Epiparasitic plants specialized on arbuscular mycorrhizal fungi

Over 400 non-photosynthetic species from 10 families of vascular plants obtain their carbon from fungi and are thus defined as myco-heterotrophs. Many of these plants are epiparasitic on green plants from which they obtain carbon by 'cheating' shared mycorrhizal fungi. Epiparasitic plants examined to date depend on ectomycorrhizal fungi for carbon transfer and exhibit exceptional specificity for these fungi, but for most myco-heterotrophs neither the identity of the fungi nor the sources of their carbon are known. Because many myco-heterotrophs grow in forests dominated by plants associated with arbuscular mycorrhizal fungi (AMF; phylum Glomeromycota), we proposed that epiparasitism would occur also between plants linked by AMF. On a global scale AMF form the most widespread mycorrhizae, thus the ability of plants to cheat this symbiosis would be highly significant. We analysed mycorrhizae from three populations of Arachnitis uniflora (Corsiaceae, Monocotyledonae), five Voyria species and one Voyriella species (Gentianaceae, Dicotyledonae), and neighbouring green plants. Here we show that non-photosynthetic plants associate with AMF and can display the characteristic specificity of epiparasites. This suggests that AMF mediate significant inter-plant carbon transfer in nature.     

Plant sesquiterpenes induce hyphal branching in arbuscular mycorrhizal fungi

Arbuscular mycorrhizal (AM) fungi form mutualistic, symbiotic associations with the roots of more than 80% of land plants. The fungi are incapable of completing their life cycle in the absence of a host root. Their spores can germinate and grow in the absence of a host, but their hyphal growth is very limited. Little is known about the molecular mechanisms that govern signalling and recognition between AM fungi and their host plants. In one of the first stages of host recognition, the hyphae of AM fungi show extensive branching in the vicinity of host roots before formation of the appressorium, the structure used to penetrate the plant root. Host roots are known to release signalling molecules that trigger hyphal branching, but these branching factors have not been isolated. Here we have isolated a branching factor from the root exudates of Lotus japonicus and used spectroscopic analysis and chemical synthesis to identify it as a strigolactone, 5-deoxy-strigol. Strigolactones are a group of sesquiterpene lactones, previously isolated as seed-germination stimulants for the parasitic weeds Striga and Orobanche. The natural strigolactones 5-deoxy-strigol, sorgolactone and strigol, and a synthetic analogue, GR24, induced extensive hyphal branching in germinating spores of the AM fungus Gigaspora margarita at very low concentrations.     

AM真菌克服作物连作障碍的潜力

连作障碍是农业生产和设施栽培模式下的主要限制因子之一。连作障碍主要与土壤微生物区系的变化、土壤理化性状的变化和根系分泌物的自毒作用三方面密切相关。已有证据表明,丛枝菌根(AM)真菌在一定程度上能够克服连作障碍。这很可能与AM真菌减少有害生物数量,改变土壤微生物区系、改善土壤理化性状、提高植物防御性酶活性、改变根系分泌物的种类与数量等生理功能有关。正确合理评价AM真菌克服作物连作障碍的潜力,可为连作障碍提供新的解决途径,并为建立和发展新的生物技术提供依据。     

Evidence for the evolution of multiple genomes in arbuscular mycorrhizal fungi.

Ancient asexuals directly contradict the evolutionary theories that explain why organisms should evolve a sexual life history. The mutualistic, arbuscular mycorrhizal fungi are thought to have been asexual for approximately 400 million years. In the absence of sex, highly divergent descendants of formerly allelic nucleotide sequences are thought to evolve in a genome. In mycorrhizal fungi, where individual offspring receive hundreds of nuclei from the parent, it has been hypothesized that a population of genetically different nuclei should evolve within one individual. Here we use DNA-DNA fluorescent in situ hybridization to show that genetically different nuclei co-exist in individual arbuscular mycorrhizal fungi. We also show that the population genetics techniques used in other organisms are unsuitable for detecting recombination because the assumptions and underlying processes do not fit the fungal genomic structure shown here. Instead we used a phylogenetic approach to show that the within-individual genetic variation that occurs in arbuscular mycorrhizal fungi probably evolved through accumulation of mutations in an essentially clonal genome, with some infrequent recombination events. We conclude that mycorrhizal fungi have evolved to be multi-genomic.     

