The Population Genetic Characteristics Of Stipa Pururea Under Different Grazing Intensity

Livestock grazing is the dominant form of land use in arid region. Grazing not only have consequence on plant community composition、community structure and individual characteristics, but also was considered as one of the key disturbance factors which resulted in grassland degradation, an alteration of community function, influence ecosystem properties and loss of species diversity. Dominant species embodies the physiognomy, structure and the main function characteristics of community. Maintaining the dominant species diversity is important for the restoration of grassland productivity. To investigate the effect of grazing on dominant species of grassland species is also urgent. Stipa purpurea is cross-pollinated plant, and is one the of the dominant species in alpine steppe. By using a set of12ISSR markers,we detecting spatial distribution pattern, genetic diversity level and gene flow of S. purpurea populations in different grazing to reveal the molecular mechanisms.The main findings and conclusions of this research are as follows:Grazing has great influence on the population genetic diversity of S. purpurea. The genetic diversity of No grazing population is higher than the other three grazing population. Through experiments prove, no grazing is beneficial for the maintenance of genetic diversity. For pastureland, grazing at a moderate intensity has a positive effect on the diversity of germplasm resources of S. purpurea.The genetic differentiation coefficient among the S. purpurea population of different grazing intensity was low (Gst=0.2649,Nm=1.3875>1), which showed most genetic variation occurred within population, small partial genetic diversity present among populations and a certain frequency of gene flow existed among populations. This result coincide with the populations’genetic differentiation character of Stipa purpurea as cross pollination plant. The main reason is that high gene flow would reduce the effect of genetic differentiation among populations in different grazing pressure.(Wright and Nei noted that the population genetic differentiation coefficient of self pollinate plant Gst is more than0.5, while Nm is less than1. By using Structure analysis, there was no evident population mixed structure detected among populations.We detected the total of192candidate ISSR loci to test which ISSR loci scored could be subject to selection under different grazing pressure. The result showed that15(7.89%) loci has been affected by grazing,8(4.17%) under very strong selection. It is thus concluded that grazing has a certain degree of selectivity to individual loci.