Genetic differentiation within and between Leymus chinensis populations from different zones of Mid-Eastern Inner Mongolia steppe
内蒙古中东部不同草原地带羊草种群遗传分化

Randomly amplified polymorphic DNA(RAPD) analysis was applied to five populations(100 individuals altogether)of Leymus chinensis from different steppe zones of Inner Mongolia. The number of DNA bands amplified per primer was 15.7 on average. The number of DNA bands amplified per plant among the five populations decreased with the increase of longitude, and there existed a negative correlation between the number of bands per plant and the longitude. A total of 496 amplified fragments were detected using 31 random primers, among which 489 loci (98.6%) were polymorphic. The genetic diversity of Leymus chinensis was relatively high and the genetic variation existed mainly within the populations (Nei Index and Shannon Index were 85.4% and 72.5% respectively). High intraspecific genetic diversity of Leymus chinensis was the genetic basis for its adaptive ability to various environments, its wide distribution and high tolerance. The genetic diversity level among the five populations varied with their geographic locations that differed in environmental factors such as humidity and temperature. Natural selection pressure might have had an effect on the level of genetic diversity. In terms of proportion of polymorphic loci and genetic diversity of the populations, Keshiketeng population had the highest genetic diversity, followed by Abaga population, and Huolinguole population had the lowest genetic diversity. A strong flow occurred among the populations, with the number of migrants per generation (Nm) being 1.622, which might have prevented Leymus chinensis populations from differentiation due to genetic drift. Similarity and genetic distance matrices were established from the RAPD data on the basis of Nei's estimation methods, and dendrograms were constructed based on UPGMA clustering. The average genetic distance among the five populations was 0.5095, varying from 0.4684 to 0.5476, which indicated that there were relatively high genetic variations and differentiations among the five populations in the study area. There was a significantly positive correlation between genetic differentiation and geographic distance among Leymus chinensis populations. The populations from farther locations were clustered into a group lastly, while the populations with shortest geographic distance were not aggregated in the first group. These results implied that the level of genetic differentiation of Leymus chinensis was related in a large scale to environment gradient, but was affected in a smaller scale by more ecological factors of its habitat.