AM plants, and which are expected due to the well-known enhancement of AM-induced mineral uptake, our analysis revealed some novel traits. We detected a massive systemic reprogramming of translation with a central role played by the ribosomal translational apparatus. On one hand, these new protein-synthesis efforts well support the root cellular re-organization required by the fungal penetration, and on the other they have a systemic impact on primary metabolism.

Effects of Different Arbuscular Mycorrhizal Fungi on Physiology of Viola prionantha under Salt Stress

Arbuscular mycorrhizal (AM) fungi distribute widely in natural habits and play a variety of ecological functions. In order to test the physiological response to salt stress mediated by different AM fungi, Viola prionantha was selected as the host, the dominant AM fungus in the rhizosphere of V. philippica growing in Songnen saline-alkali grassland, Rhizophagus irregularis, and their mixtures were used as inoculants, and NaCl stress was applied after the roots were colonized. The results showed that V. philippica could be colonized by AM fungi in the field and the colonization rate ranged from 73.33% to 96.67%, and Claroideoglomus etunicatum was identified as the dominant AM fungi species in the rhizosphere of V. philippica by morphology combined with sequencing for AM fungal AML1/AML2 target. Inoculation with both the species resulted in the formation of mycorrhizal symbiosis (the colonization rate was more than 70%) and AM fungi significantly enhanced plants’ tolerance to salt stress of varying magnitude. Higher activity of antioxidant enzymes and augmented levels of proline and other osmoregulators were observed in AM plants. The content of MDA in CK was higher than that in the inoculations with the stress of 100, 200, and 250 mM. All indices except soluble protein content and MDA content were significantly correlated with AM fungal colonization indices. The analysis for different AM fungal effects showed that the mixtures and R. irregularis worked even better than C. etunicatum. These results will provide theoretical support for the exploration and screening of salt-tolerant AM fungi species and also for the application of AM-ornamental plants in saline-alkali urban greening.

Arbuscular Mycorrhiza Symbiosis as a Factor of Asteraceae Species Invasion

Invasive weeds of the Asteraceae family are widespread in the world. Arbuscular mycorrhiza (AM) is one of the main factors contributing to the successful distribution of these species that is most clearly manifested in the subfamily Asteroideae. The benefits of plant-AMF symbiosis are most significant under unfavorable biotic and abiotic conditions. The specificity of the relationship between arbuscular mycorrhizal fungi (AMF) communities and plants and is determined at the presymbiotic stage. The AMF colonization level is higher in invasive species than in native ones, but AMF communities associated with Asteraceae invasive species are less diverse. AMF communities of Asteraceae invaders often include fewer common species (e.g., species belonging to Diversisporales). Invaders also reduce native AMF species richness in new areas. Arbuscular mycorrhizal fungi can form mycorrhizal networks that allow the redistribution of nutrients in plant communities. The most significant influence of AMF associated with invasive Asteraceae plants is seen in the formation of soil and rhizosphere microbiota, including the suppression of beneficial soil bacteria and fungi. This review could be useful in the development of practical recommendations for the use of AMF-based fertilizers.

Synergistic combination of arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria modulates morpho-physiological characteristics and soil structure in Nitraria tangutorum bobr. Under saline soil conditions

Nitraria tangutorum Bobr., a typical xero-halophyte, can be used for vegetation restoration and reconstruction in arid and semiarid regions affected by salinity. However, global climate change and unreasonable human activity have exacerbated salinization in arid and semi-arid regions, which in turn has led to the growth inhibition of halophytes, including N. tangutorum. Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) have the potential to improve the salt tolerance of plants and their adaptation to saline soil environments. In this study, the effects of single and combined inoculations of AMF (Glomus mosseae) and PGPR (Bacillus amyloliquefaciens FZB42) on N. tangutorum were evaluated in severe saline soil conditions. The results indicate that AMF and PGPR alone may not adapt well to the real soil environment, and cannot ensure the effect of either growth promotion or salt-tolerance induction on N. tangutorum seedlings. However, the combination of AMF and PGPR significantly promoted mycorrhizal colonization, increased biomass accumulation, improved morphological development, enhanced photosynthetic performance, stomatal adjustment ability, and the exchange of water and gas. Co-inoculation also significantly counteracted the adverse effect of salinity on the soil structure of N. tangutorum seedlings. It is concluded that the effectiveness of microbial inoculation on the salt tolerance of N. tangutorum seedlings depends on the functional compatibility between plants and microorganisms as well as the specific combinations of AMF and PGPR.

