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.     

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.     

Response of Three Arbuscular Mycorrhizal Fungi to Simulated Acid Rain and Aluminium Stress

Simulated acid rain (SAR) combined with higher concentration of aluminium (SAR+Al) influenced the ecophysiology of three arbuscular mycorrhizal fungi (AMF) in both the germination and symbiotic phases of their life cycle. Acaulospora tuberculata, an isolate from the soil with low pH, exhibited a higher tolerance to environmental stress as compared to Glomus mosseae and G. fistulosum. This higher tolerance may be related to the edaphic conditions of soil of the isolate origin. The histochemical staining of the alkaline phosphatase and NADH-diaphorase activities in the extraradical mycelium (ERM) of the AMF proved to be more sensitive indication of negative effects of the SAR or SAR+Al stress compared to commonly measured parameters of the AMF such as mycorrhizal colonisation or growth of the ERM. This revised version was published online in July 2006 with corrections to the Cover Date.     

丛枝菌根真菌对植物生长影响的研究

菌根是自然界中一种极为普遍和重要的共生现象,其中分布最为广泛的菌根类型就是丛枝菌根,可以增强植物从土壤中获取水分的能力,改善植物根系对磷、镉等矿质元素及养分的吸收,从而促进植物的生长。本文综述了丛枝菌根真菌对植物生长影响的概况。有关丛枝菌根真菌对植物水分和矿质营养的利用,尤其是磷素营养的研究较为深入,而对植物光合特性的研究较少,这些研究工作为深入理解菌根真菌与植物的相互关系提供基础资料。     

长期定位施肥土壤中的丛枝菌根真菌

从连续26年长期定位施肥土壤中的玉米和小麦根围采集土样,从中鉴定出丛枝茵根(Arbuscular Myc- orrguza,AM)真菌5属19种,包括Glomus属11种:G．caledonium,G．constrictum,G．eburneum,G．ebunicatum, G．hyderabadensis,G．mossese,G．sinuosum,G．tortuosum,G．versiforme,G．sp1,G．sp2;Acaulospora属2种: A．excacota,A．sp;Gigaspora属2种:Gi．margarita,Gi．sp;Scutellospora属3种:S．cerradensis,S．coralloidea, S．pellucida;Archaespora属1种:Ar．leptoticha。     

丛枝菌根真菌提高植物抗逆性的效应及其机制研究进展

丛枝菌根（arbuscularmycorrhizal,AM）真菌是土壤中重要的生物成员之一,对植物具有多种有益效应。AM真菌的基本功能之一是增强植物的抗逆性,在全球气候变化的今天尤其重要。本文总结了AM真菌降低温度胁迫、水分胁迫、盐胁迫、重金属胁迫、病虫害、以及杂草对植物造成的危害和提高植物抗逆性的效应;阐述了AM真菌提高植物抗逆性的作用机制;并讨论了当前该领域研究存在的难题及今后的展望。旨在为探讨提高植物抗逆性策略与途径提供参考。     

Arbuscular Mycorrhizal Fungi as Components of Sustainable Soil-Plant Systems

Abstract

Increased pressure for food production has, in recent years, led to the development of intensive agricultural systems that use significant quantities of inorganic fertilizers and pesticides. However, there is now substantial evidence for the environmental costs of this high-input strategy and this has led to demands for agricultural systems to be modified in order to make them more sustainable. Arbuscular mycorrhizal fungi (AMF) play a key role in natural and agricultural ecosystems through major functions in the enhancement of plant phosphorus and nitrogen nutrition, nutrient and soil conservation, and the biological control of plant pathogens. They are essential to the sustainability of systems and their importance in agricultural ecosystems is likely to increase as inputs are reduced and/or rationalized. In order to maximize their benefits it is essential to ensure that management practices include minimum tillage, reduced use of inappropriate fertilizer, appropriate crop rotations with minimal fallow, and rationalized pesticide use. Furthermore, crop breeders should take full account of the symbiosis in selection. Future research should be targeted to understanding the functional ecology of AMF in agroecosystems.     

