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.

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.

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.

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.

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.

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.

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.

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.

Application of Arbuscular Mycorrhizal Inocula Might Be A Promising Method in the Restoration of Severely Degraded Wetlands

The application of arbuscular mycorrhizal (AM) inocula in severely degraded wetlands could ensure success in restoration.Mycorrhizal fungi play an important role in plant individual's survival and development in a low nutrient condition.Based on the importance that mycorrhizal fungi have to their host plants,mycorrhizal inocula have been produced and applied in terrestrial ecosystems in order to let the plants become mycorrhizal.However,mycorrhizal inocula have not been used in wetland restorations,despite increasing evidence that mycorrhizal fungi are commonly found in various wetland systems and have the ability to survive under anoxic conditions.Evidence also shows that mycorrhizal fungal inocula in the soil could have been destroyed in the degraded wetland or could be destroyed during traditional wetland restoration process.Therefore,AM inocula production is strongly recommended for wetland restoration.In this paper,I will argue that AM inocula production is required when introduced recovery is necessary,and aeroponic culture technique is a preferable method to produce AM inocula.Last,a renewed wetland restoration flow chart is summarized.

A 60-year journey of mycorrhizal research in China:Past,present and future directions

The significance of mycorrhizas(fungal roots in 90% of land plants) in plant nutrient acquisition and growth,element biogeo-chemical cycling and maintaining of terrestrial ecosystem structures has been globally established for more than 120 years.Great progress in mycorrhizal research in the past 60 years(1950-2009,1981-2009 in particular) has also been made across China,particularly in the mainland,Hong Kong and Taiwan.For instance,a total of 20 new and ~120 records of arbuscular mycorrhizal(AM) fungal species,30 new and ~800 records of ectomycorrhizal(EM) fungal species,a dozen of new and ~100 records of orchid mycorrhizal(OM) fungal species have been isolated by morphological observation and/or molecular identification in China since the 1950s.Great accomplishment has also been made in the following area,including fungal species richness and genetic structure,relationships between species composition and plant taxa,effects of mycorrhizal fungi on plant nutrient uptake and growth,resistances to pathogens and interactions with other soil microorganisms,potential of mycorrhizal fungi in phytoremediation and/or land reclamation,alterations of enzymatic activities in mycorrhizal plants,and elevated CO2 and O3 on root colonization and species diversity.Unfortunately,the international community cannot easily appreciate almost all Chinese mycorrhizal studies since the vast majority of them have been published in Chinese and/or in China-based journals.The aim of this review is to make a comprehensive exposure of the past and present China's major mycorrhizal research to the whole world,and then to suggest potential directions for the enhancement of future mycorrhizal research within and/or between the Chinese and international mycorrhizal community.

Mycorrhizal symbiosis modulates the rhizosphere microbiota to promote rhizobia–legume symbiosis

Plants establish symbioses with mutualistic fungi,such as arbuscular mycorrhizal(AM)fungi,and bacteria,such as rhizobia,to exchange key nutrients and thrive.Plants and symbionts have coevolved and represent vital components of terrestrial ecosystems.Plants employ an ancestral AM signaling pathway to establish intracellular symbioses,including the legume–rhizobia symbiosis,in their roots.Nevertheless,the relationship between the AM and rhizobial symbioses in native soil is poorly understood.Here,we examined how these distinct symbioses affect root-associated bacterial communities in Medicago truncatula by performing quantitative microbiota profiling(QMP)of 16S rRNA genes.We found that M.truncatula mutants that cannot establish AM or rhizobia symbiosis have an altered microbial load(quantitative abundance)in the rhizosphere and roots,and in particular that AM symbiosis is required to assemble a normal quantitative root-associated microbiota in native soil.Moreover,quantitative microbial co-abundance network analyses revealed that AM symbiosis affects Rhizobiales hubs among plant microbiota and benefits the plant holobiont.Through QMP of rhizobial rpoB and AM fungal SSU rRNA genes,we revealed a new layer of interaction whereby AM symbiosis promotes rhizobia accumulation in the rhizosphere of M.truncatula.We further showed that AM symbiosis-conditioned microbial communities within the M.truncatula rhizosphere could promote nodulation in different legume plants in native soil.Given that the AM and rhizobial symbioses are critical for crop growth,our findings might inform strategies to improve agricultural management.Moreover,our work sheds light on the co-evolution of these intracellular symbioses during plant adaptation to native soil conditions.

