Phytoprotective Effect of Arbuscular Mycorrhizal Fungi Species Against Arsenic Toxicity in Tropical Leguminous Species

Arbuscular mycorrhizal fungi (AMF) improve the tolerance of hosting plants to arsenic (As) in contaminated soils. This work assessed the phytoprotective effect of Glomus etunicatum, Acaulospora morrowiae, Gigaspora gigantea, and Acaulospora sp. on four leguminous species (Acacia mangium, Crotalaria juncea, Enterolobium contortisiliquum, and Stizolobium aterrimum) in an As-contaminated soil from a gold mining area. AMF root colonization, biomass production, As and P accumulation, as well as arsenic translocation index (TI) from roots to shoots were measured. The AMF phytoprotective effect was assessed by the P/As ratio and the activity of plant antioxidant enzymes. The AMF colonization ranged from 24 to 28%. In general, all leguminous species had low As TI when inoculated with AMF species. Inoculation of C. juncea with Acaulospora sp. improved significantly As accumulation in roots, and decreased the activity of ascorbate peroxidase (APX) and superoxide dismutase (SOD), highlighting its phytoprotective effect and the potential use of this symbiosis for phytoremediation of As-contaminated soils. However, S. aterrimum has also shown a potential for phytoremediation irrespectively of AMF inoculation. APX was a good indicator of the phytoprotective effect against As contamination in C. juncea and A. mangium. In general P/As ratio in shoots was the best indicator of the phytoprotective effect of all AMF species in all plant species.     

Variation among Populations of Belonolaimus longicaudatus

Three North Carolina populations of Belonolairnus longicaudatus differed significantly from three Georgia populations in stylet measurements, the c ratio, the distance of the excretory pore from the anterior end for both sexes; the a ratio for females only; and the total body length, tail length, and spicule length for males only. The Georgia nematodes were stouter, and the females possessed sclerotized vaginal pieces. The distal portion of the spicules of North Carolina males had an indentation and hump lacking in those of the Georgia males. The haploid number of chromosomes was eight for males from all populations of B. longicaudatus and a North Carolina population of B. maritimus. Interpopulation matings of the Tarboro, N.C. and Tifton, Ga. populations indicated that the offspring produced were infertile. Morphological differences and reproductive isolation suggest that the North Carolina and the Georgia populations belong to different species.     

3种杓兰属植物菌根真菌系统发育和多样性分析

兰科植物菌根真菌(Orchid mycorrhizal fungi, OrMF)在兰科植物种子萌发和后续生长发育过程中具有重要作用。该研究采用培养(菌丝团分离)和非培养(克隆文库)2种方法获得同一栖息地3种不同杓兰属植物根中菌根真菌ITS序列并划分可操作分类单元(Operational taxonomic units, OTUs),分析其系统发育关系和多样性。结果表明:(1)所有根段中都有菌丝团定植,共分离出菌根真菌64株,其中63株为胶膜菌科(Tulasnellaceae)真菌,1株为角担菌科(Ceratobasidiaceae)真菌;可划分为7个OUT,每个OTU代表菌株的菌丝都能形成OrMF典型的近球形或椭球形链状排列的念珠状细胞;分离出来的菌根真菌均为无性型菌丝且不产生无性孢子。(2) 非培养法得到的3种杓兰属植物的根中OrMF分别隶属于胶膜菌科(Tulasnellaceae),腊壳菌科(Sebacinaceae)、角担菌科(Ceratobasidiaceae)和革菌科(Thelephoraceae),其中胶膜菌科OTU在种类和数量上占有绝对优势,培养和非培养2种方法得到的OrMF OTU类型和数量均为西藏杓兰(Cypripedium tibeticum)>无苞杓兰(C. flavum)>黄花杓兰(C. bardolphianum),但培养法少于非培养法。(3)对胶膜菌进行系统发育分析显示,优势和非优势OTU均分布在系统发育树的3个不同分支上,这种与多种亲缘关系较远的OrMF共生的现象可能与杓兰属植物对环境的适应性有关,且不同杓兰的OrMF物种丰富度没有显著差异,但群落结构存在差异。     

Genetic Variation in Natural Populations of Five Drosophila Species and the Hypothesis of the Selective Neutrality of Protein Polymorphisms

