Improved observation of colonized roots reveals the regulation of arbuscule development and senescence by drought stress in the arbuscular mycorrhizae of citrus

Citrus is the typical mycorrhizal fruit tree species establishing symbiosis with arbuscular mycorrhizal (AM) fungi. However, arbuscule development and senescence in colonized citrus roots, especially in response to drought stress, remain unclear, which is mainly due to the difficulty in clearing and staining lignified roots with the conventional method. Here, we improved the observation of colonized roots of citrus plants with the sectioning method, which enabled the clear observation of AM fungal structures. Furthermore, we investigated the effects of one week of drought stress on arbuscule development and senescence with the sectioning method. Microscopy observations indicated that drought stress significantly decreased mycorrhizal colonization (F%and M%) although it did not affect plant growth performance. Fluorescence probes (WGA 488 and/or Nile red) revealed that drought stress inhibited arbuscule development by increasing the percentage of arbuscules at the early stage and decreasing the percentages of arbuscules at the midterm and mature stages. Meanwhile, drought stress accelerated arbuscule senescence, which was characterized by the increased accumulation of neutral lipids. Overall, the sectioning method developed in this study enables the in-depth investigation of arbuscule status, and drought stress can inhibit arbuscule development but accelerate arbuscule senescence in the colonized roots of citrus plants. This study paves the way to elaborately dissecting the arbuscule dynamics in the roots of fruit tree species in response to diverse abiotic stresses.

General and specialized metabolites in peanut roots regulate arbuscular mycorrhizal symbiosis

Arbuscular mycorrhizae(AM)fungi form symbiotic associations with plant roots,providing nutritional benefits and promoting plant growth and defenses against various stresses.Metabolic changes in the roots during AM fungal colonization are key to understanding the development and maintenance of these symbioses.Here,we investigated metabolic changes in the roots of peanut(Arachis hypogaea L.)plants during the colonization and development of AM symbiosis,and compared them to uncolonized roots.The primary changes during the initial stage of AM colonization were in the contents and compositions of phenylpropanoid and flavonoid compounds.These compounds function in signaling pathways that regulate recognition,interactions,and pre-colonization between roots and AM fungi.Flavonoid compounds decreased by 25%when the symbiosis was fully established compared to the initial colonization stage.After AM symbiosis was established,general metabolism strongly shifted toward the formation of lipids,amino acids,carboxylic acids,and carbohydrates.Lipid compounds increased by 8.5%from the pre-symbiotic stage to well-established symbiosis.Lyso-phosphatidylcholines,which are signaling compounds,were only present in AM roots,and decreased in content after the symbiosis was established.In the initial stage of AM establishment,the content of salicylic acid increased two-fold,whereas jasmonic acid and abscisic acid decreased compared to uncolonized roots.The jasmonic acid content decreased in roots after the symbiosis was well established.AM symbiosis was associated with high levels of calcium,magnesium,and D-(+)-mannose,which stimulated seedling growth.Overall,specific metabolites that favor the establishment of AM symbiosis were common in the roots,primarily during early colonization,whereas general metabolism was strongly altered when AM symbiosis was well-established.In conclusion,specialized metabolites function as signaling compounds to establish AM symbiosis.These compounds are no longer produced after the symbiosis between the roots and AM becomes fully established.

Effect of arbuscular mycorrhiza on the growth of Camptotheca acuminata seedlings

Camptotheca acuminata seeds were sown in sterilized sands in the greenhouse in February of 2005. After 90-day growth, seedlings were inoculated with three species of arbuscular mycorrhizal fungi （AMF）, Acaulospora mellea, Glomus diaphanum and Sclerocystis sinuosa.. The height, biomass, and absorptions of nitrogen and phosphorus of C. acuminata seedlings inoculated with AMF were investigated. The results showed that the formation of AM promoted the height growth and biomass accumulation of seedlings significantly and improved the absorption of phosphorus in seedlings. The height and biomass of mycorrhizal seedlings were 1.2 and 1.6 times higher than those of the non-mycorrhizal seedlings. The absorption of nitrogen was less influenced by the formation of AM. The nitrogen content in mycorrhizal seedling was equal to that of non-mycorrhizal seedlings. Compared with non-mycorrhizal seedlings, the nitrogen content of mycorrhizal seedlings inoculated with A. mellea changed considerably in the root, stem and leaves. The difference in nitrogen content was not significant between mycorrhizal seedlings inoculated with G. diaphanum and S. sinuosa. The AM formation stimulated the absorption of phosphorus, especially in roots, and also changed the allocation of nitrogen and phosphorus in different organs of seedlings. Compared with non-mycorrhizal seedlings, the ratio of nitrogen and phosphorus in mycorrhizal roots increased, but reduced in stem and leaves.