蒙古沙冬青AM真菌物种多样性与土壤因子的相关性

为了探明蒙古沙冬青(Ammopiptanthus mongolicus)根围AM真菌物种多样性年际变化规律以及土壤因子的生态功能,于2012年7月和2013年7月从宁夏银川、沙坡头和甘肃民勤3个样地分别从O～10,10～20,20～30,30～40,40～50 cm 5个土层对沙冬青根围土样进行采集,共分离鉴定出AM真菌5属36种,其中,球囊霉属Glomus 16种,无梗囊霉属Acaulospora 13种,管柄囊霉属Funneliformis 3种,盾巨孢囊霉属Scutellospora 3种,多孢囊霉属Diversispora 1种.不同样地和土壤深度,AM真菌种类组成、孢子密度和种丰度在年际间均有明显差异.相关性分析表明,孢子密度与土壤酸性磷酸酶和总球囊霉素显著正相关;种丰度与土壤脲酶、有机质和碱解氮显著正相关.主成分分析表明,土壤有机质、碱解氮、速效磷、速效钾、脲酶、碱性磷酸酶是影响AM真菌物种多样性的主要因子.研究结果说明,AM真菌物种多样性及其分布规律可以用作检测和评价荒漠环境土壤状况的生态指标.     

丛枝菌根真菌在农业中的应用：研究进展与挑战

 丛枝菌根（arbuscular mycorrhiza，AM）真菌能够和大多数农作物形成互利共生体系，有效改善作物矿质营养，减轻环境胁迫对作物生长的不利影响，提高作物产量和品质。由于AM真菌的功能多面性，其在农业生产中具有潜在重要作用和广阔应用前景。结合AM真菌农业应用技术途径和适用情景，讨论了作物种植制度和管理措施对AM真菌功能的影响及可能的调控途径，分析了菌根技术发展趋势及面临的机遇和挑战，提出加强AM真菌功能多面性及其应用途径优化研究，将有助于促进AM真菌菌剂相关产业的发展以及AM真菌在农业生产中的广泛应用。     

蒙古沙冬青AM真菌物种多样性空间异质性

2013年7月在内蒙古阿拉善、磴口、乌拉特后旗和乌海4个样地采集蒙古沙冬青(Ammopiptanthus monglicus)根围土壤样品,研究了不同样地AM真菌群落组成和物种多样性空间分布规律.共分离鉴定AM真菌5属25种,其中,球囊霉属12种,无梗囊霉属8种,是4样地优势属;管柄囊霉属和盾巨孢囊霉属是4样地亚优势属,内养囊霉属1种,仅在磴口和阿拉善出现.4样地共有种包括粘质球囊霉、黑球囊霉、网状球囊霉、凹坑无梗囊霉、细凹无梗囊霉、光壁无梗囊霉和黑色盾巨孢囊霉.黑球囊霉是4样地共同优势种.不同样地孢子密度、种丰度、香农指数、辛普森指数和均匀度总体变异趋势是乌拉特后旗≈阿拉善＞磴口＞乌海.乌海样地AM真菌组成与其他样地差异显著.结果表明,AM真菌群落组成随蒙古沙冬青地理分布变化而产生空间演替,这为进一步研究蒙古沙冬青与AM真菌共生关系及其生态分布规律提供了依据.     

沿海造林树种根际丛枝菌根真菌与土壤因子的通径分析

【目的】探讨苏北沿海土壤理化性质对当地主要造林树种根际丛枝菌根真菌(AMF)侵染及球囊霉相关蛋白数量的影响,为丛枝菌根真菌在沿海困难立地造林提供理论依据。【方法】以江苏盐城大丰林场内的8个不同树种为研究对象(薄壳山核桃、杨树、水杉、榉树、中山杉、杜仲、银杏、胡颓子),测定土壤理化性质,根据通径分析,探讨造林树种根际丛枝菌根真菌与土壤因子的关系。【结果】丛枝菌根真菌(AMF)侵染率最高为薄壳山核桃,最低为银杏; 孢子密度最高为杜仲,最低为银杏; 总球囊霉素最高为榉树,最低为中山杉; 易提取球囊霉素最高为杨树,最低为银杏。AMF侵染率与土壤全磷含量呈极显著负相关(P<0.01); 总球囊霉素与pH呈极显著负相关(P<0.01),与速效钾和有机碳呈极显著正相关(P<0.01); 易提取球囊霉素与土壤全钠含量呈极显著正相关(P<0.01),与土壤全磷呈显著负相关(P<0.05); 孢子密度与土壤因子并无显著性关系。通径分析显示,土壤全磷对AMF侵染率直接作用最强,土壤全钾、电导率的作用次之; 土壤速效钾对总球囊霉素的直接作用最强,pH、可溶性有机碳、全钠、电导率的作用次之,硝态氮对总球囊霉素含量的影响表现在间接作用上; 全钠对易提取球囊霉素的直接作用最强,电导率、全磷的作用次之,全钾对易提取球囊霉素的影响表现在间接作用上。【结论】沿海地区生长的8个树种均检测到AMF侵染,且土壤因子对AMF与树种的互利共生关系有显著影响。     

