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.

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 cowpea seeds. After 60 days the positive impact of AM inoculation on the growth of cowpea was more pronounced in the red soil than in the yellow-brown soil, with significantly higher (P ＜ 0.01)mycorrhizal colonization rate, shoot dry weight and total P content in shoot tissues for the red soil. Both in the yellowbrown and red soils, AM inoculation significantly (P ＜ 0.01) reduced shoot DEHP content, implying that AM inoculation could inhibit the uptake and translocation of DEHP from roots to the aboveground parts. However, with AM inoculation no positive contribution to the degradation of DEHP was found.

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.

Soil compaction and arbuscular mycorrhizae affect seedling growth of three grasses

Soil compaction is a limitation to establishment of native forest species on reclaimed surfacemined lands in Appalachia. Previously, non-native forage species such as tall fescue (Schedonorus arundinaceus(Schreb.) Dumort., nom. cons.) have been planted because they easily established on reclaimed mine soil. There is now interest in establishing robust native prairie species to enhance biodiversity and provide greater potential for root activity in the compacted soil. We conducted a 10-week glasshouse study comparing growth of “Pete” eastern gamagrass (Tripsacum dactyloidesL.), “Bison” big bluestem (Andropogon gerardiiVitman), and “Jesup MaxQ” tall fescue at soil bulk densities (BD) of 1.0, 1.3, and 1.5 g·cm-3. We also examined effects of arbuscular-mycorrhizal fungi (AMF) on plant growthin relation to compaction. Sources of AMF were a reclaimed surface coal mine soil and a native tallgrass prairie soil. Shoot and root biomass of tall fescue and big bluestem were reduced at 1.5 BD while eastern gamagrass growth was not affected. Growth ofbig bluestem and eastern gamagrass was greaterwith AMF than without, butsimilar between AMF sources. Tall fescue growthwas not enhanced by AMF. Overall, tall fescue biomass was 3 times greater than eastern gamagrass and 6 times greater than big bluestem when comparing only AMF-colonized grasses. Eastern gamagrass and big bluestem are both slower to establish than tall fescue. Eastern gamagrass appears to be more tolerant of compaction, while big bluestem appears somewhat less tolerant.

Effect of Arbuscular Mycorrhizal (AM) Fungi on the Physiological Performance of Phaseolus vulgaris Grown under Crude Oil Contaminated Soil

An experiment was conducted to assess the influence of arbuscular mycorrhizal (AM) fungi on the performance of Phaseolus vulgaris under crude oil contaminated soil. P. vulgaris was grown on soil under 2%, 4% and 8% (v/w) crude oil contamination. The experimental units were biostimulated with 2 g NPK fertilizer pot-1 and were inoculated with 12 g AM inoculum pot-1. Non inoculated pots served as control. The results showed that AM inoculated pots recorded higher and significantly (P < 0.05) different dry matter yields and chlorophyll content than non AM inoculated pots. Residual total petroleum hydrocarbon (TPH) increased as percent crude oil contamination increased. Total petroleum hydrocarbon decomposition and removal was higher on pots inoculated with AM than non inoculated pots. With AM colonization, physiological characteristics of P. vulgaris and TPH decomposition improved. This is evinced by the linear regression analysis between colonization and TPH (R2 = 0.77).

Effectivity of arbuscular mycorrhizal fungi collected from reclaimed mine soil and tallgrass prairie

We examined suitability of arbuscular mycorrhizal fungi (AMF) associated with cool-season nonnative forages on reclaimed surface-mined land in southeast Ohio for establishment of native warm-season grasses. The goal of establishing these grasses is to diversify a post-reclamation landscape that is incapable of supporting native forest species. A 16-week glasshouse study compared AMF from a 30-year reclaimed mine soil (WL) with AMF from native Ohio tallgrass prairie soil (CL). Four native grasses were examined from seedling through 16 weeks of growth. Comparisons were made between CL and WL AMF on colonized (+AMF) and non-colonized plants (–AMF) at three levels of soil phosphorus (P). Leaves were counted at 4 week intervals. Shoot and root biomass and percent AMF root colonization were measured at termination. We found no difference between WL and CL AMF. Added soil P did not reduce AMF colonization, but did reduce AMF efficacy. Big bluestem (Andropogon gerardii Vitman), Indiangrass (Sorghastrum nutans (L.) Nash), and tall dropseed (Sporobolus asper (Michx.) Kunth) benefited from AMF only at low soil P while slender wheatgrass (Elymus trachycaulus (Link) Gould ex Shinners) exhibited no benefit. Establishment of tallgrass prairie dominants big blue-stem and Indiangrass would be supported by the mine soil AMF. It appears that the non-native forage species have supported AMF equally functional as AMF from a regionally native tallgrass prairie. Tall dropseed and slender wheatgrass were found to be less dependent on AMF than big bluestem or Indiangrass and thus would be useful in areas with little or no AMF inoculum.