Arbuscular mycorrhizal fungi induce flavonoid synthesis for mitigating oxidative damage of trifoliate orange under water stress

Arbuscular mycorrhizal (AM) fungi can increase the tolerance of host plants to drought, whereas the intrinsic mechanisms are not still fully elucidated. Flavonoids are a kind of antioxidants to scavenge reactive oxygen species (ROS), whereas whether and how flavonoids are involved in increased drought tolerance of host plants by AM fungi is not known. Here, Funneliformis mosseae , was inoculated into potted trifoliate orange seedlings, which were subjected to adequate water and water stress conditions. The AM effect on plant growth, concentrations of flavonoid substances and total flavonoids, and activities and expression levels of enzymes related to flavonoids synthesis (clnnamate 4-dydroxylate (C4H), phenylalanine ammonialyase (PAL), chalcone isomerase (CHI), and 4-coumaroyl-CoA ligase (4CL)) in roots was analyzed, along with changes in scavenging activity of ROS by root flavonoid extracts. Compared with non-AM control, F . mosseae inoculation distinctly improved plant growth performance and increased phenylalanine, glycitin, luteolin-7- O -glucoside, and total flavonoid concentrations, coupled with the decrease in p -coumaric acid, regardless of soil water regimes. Activities of C4H, CHI, 4CL, and PAL and expression levels of PtPAL1 and Pt4CL were induced by F . mosseae inoculation under water stress. AM plants exhibited higher scavenging activity of hydroxyl radical and superoxide (O 2 •− ) by root flavonoid extracts under water stress, along with lower levels of O 2 •− and hydrogen peroxide and the degree of membrance lipid peroxidation, compared with non-AM plants. It is concluded that AM fungi accelerated flavonoids synthesis of trifoliate orange for mitigating oxidative damage under water stress. • AMF increased phenylalanine, glycitin, luteolin-7- O -glucoside, and total flavonoid concentrations, regardless of soil moisture regimes. • C4H, CHI, 4CL, and PAL activities and PtPAL1 and Pt4CL expressions were induced by AMF under water stress. • AMF plants exhibited higher scavenging activity of ROS by root flavonoid extracts under water stress. • AM fungi accelerated flavonoids synthesis for mitigating oxidative damage under water stress.

Biostimulants as Innovative Tools to Boost Date Palm (Phoenix dactylifera L.) Performance under Drought, Salinity, and Heavy Metal(Oid)s’ Stresses: A Concise Review

Date palm (Phoenix dactylifera L.) is constantly subjected to abiotic stresses. Hence, the application of biostimulants, such as the arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR), and organic amendments hold tremendous potential to significantly improve the growth and yield of date palm. The strengthening of biostimulants’ main common modes of action is exerted through five main functions: biostimulation (essentially), biofertilization, bioprotection, biological control, and the role of bio-effector. Moreover, synergistic and complementary effects manifest through biochemical and nutritional benefits, in addition to molecular modulation. In this regard, the present concise review focuses on highlighting the beneficial impact of AMF and PGPR, as well as the organic amendments, in boosting the health status and productivity of date palm plants subjected to abiotic stresses. Furthermore, mechanisms reinforcing date palm plants’ resilience to abiotic stresses, powered by biostimulants, are particularly emphasized. Based on this review, we could conclude that the overall findings corroborate the beneficial effects of AMF–PGPR and/or compost and manure application in terms of boosting date palm’s growth traits, development, yielding, as well as soil properties under extreme environmental factors, such as those of drought, salinity, and excessive heavy metal(oid)s. Thus, biostimulants can confer resilience to date palm plants against abiotic stresses.