内蒙古农牧交错区沙蒿根围AM真菌物种多样性

2009年4月、7月和10月分别在内蒙古农牧交错区元上都、黑城子和大河乡样地采集沙蒿(Artemisia sphaerocephala)根围土壤样品,利用形态学和微形态学特征分离鉴定沙蒿根围AM真菌种类,研究了AM真菌物种多样性.共分离鉴定出AM真菌3属20种,其中盾巨孢囊霉属(Scutellospora)2种,无梗囊霉属(Acaulospora)4种,球囊霉属(Glomus)14种.3属AM真菌在3个样地均有分布.3个样地共同优势种是黑球囊霉(G.melanosporum)和网状球囊霉(G.reticulatum).AM真菌物种丰度、香浓-威纳指数和均匀度在时间上表现为4月<7月<10月,空间上表现为元上都<黑城子<大河乡.扫描电镜下不同属种孢子表面纹饰特征差异明显,可作为AM真菌分类的参考依据.     

Low gene copy number shows that arbuscular mycorrhizal fungi inherit genetically different nuclei

Arbuscular mycorrhizal fungi (AMF) are ancient asexually reproducing organisms that form symbioses with the majority of plant species, improving plant nutrition and promoting plant diversity. Little is known about the evolution or organization of the genomes of any eukaryotic symbiont or ancient asexual organism. Direct evidence shows that one AMF species is heterokaryotic; that is, containing populations of genetically different nuclei. It has been suggested, however, that the genetic variation passed from generation to generation in AMF is simply due to multiple chromosome sets (that is, high ploidy). Here we show that previously documented genetic variation in Pol-like sequences, which are passed from generation to generation, cannot be due to either high ploidy or repeated gene duplications. Our results provide the clearest evidence so far for substantial genetic differences among nuclei in AMF. We also show that even AMF with a very large nuclear DNA content are haploid. An underlying principle of evolutionary theory is that an individual passes on one or half of its genome to each of its progeny. The coexistence of a population of many genomes in AMF and their transfer to subsequent generations, therefore, has far-reaching consequences for understanding genome evolution.     

盐胁迫下丛枝菌根对植物幼苗生长和营养元素吸收的影响

在盆栽中,研究了4种土壤盐度下接种真菌从枝菌根真菌(arbuscular mycorrhiza fungi,AMF)摩西球囊霉(Glomus mosseae)对玉米、水稻、小麦和油菜的幼苗生长和营养元素吸收的影响.结果表明,土壤盐度提高会导致玉米、水稻、小麦和油菜的生长量以及AM的侵染率降低,接种AM显著提高了非盐和盐胁迫下玉米、小麦和油菜3种植物的生物量、株高、根长、叶绿素含量及K、P养分吸收量,且这种效应在高盐度条件下更显著.接种AM真菌提高植物的耐盐性可能跟营养元素的吸收和运输有关.     

Nitrogen transfer in the arbuscular mycorrhizal symbiosis

Most land plants are symbiotic with arbuscular mycorrhizal fungi (AMF), which take up mineral nutrients from the soil and exchange them with plants for photosynthetically fixed carbon. This exchange is a significant factor in global nutrient cycles as well as in the ecology, evolution and physiology of plants. Despite its importance as a nutrient, very little is known about how AMF take up nitrogen and transfer it to their host plants. Here we report the results of stable isotope labelling experiments showing that inorganic nitrogen taken up by the fungus outside the roots is incorporated into amino acids, translocated from the extraradical to the intraradical mycelium as arginine, but transferred to the plant without carbon. Consistent with this mechanism, the genes of primary nitrogen assimilation are preferentially expressed in the extraradical tissues, whereas genes associated with arginine breakdown are more highly expressed in the intraradical mycelium. Strong changes in the expression of these genes in response to nitrogen availability and form also support the operation of this novel metabolic pathway in the arbuscular mycorrhizal symbiosis.     