We have studied genetic variation at 30-32 loci coding for enzymes in natural populations of five species of Drosophila. The average proportion of heterozygous loci per individual is 17.7 +/- 0.4%. The average proportion of polymorphic loci per population is 69.2 +/- 2.6% or 49.8 +/- 2.2%, depending on what criterion of polymorphism is used. The following generalizations are advanced: (1) The amount of genetic polymorphism varies considerably from locus to locus. (2) At a given locus, populations of the same species are very similar in the amount and pattern of genetic variation. (3) However, at some loci large differences sometimes occur between local populations of the same species. (4) The amount of variation at a given locus is approximately the same in all five species. (5) When different species are compared, the pattern of the variation is either essentially identical or totally different at a majority of loci. We have tested the hypothesis that protein polymorphisms are selectively neutral by examining four predictions derived from the hypothesis. Our results are at variance with every one of the predictions. We have measured the amount of genetic differentiation, D, between taxa of various degrees of evolutionary divergence. The average value of D is 0.033 for local populations, 0.228 for subspecies, 0.226 for semispecies, 0.538 for sibling species, and 1.214 for morphologically distinguishable species. Our results indicate that a substantial degree of genetic differentiation (22.8 allelic substitutions for every 100 loci) occurs between allopatric populations that have diverged to the point where they might become different species if they were to become sympatric. However, very little additional genetic change is required for the development of complete reproductive isolation. After the speciation process is completed, species continue to diverge genetically from each other.     

Parallel Patterns of Morphological and Behavioral Variation among Host-Associated Populations of Two Gall Wasp Species

A powerful approach to address the general factors contributing to ecological speciation is to compare distantly related taxa that inhabit the same selective environments. In this design, similarities among taxa can elucidate general mechanisms of the process whereas differences may uncover specific factors important to the process for individual taxa. Herein, we present evidence of parallel patterns of morphological and behavioral variation among host-associated populations of two species of cynipid gall wasps, Belonocnema treatae and Disholcaspis quercusvirens, that each exhibit a life cycle intimately tied to the same two host plant environments, Quercus geminata and Q. virginiana. Across both gall-former species we find consistent differences in body size and gall morphology associated with host plant use, as well as strong differences in host plant preference, a measure of habitat isolation among populations. These consistent differences among taxa highlight the important role of host plant use in promoting reproductive isolation and morphological variation among herbivorous insect populations–a prerequisite for ecological speciation.     

Morphological Variation among 23 Xiphinema americanum Populations

Morphometrics of 23 United States populations of Xiphinema americanum sensu lato, sharing the characteristics of an offset lip region and conoid tail, were examined and analyzed statistically by canonical discriminant analysis (CDA). Specimens were collected from Arkansas, Georgia, Tennessee, Mississippi, Florida, Oklahoma, California, and North Dakota. Eleven measurements and body ratios obtained from female specimens were used in the analysis. Xiphinema americanum, X. bricolensis, X. californicum, X. citricolum, X, intermedium, X. tarjanense, and X. thornei, and one undescribed species were identified among the 23 populations. Three groups -- X. americanum-group, X. californicum-group, and X. intermedium-group (X. intermedium and X. tarjanense) -- were formed and four populations belonging to four different species were separated consistently from these groups in CDA scatterplots of the 23 populations. Composition of the groups was somewhat related to the geographical origins of the populations in the groups. A population from California had morphometrics intermediate between X. americanum and X. californicum. Separation between the X. americanum-group and X. californicum-group in the CDA scatterplots was not as distinct as that between them and the X. intermedium-group or between any of the three groups and the four single outlying populations.     

Antagonistic Activity of Five Myrothecium Species Against Fungi and Bacteria in Vitro

Antagonistic activity of 69 Myrothecium isolates belonging to M. carmichaelü, M. cinctum, M. roridum, M. tongaense and M. verrucaria against six soil-borne plant pathogenic fungi was investigated by using the streak method. Results clearly showed that M. carmichaelü is a strong antibiont having a very high degree of antifungal efficacy. M. cinctum and M. tongaense isolates were found to have an antagonistic activity either through antibiosis or mycoparasitism or both against the test fungi. M. roridum and M. verrucaria isolates also possessed both kinds of activities. After this first screening (of all Myrothecium isolates), one isolate from each species exhibiting the highest degree of antagonistic activity was selected for further studies. Inhibitory effects of culture filtrates of these representative isolates on the mycelial growth of the test fungi were investigated by incorporating them into PDA at a dilution of 1:8. M. carmichaelü was the most and M. cinctum the least effective species under assay. Moreover, culture filtrates and mycelium extracts of the selected isolates were found to have both antifungal and antibacterial properties using the agar-well method. Among the test fungi, Sclerotinia sclerotiorum proved to be generally the most, and Pythium debaryanum the least sensitive to the antibiotic effects. M. cinctum showed the widest antibacterial spectrum inhibiting five bacterial species except for Pseudomonas syringae Pv. Phaseolicola. Additionally, the observations using light and scanning electron microscopy clearly demonstrated that all of the five Myrothecium species were able to parasitize all of the tested fungi.     

