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2000 * * * * * * * * * * * * * * * * * * * * * * *
Title: Biogeochemical characterization of Metalliferous wastes and potential of arbuscular mycorrhizae in their phytoremediation.
Author: T. M. Chaudhry
Institution: & address: School of Science, Food and Horticulture, College of Science, Technology and Environment, University of Western Sydney, Locked Bag 1797, Penrith South, DC NSW 1797, AUSTRALIA
Kothamasi DM (2000). Arbusular muycorrhizal diversity and plant community patterns in the insular tropical rainforest ecosystems of Great Nicobar Biosphere Reserve. Ph.D Thesis. University of Delhi, Delhi 110007, India.
Tropical rainforests are found in all the three tropical lands (South America, Eastern tropics and Africa). These luxuriant species-rich forest formations (biomes) constitute a genetic treasure and harbour 50-90% of the estimated 14-45 million species of the biosphere Mutualism is one of the underlying mechanisms of coexistence contributing to the maintenance of species diversity. Mycorrhizae- the symbiotic association between fungi and plant roots is a mutualistic interaction wherein the phytobiont provides carbon source to the mycobiont which in turn helps the phytobiont in the uptake of nutrients, particularly P. There are two major types of mycorrhizae: (i) the ectomycorrhizae, where the fungus does not penetrate living cells of the host root and (ii) the endomycorrhizae, where the fungal partner penetrates the roots to form characteristic intracellular vesicles and arbuscules. About 80% terrestrial plants belonging to 90% families are mycotrophic with arbuscular mycorrhizal fungi (AMF) belonging to the order Glomales of the class Zygomycetes. The AMF act as a determinant in the regulation of plant community structure by influencing successional trends and are known to form AMF communities which differ in species composition, number and spore abundance.
Great Nicobar is the southern most continental island of the Andaman and Nicobar archipelago in the Bay of Bengal. Being located at 6°N of equator, it has equatorial perhumid climate and supports luxuriant 3-5 storeyed tropical evergreen rainforests with high percentage of endemism. In other words, it is a unique biotope. Consequently, entire geographical area (1045 sq.km) of the island was declared as the Great Nicobar Biosphere Reserve in 1989. The major issue relating to the conservation management plan of the reserve is how to achieve persistence. To answer this question, it is essential to understand the ecosystem processes leading to the development and stability of communities. Except for the general information on the flora and fauna, there is no ecological data on the reserve, particularly relating to the diversity at the community and ecosystem levels.
The present research work was undertaken with the following objectives: (i) to analyse the landscape heterogeneity; (ii) to assess the diversity in plant and AMF communities and (iii) to understand the role of AMF in the development and stability of plant communities and in monitoring biodiversity.
Observations on the landscape heterogeneity suggest that the spatial and temporal variations in weather patterns, photosynthetically active radiation level inside the forest canopies and edaphic factors, particularly the nutrient levels are narrow and hence niche differentiation may not be the mechanism for coexistence of species in species rich communities of the reserve.
The data on the variations in floristic composition and sociological values of the species in different stands indicate that: (i) the 11 communities recognised are floristically and structurally well differentiated and diverged from one another; (ii) the competitive interspecific trade-offs in species traits that acquire and utilize environmental resources particularly nutrients might be involved in the coexistence of species and maintenance of species rich communities.
The results on the diversity in AMF demonstrate that: (i) the taxonomic diversity represented by 54 spore Types belonging to 12 known species and 39 putative new species distributed among 5 genera of 2 families is extraordinarily high; (ii) the AMF form 11 communities that are markedly diverged from one another in kinds of spore Types and spore abundance and (iii) the AMF community diversity appears to regulate the successional trends leading to community development through interspecific trade-offs in species abilities to mycotrophism and growth rates.
The observations on correlative analysis of diversity patterns in plant communities and AMF communities demonstrate that AMF communities and spore abundance, and some obligate mycotrophic dominant plant species can be used as conservation indicators for monitoring biodiversity of the reserve.
Title : Ectomycorrhizal community structure and function in relation to forest residue harvesting and wood ash applications
AUTHOR: Mahmood, Shahid
DEGREE: PH.D.
YEAR: 2000
INSTITUTION: Department of Microbial Ecology, University of Lund, Sweden.
SUMMARY: Ectomycorrhizal fungi form symbiotic associations with tree roots and assist in nutrient-uptake and -cycling in forest ecosystems, thereby constituting a most significant part of the microbial community. The aims of the studies described in this thesis were to evaluate the potential of DNA-based molecular methods in below-ground ectomycorrhizal community studies and to investigate changes in ectomycorrhizal communities on spruce roots in sites with different N deposition, and in sites subjected to harvesting of forest residues or application of wood ash. The ability of selected ectomycorrhizal fungi to mobilise nutrients from wood ash and to colonise root systems in the presence and absence of ash was also studied.
