Response Of Kobresia Pygmaea Population Under The Disturbance Of Grazing

Kobresia pygmaea is typical cold mesophyte, the Cyperaceae Kobresia perennial herb. It has a very vigorous vegetative propagation, meanwhile, it is able to continue to update propagation to maintain a certain level of productivity in the harsh natural environment and under the strong animals grazed. It is an important material foundation of plateau livestock, moreover, it plays an important role in blocking alpine meadow ecosystem on the further degradation. From the points of view of morphological, physiological and genetic diversity, based on existing research results, using of plant population ecology, plant physiological ecology and plant population genetics method of study, the study discussed the response to K. pygmaea population under different grazing intensities. The results were as follow:(1) With the grazing intensities increased, the height of vegetative shoot and reproductive shoot of K. pygmaea populations decreased. The height of vegetative shoots in the light grazing (LG), moderate grazing (MG), heavy grazing (HG) compared with the control interference (CK) decreased by 16.18%,42.65% and 72.06%, meanwhile, which of reproductive shoots decreased by 18.06%,41.67% and 70.83%. The length of rootstalk of K. pygmaea populations increased significantly, compared with CK, rootstalk length in LG, MG and HG interference increased by 43.00 cm,77.04 cm and 167.78 cm. The density of vegetative shoots of K. pygmaea populations in the LG, MG and HG compared with the CK increased by 8.37%,20.47%和31.86%, and which of reproductive shoots decreased by 7.95%,62.39% and 92.35%. Differences of these data above between CK and LG, MG, HG were highly significant (P<0.01).(2) With the grazing intensities increased, the differentiation rate of reproductive shoots decreased, compared with CK, which in LG, MG and HG interference decreased by 3.96%,24.01% and 38.98%, at the same time, which of vegetative shoots increased. The sexual reproductive effort of K. pygmaea populations decreased, which in the LG, MG and HG compared with the CK decreased by 2.73%,5.49% and 8.64%, meanwhile, the cloning reproductive effort increased, and reproductive pattern of K. pygmaea populations has adjusted. Significant adjustment. Differences of these data above between CK and LG, MG, HG were highly significant (P<0.01).(3) With the grazing intensities increased, the changes of contents of chlorophyll a, b and total chlorophyll were not significant in every growth periods(P>0.05). In addition to the proline content in leaves in a late growth period in decline, in fact the contents of proline and MDA in leaves and roots in every growth period are increasing, and the increasing scopes of proline and MDA in leaves are bigger than that of roots. The activities of SOD, CAT, POD in roots were more marked increase than that of leaves in every growth period of K. pygmaea. These results suggested that leaves of K. pygmaea tolerates grazing stresses by increasing the amount of osmolyte, and roots by defensive enzyme mainly.(4) By using SRAP (Sequence-related Amplified Polymorphism) molecular marks, we lead the K. pygmaea population under research with regard to genetic diversity through the effect of grazing disturbance:Firstly,20 primers were used and produced 448 clear bands in total.376 out of those were polymorphic. The percentage of polymorphic loci was 83.93%. With the increase of grazing intensities, the percentage of polymorphic loci, Nei's genetic diversity index and Shannon information index of K. pygmaea population decreased. Secondly, Total genetic diversity (Ht) of four K. pygmaea populations under different grazing intensities was 0.2766, Genetic diversity within four populations (Hs) was 0.2436, Genetic differentiation coefficient among populations (Gst) was 0.1194, gene flow (Nm*) was 1.8434. Meanwhile, with the increase of grazing intensities, the Gst were increasing, while the gene flow decreased. The result suggested that grazing increased genetic differentiation coefficient among population, restrained the gene communication among the populations and promoted population gene differentiation. Thirdly, genetic distance of 4 K. pygmaea populations on different grazing intensities was small. Yet with the increase of grazing intensities, genetic distance slowly increased, genetic consistency among populations decreased. According to UPGMA dendrogram constructed by genetic distance,4 K. pygmaea populations were gathered progressively with the grazing pressure increasing.Thus, the grazing does affect the modeling components, reproductive allocation, osmotic adjustment and defensive enzyme system, and genetic differentiation of K. pygmaea population. With the grazing intensities increased, the advantages of vegetative reproduction increasingly obvious, biomass allocation of storage organ increased. The contents of proline and MDA, activities of defensive enzyme also will change, while the genetic differentiation is increasing. These reactions not only the response of K. pygmaea population under the disturbance of grazing, but also the basis to adapt to extreme weather of the Tibetan Plateau and maintain the dominance of the population.