不同生境外生菌根真菌对铝胁迫的响应

以南北方不同生境下的10株外生菌根真菌为研究对象,采用液体培养的方法,研究了铝对不同菌根真菌的生物量、有机酸分泌及养分含量的影响,以期筛选出抗铝性强的优良菌株,并探讨其抗铝机理。结果表明:外生菌根真菌Sl 08抗铝性最强;Pt 715、Ld 03、Bo 11、Sl 01、Bo 15也具有不同程度的耐铝性;Sl 14、Gc 99、Cg 04抗铝性较差;Sg 11抗铝性最差。来自南方酸性森林土壤的菌株总体抗铝性强于来自北方石灰性土壤的菌株,这表明外生菌根真菌的铝耐受能力与其原始生境有着密切的联系。外生菌根真菌能分泌多种有机酸,且不同菌株分泌的有机酸种类不同。其中,受铝胁迫分泌量增加最多的是草酸。研究中,铝胁迫能增加大多数铝抗性菌株的草酸分泌量,其中铝抗性最强的Sl 08表现最为明显。但铝胁迫并没有促进具备一定铝抗性的Bo 11和Sl 01草酸的分泌量,同时在铝敏感的菌株中均观察到了草酸分泌量的增加。这表明分泌草酸可能并不是外生菌根真菌抵抗铝毒的唯一途径。对各菌株铝胁迫下对氮,磷及钾的吸收研究表明,除铝敏感菌株Sl 14外,铝胁迫均能促进各供试菌株对氮,磷或钾的吸收。综上,在一定铝浓度下,一些外生菌根真菌可通过增加草酸分泌来抵御铝毒。此外,铝胁迫下外生菌根真菌还可通过调控氮、磷、钾等营养元素的吸收来抵抗铝毒,即通过增加对营养元素的吸收来增强其在铝胁迫下的生存能力,这可能是其抵御铝胁迫的应激反应之一。     

Effect of ectomycorrhizal fungi on nitrogen mineralisation and the growth of Scots pine seedlings in natural peat

The aim of this study was to investigate the potential of different isolates of ectomycorrhizal (EM) fungi to enhance the growth of Pinus sylvestris seedlings in five natural peat substrates with different nitrogen concentrations, and the effect of the Scots pine seedlings and fungal inoculum on the formation of dissolved inorganic and organic nitrogen in peat. Utilization of different organic nitrogen compounds by microbial community in the peat was also investigated using Biolog MT MicroPlates. Inoculation of the seedlings with EM fungi enhanced seedling growth. Piloderma croceum increased root growth especially, whereas Lactarius rufus increased needle growth and Suillus variegatus I, II and III improved both root and needle growth. All the EM fungi also significantly affected stem growth. Nitrogen concentration of the peat did not affect seedling growth as much as the EM fungi. At the lowest peat N concentration (1.17%) NH ₄ ⁺ mineralisation was lower and DON (dissolved organic nitrogen) accumulation higher than at higher peat N concentrations. The EM fungal isolates had different effects on NH ₄ ⁺ and DON accumulation/degradation in peat. The EM fungal isolates significantly increased NH ₄ ⁺ formation in the peat, whereas L. rufus and P. croceum had an opposite effect on DON accumulation. S. variegatus I significantly decreased the DON concentrations during peat incubation. The N concentration of the peat slightly affected the utilization of amino acids and polyamines by the microbial community, whereas inoculation with S. variegatus I, II or III had no effect.     

Native and non-native mammals disperse exotic ectomycorrhizal fungi at long distances from pine plantations

We aimed to evaluate if exotic ectomycorrhizal fungi from exotic pine plantations disperse through non-native, but also native, mammals in a mountain ecosystem devoid of native ECM plants. Among four non-native and three native mammal species, feces of non-native wild boar (Sus scrofa) and brown hare (Lepus europaeus), and native pampa fox (Lycalopex gymnocercus) were selected to inoculate seedlings of Pinus elliottii. These feces came from two transects in an elevation gradient (1350–2250 m asl) and different distances from a pine plantation (100–6000 m). We show that feces of wild boar, brown hare (non-native), and pampa fox (native) were effective as inoculum for establishing ectomycorrhizal pine seedlings. Through molecular analyses, we determined that two species are mostly consumed and successfully form ectomycorrhizas with pine roots: Suillus granulatus and Rhizopogon pseudoroseolus. We provide novel evidence for the long-distance dispersal of exotic ectomycorrhizal fungi by non-native and native animal vectors.     

