| Seriphidium transiliense belongs to Compositae Seriphidium and grows in Russia and Xinjiang in China mianland, which has an obvious characteristic of xeromorphic structure and a good feed value in arid grassland in Xinjiang. Recently, the S. transiliense desert grassland taking the S. transiliense as constructive species formed different intensities of grazing land and showed obvious degradation due to long-time grazing. Meanwhile, the grassland plants also formed respective adaption mechanism to reduce the damage to them from grazing. Grassland plants’ adaptation to grazing not only reflects in phenotypic plasticity, but also closely relates to genetics. In this paper, S. transiliense of northern slope of Tianshan Mountains in Xinjiang were chosen as research objects. Responding mechanism of S. transiliense to grazing was discussed by studying on individual plant morphological characteristics anatomic structure of leaves and genetic diversities under molecular levels under different grazing intensities(no grazing, light grazing, moderate grazing and heavy grazing). The main conclusions were listed as follows:(1) Plant heights, crown widths, short axis lengths, long axial lengths, root diameters, stem dry weight, above-ground biomass decreased under grazing. Grazing showed significant negative correlation with plant height, crown widths, short axis length, long axial length, root length, root diameter, the first grade branch, the secondary branch, the third grade branch. Mean coefficient of variation range was 20.26%–134.24%.(2)Blade thickness, blade widths, main vein thicknesses, cutin thicknesses of upper epidermal cells, cutin thicknesses of lower epidermal cells, thicknesses of palisade tissue of upper epidermis, thicknesses of palisade tissue of lower epidermis, main vein vascular bundle diameters, lateral vein vascular bundle diameters of S. transiliense decreased under grazing, decline of 10.41%-34.59%; Variation coefficients and correlation analysis indicated that blade thicknesses, blade widths, main vein thicknesses, cutin thicknesses of upper epidermal cells, palisade tissue, lateral vein vascular bundle diameters were sensitive to grazing. Scanning electron microscopy showed that compared with the control, arachnoid tomentum of S. transiliense leaf epidermis increased elongately, ridges at outer wall of leaf epidermis became irregular and strip pattern varied in length and distributed not evenly after grazing and gaps between bumps under heavy grazing were deeper than these under light or medium grazing.(3)The results showed that optimum 20μl SRAP-PCR reaction system of S. transiliense was 1.0mmol/L Mg2+, 0.3 mmol/L dNTP, 0.75 UTaq DNA polymerase, 0.45 μmol/L primer and 30 ng DNA. 19 pairs of highly polymorphic primers which had good repeatability were selected from 400 pairs of random primers for SRAP amplification, 195 clear bands had emerged, of which 171 were pleomorphic, accounting for 87.69%. Contrust with no grazing(CK) population, population Nei’s genetic diversity index and Shannon information index decreased under grazing and these values were the lowest under the moderate grazing(MG) population. The total genetic diversity(Ht) among S. transiliense populations under 4 grazing intensities was 0.2528, genetic diversity within populations(Hs) was 0.2201, genetic differentiation(Gst) among S. transiliense populations under 4 grazing intensities was 0.1040, which suggested that 10.40 percent of the total gene diversity in the S. transiliense’s population belonged to genetic differences of materials among populations. Majority(89.60%) of genetic variation came from individuals within populations. And gene flow(Nm) was 11.3715, which suggested that there were gene exchanges among populations. UPGMA cluster constructed by genetic distance demonstrated that light grazing group and over grazing group were clustered into one group first, then middle grazing group were clustered into one group with the new groups, finally the two new groups were clustered together. |
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