Summary


1
Arbuscular mycorrhizal (AM) fungi are obligate root symbionts that are present in most terrestrial ecosystems and have roles in plant mineral nutrition, carbon cycling and biotic interactions. In this work, 26 publications were surveyed that report on the occurrence of natural root-colonizing AM fungi identified using rDNA region sequences. A total of 52 host plant species were investigated. Sixteen publications provided data enabling a comparison to be made of AM fungal taxon richness and community composition across 36 host plant species and 25 locations. Ninety-five fungal taxa (small subunit rRNA gene sequence types) were involved, 49 of which were recorded from at least two study sites, and 65 from more than one host plant species.

2
The number of AM fungal taxa per host plant species differed between habitat types: a significantly higher richness was found in tropical forests (18.2 fungal taxa per plant species), followed by grasslands (8.3), temperate forests (5.6) and habitats under anthropogenic influence (arable fields and polluted sites, 5.2).

3
AM fungal communities exhibit differing compositions in broadly defined habitat types: tropical forests, temperate forests and habitats under anthropogenic influence. Grassland locations around the world host heterogeneous AM fungal communities.

4
A number of AM fungi had a global distribution, including sequence types related to the Glomus intraradices/fasciculatum group, G. mosseae, G. sp. UY1225 and G. hoi, as well as the Glomus and Scutellospora types of unknown taxonomic affiliation. Widespread taxa occur in both natural and anthropogenic (disturbed) habitats, and may show high local abundance. However, about 50% of taxa have been recorded from only a single site.

5
The current global analysis of AM fungal communities suggests that soil micro-organisms may exhibit different distribution patterns, resulting in a high variability of taxon richness and composition between particular ecosystems.

Composition of root-colonizing arbuscular mycorrhizal fungal communities in different ecosystems around the globe

The enhanced growth of plants infected by vesicular–arbuscular (VA) mycorrhizal fungi results primarily from improved uptake of soil phosphate. Extra phosphate reaches the root through the fungal h...

The physiology of vesicular-arbuscular endomycorrhizal symbiosis

SUMMARY
Leeks were grown on a γ-irradiated soil selected for its low copper status, in a factorial experiment with additions of phosphorus and copper, and with or without inoculation with Glomus mosseae. There was no response in growth to added phosphorus, but responses to added copper and to inoculation. The results indicate that an infection with mycorrhizal fungi can increase the supply of copper to the host plant, in conditions where increased phosphorus nutrition does not increase dry weight. It is suggested that copper is absorbed and translocated by mycorrhizal hyphae in a manner analogous to that which occurs for phosphorus.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1983.tb03491.x

Interactions of vesicular‐arbuscular mycorrhizal infection and heavy metals in plants

Ecological and physiological effects of heavy metals on terrestrial organisms are reviewed, considering evidence from both laboratory and field studies. Problems concerning how to define heavy-metal exposure and to assess the sensitivity of field biota to heavy metals are discussed. Mechanisms of heavy-metal tolerance are considered including avoidance, exclusion, immobilization and excretion, as well biochemical mechanisms including enzymatic change. The taxonomy of heavy-metal tolerance and problems concerning tolerance and ecological performance are discussed briefly. Efforts are made to compare the relative sensitivity of various groups, including bacteria, fungi, bryophytes, lichens, vascular plants and soil invertebrates. An emphasis is placed on organisms of temperate forest ecosystems, particularly coniferous forests.

Heavy-metal ecology of terrestrial plants, microorganisms and invertebrates

Publisher Summary This chapter has attempted to synthesize the available literature on mycorrhizal fungi-host plant adaptation to metal-contaminated soils in order to draw conclusions on the co-evolutionary strategies for the establishment of mycorrhizal associations on contaminated sites. Arbuscular mycorrhizas are discuused in detail, wherein, arbuscular mycorrhiza and metal-contaminated sites, species diversity, spore germination, germ tube growth, hyphal penetration, root colonization, spore production, metal assimilation in plant tissues, plant sensitivity, and nutritional aspects have been described and whether or not plants benefit from being colonized with resistant arbuscular mycorrhizal strains. Ericoid mycorrhizas are discussed and in that topic, the Ericaceae and metal-contaminated environments, copper, zinc, and the role of mycorrhizas in metal resistance of the Ericaceae are explored. Furthermore, the chapter turns to the discussion of ectomycorrhizal fungi, starting with its introduction goes on to discuss about general response of ectomycorrhizal associations to raised levels of metals, genetic adaptation of trees to metal contaminants, intraspecific variation in metal resistance in ectomycorrhizal fungi, studies conducted with hosts colonized with resistant and sensitive strains, and role of ectomycorrhizal fungi in facilitating host metal resistance. Finally the chapter closes with conclusions regarding current state of knowledge and future research requirements.

Co-evolution of Mycorrhizal Symbionts and their Hosts to Metal-contaminated Environments

Although reliable germination of Endogone spores has previously been difficult to achieve, it was possible to obtain greater than 90% yields of germinated E. mosseae Nicolson & Gerdemann spores on distilled water agar. Zinc and manganese, at the concentrations present in many commercially available agars could completely inhibit spore germination. Spores from freshly harvested sporocarps germinated slowly and this was improved by storing the sporocarps at 6° for several weeks. The germination of some spore sources was improved by the addition to the agar of nicotinic acid or thiamine HCl.

G.A. Smith

Papers

Observation's on the germination of Endogone spores