Vascular plant and cryptogam abundance as well as soil chemical properties shape microbial communities in the successional gradient of glacier foreland soils

In the glacier forelands, microbes play a fundamental role in soil development and shaping the vegetation structure. Such ecosystems represent various stages of soil development and are, therefore, an excellent place to study the interrelationship between soil, plants, and microorganisms. The aim of the study was to assess the effects of vegetation and soil physicochemical properties developing after glacier retreat on soil microbial communities. Specifically, abundance, species richness and the composition of arbuscular mycorrhizal fungi (AMF), as well as microbial biomass and community structure in soils were compared between plots established in 800-meter transects of three glacier forelands in northern Sweden. The cover of vascular plants and cryptogams, soil C content, AMF spore density and species richness, AMF biomass indicators, total microbial biomass, and bacterial phospholipid fatty acids (PLFA) were significantly and positively related to the distance from the glacier terminus. On the other hand, macronutrient concentrations and pH decreased along with increasing distance. No significant impact of the distance from the glacier terminus on the ratio fungal/bacterial PLFA was observed. Moreover, we found a significant effect of both glacier and the distance from the glacier terminus on the microbial community structure. AMF species richness and spore density in the glacier forelands were generally low, which is probably due to a limited supply of inoculum in primary successional ecosystems. Most microbial biochemical markers and AMF parameters were positively associated with the number of arbuscular mycorrhizal plant species and vascular plant and lichen cover as well as C content in soil, whereas negatively with soil macronutrients and pH. This could be related to an increase in plant cover and a decrease in soil nutrient levels as plant succession progresses. Our results showed that vegetation, soil C content, and microbial communities are interlinked and exhibit concordant patterns along successional gradients.

A phosphate starvation response-regulated receptor-like kinase, OsADK1, is required for mycorrhizal symbiosis and phosphate starvation responses.

Most land plants associate with arbuscular mycorrhizal (AM) fungi to secure mineral nutrient acquisition, especially that of phosphorus. A phosphate starvation response (PHR)-centered network regulates AM symbiosis. Here, we identified 520 direct target genes for the rice transcription factor OsPHR1/2/3 during AM symbiosis using transcriptome deep sequencing and DNA affinity purification sequencing. These genes were involved in strigolactone biosynthesis, transcriptional reprogramming, and bidirectional nutrient exchange. Moreover, we identified the receptor-like kinase, Arbuscule Development Kinase 1 (OsADK1), as a new target of OsPHR1/2/3. Electrophoretic mobility shift assays and transactivation assays showed that OsPHR2 can bind directly to the P1BS elements within the OsADK1 promoter to activate its transcription. OsADK1 appeared to be required for mycorrhizal colonization and arbuscule development. In addition, hydroponic experiments suggested that OsADK1 may be involved in plant Pi starvation responses. Our findings validate a role for OsPHR1/2/3 as master regulators of mycorrhizal-related genes involved in various stages of symbiosis, and uncover a new RLK involved in AM symbiosis and plant Pi starvation responses.

Arbuscular mycorrhiza mitigates zinc stress on Eucalyptus grandis through regulating metal tolerance protein gene expression and ionome uptake.