青蒿素对外生菌根真菌化感效应

青蒿素是治疗疟疾的首选药物,主要从黄花蒿(Artemisia annua L.)中提取,然而黄花蒿在生长过程中会向周围环境分泌青蒿素。为正确评估青蒿素对森林生态系统中的重要成分""外生菌根真菌的影响,试验以重庆地区有代表性的两株外生菌根真菌——褐环乳牛肝菌(Suillus luteus)Sl 8和松乳菇(Lactarius delicious)Ld 3为材料,研究了青蒿素对菌丝生长,H+和有机酸分泌,以及养分吸收的影响。结果表明,在液体培养基中加入青蒿素,外生菌根真菌的生长受到明显抑制,菌丝生物量降幅高达26.89%(Ld 3)和89.13%(Sl 8);Ld 3分泌H+和草酸的能力增强,而Sl 8分泌量下降。随着青蒿素浓度的增加,菌丝的N、P、K含量及吸收量显著减少。当培养基中青蒿素达到80 mg/L时,Ld 3的N、P、K吸收量比不加青蒿素的处理分别降低了50.55%、46.30%和42.28%;Sl 8几乎丧失对N、P、K的吸收能力。说明青蒿素不同程度地抑制了外生菌根真菌的生长和养分吸收,但对H+和草酸的分泌作用因菌株不同而异。     

氮沉降对外生菌根真菌的影响

综述了国外氮沉降对外生菌根真菌的影响研究现状 ,主要从菌根形成、形态 (菌丝体、菌根 )变化、子实体生产力和外生菌根真菌群落结构等方面对氮沉降的响应进行了综述 ,并初步探讨了氮饱和的临界负荷。研究表明 ,过量氮沉降会给外生菌根真菌在以下几个方面带来负影响 :(1)影响外生菌根真菌与寄主植物之间的养分分配和循环 ;(2 )降低子实体生产力 ;(3)减少菌丝 ;(4 )降低菌根量及其活力 ;(5 )降低外生菌根真菌丰富度 ;(6 )改变外生菌根真菌群落结构组成 ;(7)降低外生菌根真菌群落功能。还指出了未来该方面研究重点和方向     

Invasion biology of Australian ectomycorrhizal fungi introduced with eucalypt plantations into the Iberian Peninsula

In the last two centuries, several species of Australian eucalypts (e.g. Eucalyptus camaldulensis and E.␣globulus) were introduced into the Iberian Peninsula for the production of paper pulp. The effects of the introduction of exotic root-symbitotic fungi together with the eucalypts have received little attention. During the past years, we have investigated the biology of ectomycorrhizal fungi in eucalypt plantations in the Iberian Peninsula. In the plantations studied, we found fruit bodies of several Australian ectomycorrhizal fungi and identified their ectomycorrhizas with DNA molecular markers. The most frequent species were Hydnangium carneum, Hymenogaster albus, Hysterangium inflatum, Labyrinthomyces donkii, Laccaria fraterna, Pisolithus albus, P. microcarpus, Rhulandiella berolinensis, Setchelliogaster rheophyllus, and Tricholoma eucalypticum. These fungi were likely brought from Australia together with the eucalypts, and they seem to have facilitated the establishment of eucalypt plantations and their naturalization. The dispersion of Australian fungal propagules may be facilitating the spread of eucalypts along watercourses in semiarid regions increasing the water lost. Because ectomycorrhizal fungi are obligate symbionts, their capacity to persist after eradication of eucalypt stands, and/or to extend beyond forest plantations, would rely on the possibility to find compatible native host trees, and to outcompete the native ectomycorrhizal fungi. Here we illustrate the case of the Australasian species Laccaria fraterna, which fruits in Mediterranean shrublands of ectomycorrhizal species of Cistus (rockroses). We need to know which other Australasian fungi extend to the native ecosystems, if we are to predict environmental␣risks associated with the introduction of Australasian ectomycorrhizal fungi into the Iberian Peninsula. This revised version was published online in July 2006 with corrections to the Cover Date.     

Release of a reducing substance by the ectomycorrhizal fungi Pisolithus tinctorius and Paxillus involutus

Culture solutions of the ectomycorrhizal fungi Pisolithus tinctorius and Paxillus involutus are shown to reduce a high valency oxide of manganese at a range of pH values from 3.0 to 13.0. Manganese reduction in unmoculated culture media was confined to pH values below 5.0 and above 10.0. The results are consistent with the release of a reducing substance from the fungal mycelium.     