盐胁迫下丛枝菌根真菌对桢楠根系生长和激素的影响

研究不同浓度盐胁迫下,桢楠接种丛枝菌根真菌（arbuscular mycorrhizal fungi, AMF）后根系形态结构和激素含量及其动态变化情况,为桢楠在盐碱地造林提供技术支撑。     

丛枝菌根真菌对植物营养代谢与生长影响的研究进展

综述了国内外有关丛枝菌根(AM)真菌对于改善植株水分代谢与碳素营养,促进植株对N,P等矿质营养吸收及其运转途径与机制的研究进展,提出了AM真菌研究中存在的问题,以期今后加强对AM真菌的深入研究,进而提高植物对矿质元素的吸收转运效率,增强植株的代谢能力.可以预见,AM真菌作为一种经济而有效的生物肥料,将广泛应用于农业生产与生态农业中,带来不可估量的经济效益和生态效益.     

Diversity of arbuscular mycorrhizal fungi associated with desert ephemerals growing under and beyond the canopies of Tamarisk shrubs

The arbuscular mycorrhizal （AM） fungal status of the four most common ephemeral plant species, Chorispora tenella （Pall.） DC., Ceratocephalus testiculatus （Crantz） Bess., Eremopyrum orientale （L.） Jaub et. Spash and Veronica campyIopoda Boiss growing in an area dominated by Tamarisk shrubs （Tamarix spp.） was investigated. Samples of the four ephemerals and their rhizosphere soils were collected from underneath and beyond the canopies of the Tamarisk shrubs. Plant mycorrhizal status and soil AM fungal spore densities and community structures were analyzed and compared under and beyond the shrub canopies. The mycorrhizal colonization rates of the ephemerals and spore densities in their corresponding rhizosphere soils were significantly lower under the shrub canopies than beyond. The number of AM fungal species under the shrubs （12） was also lower than beyond the canopies （19）. When soil properties in the rhizospheres of the four ephemerals were examined, available N and P and total P, organic matter content, total salt content and electrical conductivity （EC） were all higher under the canopies than beyond. In contrast, soil available K and pH showed no such trend. A total of 21 AM fungal species were isolated from rhizosphere soils of the four ephemerals. Five belonged to Acaulospora, one to Archaeospora, thirteen to Glomus and two to Paraglomus. We conclude that the canopies of Tamarix spp. exerted some influence on the AM status of the ephemerals and on the AM fungal communities and some of the properties of their rhizosphere soils.     

云南寻甸石漠化土壤易氧化碳对丛枝菌根真菌共生的响应

【目的】运用菌根技术改良石漠化土壤性状,已成为石漠化地区植被与土壤恢复的重要生物学途径。揭示丛枝菌根(AM)真菌与植物共生驱动下石漠化土壤碳库及养分状况的变化,探明石漠化土壤易氧化碳(ROC)对土壤碳库及养分变化的响应过程及机制,为石漠化土壤的微生物修复及提高石漠化治理效率提供参考。【方法】采集云南昆明寻甸石漠化土壤,以尼泊尔桤木(Alnus nepalensis)为寄主植物,分别接种摩西斗管囊霉(Funneliformis mosseae, FM)、幼套近明球囊霉(Claroideoglomus etunicatum, CE)、根内根孢囊霉(Rhizophagus intraradices, RI),并设置对照处理(无寄主植物及无AM接种),采用高锰酸钾氧化法测定不同试验处理下土壤ROC含量,探究土壤ROC与碳库组成、养分状况及植物生长之间的相互关系。【结果】不同AM真菌均具有显著的侵染与促生效应,其中RI的侵染率与菌丝侵染密度最大,相较于对照分别提高155%和100%,并显著促进桤木树高(60%)与基径(46%)生长;不同AM真菌均显著提高ROC含量,3菌种对ROC含量的提升率大小顺序为:RI(122%)> CE(78%)> FM(61%)。ROC在土壤总有机碳库中所占比例(52%)远高于微生物生物量碳(3%~6%);3种菌种对土壤养分含量的提升效应表现为:RI > CE > FM。相较于对照,RI 菌种对植物可利用性氮、微生物生物量碳、总有机碳及植物可利用性磷的提升率分别为161%、127%、110%及97%;对ROC变化具有较大贡献的土壤环境因子分别为AM真菌侵染率(96%)、植物可利用性氮(94%)、微生物生物量碳(85%)、总有机碳(78%)及植物可利用性磷(72%)。【结论】AM真菌与尼泊尔桤木共生,显著驱动石漠化土壤碳库与养分含量变化并促进植物生长,进而增加石漠化土壤易氧化碳的积累。研究结果有助于理解石漠化地区植物生长、土壤恢复及活性有机碳沉积的微生物学调控机制。     

