| The south edge of MU Us Desert belongs to the muti-level transition zone. The ecological environment of this area was fragile and sand dunes moved actively. Hedysarum mongolicum, a kind of leguminous plant, it has some characters such as tolerate infertility, cold, drought and sand wind. It also shows good vitality on semifluid and fluid sand dunes. Currently, Hedysarum mongolicum is one of the best shrubs for desert protection in MU US Desert. This research selected55-year-old,28-year-old and8-year-old Hedysarum mongolicum planted in Jingbian of Shaanxi province, which located on the edge of MU Us Desert. We analyzed19phenotypic characters including natural height, canopy, leaf length and width, first-order lateral branch length,biomass and other indexes. The variation of17phenotypic characters were analyzed by principal component analysis (PCA) and4principal components were found out. The relationship between these17main factors with rhizosphere soil nutritions were also analyzed for investigating of the variations of Hedysarum mongolicum growth in MU Us Desert and its growth evolution trend and the response of adaptation to the arid and semi-arid environment. This research could provide theoretical basis and technical support for Hedysarum mongolicum extention in large area and also provided some reference for the research on biological evolution. This essay also counted and analyzed the species richness of grass vegetation which grew around the communities of different-age Hedysarum mongolicum, and provided theoretical basis for the desertification grassland restoration and management. The mian results were as follows:1. With the increasing of plant age, the phenotype of Hedysarum mongolicum showed mutating, Which indicated that it had phenotypic plasticity One-way ANOVA analysis showed that, except for leaf length and width, first and second-order lateral branch diameter, taproot diameter, other indexes of55-year-old plant were the highest and the ranking always was8-year-old<28-year-old <55-year-old. The major branch weight and second-order lateral branch weight of55-year-old were15times and16times over than8-year-old respectively, but taproot diameter, the leaf length and width were deceasing with the increase of age. Overall bifurcation ratio, Stepwise bifurcation ratio and branch angle between the second-order and the first-order lateral branch of55-year-old were the maximum. Ratio of branch diameter between the First-order lateral branch and mian branch, the second-order lateral branch and the first-order lateral branch of8-year-old was the maximum. Branch angle between the first-order lateral branch and mian branch did not change in different ages.2. The variation of17phenotypic characters was analyzed by principal component analysis (PCA) and four principal components were formed. The first two principal components cumulative contribution rate was78.4%, which summarized the most plant growth information. The characteristic value of first component was9.428, the contribution of natural height, taproot weight, second-order lateral branch weight, total length of second-order lateral branch, crown diameter, main branch weight and first-order lateral length occupied the absolute value was large, they represented the information of length of roots and branches. In the second component, the largest eigenvector was first-order lateral branch diameter and taproot diameter, which both represented the root information. Ranking first and second components, three relatively obvious area were found on the first principal component with increasing of age of Hedysarum mongolicum, which showed that the stability of the plasticity of Hedysarum mongolicum, The distance between55age and28age was smaller than the that distance between28age and8age.3. The relationship between the nine main factors which influence the main phenotypic variation and rhizosphere soil nutrient content showed that the first-order root length, weight and the second-order root length showed significant negative relationship with ammonium nitrogen and the correlation of the first-order root diameter with available phosphorus and total potassium(P<0.05) was also negative.4. Investigating of the grass vegetation which grew around the communities of different-age Hedysarum mongolicum, showed that there were more than20species around the Hedysarum mongolicum group, total biomass was similar between each plot. But species numbers of8-year-old plot were greater than that of28and55-year-old plots. Simpson index,Shannon-Weiner index, Pielou evenness index was less than the latter. These results indicated that the grass vegetation restoration effect was more obvious with the year growth, a certain performance was achieved and the stability of the ecosystem had been secured. The important value of Artemisia scoparia, Potentilla bifurca, Setaria viridis was bigger than other plants, which stated that they occupied an important position in the plant community in MU Us Desert. |
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