Testing the Effect of Soil Heterogeneity on Arbuscular Mycorrhiza Fungi (AMF) Contribution to Plant Productivity

Most natural soils are heterogeneous and nutrient availability and soil structure change greatly over small distances. It is still unclear whether AMF are advantageous for plants under such heterogeneous soil conditions. The objective of this study was to determine whether diverse AMF community support host plant community productivity in heterogeneous soil. It was also tested whether soil heterogeneity affects plant productivity. This was carried out in a greenhouse experiment made up of two factors: soil heterogeneity and AMF richness. Soil heterogeneity was simulated by mixing three soil types (sand, field soil and organic soil) together (homogenous soil (HM)), mixing them partly (semi homogenous (SH)) or keeping the three soil types separate in three compartments within one pot (heterogeneous (HT)). AMF richness was simulated by adding no AMF, one of four different AMF species separately, or all four different AMF together. The pots were planted with a mixture of Trifolium pratense and Lolium multiflorum. There was no effect of soil heterogeneity on total plant biomass. However, the biomass of the individual plant species was greatly affected by soil heterogeneity with Lolium being the most abundant in the heterogeneous soil and Trifolium being the most abundant in the homogenous soil. Total plant biomass did not increase with AMF richness. Moreover, opposite to the hypothesis, AMF richness was not beneficial for plant productivity in a heterogenous soil environment. However, there were significant differences in plant biomass with different AMF treatments in the SH and HT treatment indicating that effects of AMF on plant productivity are influenced by soil type. These effects on yield and AMF reflect a combination of local responses to growing conditions. The results show that AMF influence on plant yield may not always be positive but is strongly dependent on ecological elasticity and environmental condition.

Interactions between a Root Knot Nematode (<i>Meloidogyne exigua</i>) and Arbuscular Mycorrhizae in Coffee Plant Development (<i>Coffea arabica</i>)

This paper focuses on parasitic root knot nematodes (Meloidogyne exigua) and how to decrease their pathogenic effect on coffee plants (Coffea arabica), by examining the behaviour of and the interactions between nematodes, coffee plant and arbuscular mycorrhizae (AM). The experiment was carried out at the seedling stage, with six (6) treatments (plants with M. exigua, plants with arbuscular mycorrhizae, plants with both organisms, and the same time, first mycorrhizae plants, then nematodes were inoculated and vice versa). After 5 months the measured variables were: dry biomass (roots and shoot), nematode knots caused by M. exigua in root, nematode juvenile (J2) found in 100.0 g of soil, and mycorrhizal percentage. Plant nutrients (P and N) contents were analysed. Significant differences were found in all the variables, but concentration N content in plants. Plants with mycorrhizae and plants with mycorrhizae and then inoculated with nematodes have the same behaviour. Control plants and plants with nematode and then inoculated with mycorrhizae behave similarly. It is thought that arbuscular mycorrhizae are formed before the nematode infestation, allowing coffee plants to regain the energy lost by the parasitic interaction. AM may help coffee plants with lignifications of the plant cell wall cuticle. As the cuticle thickens it is more difficult for nematodes to penetrate and enter into plant roots. Therefore, arbuscular mycorrhizae help coffee plants to uptake and transport nutrients, improving its nutritional status and stabilizing nematode attacks. It is suggested that symbiotic interactions help neutralize parasitic interactions.

Molecular Characterization of Arbuscular Mycorrhizal Symbiosis for Defense,Nutrient Absorption and Secondary Metabolism in Plants

Arbscular mycorrhiza(AM),a symbiosis between plants and members of fungi Glomeromycota,improves the resistance,nutrition and material metabolism of plant.Arbuscules generated by symbiotic development,is the main site of nutrient exchange and genetic material recombination,resulting in physiological changes and gene expression regulation.AM regulates pathogenesis-related protein(PRs) genes and antioxidant enzyme genes against biotic and abiotic stresses.Nutrient exchange induced by AM is directly involved in uptake,transformation and utilization of nutrient elements in plants.Importantly,transporter genes play an important role in phosphate,nitrogen and carbon acquisition.In AM interactions,phosphate transporter(PT) genes,from both arbuscular mycorrhizal fungi and plant root,are induced and there product promote phosphate acquisition;increasing expression of ammonium transporter(AMT) genes and arginine biosynthesis/degradation enzyme genes is in charge of nitrogen acquisition;and promotion mechanism of carbon acquisition is involved in up-regulation of sugar transporter genes.In addition,secondary metabolites,functioned as signal moleculars and defense compounds,are increased with development of AM symbiont by up-regulating related synthetic genes based on different promotion mechanism.Taken together,molecular regulation of plant and arbuscular mycorrhizal fungi,induced by infection process,stimulate plant nutrient acquisition and resist to biotic/abiotic stress.