Arbuscular mycorrhizal (AM) fungi are symbionts of most terrestrial plants and enhance their adaptability in metal-contaminated soils. In this study, mycorrhized and non-mycorrhized Eucalyptus grandis were grown under different Zn treatments. After 6 weeks of treatment, the growing status and ionome content of plants as well as the expression patterns of metal tolerance proteins and auxin biosynthesis-related genes were measured. In this study, mycorrhized E. grandis showed higher biomass and height at a high level of Zn compared with non-mycorrhized plants. In addition, AM plants accumulated P, Mg, and Mn in roots and P, Fe, and Cu in shoots, which indicate that AM fungi facilitate the uptake of ionome nutrients to promote plant growth. In addition, mycorrhiza upregulated the expression of EgMTP1 and EgMTP7, whose encoding proteins were predicted to be located at the vacuolar membrane. Meanwhile, Golgi membrane transporter EgMTP5 was also induced in AM shoot. Our results suggest that AM likely mitigates Zn toxicity through sequestrating excess Zn into vacuolar and Golgi. Furthermore, the expression of auxin biosynthesis-related genes was facilitated by AM, and this is probably another approach for Zn tolerance.

Streptomyces rimosus rhizobacteria and Glomus mosseae mycorrhizal fungus inoculation alleviate salinity stress in grapevine through morphophysiological changes and nutritional balance

Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) have positive impacts on growth and production of plants under saline condition. However, their interactive effects on plant behavior under salt stress remained unclear. To address this, a glasshouse experiment was conducted to elucidate the effect of the single and combined (co-inoculation) application of Glomus mosseae (Gm) AMF and Streptomyces rimosus (Sr) PGPR on salt tolerance of Sultana grapevine (Vitis vinifera L.). Based on results, the combined inoculation with Gm AMF and Sr PGPR markedly improved shoot and root morphometric traits and also soluble carbohydrate, soluble proteins, proline content compared to those vines inoculated with these symbionts alone or uninoculated vines under saline condition. The highest main root length was related to inoculated vines with Sr PGPR, which was 18.5% higher than uninoculated control plants under saline condition. Under saline condition, co-inoculation with Gm AMF and Sr PGPR decreased leaf necrotic, leaf ion leakage and malondialdehyde content by 31%, 43% and 38% but increased SPAD index, relative water content, catalase and guaiacol peroxidase activity by 45%, 26%, 30% and 53% compared with control uninoculated plant. Among salt stressed plants, the single inoculated vines with Gm AMF showed the highest total phenol and flavonoid content compared to control plants. In vines grown under saline condition, the highest content of leaf P, Mg, Fe, Zn and Mn were related to Gm plus Sr -inoculated vines. Leaf NO−3 and K of all inoculated vines did not showed statistically significant difference with each other's. Under saline condition, root NO3, K, Mg, Fe, Zn and Mn did not showed significant difference among inoculated plants but differed significantly with control vines. Therefore, combined application of Gm AMF and Sr PGPR assisted host plants to uptake higher nutrients during salt stress; confer salt tolerance to vines by increase in osmoregulants, phenolic compounds and antioxidant enzymes activities in their tissues.

Transcriptomics and metabolomics revealeffect of arbuscular mycorrhizal fungion growth and developmentof apple plants.

Arbuscular mycorrhizal fungi (AMF) and plants form a symbiotic relationship that promotes plant growth and development. However, the regulatory mechanisms through which AMF promote plant growth and development are largely unexplored. In this study, the apple rootstock M26 was assessed physiologically, transcriptionally and metabolically when grown with and without AMF inoculation. AMF significantly promoted the number of lateral root (LR) increase and shoot elongation. Root transcriptomic and metabolic data showed that AMF promoted lateral root development mainly by affecting glucose metabolism, fatty acid metabolism, and hormone metabolism. Shoot transcriptomic and metabolic data showed that AMF promoted shoot elongation mainly by affecting hormone metabolism and the expression of genes associated with cell morphogenesis. To investigate whether shoot elongation is caused by root development, we analyzed the root/shoot dry weight ratio. There was a correlation between shoot growth and root development, but analysis of root and shoot metabolites showed that the regulation of AMF on plant shoot metabolites is independent of root growth. Our study bridged the gap in the field of growth and development related to AMF.

Faster accumulation and greater contribution of glomalin to the soil organic carbon pool than amino sugars do under tropical coastal forest restoration.