石油污染土壤中不同人工林木根际丛枝菌根真菌与球囊霉素的研究

以陕西延长县石油污染区常见的13种人工种植林木为材料,测定了各人工种植林木根际丛枝菌根(AM)真菌发育状况、污染土壤的理化性质、土壤酶活性和球囊霉素含量,探讨AM真菌在石油污染土壤生态修复中的作用。结果表明,13种林木均能形成AM,其定殖率平均为63.2%,孢子密度平均为1.93个.g-1干土,其中受污染程度最低的柠条AM真菌定殖率和孢子密度最高,分别为91.6%和4.73个.g-1干土;毛白杨、狼牙刺和刺槐的根际土壤养分(有机碳、碱解氮、速效磷)含量相对较高;各种人工种植林木的根际土壤球囊霉素含量、多酚氧化酶和过氧化氢酶活性随根际土壤石油烃污染浓度的增加而明显升高,其中刺槐、狼牙刺和酸枣根际土壤的过氧化氢酶和多酚氧化酶活性都较高,同时这3种林木的球囊霉素含量也较高。因此,林木根际土壤球囊霉素含量、多酚氧化酶和过氧化氢酶活性可以作为石油污染的敏感指标。     

云南松幼苗上红菇类菌根真菌的物种多样性及其菌根形态

以滇中1～2年生云南松幼苗为研究对象,观察鉴定与其共生的红菇属真菌外生菌根。形态观察发现了6种形态型（morphotypes）。本文对这6种形态型的外观和显微特征进行了详细描述,尤其强调了菌套形态特征。对rDNAITS片段比对分析表明,6种形态型对应6种红菇属真菌,它们分别是与Russula li-vescens、R.violeipes、R.densifolia、R.nigricans、R.sanguinea及R.nauseosa相近的红菇种类。本研究表明,形成的菌根及其菌套和囊状体的特征在红菇属真菌的系统分支间表现出较为稳定的差异。这一研究与前人对该属真菌的菌根形态及分类学研究基本吻合。红菇属真菌是云南松1～2年幼苗期的主要共生真菌类群。     

Interaction of Vesicular-Arbuscular Mycorrhizal Fungi with Erosion in an Oxisol

The development of vesicular-arbuscular mycorrhizal (VAM) symbiosis was monitored in Leucaena leucocephala grown in an Oxisol subjected to incremental simulated erosion. The density of VAM infective propagules in the soil diminished as the level of simulated erosion (removal of surface soil) was increased from 0 to 50 cm. The level of infection on L. leucocephala roots observed at harvest was not significantly influenced by simulated erosion unless removal of surface soil exceeded 25 cm. Inoculation of this soil and the uneroded soil with Glomus aggregatum enhanced the early onset of infection but did not significantly influence the level of infection observed at the time of harvest. Simulated erosion in excess of 7.5 cm of surface soil removal significantly delayed the development of VAM effectiveness monitored in terms of the P status of L. leucocephala subleaflets and also curtailed the level of maximum effectiveness observed. Decreases in VAM effectiveness were significantly correlated with decreases in soil chemical constituents. However, VAM effectiveness in a soil subjected to 30 cm of surface soil removal was not restored to a significant extent unless the soil was amended with P, even though other nutrients were restored to sufficiency levels. Our results demonstrate that the development of VAM effectiveness is the phase of the VAM symbiosis that is most adversely influenced by simulated erosion and that this effect appears to be caused primarily by insufficient P in the soil solution.     

