The Study On Reproductive Ecology Of The Endangered Species Euonymus Chloranthoides Yang

Euonymus chloranthoides Yang is an endangered plant species which is endemic to Mt. Jinyun and Dongwenquan of Chongqing with the most favorable habitat in the forest of Sinocalamus affinis (Rendle) Mclure. In this paper, with the help of the field investigation we have rudimental researches on the breeding system and flowering phenology in 2 different habitats, covering the following features, i.e., pollen viability, stigma receptivity, pollen-ovule ratio, out-crossing index, emasculation, bagging and artificial pollination treatments, flowering onset, duration, median, mean flowering amplitude (flowers/plant/day) and end of flowering. We collected fruits and seeds of E. chloranthoides Yang from 7 natural populations to study the morphological differentiation of fruits and seeds among populations. We further analyzed the gray relatedness degree between morphological characters and environmental factors. Based on the above-mentioned studies, we analyzed the factors resulting in the endangering of E. chloranthoides and put forward some procedures for the conservation of the species. The results show as followings:1 The flower of E. chloranthoides is bisexual, opening of the single flower could lasted 4 to 5 days. The pattern of anther's dehiscence is transverse and aclinic. According to its modality and anther's dehiscence characters, we could divide the flowering duration into 5 phases, i.e., Pre-dehiscence (the anther appeared cranny but didn't dehisce), Initial dehiscence ( partial anther dehisced and spilled out pollens), Full dehiscence (All anthers dehisced and spilled out pollens entirely), Telo-dehiscence (A major of pollen had spilled out), Withering period(Almost all pollen spilled out and the anthers faded). And the flowering process was influenced by the temporal climate.2, In 1 to 3 days after its anther crazed, there were above 50% of pollen has viability, the most was 97% of pollen has viability. Six days after the anther crazed, the pollen viability drop down to 1.36%. So its pollen quality is relatively higher and could keep relatively longer. The pollen quality may not the major factor leading to the endangered status of this species.3 Both the flowering morphology dynamics of a single flower and test for stigma receptivity indicate the mature period of stamens earlier than the pistils in this species. Namely, the flower of E. chloranthoides is dichogamy at single flower level. But its pollen viability could keep relatively longer time, and all the mean synchrony of its florescence in 2 different habitats is high. So the expression period of sexual function is overlapped to a certain degree, and it increased the probability of geitonogamy. Therefore, the difference between the expression of sexual function is not the major factor which influences the ratio of seed-setting of the species.4 By means of observation on pollen viability, stigma receptivity, pollen-ovule ratio, out-crossing index, and with emasculation, bagging and artificial pollination treatments, we gained the results as follows: the pollen-ovule ratio of E. chloranthoides is about 764-1340. Based on the Cruden's ( 1977) criterion, the breeding system would be facultative xenogamy; its out-crossing index=3, according to Dafni's(1992) criteria, the breeding system of this species is likely to self-compatible and needs pollinators sometimes during the pollinating process. These two results are coincident. The result of the treatments of emasculated, bagged and without artificial pollination shows that E. chloranthoides does not have apomixes. The fruit set ratio is 13.51% in natural conditions; the fruit set ratio of the flowers with bagged, unemasculated treatments before flowering is as low as 6.25%. The fruit set ratio of the flowers which were bagged, emasculated and with hand cross-pollination treatments is the highest of 78.95%, and theflowers were bagged, emasculated and with hand geitonogamy treatments is 25%. The fruit set ratio of the flowers were emasculated, unbagged and with free pollination treatments is near to the ratio of the flowers which have been emasculated, and bagged with net treatments. Above-mentioned results show that this species may belong to self-compatible type but needs pollinators. The results of above three experiments almost are unanimous. So the breeding system of E. chloranthoides can be determined to be self-compatible and needs pollinators during the pollinating process.5 We could not find steadfast pollinating insects during the whole field observation (July to September). And among the fruit set ratios of the flowers which were emasculated, and bagged with net treatments, emasculated, unbagged and with free pollination, and free pollination in nature are more or less similar, which indicates that the pollination of the species may mostly depend on anemophily.6 There are more overcast and rainy days and less wind during the flowering period of E. chloranthoides. Such climate is disadvantage to anemophily and leads to the drop down of fruit set ratio. In the field, we found that the ripe fruits and seeds are few because of the fade of young fruits and the destruction of some animals to the fruits and seeds. These phenomena result in its ability of zoogamy to decline. It may be one main reason of E. chloranthoides imminent endanger.7 From the flowering phenology curves of the species we can see the total trends of flowering proportion in 2 habitats are all raising gradually, then decreasing gradually along with the flowering data. But there are abortive flowering phenomena from the end of July to the begin of September. The flowering extents are different in different period. It shows that the flowering process of E. chloranthoides is influenced by the temporal climate conditions to large extent.8 According to the study of the flowering phenology at the individual and population levels in E. chloranthoides, we can see that there are some...