Arbuscular mycorrhizal fungi: hyphal fusion and multigenomic structure

Arbuscular mycorrhizal (AM) fungi (Glomeromycota) reproduce asexually, are multinucleate, and have high genetic variation within single cells. Pawlowska and Taylor find that genetic variation within AM fungal cells is not lost as a result of segregation, and they interpret this as evidence that the variation is present within each nucleus and that all nuclei within individual spores are genetically identical (that is, homokaryotic). Here we show that their empirical observations are also consistent with a distribution of genetic variation between nuclei within spores (that is, heterokaryotic), given that there is fusion of fungal hyphae. This analysis, together with complementary findings, suggests that AM fungi have an unusual genomic structure in which multiple, genetically diverse nuclei are maintained within cells through remixing by hyphal fusion.     

Rapid assessment of acid phosphatase activity in the mycorrhizosphere and in arbuscular mycorrhizal fungal hyphae

A pot experiment has been carried out under controlled conditions to study the possibility of applying the technique ofin vivo staining for acid phosphatase activity on the roots of mycorrhizal plants and arbuscular mycorrhizal hyphae. The pots had 5 compartments. The central root compartment was separated from the two adjacent hyphal compartments using nylon nets of 30 μm mesh, and the two hyphal compartments were separated from the two outermost compartments with 0.45 μm membranes. Red clover was grown in the root compartment and was either inoculated with the arbuscular mycorrhizal fungus (AMF)Glomus mosseae or unlnoculated. Sodium phytate was applied to all compartments. The results show that AMF can increase acid phosphatase activity of clover roots. The plant roots acquired deep red “mycorrhizal prints”. The external hyphae also had obvious “hyphal prints” on the test papers, indicating the ability of mycorrhizal hyphae to release acid phosphatase.     

菌根真菌对榉树光合特性的影响

【目的】探究丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)对木本植物生长和光合特性的影响以及樟树光响应模型的适用性。【方法】以自培无菌榉树(Zelkova serrata Thunb.)幼苗为试验材料,设置3个处理,分别为不接种菌根真菌(CK)、接种来自贵州毕节的摩西球囊霉(GM1)、接种来自云南楚雄的摩西球囊霉(GM2),测定榉树的光响应曲线,通过对5种常用的光响应曲线模型进行比较分析,探索菌根真菌对榉树光合特性的影响,并通过5种模型对光响应曲线进行拟合,评定5种模型的适用性。【结果】接种菌根真菌明显提高了榉树的一些形态指标,体现在苗高、地径的增加。接种菌根真菌提高了榉树的净光合速率(P_n)、气孔导度(G_s)、胞间CO₂浓度(C_i)。其中,GM1的效果要好于GM2,同时,GM1对榉树的蒸腾速率(T_r)也有提升效果。通过5种模型的拟合,发现模拟效果都很好,只有指数模型在拟合接种GM1的榉树光响应曲线时,R²为0.977,其余的都达到了0.99以上。从决定系数的均值分析,叶子飘模型的拟合效果最好,其次是非直线双线模型,拟合效果相对最差的是指数模型。相关性分析表示,叶绿素含量与侵染率呈负相关关系,苗高与侵染率无显著相关性,地径、C_i、G_s、P_n均与侵染率呈显著正相关。【结论】接种菌根真菌可以促进宿主植物的生长,对植物的光合特性也有一定的提升效果。5种光响应模型中,叶子飘模型的模拟效果最好,所以在对榉树的光响应情况的描述上,应该以叶子飘模型为主,其余几个模型可以作为参考。