Effect of Arbuscular Mycorrhiza on the Content of Nitrogen and Nitrogenous Matter in Amur Corktree Seedlings

[Objective] This study aimed to explore the effect of arbuscular mycorrhiza on the content of nitrogen and nitrogenous matter in amur corktree（Phellodendron amurense Rupr.）seedlings. [Method] The annual seedlings of Phellodendron amurense Rupr. were inoculated with four arbuscular mycorrhiza fungi in a pot experiment to study the influences of arbuscular mycorrhiza on the content of nitrogen and nitrogenous matter in Phellodendron amurense Rupr. [Result] After inoculation with arbuscular mycorrhiza fungi, the Phellodendron amurense Rupr. seedlings developed arbuscular mycorrhiza, leading to an enhancement of photosynthetic capacity. The leaf nitrogen content of those inoculated with Glomus mosseae increased to 1.28- 1.60 times as compared with the control. The chlorophyll content and chlorophyll a/b ratio were also raised, with an increase over 25% of chlorophyll a content. In addition, IAA content in plants increased to 1.65-2.41 times; and nitrate reductase activity was also enhanced, as well as soluble protein content, 1.67-2.49 times as high as the control, which improved the nitrogen metabolic ability, and promoted the plant growth, as well as the secondary metabolic ability. [Conclusion] This study provides a theoretical basis for the application of arbuscular mycorrhiza on Phellodendron amurense Rupr.

Effect of Arbuscular Mycorrhizal Inoculation on Plant Growth and Phthalic Ester Degradation in Two Contaminated Soils

A 60-day pot experiment was carried out using di-(2-ethylhexyl) phthalate (DEHP) as a typical organic pollutant phthalic ester and cowpea (Vigna sinensis) as the host plant to determine the effect of arbuscular mycorrhizal inoculation on plant growth and degradation of DEHP in two contaminated soils, a yellow-brown soil and a red soil. The air-dried soils were uniformly sprayed with different concentrations of DEHP, inoculated or left uninoculated with an arbuscular mycorrhizal (AM) fungus, and planted with…

Research Progress on the Process and Mechanism of Arbuscular Mycorrhizal Fungi Colonizing Roots

The arbuscular mycorrhiza （AM） is a kind of fungi-plant associated sym- biont formed by the arbuscular mycorrhizal fungi and plants in soil. Present study was limited to the population and community level, mainly in horticulture, land recla- mation, forest and environmental restoration. Research progress was also made at the cellular level and molecular level. Process and related mechanism of mycorrhizal fungi infecting root were reviewed, and future study on the mechanism of arbuscular mycorrhizal fungi infecting root should be continued.

Arbuscular Mycorrhizal (AM) Diversity in Prosopis cineraria (L.) Druce Under Arid Agroecosystems

Arbuscular mycorrhizal （AM） fungi associated with Prosopis cineraria （Khejri） were assessed for their qualitative and quantitative distribution from eight districts of Rajasthan. A total of three species of Acaulospora, one species of Entrophospora, two species of Gigaspora, twenty-one species of Glomus, seven species of Sclerocystis and three species of Scutellospora were recorded. A high diversity of AM fungi was observed and it varied at different study sites. Among these six genera, Glomus occurred most frequently. Glomus fasciculatum, Glomus aggregatum, and Glomus mosseae were found to be the most predominant AM fungi in infecting Prosopis cineraria. Acaulospora, G. fasciculatum, Sclerocystis was found in all the fields studied, while Scutellospora species were found only in few sites. A maximum of thirty-six AM fungal species were isolated and identified from Jodhpur, whereas only thirteen species were found from Jaisalmer. Spores of Glomusfasciculatum were found to be most abundant under Prosopis cineraria.

