| Kobresia species distribute mainly in east and south of the Qinghai-Tibet plateau in China. All Kobresia species are perennial herb that most of Kobresia plants are the dominant species in the alpine-meadow. Especially, the five Kobresia plants, including K humilis, K. royleana, Ksetchwanensis, K.tibetica and Kkansuensis, are more extensively to distribute in the Qinghai-Tibet plateau and adapt to sampling in population. Kobresia plants are very important fine pasture and ecological grass in the Qinghai-Tibet plateau . There are a lot of crude protein and fat in them. All livestock are prefer them. In addition, Kobresia meadow is important in retaining the ecological environment of Qinghai-Tibet plateau. In recent years, the problems that Kobresia meadow faced are very prominent and serious. Environmental degradation and decreasing carrying capacity of the Kobresia pastures result both from natural and man-induced impacts. We selected the above five dominant species (K humilis, K. royleana, Ksetchwanensis, Ktibetica and Kkansuensis) to reveal the genetic diversity and genetic structure. The main results are as follows:The genetic diversity of five Kobresia plants, K humilis, K. royleana, Kkansuensis , Ktibetica and Ksetchwanens were collected from eastern of the Qinghai-Tibet plateau in China, were investigated using RAPD markers. In five species, 179-194 loci were identified with 14 oligonucleotide primers, out of which 138-168 loci were polymorphic. The five species all showed high genetic diversity, with values for mean percentage polymorphic loci, PPB 58.06%-71.13%; mean Nei's gene diversity, h 0.1997-0.2521; mean Shannon's Information index I 0.2998-0.3772 at the population level. At the species level, percentage polymorphic loci, PPB was 76.67%-87.70%; Nei's gene diversity, h was 0.2527-0.3106; Shannon's Information index I was 0.3805-0.4628. We found by SPSS analysis that there was no relationship between altitude and genetic diversity in five species ( P=0.217-0.768>0.05, r=-0.783-0.873 ) . The habitats were found to influence genetic diversity of K.humilis and Ksetchwanensis. In five species, AMOVA showed that most of the genetic variability (77.45%-89.06%) resided among individuals within populations, whereas only a minor part (10.94%-22.55%) resided among populations. The Gst-values(0.1066-0.2101) showed the similar result. We concluded that these five Kobresia plants accorded with outcrossing plants. Among the five species, K.royleana (Nm=4.1906,Gst=0.1066) and Kkansuensis (Nm=2.9766,Gst=0.1438)had the greater gene flow and the genetic differentiation was lower. Ksetchwanensis (Nm=1.8801, Gst=0.2101) had the lowest gene flow and the genetic differentiation was the greatest. The gene flow and mating system played a critical role in genetic structure. Additionally, we compared Nei's unbiased genetic distance matrix with a corresponding geographic distance matrix, the two matrices were not significantly correlated (r=0.07999-0.61211, P=0.5575-0.9718>0.05). Furthermore, correlation also did not be found between genetic distance and altitude (r=0.19985-0.52824, P=0.8052-0.9713>0.05).Based on the above results, it may obtain the below conclusions: (1) the Kobresia.humilis, K.royleana , K.kansuensis , Ktibetica and Ksetchwanensis showed high genetic diversity both at species level and populations level; (2) There was no relationship between altitude and genetic diversity in five species;(3) The habitats were found to influence genetic diversity of K.humilis and Ksetchwanensis; (4) In five species, most of the genetic variability resided among individuals within populations, whereas only a minor part resided among populations. we considered that the five Kobresia species should accorde with out-crossing and wind-pollination;(5) The difference of gene-flow and genetic differentiation in five species correlated with floral morphological features and display patterns and so on; (6) There were no correlations between genetic distance and geographic distance, and between genetic distance and altitude.
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