Biodiversity Of Arbuscular Mycorrhizal Fungi In Grasslands Of Tibet

Arbuscular mycorrhizal (AM) fungi are important components of terrestrial ecosystems. The symbiosis is of great interest because of its potential influence on ecosystem processes, its role in determining plant diversity in natural communities and the ability of AMF to induce a wide variety of growth responses in coexisting plant species. Tibet is one of the most typical areas of biodiversity in the world. But Tibetan ecosystem is very fragile, that degradation in the grassland becomes more and more severe. The research is focused on the investigation of the species composition and diversity of native AM fungi in different Tibetan grassland styles. The aim is to understand the relationship of distribution of AMF and vegetation styles or environmatal conditions.(1) 50 representative soil samples in the rhizosphere of 32 plant species were collected from different ofTibetan grasslands. Isolation and purification of the mycorrhizal fungi led to the identification of 34 species in seven genus. 16 pure isolates were obtained from the single spore culture. The small spore-type species that the spore diameters were smaller than 150um in Tibet were common. 47% of the species belong to such type in Northern Tibet altiplano lake-basin area.(2) There were a significant difference between species composition and distribution of AMF indifferent kinds of grassland in Tibet. Glomus mosseae was dominant species in grassland of Brahmaputra middle course area, while Acaulospora laevis and Pasipora dominikii in grassland of Northern Tibet altiplano lake-basin area. Species diversity and evenness of AMF in frigid grassland were the highist, while those indexes were the lowest in upland brushy grassland. Shannon-Weiner index, Simpson index and Species evenness index were 2.13, 0.85 and 0.81 of frigid grassland, which were 1.36, 0.65 and 0.65 of upland brushy grassland. Elevation was another important factor of AMF distribution. Acaulospora and Paraglomus were suitable to the extreme environment at 4700-4900 m. Glomus was a kind of broad-spectrum AMF with strong adaptability. Scutellospora had strong adaptability too. Entrophospora only existed 3500-3700 m and Archeospora only at 4400-4600 m. These two genus were narrow-spectrum AMF with weak adaptability. Pasipora only existed in the area which was higher than 4400 m. Community composition of AMF was affected greatly by host plant species. Species richness of AMF associated with Gramineae was the highest in seven dominant plant families in Brahmaputra middle course area, while spore density of AM fungi associated with Cyperaceae was the highest. There was a decline of AMF species with the degradation degree of grasslands: there was 10 species AMF which belonged to 4 genus in normal grassland, while there were only 7 species of 2 genus of AMF in seriously degraded grassland.