Interaction of Acaena elongata L.with Arbuscular Mycorrhizal Fungi under Phosphorus Limitation Conditions in a Temperate Forest

The aim of this study was to analyze the performance of Acaena elongata colonized by arbuscular mycorrhizal fungi(AMF)to different phosphorus(P)concentrations,as a measure of AMF dependency.A.elongata,is a species from soils where P availability is limited,such as temperate forests.Our research questions were:1)How do different P concentrations affect the AMF association in Acaena elongata,and 2)How does the AMF association influence A.elongata’s growth under different P concentrations?A.elongata’s growth,P content in plant tissue,AMF colonization and dependency were measured under four P concentrations:control(0 g P kg^(-1)),low(0.05 g P kg^(-1)),intermediate(0.2 g P kg^(-1))and high(2 g P kg^(-1))in different harvests.A complete randomized block design was applied.A.elongata’s growth was higher under-AMF in intermediate and high P concentrations,and the lowest growth corresponded to+AMF in the low and intermediate P concentration.We observed a negative effect on the root biomass under+AMF in intermediate P concentration,while the P concentration had a positive effect on the leaf area ratio.The AMF colonization in A.elongata decreased in the highest P concentration and it was favored under intermediate P concentration;while the low and the high concentrations generated a cost-benefit imbalance.Our results suggest that the performance of some plant species in soils with low P availability may not be favored by their association with AMF,but a synergy between AMF and intermediate P concentrations might drive A.elongata’s growth.

Role of arbuscular mycorrhizal fungi in sustainable crop production and forestry in Sri Lanka-A review

Mycorrhizae are symbiotic associations between a soil-borne fungus and plant root.Arbuscular mycorrhizal fungi(AMF)are the most common type of mycorrhizal associations occurring in plants.AMF can increase plant growth mainly by improving nutrient uptake and making plants resistant to several biotic and abiotic stresses.Thus,AMF could be referred to as an important biofertilizer for the crop production.However,in Sri Lankan context,seems the knowledge and use of AMF is limited,though there is a great potential of using AMF for sustainable crop production and forestry.This review provides an overview on the benefits of AMF for agriculture and forestry with the studies that have been carried out to attain them,in Sri Lanka.

Arsenic uptake by arbuscular mycorrhizal maize (Zea mays L.) grown in an arsenic-contaminated soil with added phosphorus

The effects of arbuscular mycorrhizal （AM） fungus （Glomus mosseae） and phosphorus （P） addition （100 mg/kg soil） on arsenic （As） uptake by maize plants （Zea mays L.） from an As-contaminated soil were examined in a glasshouse experiment. Non-mycorrhizal and zero-P addition controls were included. Plant biomass and concentrations and uptake of As, P, and other nutrients, AM colonization, root lengths, and hyphal length densities were determined. The results indicated that addition of P significantly inhibited root colonization and development of extraradical mycelium. Root length and dry weight both increased markedly with mycorrhizal colonization under the zero-P treatments, but shoot and root biomass of AM plants was depressed by P application. AM fungal inoculation decreased shoot As concentrations when no P was added, and shoot and root As concentrations of AM plants increased 2.6 and 1.4 times with P addition, respectively. Shoot and root uptake of P, Mn, Cu, and Zn increased, but shoot Fe uptake decreased by 44.6%, with inoculation, when P was added. P addition reduced shoot P, Fe, Mn, Cu, and Zn uptake of AM plants, but increased root Fe and Mn uptake of the nonmycorrhizal ones. AM colonization therefore appeared to enhance plant tolerance to As in low P soil, and have some potential for the phytostabilization of As-contaminated soil, however, P application may introduce additional environmental risk by increasing soil As mobility.