Cation exchange capacity and lead sorption in ectomycorrhizal fungi

Two ectomycorrhizal fungi, Paxillus involutus 533 and Laccaria bicolor S238, differing greatly in their mycelial characteristics, were investigated with regard to their cation exchange capacity and Pb-binding capacity in vitro after growth with either NO₃ ^- or NH₄ ⁺ as N source. The CECs of 800–1200 mol g-1 dry weight for Paxillus involutus 533 and 2000–3000 mol g-1 dry weight for Laccaria bicolor S238, were high compared to plant roots. The fungal mycelium also had a high Pb sorption capacity. It was higher in Laccaria bicolor S238 than in Paxillus involutus 533 and higher after pregrowth in NO₃ ^- compared to NH₄ ⁺. Both the higher CEC and the higher Pb sorption capacity of Laccaria bicolor S238 compared to Paxillus involutus 533 might have been the result of the hydrophilic nature of the of Laccaria bicolor S238 mycelium. It would have absorbed the solutions better than the hydrophobic mycelium of Paxillus involutus 533. X-ray microanalysis of the cell walls revealed that the Pb content of the cell walls was higher in Paxillus involutus 533 than in Laccaria bicolor S238. Nevertheless, electron dense deposits in the cell walls of Laccaria bicolor S238 contained large amounts of Pb, P and S. Thus, while Pb was evenly distributed in the cell walls of Paxillus involutus 533, Pb was accumulated in electron dense deposits in Laccaria bicolor S238. The results are discussed in view of their significance for the mycorrhizal symbiosis.     

The screening and selection of inoculant arbuscular-mycorrhizal and ectomycorrhizal fungi

The initiation of a programme of screening and selection of arbuscular-mycorrhizal fungi (AM fungi) and ectomycorrhizal fungi (ECM fungi) for use as inoculant fungi in agriculture, horticulture of forestry will depend on whether inoculation is more appropriate as a management option than manipulation of the indigenous mycorrhizal populations. The greatest immediate potential for the successful use of mycorrhizal inoculants will be in soils and growth media where phosphorus (P) limits plant growth and where the indigenous mycorrhizal fungi are either ineffective at increasing P uptake by the plant or their numbers have been drastically reduced by human influence or natural disturbance. In recent investigations, however, additional benefits to the plant following colonization of roots by effective AM or ECM fungi have been demonstrated. These additional benefits of an effective mycorrhizal association have necessitated a re-evaluation of the optimum screening procedures for isolates of AM and ECM fungi. Both current methodologies and suggestions for alternative approaches to the screening of AM and ECM fungi are discussed in this paper. The problems inherent in choosing suitable experimental conditions to compare different isolates at the screening stage are also addressed. The review also stresses the importance of continued monitoring of introduced mycorrhizal fungi to learn more about their longer-term ecological role, particularly within reforestation or revegetation studies.     

Ability of ectomycorrhizal fungi to utilize starch and related substrates

Basidiomycetous fungi of 55 strains of 33 species in 15 genera which are thought to be ectomycorrhizal were grown on starch and related substrates as a sole carbon source, and their ability to utilize these substrates was determined. Mycellial weights of the fungi grown on agar media containing starch and amylose varied between the strains from 1.1 to 94.9 mg/flask and from 0.4 to 93.3mg/flask, respectively. Mycelial growth rates ranged from 0 to 1.17 mm/d on barley grain medium and from 0 to 2.03 mm/d on rice grain medium; the highest rate corresponded to about half of the average of reference wood-rotting fungi. Most of the mycorrhizal fungi that grew well on amylose gave higher growth rates on barley. Several strains inLyophyllum, Hebeloma, Sarcodon, andTricholoma grew well on both glucose and starch media.     

Growth of ectomycorrhizal fungi stimulated by lipids from a pine root exudate

Summary The content of fatty acids was analysed in an exudate from roots of pine seedlings grown axenically in vermiculite with a synthetic nutrient medium. The dominating fatty acdis were fewer in the exudate than in the roots. Unsaturated fatty acids were predominant. The total lipid fraction of the exudate promoted mycelial growth in two of the three ectomycorrhizal fungi tested.     