In total 39 ectomycorrhizal species were detected in the experimental forests located in southern Sweden. At each site five to six species colonised around 60% of the root tips. The dominant species, common to the sites, were Tylospora fibrillosa, Thelephora terrestris and Cenococcum geophilum. Differences between two sites with differing levels of N deposition suggested that community structure may be influenced by N deposition, although site history, location and degree of isolation may also influence species composition. Repeated harvesting of forest residues reduced numbers of mycorrhizal roots in the humus layer to approximately 50% of that in control plots but no shift in the ectomycorrhizal community could be detected. At another site, application of granulated wood ash induced a shift in ectomycorrhizal community structure and three ectomycorrhizal fungi ("ash fungi") were found to colonise ash granules.
Two "ash fungi" showed a superior ability to solubilise stabilised wood ash in laboratory experiments compared to other ectomycorrhizal isolates from the same site. In laboratory microcosms containing intact mycorrhizal mycelia, colonisation of wood ash patches by one "ash fungus" was good whereas colonisation by Piloderma croceum was poor. In a competition experiment with these two fungi, colonisation of spruce roots by the "ash fungus" increased significantly in the presence of wood ash, whereas colonisation by P. croceum decreased.
Key words: Ectomycorrhiza, Community structure, Spruce, PCR-RFLP, ITS region, rDNA, N deposition, Forest residue, Wood ash, Tricalcium phosphate, Solubilisation, Calcium oxalate, P uptake, 14C allocation, Wood ash colonisation, Spruce colonisation, Competition
Manjunath, V.G. 2000. Effect of Vesicular arbuscular mycorrhizal species and Phosphorus leveles on growth and yield of Papaya, cv. Sunset Solo. University of Agricultural Sciences, Dharwad- 580 005 Karnataka state, India.
Title : Diversity and dynamics of mycorrhizal associations in tropical rain forests with different disturbance regimes in South Cameroon
AUTHOR: Onguene, N.A.
DEGREE: PH.D.
YEAR: 2000
INSTITUTION: Wageningen University, Subdepartment Soil Quality. The Netherlands
TITLE: Above- and belowground views of ectomycorrhizal fungi in spruce
forests: community structure and impacts of increased nitrogen deposition
AUTHOR: PETER, Martina
DEGREE: PH.D.
YEAR: 2000
INSTITUTION: Institute of Plant Biology, University of Zürich; Swiss
Federal Research Institute WSL, Birmensdorf. Switzerland
Author: TUFFEN, F
Title: Interactions between Earthworms and Arbuscular Mycorrhizas
Degree: PH.D
Advision (major advisor): Dr. Scullion, J.S.
Year: April 2000
Institution: Institute of Biological Sciences
University of Wales
Aberystwyth, Ceredigion, WALES, UK, SY23 1JX
E-mail: fat95@aber.ac.uk
Summary:
Both earthworms and arbuscular mycorrhizal fungi (AMF), which coexist in the rhizosphere of most temperate soils, are known to improve plant growth. Earthworms may affect efficiency of the arbuscular mycorrhizal (AM) symbiosis, but knowledge of earthworm-AM interactions is inadequate to advise the manipulation of these organisms for optimum AM efficiency in agriculture.
The present programme of research investigated a range of earthworm-AM interactions, including effects of disruption of the extraradical AMF mycelium by earthworms on AM response and of redistribution of AMF propagules in cast material on AM establishment. Greenhouse trials involved the AM-responsive host leek (Allium porrum) and either mixed populations of AMF native to soil under organic management, or single AMF species. Most experiments involved Aporrectodea caliginosa, a common endogeic earthworm species; the anecic Lumbricus terrestris was used to a lesser extent.
Earthworms increased significances of relationships between plant growth responses and both intraradical colonisation levels and extraradical AMF hyphal abundance, whilst not directly affecting the colonisation process or mycorrhizal plant growth. Earthworms slightly increased rock phosphate P availability, and interacted with other nutrients to reduce AM response. Earthworm effects on mycorrhizal efficiency therefore appeared to reflect greater availabilities of P and other nutrients.
Greater AMF propagule concentrations in casts than parent soils suggested earthworm feeding selectivity for AMF, but parent soils contained sufficient propagules for optimum colonisation. Colonisation by earthworm-borne AMF propagules was localised to roots associated with burrows, but distributions of cast did not influence root distributions.
Although mechanical severing of AMF hyphae reduced the AM response and 32P transfer between plants, earthworms increased 32P transfer between plants. Therefore any earthworm disruption of hyphal interconnections was outweighed by increased 32P transfer via alternative pathways.
These results suggest that, under certain soil conditions found in low-input agriculture, earthworms may have a positive effect on AM benefit.
Title : Mycorrhizal symbioses of Salix repens - Diversity and functional significance.
AUTHOR: van der Heijden, E.W.
DEGREE: PH.D.
YEAR: 2000
INSTITUTION: Wageningen University, Subdepartment Soil Quality. The Netherlands
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