Microbial metabolic products play a vital role in maintaining ecosystem multifunctionality, such as soil physical structure and soil organic carbon (SOC) preservation. Afforestation is an effective strategy to restore degraded land. Glomalin-related soil proteins (GRSP) and amino sugars are regarded as stable microbial-derived C, and their distribution within soil aggregates affects soil structure stability and SOC sequestration. However, the information about how afforestation affects the microbial contribution to SOC pools within aggregates is poorly understood. We assessed the accumulation and contribution of GRSP and amino sugars within soil aggregates along a restoration chronosequence (Bare land, Eucalyptus exserta plantation, native species mixed forest, and native forest) in tropical coastal terraces. Amino sugars and GRSP concentrations increased, whereas their contributions to the SOC pool decreased along the restoration chronosequence. Although microaggregates harbored greater microbial abundances, amino sugars and GRSP concentrations were not significantly affected by aggregate sizes. Interestingly, the contributions of amino sugars and GRSP to SOC pools decreased with decreasing aggregate size which might be associated with increased accumulation of plant-derived C. However, the relative change rate of GRSP was consistently greater in all restoration chronosequences than that of amino sugars. The accumulation of GRSP and amino sugars in SOC pools was closely associated with the dynamics of soil fertility and the microbial community. Our findings suggest that GRSP accumulates faster and contributes more to SOC pools during restoration than amino sugars did which was greatly affected by aggregate sizes. Afforestation substantially enhanced soil quality with native forest comprising species sequestering more SOC than the monoculture plantation did. Such information is invaluable for improving our mechanistic understanding of microbial control over SOC preservation during degraded ecosystem restoration. Our findings also show that plantations using arbuscular mycorrhizal plants can be an effective practice to sequester more soil carbon during restoration.

Influence of Aged Wood Biochar on Mycorrhizal Colonisation, Growth and Leaf Gas Exchange of Wheat and Clover with Different Water Regimes

Water scarcity is one of the most limiting environmental factors for crop productivity globally, where biochar application can play a role. To test this, a glasshouse experiment was conducted with aged biochar application with water regimes on arbuscular mycorrhizal fungi colonisation, plant growth, phosphorus nutrition and leaf gas exchange in wheat and subterranean clover. Six treatment combinations (two biochar levels of 0 and 6 t ha−1; and three water regimes of well-watered, water-stressed and watering intermittently) were arranged in factorial completely randomized block design with three replications. The wheat and subterranean clover were grown and harvested 14, 24, 34 and 44 days after sowing. In this study, aged biochar had no significant effect on plant growth for both wheat and clover, regardless of water regimes. Shoot and root dry weights increased in well-watered conditions compared to water-stressed conditions. Root length and colonised root length increased with biochar addition for wheat, mostly in well-watered treatment. Phosphorus uptake increased in biochar treatment, and the effect was higher in well-watered conditions. Leaf photosynthetic rate (PN), stomatal conductance (gs), intercellular CO2 concentration (Ci) and transpiration rate (E) increased with biochar addition. For clover, the effect was higher in water-stressed than well-watered conditions. These results suggest that biochar may enhance water availability to clover plants in water-stressed conditions. However, the positive effect of biochar on plant growth under water-stressed conditions, varied with plant species, needs to be explored further in a range of crop species and biochar sources in addition to the material used in the current investigation.

Field inoculation responses of arbuscular mycorrhizal fungi versus endophytic fungi on sugar metabolism associated changes in fruit quality of Lane late navel orange