白皮松天然林外生菌根土壤繁殖体库

为更好地恢复和保存白皮松天然林,在陕西省白皮松残存林地采集根际土壤,采用幼苗检测法获取土壤外生菌根真菌繁殖体,用形态观察分类与ITS-PCR-sequencing相结合的方法进行菌根鉴定,研究白皮松林地外生菌根真菌土壤繁殖体库的组成.结果表明: 在白皮松幼苗菌根中共获得73个特异性序列;按照97%的相似度阈值,将序列划分为12个可操作分类单元(OTUs);稀疏曲线分析表明,本研究基本获得了白皮松土壤外生菌根繁殖体库的多样性.常见种有土生空团菌、Tomentella sp.、Tuber sp.等.出现频率最高的一个OTU(80%)与已知种类相似度较低(75%),说明其可能是一个新的菌根菌种类.白皮松残存天然林地的外生菌根繁殖体库中具有其他松科植物土壤繁殖体库常见的种类,但是频率最高的种类未能鉴定到已知属或科,说明白皮松菌根繁殖体库具有其宿主特异性.这种群落特异构成也说明研究和利用白皮松土壤外生菌根真菌繁殖体库具有特殊性和重要性.     

钾与信号抑制剂对外生菌根真菌分泌乙酸的调控作用

外生菌根真菌是森林生态系统中的重要成分,参与树木养分的吸收利用。试验液体培养外生菌根真菌,设置不同供钾水平,添加钙信号抑制剂,研究了它们的有机酸和氢离子分泌,以及乙酸分泌对供钾和信号抑制剂的响应。结果表明,供试菌株的生长,氮、磷、钾含量和吸收量因菌株不同而异,生物量变化于52.91—121.72 mg/瓶之间,相差1倍以上。外生菌根真菌吸收养分的差异可能与它们对土壤养分环境的长期适应、进化、选择有关。在外生菌根真菌的培养液中,分别检测出草酸、乙酸、苹果酸、柠檬酸和丁二酸等,以及大量的氢离子,说明菌根真菌能分解土壤含钾矿物,释放钾离子,改善寄主植物的钾营养。其中,乙酸分泌量较大,具有普遍性,低钾刺激分泌乙酸,高钾时分泌减少,其分泌速率与供钾浓度和菌丝吸钾量之间呈显著负相关(r=-0.734,r=-0.617,n=60)。钾对菌根真菌分泌乙酸的调控作用具有改善森林钾素营养,防止土壤养分淋失的生理和生态意义。此外,在低钾条件下,阴离子通道和钙信号抑制剂抑制外生菌根真菌分泌乙酸。说明钙信号和阴离子通道参与了乙酸分泌,缺钾可能是刺激乙酸分泌的原初信号,通过信号转导和一系列级联反应促进乙酸分泌。     

Restriction fragment length polymorphisms distinguish ectomycorrhizal fungi

Basidiomycetous fungi, two saprophytes and three mycorrhizal, were used to assess the specificity of DNA hybridization for distinguishing genera from one another. Interspecific comparisons were done with several isolates of mycorrhizal fungi,Laccaria bicolor andL. laccata, collected from diverse geographical sites. The DNAs were digested with four restriction nucleases and separated by gel electrophoresis into patterns of DNA fragments called restriction fragment length polymorphisms (RFLPs). The RFLPs were hybridized with a radioactively-labeled DNA probe encoding Basidiomycetous ribosomal RNA genes. The five genera were discernable using both unprobed and probed RFLPs. Hybridization of probe DNA with RFLPs was isolate-specific for all nine Laccaria isolates examined. The reclassification of aL. bicolor isolate is supported, demonstrating that hybridization of RFLPs offers an additional tool for taxonomy of ectomycorrhizal fungi. The method may have field application for distinguishing known isolates if their DNA fingerprints are previously ascertained and are distinct from RFLPs of indigenous organisms.     