伞形科3个种5个居群的核型分析

对伞形科前胡属(PeucedanumL.)2个种以及羌活属(NotopterygiumH.Boiss.)1个种3个居群的染色体数目和核型进行了研究。研究表明,它们的染色体数目均为2n=22,核型公式可分别表示为长前胡:2n=2x=22=22 m(1 SAT),属1A型;松潘前胡:2n=2x=22=20 m 2 sm,属2A型;宽叶羌活的3个居群分别是:马边大风顶居群1为2n=2x=22=6 m 12 sm 4 st,属2A型;马边大风顶居群2为2n=2x=22=12 m 4 sm 6 st,属2B型;屏山老君山居群为2n=2x=22=4 m 14 sm 4 st,属2A型。其中长前胡和松潘前胡的染色体数目和核型为首次报道。     

Sheared-Root Inocula of Vesicular-Arbuscular Mycorrhizal Fungi

For efficient handling, vesicular-arbuscular mycorrhizal fungi should be processed into small and uniform inocula; however, processing can reduce the inoculum density. In this article we describe the preparation and use of sheared-root inocula of Glomus spp. in which inoculum densities were increased during processing. Our objectives were to determine inoculum viability and density after shearing and to ascertain if the sheared inocula could be pelletized or used with a gel carrier. Root samples were harvested from aeroponic cultures, blotted dry, cut into 1-cm lengths, and sheared in a food processor for up to 80 s. After shearing, the inoculum was washed over sieves, and the propagule density in each fraction was determined. Sheared inocula were also encapsulated in carrageenan or used in a gel carrier. Shearing aeroponically produced root inocula reduced particle size. Propagule density increased with decreasing size fraction down to a size of 63 μm, after which propagule density decreased. The weighted-average propagule density of the inoculum was 135,380 propagules g (dry weight) of sheared root material^-1. Sheared roots were encapsulated successfully in carrageenan, and the gel served as an effective carrier. Aeroponic root inoculum was stored dry at 4°C for 23 months without significant reduction in propagule density; however, this material was not appropriate for shearing. Moist roots, useful for shearing, began to lose propagule density after 1 month of storage. Shearing proved to be an excellent method to prepare viable root inocula of small and uniform size, allowing for more efficient and effective use of limited inoculum supplies.     

Global Distributions of Arbuscular Mycorrhizal Fungi

We examined potential large-scale controls over the distribution of arbuscular mycorrhizal (AM) fungi and their host plants. Specifically, we tested the hypothesis that AM fungi should be more prevalent in biomes where nutrients are primarily present in mineral, and not organic, forms. Values of percentage root length colonized (%RLC) by AM fungi, AM abundance, and host plant availability were compiled or calculated from published studies to determine biome-level means. Altogether, 151 geographic locations and nine biomes were represented. Percent RLC differed marginally significantly among biomes and was greatest in savannas. AM abundance (defined as total standing root length colonized by AM fungi) varied 63-fold, with lowest values in boreal forests and highest values in temperate grasslands. Biomes did not differ significantly in the percentage of plant species that host AM fungi, averaging 75%. Contrary to the hypothesis, %RLC, AM abundance, and host plant availability were not related to the size, influx, or turnover rate of soil organic matter pools. Instead, AM abundance was positively correlated with standing stocks of fine roots. The global pool of AM biomass within roots might approach 1.4 Pg dry weight. We note that regions harboring the largest stocks of AM fungi are also particularly vulnerable to anthropogenic nitrogen deposition, which could potentially alter global distributions of AM fungi in the near future.     

大王马先蒿云南五个居群遗传变异研究

采用随机扩增多态DNA(RAPD)分子标记方法,对大王马先蒿(PedicularisrexL.)分布在云南中甸、丽江、大理、武定和昆明的5个居群(其中中甸居群有3个亚居群)的遗传多样性和遗传结构进行了研究。结果表明,大王马先蒿居群具有较高的遗传多样性,多态位点百分率P、Shannon表型多样性指数I和Nei的基因多样性指数h分别为82.0%、0.361和0.240,遗传多样性水平与居群的地理分布范围相关;大王马先蒿居群间的遗传变异较高,遗传变异主要发生在居群之间,而不是居群内部;居群间遗传分化系数Gst为0.747,遗传分化明显,居群间基因交流较少。居群间的遗传距离与居群间的相对地理距离具有一定的相关性。对云南西北部中甸居群的3个亚居群的遗传多样性分析表明,居群的遗传多样性水平与海拔高度有一定的相关性。居群间遗传变异较高可能是由于大王马先蒿为短命多年生植物,繁育系统为混交型,且自交占较大比例等原因造成的。     