The role of arbuscular mycorrhiza on change of heavy metal speciation in rhizosphere of maize in wastewater irrigated agriculture soil

To understand the roles of mycorrhiza in metal speciation in the rhizosphere and the impact on increasing host plant tolerance against excessive heavy metals in soil, maize(Zea mays L.) inoculated with arbuscular mycorrhizal fungus(Glomus mosseae) was cultivated in heavy metal contaminated soil. Speciations of copper, zinc and lead in the soil were analyzed with the technique of sequential extraction. The results showed that,in comparison to the bolked soil, the exchangeable copper increased from 26% to 43% in non-infected and AM-infected rhizoshpere respectively; while other speciation (organic, carbonate and Fe-Mn oxide copper) remained constant and the organic bound zinc and lead also increased but the exchangeable zinc and lead were undetectable. The organic bound copper, zinc and lead were higher by 15%, 40% and 20%, respectively, in the rhizosphere of arbuscular mycorrhiza infected maize in comparison to the non-infected maize. The results might indicate that mycorrhiza could protect its host plants from the phytotoxicity of excessive copper, zinc and lead by changing the speciation from bio-available to the non-bio-available form. The fact that copper and zinc accumulation in the roots and shoots of mycorrhia infected plants were significantly lower than those in the non-infected plants might also suggest that mycorrhiza efficiently restricted excessive copper and zinc absorptions into the host plants. Compared to the non-infected seedlings, the lead content of infected seedlings was 60% higher in shoots. This might illustrate that mycorrhiza have a different mechanism for protecting its host from excessive lead phytotoxicity by chelating lead in the shoots.

Comparison of Arbuscular Mycorrhizal Fungal Community in Roots and Rhizosphere of Invasive Cenchrus incertus and Native Plant in Inner Mongolia,China

Plant invasions could significantly alter arbuscular mycorrhizal(AM) fungal communities, but the effect may vary with plant species and local environments. Identifying changes in the AM fungal community due to plant invasion could improve our understanding of the invasion processes. Here, we examined the AM fungal community composition both in roots and rhizosphere soils of the invasive plant Cenchrus incertus and the dominant native plant Setaria viridis in a typical steppe in Inner Mongolia by using terminal restriction fragment length polymorphism analyses(T-RFLP). The results showed that AM fungal abundance in the rhizosphere soils of C. incertus was significantly lower than that of S. viridis. The AM fungal community composition in the rhizosphere soils of the two plant species also largely differed. In general, AM fungal community structures in roots corresponded very well to that in rhizosphere soils for both plant species. The dominant AM fungal type both in invasive and native plants was T-RFLP 524 bp, which represents Glomus sp.(Virtual taxa 109 and 287). Three specific T-RF types(280,190 and 141bp) were significantly more abundant in C. incertus, representing three clusters in Glomus which also named as VT(virtual taxa) 287, 64 and 214, Rhizophagus intraradices(VT 113) and Diversispora sp.(VT 60). While the specific T-RF types,189 and 279 bp, for S. viridis, only existed in Glomus cluster 1(VT 156), were significantly less abundant in C. incertus. These results indicated that AM fungi might play an important role in the invasion process of C. incertus, which still remains to be further investigated.

A Preliminary Survey of Arbuscular Mycorrhizal Fungi Associated with Marsh Plants in Lhalu Wetland,Suburban Lhasa,South Tibet

A survey was made of the spore community of arbuscular mycorrhizal fungi (AMF) and root colonization by AMF in 16 plant species in Lhalu wetland on the outskirts of Lhasa city in Tibet. It was found that 13 of the 16 plant species investigated (81. 5% ) formed arbuscular mycorrhizal structures and dark septate endophytic fungi colonized the roots of most species. Total AMF colonization ranged from 0 to 82. 6% in dicots and 0 to 54. 5% in monocots. Both total AMF and arbuscular colonization were greater in dicots than that in monocots. A total of 48 taxa representing 7 genera of AMF were isolated and identified. Of these,9 species belonged to Acaulospora,2 to Appendicispora,34 to Glomus,and 1 each to Pacispora,Paraglomus and Scutellospora. Spores of Glomus aggregatum,G. deserticola and G. etunicatum were most common and abundant in the spore survey. Spores of 8 to 26 AMF species were isolated from the rhizosphere soil of individual plant species. Spore densities in soil associated with the 16 plant species ranged from 20 to 475 per 20 g soil,with an average of (92. 3 ± 14. 6). Species richness of AMF ranged from 6 to 12. 7. There were no significant differences between dicots and monocots in AMF spore density or species richness. Future work directed towards under- standing the response of the wetland plants to AMF may provide some insight into the role that these fungal symbionts may play in influencing plant diversity in this important urban wetland.