Arbuscular Mycorrhizal Fungi in Plant Production of Temperate Agroecosystems

Abstract

The importance of arbuscular fungi for plant development and health is now widely demonstrated. However, although it is more and more evident that they are not only an integral part of many cultivated plants but also an essential component of soil fertility, their rational use in plant production is still in its infancy. Because of their role as bioregulators, biofertilizers, and biocontrol agents, they represent potentially important tools for new orientations in agriculture, particularly in Europe, where there is increasing demand for development of new plant management techniques that are less dependent on chemical inputs. The discovery of mycmutants turned out to be an excellent tool for better understanding the ecophysiology of arbuscular mycorrhizas under field conditions and for allowing considerable progress in our knowledge on the genes controlling this symbiosis. Progress in this area, together with ongoing generation of specific nucleic acid probes for arbuscular mycorrhizal fungi, appear to be essential for promoting mycorrhizal biotechnology. Despite this, arbuscular mycorrhizal fungi can already be exploited successfully in certain areas of plant production, such as orchards and ornamental nurseries.     

Progress and Challenges in Agricultural Applications of Arbuscular Mycorrhizal Fungi

Arbuscular mycorrhiza is a widespread interaction between plant roots and mutualistic fungi that both promotes plant mineral nutrition and supports stability in many natural ecosystems. Given the demand in current agriculture for these ecosystem services, it appears desirable to further integrate this interaction in current management schemes. While two different approaches can be identified in this regard, a number of problems have limited the agricultural application of mycorrhiza to date. In this review, the sensitivity of arbuscular mycorrhizal fungi to certain agricultural management methods, the functional variability of arbuscular mycorrhizal fungi, and the variability of plant responsiveness will be discussed in particular. In addition we will focus on recent advances in the study of mycorrhiza in natural ecosystems, and illustrate how such knowledge might be used to further the integration of arbuscular mycorrhizal fungi in agricultural regimes, and so increase the sustainability and robustness of current practice.     

丛枝菌根真菌分类最新进展

近10a来,随着分子生物学技术在丛枝菌根(arbuscularmycorrhiza,AM)研究中的应用,AM真菌分类学得到迅速发展。重点介绍AM真菌的最新分类系统,并对其发展简史作一简单回顾。     

丛枝菌根真菌离体培养研究概况(综述)

本文综述丛枝菌根真菌在离体条件下的生长发育、生长促进物质及生理生化代谢等方面的研究概况。     

黄檗丛枝菌根真菌鉴定

目的：利用形态学特征与Nested-PCR技术鉴定黄檗丛枝菌根真菌。方法：采用酸性品红染色法挑选黄檗丛枝菌根。同时,利用湿筛法获得AM真菌孢子,进行形态学鉴定。运用Nested-PCR技术,对黄檗粗提DNA进行特异性扩增,采用blastn进行序列相似性比较。并构建系统进化树,确定侵染黄檗根系的AM真菌。结果：编号为HDAM-1的AM真菌孢子,形态特征与G．intraradices的特征描述一致。Nested-PCR检测到约455bp的目的片段,其序列与G．intraradices（DQ469118）相似性最高,达97．8％,有11个碱基的差异。系统进化树显示该序列在基于25S rDNA的进化树中与G．intraradices（DQ469118．1）处于同一分支,确定G．intraradices侵染黄檗根系。结论：将形态学特征与Nested-PCR技术相结合鉴定AM真菌,不仅简易、经济,而且能够提高研究结果的可靠性。     

Anastomosis Formation and Nuclear and Protoplasmic Exchange in Arbuscular Mycorrhizal Fungi

We observed anastomosis between hyphae originating from the same spore and from different spores of the same isolate of the arbuscular mycorrhizal fungi Glomus mosseae, Glomus caledonium, and Glomus intraradices. The percentage of contacts leading to anastomosis ranged from 35 to 69% in hyphae from the same germling and from 34 to 90% in hyphae from different germlings. The number of anastomoses ranged from 0.6 to 1.3 per cm (length) of hyphae in mycelia originating from the same spore. No anastomoses were observed between hyphae from the same or different germlings of Gigaspora rosea and Scutellospora castanea; no interspecific or intergeneric hyphal fusions were observed. We monitored anastomosis formation with time-lapse and video-enhanced light microscopy. We observed complete fusion of hyphal walls and the migration of a mass of particles in both directions within the hyphal bridges. In hyphal bridges of G. caledonium, light-opaque particles moved at the speed of 1.8 ± 0.06 μm/s. We observed nuclear migration between hyphae of the same germling and between hyphae belonging to different germlings of the same isolate of three Glomus species. Our work suggests that genetic exchange may occur through intermingling of nuclei during anastomosis formation and opens the way to studies of vegetative compatibility in natural populations of arbuscular mycorrhizal fungi.     