Arbuscular mycorrhizal (AM) fungi and plants require sugars, especially during fruit ripening stage, while the underlying mechanism influencing sugar accumulation in response to AM fungi is still unclear. The objective of this study was to analyze the field inoculation response of three AM fungi (Acaulospora scrobiculata, Diversispora spurca, and D. versiformis) and an endophytic fungus (Piriformospora indica) on internal as well as external quality parameters of Lane late navel orange (Citrus sinensis) fruits, with emphasis on monosaccharide and disaccharide components and expressions of sucrose-associated enzyme genes and sugar transporter genes. Root fungal colonization rate increased by 51.2−109.6% with the inoculation of D. spurca displaying the best response after two years of field inoculation. The fungal introduction also improved the external fruit quality attributes to some extent, especially longitudinal and transverse diameter, sarcocarp weight, and fruit coloration value in response to inoculation of A. scrobiculata and P. indica. Fruit number increased in response to inoculation with D. versiformis. Although none of the four symbiotic fungi influenced the soluble solids of fruits, however fruit titratable acids registered a significant reduction leading to an increase in soluble solids-titratable acids ratio in response to A. scroblculata and D. spurca. Inoculation with A. scrobiculata and D. spurca also reduced sucrose while increased glucose, fructose, and trehalose concentrations in fruit sarcocarps, along with up-regulated expressions of CsVINV1, CsA/NINV4, and CsSWEET in fruit sarcocarps, suggesting that AM fungi played a pivotal role in sucrose transport, synthesis, and cleavage in fruits. In contrast, inoculation with P. indica only increased the sucrose and up-regulated expressions of CsSPS1 and CsSPS4 in fruit sarcocarps, implying that Pi mainly triggered the sucrose synthesis in fruits. These symbiotic fungi increased concentration of one of the three sweeteners (arabinose, xylitol and fucose) in fruit sarcocarps, with an exception of A. scrobiculata responding to an increase in the three sweeteners. These results provided strong clues that symbiotic fungi have an important role in improving the fruit size and different sugar components in citrus fruits by regulating the expression of genes related to sucrose synthesis, cleavage, and transport, with A. scrobiculata outplaying the response of other three symbiotic fungi.

Community Assembly of Fungi and Bacteria along Soil-Plant Continuum Differs in a Zoige Wetland.

ABSTRACTDistinct plant associated microbiomes live in rhizosphere soil, roots, and leaves. However, the differences in community assembly of fungi and bacteria along soil-plant continuum are less documented in ecosystems. We examined fungal and bacterial communities associated with leaves, roots, and rhizosphere soil of the dominant arbuscular mycorrhizal (AM) plants Taraxacum mongolicum and Elymus nutans and non-AM plant Carex enervis in the Zoige Wetland by using high throughput sequencing techniques. The operational taxonomic unit (OTU) richness of fungi and bacteria was significantly higher in rhizosphere soil than in roots and leaves, and their community compositions were significantly different in the rhizosphere soil, roots, and leaves in each plant species. The co-occurrence network analysis revealed that the sensitive fungal and bacterial OTUs with various taxonomic positions were mainly clustered into different modules according to rhizosphere soil, roots, and leaves in each plant species. Along the soil-plant continuum, the rhizosphere soil pool contributed more source on bacterial than on fungal communities in roots and leaves of the three plant species, and more source on bacterial and fungal communities in leaves of T. mongolicum and E. nutans compared with C. enervis. Furthermore, the root pool contributed more source on bacterial than on fungal communities in leaves of T. mongolicum and E. nutans but not that of C. enervis. This study highlights that the host plant selection intensity is higher in fungal than in bacterial communities in roots and leaves from rhizosphere soil in each plant species, and differs in fungal and bacterial communities along the soil-plant continuum in AM plants T. mongolicum and E. nutans and non-AM plant C. enervis in the Zoige Wetland.IMPORTANCE Elucidating the community microbiome assemblage alone the soil-plant continuum will help to better understand the biodiversity maintenance and ecosystem functioning. Here, we examined the fungal and bacterial communities in rhizosphere soil, roots, and leaves of two dominant AM plants and a non-AM plant in Zoige Wetland. We found that along the soil – plant continuum, host plant selection intensity is higher in fungal than in bacterial communities in roots and leaves from rhizosphere soil in each plant species, and differs in fungal and bacterial communities in the AM- and non-AM plants. This is the first report provides evidence of different assembly patterns of fungal and bacterial communities along the soil-plant continuum in the AM- and non-AM plants in the Zoige Wetland.