A test of the mycorrhizal-associated nutrient economy framework in two types of tropical rainforests under nutrient enrichments

Shifts in tree species and their mycorrhizal associations driven by global change play key roles in biogeochemical cycles. In this paper, we proposed a framework of the mycorrhizal-associated nutrient economy(MANE), and tested it using nutrient addition experiments conducted in two tropical rainforests. We selected two tropical rainforests dominated by arbuscular mycorrhizal(AM) and ectomycorrhizal(ECM) trees, and established eighteen20 m×20 m plots in each rainforest. Six nitrogen(N) and phosphorus(P) addition treatments were randomly distributed in each rainforest with three replicates. We examined the differences in soil carbon(C) and nutrient cycling, plant and litter productivity between the two rainforests and their responses to 10-year inorganic N and P additions. We also quantified the P pools of plants, roots, litter, soil and microbes in the two rainforests. Overall,distinct MANE frameworks were applicable for tropical rainforests, in which soil C, N and P were cycled primarily in an inorganic form in the AM-dominated rainforest, whereas they were cycled in an organic form in the ECMdominated rainforest. Notably, the effects of mycorrhizal types on soil P cycling were stronger than those on C and N cycling. The intensified N and P deposition benefited the growth of AM-dominated rainforests instead of ECMdominated rainforests. Our findings underpin the key role of mycorrhizal types in regulating biogeochemical processes, and have important implications for predicting the ecological consequences of global changes.

Mycorrhizoremediation—an enhanced form of phytoremediation

Study of plant roots and the diversity of soil micro biota, such as bacteria, fungi and microfauna associated with them, is important for understanding the ecological complexities between diverse plants, microbes, soil and climates and their role in phytoremediation of contaminated soils. The arbuscular mycorrhizal fungi (AMF) are universal and ubiquitous rhizosphere mi-croflora forming symbiosis with plant roots and acting as biofertilizers, bioprotactants, and biodegraders. In addition to AMF, soils also contain various antagonistic and beneficial bacteria such as root pathogens, plant growth promoting rhizobacteria including free-living and symbiotic N-fixers, and mycorrhiza helping bacteria. Their potential role in phytoremediation of heavy metal (HM) contaminated soils and water is becoming evident although there is need to completely understand the ecological complexities of the plant-microbe-soil interactions and their better exploitation as consortia in remediation strategies employed for contaminated soils. These multitrophic root microbial associations deserve multi-disciplinary investigations using molecular, biochemical, and physiological techniques. Ecosystem restoration of heavy metal contaminated soils practices need to incorporate microbial bio-technology research and development. This review highlights the ecological complexity and diversity of plant-microbe-soil combinations, particularly AM and provides an overview on the recent developments in this area. It also discusses the role AMF play in phytorestoration of HM contaminated soils, i.e. mycorrhizoremediation.

Mycorrhizal Networks Interacting with Litter Improves Nutrients and Growth for One Plant through the Vary of N/P Ratio under Karst Soil

