Study On Reproductive Ecology Of Cercidiphyllum Japonicum Sieb. Et Zucc. Population

Cercidiphyllum japonicum is a dioecious perennial plant, which mainly distributed in China and Japan. There is much significance at scientific research, gardening and medicine for Cercidiphyllum japonicum. At present, the number of Cercidiphyllum japonicum is rare, and its distribution is dispersed in China. Cercidiphyllum japonicum is one of the relict plants in East Asia, and now has entered into Chinese Second Class Key Protected Species. For analyzing endangering causes of Cercidiphyllum japonicum, providing some theoretical base, and protecting it, some methods were carried out in this study. After investigating natural population in Labahe Natural Reserve and Baoxing County, population structure, dynamics and spatial pattern were studied. Artificial population selected as material in Mao Xian Ecological Research Station, reproductive allocation in module and individual levels, reproductive success of female in different individuals, and distribution and variance of seed size in different individuals were discussed in this paper. Some results are as follows:(1) The population structure of Cercidiphyllum japonicum was investigated in Labahe and Baoxing with the method of space substituting time. The size structure and the static life table were drawn; the curves of survival rate, killing power and mortality rate of Cercidiphyllum japonicum populations in the two areas were given and analyzed. The results showed that seedlings were abundant in both areas, but survival rates were low. The survival rate curve of the population fell between Deevey I and Deevey II types. The trends of the killing power curve and mortality rate curve are consistent. The spectral analysis indicated that there was a periodic regularity in the process of natural regeneration of Cercidiphyllum japonicum. In these two areas the Cercidiphyllum japonicum population was generally clumpy, and the aggregation intensity tended to decrease from sapling to tree.(2) In module level of flowering, there were significant positive correlations between weights of leaves per branch and weights of flowers per branch, and the number of leaves per branch was significantly correlated with the number of flowers per branch. No trade-off between the number of flowers per branch and the weights of flowers per was found. In module level of flowering of fruiting, the weights of fruits per branch significantly correlated with the weights of leaves per branch in female, likewise, a parallel trend was showed between the number of leaves per branch and the number of fruits. There was no trade-off between the number of fruits per branch and mean weight. A similar phenomenon was indicated between the number of seeds per fruit and mean weight.(3) In individual level of flowering, lower resources were invested to reproductive growth in female, moreover, more resources were invested to reproductive in male; There were lower resources allocated to reproductive growth in female than in male. In individual level of fruiting, in female, there were more resources invested to reproductive growth than vegetative growth. In individual level, there was more resource allocation in female than in male.(4) Fruit setting of Cercidiphyllum japonicum was 31.59 %-62.55 %, and DBH didn't affect fruit setting. There were no relationships between DBH and fruit number, mean weight of fruit per branch, mean weight of seed per fruit. However, there was significant positive correlation between DBH and seed number per fruit.(5) The distribution of seed size of Cercidiphyllum japonicum was normal. The seed size was 0.4±0.1 mg, and its variable range is 0.1-1.2 mg. There was evident diversity among different individuals, and its variable range was quite obvious with variance coefficient being 31.8 %. The sources of seed size variance were probable among different individuals.(6) The asexuality of natural population of Cercidiphyllum japonicum reduced its genetic diversity. Few flowering and fruiting individuals influenced its sexual reproduction. Additionally, excess fellings of Cercidiphyllum japonicum individuals by human brought on its reduction. There are all the causes which resulted in the endangered Cercidiphyllum japonicum.