Studies On Reproductive Ecology And Genetic Differentiation Of The Endangered Species Sinocalycanthus Chinensis

Sinocalycanthus chinensis Cheng et S.Y. Chang, the only representative in the genus Sinocalycanthus in the family Calycanthaceae, is an endangered deciduous shrub endemic to Linan City and Tiantai County in Zhejiang Province. S. chinensis is recorded as the national second class protection plants of China with limited wild resources.In order to provide theoretical basis for the efficient conservation of the populations of S. chinensis, the preliminary studies on the characteristics of flowering phenology, breeding system, morphological variation of fruits and seeds and genetic structure of S. chinensis were conducted and the possible reasons for the endangered status of S. chinensis were discussed.The results show as the fallowings:1,The variation of morphology and quantity of different parts of flowers occurred commonly. Flowering lasts for 7～9 days. Based on the flower morphology and the gender function expression, the flowering course for one flower of S. chinensis could be divided into six periods: Bud stage, Prophase of flowering, Female stage, Bisexual stage, Male stage and Fade stage. The flowering duration of S. chinensis population starts on the first ten days of May and lasts till the last ten days of Jun. The flowering phenology of S. chinensis from three plots is significantly different, while the flowering progress of S. chinensis from three plots show obvious single-peak and marked flowering synchrony. The so-called "Mass-flowering" pattern is founed in S. chinensis. There is significantly negative linear correlation between the blooming day or end day and the number of fruit set or seed set. There is also significantly negative linear correlation between the mid-day and the number of seed set. At individual level, the flowering time takes significant effect on the number of fruit set but no significant effect on the number of seed set. This indicates that resource restriction might play important role in the fecundity of S. chinensis. It is the different altitude that had obvious effect on the reproductive success, nor does the different of microenvironment at the same altitude. As an endangered species, S. chinensis exhibits a so-called "Mass-flowering" pattern, which might contribute to increasing the reproductive success of individuals and formed or remained by nature selection.2,S. chinensis is protogyny with obvious biosexal stage and there is no obvious spatial isolation of male and female organs within the same flower, which would provide certain reproductive guarantee to S. chinensis in the condition of lack efficient pollinators. According to Dafni's criterion and Cruden's criterion, the outing-crossing index and the pollen-ovule ratio of S. chinensis was 3 and 29571±5839, respectively. Furthermore, combined with the results of emasculation, bagging and artificial pollination studies, the characteristics of flowering phenology and the analysis of genetic structure, outcrossing might be the main form of the breeding system of S. chinensis, which might be a mixed-mating system with self-compatibility.3,Based on the data of 12 morphological characters, the fruits and seeds traits in scrub habitat was the best, while that in bamboo grove habitat took the second place and that in evergreen broadleaved forest habitat was the worst. There was certain variation in the morphological characters of fruits and seeds within or among populations of Sinocalycanthus chinensis. The average coefficient of variation among population ranged from 61.71(number of satiation seeds per fruit) to 7.51 (seed thickness), and the characters of seeds was more stable than fruits among the characters studied. Based on the analysis of PCA, 4 populations were divided into 3 groups, Chinese fir forest population and evergreen broadleaved forest population with similar fruit and seed characters were clustered into one group. Bamboo grove population and scrub population were clustered into two group, respectively. The characters of fruit and seed of Sinocalycanthus chinensis had the closest correlation with irradiation conditions and little correlation with th soil factors.4,Genetic diversity of S. chinensis populations in four different habitats, namely, scrub, evergreen broadleaved forest, Chinese fir forest and bamboo grove, were analyzed by random amplified polymorphic DNA (RAPD) technique. 12 random primers were selected and 182 repeatable loci with 49 polymorphic loci were produced from 80 samples. The total average percentage of polymorphic loci was 26.92%. The percentage of polymorphic loci of four populations varies from 6.04% to 11.54% with an average of 8.93%, among which bamboo grove population was the highest and evergreen broadleaved forest population was the lowest with the order as follows: bamboo grove population>scrub population>Chinese fir population>evergreen broadleaved forest population. The results of Shannon index and Nei index were shown in the same trend: scrub population>bamboo grove population>Chinese fir population>evergreen broad-leaved forest population. Analysis of molecular variance (AMOVA) demonstrated that the genetic differentiation among population was high. Variation among populations occupied for 71.91%, while that within populations occupied only for 28.09%. The gene differentiation coefficient among population was 0.6726. The gene flow among population was very low (N_m=0.2970). Clustering analysis showed Chinese fir population and scrub population got together first, then evergreen broadleaf forest population joined in, and the final population was the bamboo grove. It suggested that different population had different genetic diversity, and there were remarkable genetic differentiation among populations. It also suggested that certain degree of inbreeding might took place in S. chinensi.