Arbuscular mycorrhizae(AM)fungi affect nutrient uptake for host plants,while it is unclear how AM fungi interacting with soil litter affect plant growth and nutrient utilization through mycorrhizal networks in karst soil of deficient nutrients beyond the rhizosphere.An experiment was conducted in a microcosm composed of a planting compartment for Cinnamomum camphora seedlings with or without Glomus mosseae fungus(M+vs.M−)and an adjacent litter compartment containing or not containing additional litter material of Arthraxon hispidus(L+vs.L−),where the compartments are connected either by nylon mesh of 20μm or 0.45μm which either allow available mycorrhizal networks within the litter compartment or prevent mycelium entering into the litter compartment(N+vs.N−).Plant biomass and nutrients were measured.The results showed that the addition of litter changed the symbiotic process in mycorrhizal colonization,spore,and hyphal density,which when in association with the host plant then affected the biomass,and accumulations of N(nitrogen)and P(phosphorus)in the individual plant as well as root,stem,and leaf respectively.AM fungi increased N and P accumulations and N/P ratio in individual plants and plant tissues.A decrease of the N/P ratio of the individual plant was observed when AM fungus interacted significantly with litter through mycorrhizal networks in the litter compartment.The results indicate that the C.camphora seedlings benefited from litter in nutrient utilization of N and P through the vary of N/P ratio when accessing mycorrhizal networks.These findings suggest that mycorrhizal networks interacting with litter improve growth and nutrients of N and P for plants through the vary of N/P ratio in order to alleviate nutrient limitation under karst soil.

Utilization of Sparingly Soluble Phosphate by Red Cloverin Association with Glomus mosseae and Bacillus megaterium

A pot experiment was conducted to investigate the mobilization ofsparingly soluble inorganic and organic sources of phosphorus (P) byred clover (Trifolium pratense L.) whose roots were colonized by thearbuscular mycorrhizal (AM) fungus Glomus mosseae and in associationwith the phosphate-solubilizing (PS) bacterium Bacillus megateriumACCC10010. Phosphate-solubilizing bacteria and rock phosphate had asynergistic effect on the colonization of plant roots by the AMfungus. There was a positive interaction between the PS bacterium andthe AM fungu in mobilization of rock phosphate, leading to improvedplant P nutrition. In dual inoculation with the AM fungus and the PSbacterium, the main contribution to plant P nutrition was made by theAM fungus. Application of P to be low P soil increased phosphataseactivity In the rhizosphere. Alkaline phosphatase activity wassignificantly promoted by inoculation with either the PS bacterium orthe AM fungus.

Some Evidence for Host Specificity in Arbuscnlar Myc-orrhizas

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The Role of Biofertilization in Improving Apple Productivity―A Review

Biofertilization of crops with plant growth promoting microorganisms is currently considered as a healthy alternative to chemical fertilization. Biofertilizers are microbial preparations containing living cells of different microorganisms which have the ability to mobilize plant nutrients in soil from unusable to usable form. They are environmentally friendly, play a significant role in the crop production, help to build up the lost microflora and improve the soil health. Also, they increase crop yield by 20% - 30%, stimulate plant growth, are cost effective and provide optimal conditions for soil biological activity. They suppress pathogenic soil organisms, restore natural soil fertility and provide protection against drought and some soil borne diseases. Moreover, they degrade toxic organic chemicals, improve seed germination and aid in balancing soil pH in reducing soil erosion.

Yield Attributes and Oil Safety in the Hyperaccumulator Canola Plant Grown in a Bioremediated Sewaged Soil

A field experiment was carried out at Abu-Rawash sewage farm to appraise the effect of certain novel remediative amendments on the quality of oil as well as the vegetative parameters and yield criteria of canola plant used as hyperaccumulator for the remediation of sewaged soils. The treatments included fallow soil （irrigated without growing canola）, soil cultivated with canola （Brassica napus L.） and inoculated with arbuscular mycorrhiza （AM）, soil inoculation with Thiobacillus sp. （a mixture of Thiobacillus ferrooxidans and Thiobacillus thiooxidant）, soil treated with a mixture of 250 mg bentonite plus 250 mg rock phosphate/kg soil and inoculated with phosphate dissolving bacteria （PDB）, and soil treated with all the aforementioned remediative amendments. Results indicated that the vegetative parameters and yield criteria of canola plant did not exhibit any serious adverse impact under all treatments applied. The concentrations of Zn and Cu in canola oil extracted from plants grown in soil inoculated with AM and/or Thiobacillus sp. far exceeded the safe permissible levels. On the other hand, the content of both PTEs in the oil extracted from canola plants grown in soil treated with either probentonite or with mixture of all remediative amendments followed the permissible safe levels.