Studies On Population Ecology And Genetic Diversity Of Heptacodium Miconioides

This paper focuses on Heptacodium miconioides, a rare and engangered endemic plant of China. The communities structure, species diversity, population size-classes structure, distributional pattern, genetic diversity of its populations and genetic relationship among some species of Caprifoliaceae were studied, which are the scientific basis for the efficient conservation of H. miconioides. The main results are as follows:The average dominance values of H. miconioides were 20.38%, and it was the upper dominant species of the community. In the vertical structure of community, the various indexes of diversity between the tree layer and the shrub layer have slight differences. The species richness and species diversity index of the tree layer and shrub layer are obviously bigger than those of the herb layer. The species diversity decreased form shrub layer, tree layer to herb layer in the most pattern, and the herb layer diversity had close correlation with the crown cover. The habitat conditions which were changed for the external disturbance led the species diversity to increase. The result showed that there were obviously differences of the characters among the communities by the influence, such as the habitats and people disturbances.The diameter structure of different populations had only one type, spindle-like form structure: infant seeding and big tree were thimbleful, which indicated its population recession trend, combining with high death rate of seeding and sapling. Population pattern of H. miconioides turns out to be manifestly contagious distribution. At the small sampling scale (1 m , 2 m or 4m2), the contagious degree is higher than other scales. With the extent of the sampling scale, the degree of contagition gets fewer and fewer until the sampling scale 8 m or 16 m . With the increase of age and difference of development phases, the distribution pattern usually ranged from clump to random, and different size of blocks had been found to have an effect on the spatial patterns.To estimate genetic variation and distribution within and between populations, nine populations distributed throughout its main range (Zhejiang Province, China) were analysed using Random Amplified Polymorphic DNA (RAPD) markers. Twenty-one random primers screened with 50 ones yielded 119 RAPD bands, 72 of which (60.50%) were polymorphic. Calculations of Shannon index, Nei's gene diversity, and AMOVA all consistently indicated that Tiantai Mtountain(Mt) population possessed the greatest genetic diversity, followed in order by the Changhua County, Dapan Mt.-l, Dongbai Mt.-l, Bei Mt, Dapan Mt.-2, Dongbai Mt.-2, Siming Mt., and Kuocang Mt.population was the lowest one. Percentages of genetic diversity among populations by Shannon index were 77.39% based on phenotype frequencies and 76.65% on gene frequencies,respectively. Nei's gene diversity coefficient (Gst) was 0.7610. AMOVA also demonstrated that these relict populations were highly differentiated (PHIst=0.7189, PO.001). The dendrogram constructed from genetic distances through UPGMA method showed that 9 populations clustered into two groups. The results above all indicated that genetic variation was partitioned mainly among rather than within populations. High level of population variation indicated that there might be a degree of inbreeding which were in agreement with the previous studies. The analysis showed its biological character, founder and bottleneck effect were main reasons of high level of genetic variation among populations. fProvided that the phenon line of tribal demarcation was drawn at the level of 0.36, ten-eight species of Caprifoliaceae could be roughly divided into five groups, which was similar to the results of Fukuoka N and Xu B S obtained from studies on morphology. Ten species from Viburnum Linn, clustered into one group, which indicated the similarity of these species as one same genera at the genetic level. When we classified the group continuously in lower level of similarity, the classified result was puzzling and irregular, and had many differences with the current taxonomic results on morphology. The fact that the highest degree of correlation between Group II Viburneae and Group III Sambuceae supported well some former researches, so it was reasonable to separate these two genera from Caprifoliaceae and to establish a new family.