外生菌根菌与森林树木的相互关系

生态系统的每个过程都伴随着各种微生物的活动,其中最重要的功能群之一是菌根真菌(菌根菌)。一般认为,菌根菌是自然界多数植物生存最基本的组成部分,陆地上约90％以上的高等植物都具有菌根菌。这些菌类的菌丝体与植物根系结合形成菌根,使植物生长成为可能,使不同种类植物的根系联在一起。根据菌根菌入侵植物根系的方式及菌根的形态特征,菌根可分为外生菌根、内生菌根和内外生菌根3组共7种类型。外生菌根主要出现在松科、桦木科、壳斗科等树种的森林生态系统中,在根系表面形成菌丝鞘,部分菌丝进入根系皮层细胞间隙形成哈氏网表面。菌根菌剂在森林经营中得到广泛地应用。外生菌根菌对森林树木的作用可归纳为：1)促进造林或育苗成活与生长;2)提高森林生态系统中植物的多样性、稳定性和生产力;3)对森林生态系统的综合效应,主要表现在增加植物一土壤联结,改善土壤结构,促进土壤微生物,增强植物器官的功能;4)抗拮植物根部病害病原菌等。树木与菌根菌相互关系研究主要包括：1)菌根共生的机理;2)菌根菌在退化森林生态系统恢复与改造中的作用;3)菌根菌的分布格局与森林生态系统服务功能的关系;4)菌根菌对森林生态系统的综合效应,如菌根菌与森林植物群落结构、物种多样性以及森林系统稳定性和生产力的研究。     

七株外生菌根真菌与三种松苗菌根的形成能力

松树外生菌根菌资源丰富,但实际应用的种类不多。为筛选出与松苗形成菌根能力较强的菌种,采用播种接菌和芽苗截根移栽接菌两种方法,对7株外生菌根真菌与马尾松、湿地松和黑松3种松苗的菌根合成进行了研究。结果表明：形成的菌根以二叉分枝状为主,棒状菌根相对较少,多叉状菌根以马尾松较多。PC2形成的菌根表面菌丝厚且紧密,504、EG、Pt,形成的菌根表面菌丝紧密程度中等,而505、ZJ和HX形成的菌根其表面菌丝则比较稀疏;Pt1、Pt2、EG形成的菌根外延菌丝较长,而505、HX形成的菌根外延菌丝极短。截根接菌时的感染率和感染指数要高于播种接菌。504形成菌根的能力最强,在3种松苗上的菌根感染率都达100％,感染指数最高可达90,最低也达70;Pt2和EG与马尾松和黑松形成菌根的能力较强;而505和HX仅与马尾松形成菌根的能力较强;Pt1形成菌根的能力较差,在3种松苗上菌根感染率和感染指数都较低。在3种松苗中,马尾松的菌根化状况最好,其次为黑松,湿地松的菌根化状况较差。     

Extracellular and cellular mechanisms sustaining metal tolerance in ectomycorrhizal fungi

This review focuses on recent evidence that identifies potential extracellular and cellular mechanisms that may be involved in the tolerance of ectomycorrhizal fungi to excess metals in their environment. It appears likely that mechanisms described in the nonmycorrhizal fungal species are used in the ectomycorrhizal fungi as well. These include mechanisms that reduce uptake of metals into the cytosol by extracellular chelation through extruded ligands and binding onto cell-wall components. Intracellular chelation of metals in the cytosol by a range of ligands (glutathione, metallothioneins), or increased efflux from the cytosol out of the cell or into sequestering compartments are also key mechanisms conferring tolerance. Free-radical scavenging capacities through the activity of superoxide dismutase or production of glutathione add another line of defence against the toxic effect of metals.     

Enzymes of ammonium metabolism in ectendomycorrhizal and ectomycorrhizal symbionts of pine

Ammonium assimilation enzymes from several strains of ectendo- and ectomycorrhizal fungi were assayed after three weeks culture on a buffered synthetic medium containing ammonium as sole nitrogen source. Activity of NADP-dependent glutamate dehydrogenase (GDH, EC 1.4.1.4) of ectomycorrhizal strains was very low despite excellent mycelial growth. Only ectendomycorrhizal fungus MrgX isolated from roots of Pinus sylvestris showed high GDH activity. Similar results were obtained when the enzyme extracts were subjected to starch gel electrophoresis. Growth of the fungi, except ectendomycorrhizal MrgX, was arrested when inhibitors of glutamine synthetase (GS, EC 6.3.1.2) or glutamate synthase (GOGAT. EC 1.4.7.1) (methionine sulphoximine or albizine, respectively) were included in the culture medium. Glutamine synthetase activity was found in all fungi tested. The results suggest that the GS pathway for ammonium assimilation is potentially operative in ectomycorrhizal fungi and imply only a minor role for GDH in ammonium assimilation by the studied ectomycorrhizal symbionts of pine. Some physiological and ecological implications of these results are discussed.