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 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.

Forms of nitrogen uptake,translocation,and transfer via arbuscular mycorrhizal fungi:A review

Arbuscular mycorrhizal(AM) fungi are obligate symbionts that colonize the roots of more than 80% of land plants.Experiments on the relationship between the host plant and AM in soil or in sterile root-organ culture have provided clear evidence that the extraradical mycelia of AM fungi uptake various forms of nitrogen(N) and transport the assimilated N to the roots of the host plant.However,the uptake mechanisms of various forms of N and its translocation and transfer from the fungus to the host are virtually unknown.Therefore,there is a dearth of integrated models describing the movement of N through the AM fungal hyphae.Recent studies examined Ri T-DNA-transformed carrot roots colonized with AM fungi in 15 N tracer experiments.In these experiments,the activities of key enzymes were determined,and expressions of genes related to N assimilation and translocation pathways were quantified.This review summarizes and discusses the results of recent research on the forms of N uptake,transport,degradation,and transfer to the roots of the host plant and the underlying mechanisms,as well as research on the forms of N and carbon used by germinating spores and their effects on amino acid metabolism.Finally,a pathway model summarizing the entire mechanism of N metabolism in AM fungi is outlined.

Arginine bi-directional translocation and breakdown into ornithine along the arbuscular mycorrhizal mycelium

Bi-directional translocation and degradation of Arginine (Arg) along the arbuscular mycorrhizal (AM) fungal mycelium were testified through 15N and/or 13C isotopic labeling. In vitro mycorrhizas of Glomus intraradices and Ri T-DNA-transformed carrot roots were grown in dual compartment Petri dishes. [15N- and/or13C]Arg was supplied to either the fungal compartment or the mycorrhizal compartment or separate dishes containing the uncolonized roots. The levels and labeling of free amino acids (AAs) in the mycorrhizal roots and in the extraradical mycelia(ERM) were measured by gas chromatogra- phy/mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC). The ERM of AM fungi exposed in either NH4+ or urea as sole external nitrogen source had much higher 15N enrichment of Arg, compared with those in nitrate or exogenous Arg; however, glycerol supplied as an external car- bon source to the ERM had no significant effect on the level of Arg in the ERM. Meanwhile, Arg bio- synthesized in the ERM could be translocated intact to the mycorrhizal roots and thereby the level of Arg in the mycorrhizal roots increased to about 20% after culture of ERM in 4 mmol/L NH4+ for 6 weeks. Also Arg was found to be bi-directionally transported along the AM fungal mycelium through [U-13C]Arg labeling either in the mycorrhizal compartment or in the fungal compartment. Once Arg was translo- cated to the potential N-limited sites, it would be further degraded into ornithine (Orn) and urea since either [U-13C] or [U-15N/U-13C]Orn was apparently shown up in the mycorrhizal root tissues when [U-13C] or [U-15N/U-13C]Arg was labeled in the fungal compartment, respectively. Evidently Orn formation indi- cated the ongoing activities of Arg translocation and degradation through the urea cycle in AM fungal mycelium.

Arbuscular mycorrhizal associations in the Gurbantunggut Desert

在位于 Xinjiang 的 Gurbantunggut 沙漠的植物，中国是改编的干旱种类并且在通常滋养穷人的土壤成长。调查在沙漠被进行决定与合适的荒芜的植物联系的 arbuscular mycorrhizal (AM ) 地位从 annuals 和 perennials 的 11 个家庭的 to23 种类。从所有植物的根为决定 mycorrhizal 殖民的地位和程度的内部、外部的 hyphae，泡和 coils/arbuscules 的存在被检验。调查的植物种类，(61%) 14 被发现形成 AMassociations，(22%) 5 是可能的 AM 开拓殖民地于种类，并且 4 是 non-my-corrhizal 植物。形成 AM 的 annuals 和灌木的 Theproportions 分别地是比 perennials 和植物的那些显著地低的。孢子密度在根地区的土壤每 20 g 从 5 ～ 21 变化了。在 3 个类的上午 14 点 fungaltaxa 被孤立并且识别了其 10 属于血管球， 3 到 Acaulospora， and1 到 Archaeospora。血管球是在识别的所有类的主导的类。G。deser-ticola 和 G.etunicatum 是最普通的税一孤立与 77.4% 和 74.8% 的出现频率，并且相对许多 14.4% 和 15.5% 分别地。