Plant-associated fungal communities in the light of meta’omics

Approaches for the cultivation-independent analysis of microbial communities are summarized as meta’omics,which predominantly includes metagenomic,-transcriptomic,-proteomic and-metabolomic studies.These have shown that endophytic,root-associated and soil fungal communities are strongly shaped by associated plant species.The impact of plant identity on the composition of its litterssociated fungal community remains to be disentangled from the impact of litter chemistry.The composition of the plant community also shapes the fungal community.Most strikingly,adjacent plant species may share mycorrhizal symbionts even if the plants usually have different types of mycorrhizal fungi associated with them(ectomycorrhizal,ericoid and arbuscular mycorrhizal fungi).Environmental parameters weakly explain fungal community composition globally,and their effect is inconsistent at local and regional scales.Decrease in similarity among communities with increasing distance(i.e.distance decay)has been reported from local to global scales.This pattern is only exceptionally caused by spatial dispersal limitation of fungal propagules,but mostly due to the inability of the fungi to establish at the particular locality(i.e.environmental filtering or competitive exclusion).Fungal communities usually undergo pronounced seasonal changes and also differ between consecutive years.This indicates that development of the communities is usually not solely cyclic.Meta’omic studies challenge the classical view of plant litter decomposition.They show that mycorrhizal and(previously)endophytic fungi may be involved in plant litter decomposition and only partly support the idea of a succession from an Ascomycota to a Basidiomycota-dominated community.Furthermore,vertical separation of saprotrophic and mycorrhizal species in soil and sequential degradation from easily accessible to‘recalcitrant’plant compounds,such as lignin,can probably not be generalized.The current models of litter decomposition may therefore have to be eventually refined for certain ecosystems and environmental conditions.To gain deeper insights into fungal ecology,a meta’omic study design is outlined which focuses on environmental processes,because fungal communities are usually taxonomically diverse,but functionally redundant.This approach would initially identify dynamics of chemical shifts in the host and/or substrate by metametabolomics.Detected shifts would be subsequently linked to microbial activity by correlation with metatranscriptomic and/or metaproteomic data.A holistic trait-based approach might finally identify factors shaping taxonomic composition in communities against the dynamics of the environmental process(es)they are involved in.

Variations in soil properties and native woody plant species abundance under Prosopis juliflora invasion in Afar grazing lands, Ethiopia

Introduction:Pastoralism and agro-pastoralism are the major modes of life in arid and semi-arid rangelands.However,rangeland quality and quantity are rapidly deteriorating due to a number of natural and human-induced factors,one of which is bush encroachment.Little is known on how bush encroachment affects the ecosystem functions and services expressed in terms of the native vegetation composition and structure,status of the soil seed bank,soil chemical and physical properties,and the abundance of mycorrhiza spores.Methods:We assessed woody species in 64 plots distributed across four levels of Prosopis juliflora invasion(high,medium,low,and none)at two sites,Amibara and Gewane,in the Afar Region,Ethiopia.We collected composite soil samples to investigate the soil seed bank,mycorrhizal associations,and spore abundance.Results:Plant biodiversity was generally low,with eight and four woody species in Gewane and Amibara,respectively.Prosopis juliflora was dominant in highly,moderately,and lowly invaded areas while Acacia senegal dominated the non-invaded areas.The average number of P.juliflora individuals ranged from 3/ha at non-invaded areas in Gewane to 4200/ha at highly invaded areas in Amibara while the total individual number of native woody species ranged from 0 to 88/ha at highly and lowly invaded areas,respectively.The population structure of trees/shrubs in all invasion areas showed an inverted J-shaped distribution,characterized by a high abundance of small individuals.Prosopis juliflora invasion was associated with high soil OC,Na,Ca,P,bulk density,and moisture content.Herbaceous seed numbers and species richness were highest in the moderately and highly invaded areas.All sampled tree species were associated with mycorrhiza but the percentage of root length colonization by different arbuscular mycorrhizal fungus structures varied significantly(p<0.05)across invasion categories and sites.Conclusions:Our results revealed that although P.juliflora invasion negatively impacted the availability of native woody livestock forage species,it had a positive effect on most soil physical and chemical properties.Such variable effects call out for sustainable management practices when invaded areas are restored.

Identification of micro RNAs in six solanaceous plants and their potential link with phosphate and mycorrhizal signalings

To date, only a limited number of solanaceous miRNAs have been deposited in the miRNA database. Here,Rgenome-wide bioinformatic identification of miRNAs was performed in six solanaceous plants（potato, tomato, tobacco,eggplant, pepper, and petunia）. A total of 2,239 miRNAs were identified following a range of criteria, of which 982 were from potato, 496 from tomato, 655 from tobacco, 46 from eggplant,45 were from pepper, and 15 from petunia. The sizes of miRNA families and miRNA precursor length differ in all the species.Accordingly, 620 targets were predicted, which could be functionally classified as transcription factors, metabolic enzymes, RNA and protein processing proteins, and other proteins for plant growth and development. We also showed evidence for miRNA clusters and sense and antisense miR NAs.Additionally, five Pi starvation- and one arbuscular mycorrhiza（AM）-related cis-elements were found widely distributed in the putative promoter regions of the miRNA genes. Selected miRNAs were classified into three groups based on the presence or absence of P1BS and MYCScis-elements, and their expression in response to Pi starvation and AM symbiosis was validated by quantitative reverse transcription-polymerase chain reaction（qRT-PCR）. These results show that conserved miRNAs exist in solanaceous species and they might play pivotal roles in plant growth, development, and stress responses.