关键词: 优势种群, 天然林, 生态位宽度, 生态位重叠, 生态位相似性比例

Abstract: The study on the representative steppe plant species in Tibet Plateau showed that the density of AM fungi spores in host plant rhizosphere did not correlate with the infection rate of AM fungi.The big changes in air temperature and rainfall at different altitudes played an important role in determining the growth and infection of AM fungi specific to steppe plants, and steppe type and soil texture also had obvious effects on AM fungi's growth and infection.Within a certain range,the spore density increased significantly with increasing soil pH (r=0.5319*,n=20),but showed a declining trend with the improvement of soil organic matter (r=-0.1973,n=20).In contrast,the infection rates of AM fungi to host plants were to some extent negatively and positively correlated with soil pH and soil organic matter,respectively.Phosphorus (P) enrichment in soil environment led to the inhibition of the reproduction and infection of AM fungi.The suitable soil pH,OM and Olsen P contents for the growth and reproduction of AM fungi ranged from 8.0～8.7,3.8～4.8 g·kg^-1 and 7.8～10.1 mg·kg^-1,respectively.Moderate and serious degradation of steppe (especially the serious degradation) had negative or detrimental impacts on the reproduction and infection of AM fungi. Reasonable grazing was helpful to the conservation of critical species of AM fungi.AM fungi also showed a relatively high infection rate on the roots of sedge species such as Carex praecpara,Kobresia humilis and Cyperus compressus.

Key words: Dominant populations, Natural forest, Niche breadth, Niche overlap, Niche similarity