巨孢囊霉目丛枝菌根真菌的分类研究进展

巨孢囊霉目(Gigasporales)真菌因其形态特征显著而被认为是较易归类和鉴定的一类丛枝菌根真菌(AMF)。近十余年来随着研究技术的进步,基于无性孢子形态特征而建立的AMF分类、鉴定方法得以不断补充和完善,也使得巨孢囊霉目真菌的系统分类一直处于不断变化和更新的状态。文中主要介绍了该目真菌基于形态特征的鉴定方法上的最新变化以及最新的分类系统,着重归纳已报道科、属、种分类特征,旨在为开展我国AMF资源调查、丰富其多样性提供便利。     

Production of Polyclonal and Monoclonal Antibodies Against Hyphae from Arbuscular Mycorrhizal Fungi

Abstract

Polyclonal and monoclonal antibodies were produced against hyphae of the arbuscular mycorrhizal fungus Glomus monosporum. The polyclonal antibodies (pAbs) were raised in a rabbit by immunizing with hyphae. They were tested for their specificity by a dot-immunoblot assay (DIBA). After the third immunization, a distinct difference in the signal strength was observed between the antisera and the preimmune serum. The pAbs showed cross-reactions to a number of fungal species, both mycorrhizal and other. For the production of monoclonal antibodies (mAbs), mice were immunized intraperitoneally with hyphae. The resulting hybridoma cell culture supernatants were tested by an indirect immunolabeling procedure. For this purpose the hyphae were immobilized on silane-coated microscopic slides. The mAb 8A7 reacted with hyphae from all Glomus isolates tested so far. Cross-reactivities were not observed with hyphae from fungi of the family Acaulosporaceae, phytopathogenic fungi tested so far, or from spores from Glomus species.     

Activation of Symbiosis Signaling by Arbuscular Mycorrhizal Fungi in Legumes and Rice

Establishment of arbuscular mycorrhizal interactions involves plant recognition of diffusible signals from the fungus, including lipochitooligosaccharides (LCOs) and chitooligosaccharides (COs). Nitrogen-fixing rhizobial bacteria that associate with leguminous plants also signal to their hosts via LCOs, the so-called Nod factors. Here, we have assessed the induction of symbiotic signaling by the arbuscular mycorrhizal (Myc) fungal-produced LCOs and COs in legumes and rice (Oryza sativa). We show that Myc-LCOs and tetra-acetyl chitotetraose (CO4) activate the common symbiosis signaling pathway, with resultant calcium oscillations in root epidermal cells of Medicago truncatula and Lotus japonicus. The nature of the calcium oscillations is similar for LCOs produced by rhizobial bacteria and by mycorrhizal fungi; however, Myc-LCOs activate distinct gene expression. Calcium oscillations were activated in rice atrichoblasts by CO4, but not the Myc-LCOs, whereas a mix of CO4 and Myc-LCOs activated calcium oscillations in rice trichoblasts. In contrast, stimulation of lateral root emergence occurred following treatment with Myc-LCOs, but not CO4, in M. truncatula, whereas both Myc-LCOs and CO4 were active in rice. Our work indicates that legumes and non-legumes differ in their perception of Myc-LCO and CO signals, suggesting that different plant species respond to different components in the mix of signals produced by arbuscular mycorrhizal fungi.     

Polymer-based Preparation of Soil Inoculants: Applications to Arbuscular Mycorrhizal Fungi

Arbuscular mycorrhizal fungi is an important group of soil microorganisms which form beneficial symbiotic associations with roots with a wide range of plants thus improving plant growth, nutrition and health. This paper reviews the current status of preparation and formulation of mycorrhizal inoculum applying polymer materials with determined characteristics. The most widely used methods are based on the entrapment of fungal materials in natural polysaccharide gels. The potential of such inoculant preparations is illustrated by various studies which include immobilization of mycorrhized root pieces, vesicles and spores, in some cases co-entrapped with other plant beneficial microorganisms. Suggestions for further research in this field are also discussed.