The Ecology of Arbuscular Mycorrhizal Fungi

Arbuscular mycorrhiza is a mutually beneficial biological association between species in the fungal phylum Glomeromycota and higher plants roots. The symbiosis is thought to have afforded green plants the opportunity to invade dry land ca 450 Ma ago and the vast majority of extant terrestrial plants retain this association. Arbuscular mycorrhizal (AM) fungi perform various ecological functions in exchange for host photosynthetic carbon that almost always contribute to the fitness of hosts from an individual to community level. Recent AM fungal research, increasingly delving into the ‘Black Box’, suggests that species in this phylum may play a key facilitative role in below-ground micro- and meso-organism community dynamics, even more perhaps, that of a bioengineer. The ubiquitous nature of the symbiosis in extant flora and the fact that variations from the AM symbiosis are recent events suggest that Glomeromycota and plant roots coevolved. This review considers aspects of AM fungal ecology emphasizing past and present importance of the phylum in niche to global ecosystem function. Nutrient exchange, evolution, taxonomy, phenology, below-ground microbial interaction, propagule dissemination, invasive plants interactions, the potential role in phytoremediation and some of the factors affecting AM fungal biology are discussed. We conclude that it is essential to include AM association in any study of higher plants in natural environments in order to provide an holistic understanding of ecosystems.     

Species Diversity of Russuloid Mycorrhizae forming Fungi on Pinus yunnanensis Seedlings and the Mycorrhizal Morphology

Russuloid ectomycorrhizae on 1-2 years old seedlings of Pinus yunnanensis collected from the central Yunnan, China were investigated. Six morphotypes were recognized by macro and anatomical morphological approaches as well as molecular analyses. The six morphotypes were confirmed to represent six phylotypes by matching rDNA ITS sequences. The fungal partners in the six morpho phylotypes are those closely related with Russula livescens, Rvioleipes ,Rdensifolia ,Rnigricans ,Rsanguinea and Rnauseosa respectively. The correlation between the morphology of mantles and cystidia and the phylogenetic clades is further supported in our work. The framework, in which this report is included, shows that russuloid mycorrhizae are one of the most dominant representative ectomycorrhizae formed on 1-2 years seedlings of Pinus yunnanensis.     

四种蕨类植物根际土壤中VA菌根真菌孢子种群组成和季相变化

对４ 种移栽到温室中的蕨类植物根际土壤中的ＶＡ 菌根真菌孢子种群组成和季相变化进行了研究, 结果发现, ＶＡ菌根真菌孢子的产生具有明显的宿主依赖性和季相变化。在相同气候条件下, 不同植物根际土壤中的ＶＡ菌根真菌种群组成不同; 同种ＶＡ 菌根真菌在不同宿主植物根际土壤中, 孢子的丰富度有很大的差异。本文对影响ＶＡ菌根真菌孢子种群组成和季相变化的因素进行了讨论。     

Variation in the Essential Oil Composition,Antioxidant Capacity,and Physiological Characteristics of Pelargonium graveolens L. Inoculated with Two Species of Mycorrhizal Fungi Under Water Deficit Conditions

In recent years, the application of arbuscular mycorrhizal fungi (AMF) has been considered to be an important strategy for improving crop yield and quality. In the present study, a factorial experiment based on a complete randomized design with two factors was performed to investigate the effect of AMF and water stress on the essential oil (EO) composition, antioxidant activity, and physiological and morphological characteristics of rose-scented geranium (Pelargonium graveolens L.). The factors included AMF inoculation (Rhizophagus intraradices, Funneliformis mosseae, and a mixture of both species) and irrigation levels [well-watered (WW), moderate drought stress (MDS), and severe drought stress (SDS)]. The main EO constituents were citronellol (31–37%) and geraniol (9–14%) in all treatments. Under water-stress conditions, some constituents increased, such as geraniol and geranyl formate, whereas others decreased, such as linalool, menthone and rose oxide. Overall, the highest amount of citronellol (37.3%) and geraniol (14.8%) was obtained in the plants inoculated with F. mosseae and R. intraradices under WW and MDS conditions, respectively. Antioxidant activity, total flavonoids, and phenolics were increased because of AMF inoculation, whereas a different trend was observed for the phenolic and flavonoid contents under water-stress conditions. Furthermore, water deficit elevated the amount of soluble carbohydrates as well as the proline content, whereas the amount of proline was lower in inoculated plants than in non-inoculated ones. All the growth parameters were improved in the AMF-inoculated plants compared to non-inoculated ones under different irrigation regimes. Drought conditions decreased the photosynthetic pigments and efficiency, whereas AMF plants ameliorated the adverse effect of drought conditions. In general, mycorrhizal inoculation resulted in an improvement in the growth parameters as well as the phytochemical and physiological characteristics of rose-scented geranium.