| Magnolia wufengensis is a new Magnoliaceae species found and nominated by Luyi Ma, Because the narrowness of its dispersal area, the scarcity of its individuals, M.wufengensis now is extremely endangered. This species has high ornamental value and scientific value, it has a broad application prospect as greening tree in urban and mountain area. In order to provide theoretical basis for its germplasm conservation, the breeding, introduction and cultivation, the promotion of its use, the researches on its floral traits, flower bud differentiation, development process, and drought resistance, were carried on in this paper,.Firstly, we make continuous observation and analysis of 12 floral traits of M. wufengensis, and selected individuals of different characteristics with the methods of correlation analysis, principal component analysis and cluster analysis; secondly, we make cytological observations of large and small microsporogenesis, female and male gametophyte in its sexual reproduction process through conventional paraffin section method. To study its drought resistance,1-year-old Magnolia wufengensis seedlings were potted under four different soil water content levels: optimal water content (CK), mild drought stress(T1), moderate drought stress(T2) and severe drought stress(T3).The main results are as follows:(1)the analysis of 12 floral traits indicated that Floral traits has a rich genetic variation; and flower with 12 petal has highest frequency in its populations. Cluster analysis shows that there is large difference between individuals, so that individuals within the same population clustered into different categories, there is a rich genetic variation within populations; cluster analysis among the populations shows that the diversity of floral traits growed up in Liziping and Gaofeng is in the same level with low genetic diversity among populations. Floral traits of M. wufengensis have 5 main components, the number of petals has the greatest contribution, reaching 42.91%. Correlation analysis of 12 floral traits shows that there is large interaction between different characters, the diversity of floral morphology and quantitative traits may be related to the long-term co-evolution of pollinating insects.(2)Considering the types of fine individual, there is fewer resource of M. wufengensis in Luokuangyan, the number of petals have various mutation types; The flower of M. wufengensis growed in Huangliangping have rich color, type, size and shape, the number of petals is stable; M. wufengensis growed in Liziping is rich of the number, color and shape of flower, in particular, the variation in the number of tepals is obvious; M. wufengensis growed in Gaofeng have rich variation on their color and size of flower. Cluster analysis on floral traits of 50 fine individuals in four populations indicates that M. wufengensis has rich variation within populations; principal component analysis revealed that the first three main components were the shape of flower, the size of perianth,and the color of petals, the result of cluster analysis and principal component analysis is the same as the result of research on diversity of floral traits.In the long-term process of growth and evolution, M. wufengensis has developed different adaptation mechanisms to adapt different environments, result in different variation from individual to populations.(3)The cytological observation of the process of large and small spores occurred and male and female gametophyte development of M. wufengensis shows that:This process is normal and not the reason of the endangerment of M. wufengensis, the real reasons for its endangement need further study.(4) Drought stress has a inhibitive influence on its photosynthesis, with drought stress became more and more serious, the heights, base diameters, biomass, Pn, Gs and Tr of the seedlings decreased significantly; Chla,chlb and chl content increased in treatment of T1, decreased in treatment of T2 and T3; Ci, Ls and the WUE kept stable, they are increasing slightly under low drought stress and then decreasing under high drought stress, but the root and the rhizome grew more than the above ground part, leading to higher root/shoot ratio. Parameters of osmolyte, lipid peroxidation and enzymes of seedlings showed great differences with different water supply leavel,. when drought stress became more and more serious, the RWC of seedlings' leaves decreased, the contents of soluble protein, MDA and Proline accumulated and increased. In the same level, as the time of drought stress became longer and longer, the RWC in seedlings'leaves decreased, Proline increased obviously, the variation trend in SOD, POD, CAT and APX activity was increase at first and then decreased. We can concluded that the growth of M. wufengensis seedlings were negatively influenced by different degree of drought stress, but they could adapt to diverse water stress through plastic responses in morphology and photosynthesis, which proves that M. wufengensis has the tolerant ability of drought conditions. so it is a new urban tree for forestation in water shortage city. |
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