Reproduction Strategy Of Dendrobium Sinense(Orchidaceae),A Species Endemic To Hainan Island

Under the background of global warming,the adaptation,migration and extinction of plant populations depend largely on the dynamics of populations in their changing environments,and these characteristics are closely related to their resource allocation and reproductive processes.The special geographical environment and climatic conditions of montane cloud forest in Hainan Island have bred the unique species of Dendrobium(Dendrobium Sinense Tang and Wang).This paper adopts the method of population monitoring,the sample-side investigation method and the drying weight method mainly compared the growth conditions of D.Sinense in the six largest populations in Hainan Island and found out the main ecological factors that affected its growing,and established two models to forecast the population dynamic change of D.Sinense by using the field statistic data from 5 years.This paper studies the sexual reproduction regularity,clonal growth characteristics and its effects on the population ecology of D.Sinense,and also studies the reproductive distribution,sexual reproduction and clonal reproduction of D.Sinense.The main findings are as follows:(1)On-site investigation of the habitat conditions of D.Sinense in the wild,such as the Bawangling,Jianfengling,Limushan,Diaoluoshan,Yingeling and Wuzhishan in Hainan Island,and randomly sampled the growth of D.Sinense in each group,using the membership function of fuzzy discriminant to determine the best growth of the individual in the mountain group,the worst is the individual of the D.Sinense in the Jianfengling,the results of the Pearson Correlation analysis show that the rainfall in habitats is the most important environmental factor affecting the growth of D.Sinense.Both present positive correlations(R2=0.880).(2)using the data of individual in population monitored for 5 years,the present situation of the static life table,fertility scale,age vertebra and so on population of D.Sinense population were analyzed,and two population prediction models Leslie matrix model and Lefkovitch matrix model were established.All showed that the population of D.Sinense in the five areas was in a recession,and all predicted that the population would become extinct after 80,and the reason for the decline was that the number of new seedlings was insufficient,At the same time,the extreme adverse climate increased the probability of abnormal death of the individual in D.Sinense.(3)The flowering and fruiting rate of D.Sinense varies with the environment,and the flowering and fruiting rate of the population is very low.There was a negative correlation between seed setting rate and flowering rate,and the sexual reproduction of D.Sinense was restricted by pollinators.The flowering rate of D.Sinense in the upper part of the tree stem was significantly higher than that in the crown,but there was no significant difference in the setting rate of the epiphytic tree.Flowering density did not affect the seed setting rate,but geitonogamy reduced the seed setting rate.(4)The clonal branching strength of D.Sinense increased with the increase of the age of the genet.The scale of the genet will not expand indefinitely,and the growth rate of the genet may be slowed down even by the increase of the age of the individual by the competition among the ramets and resource constraints.The different age of the ramets have their own division of labor,three-year-old ramet responsible for sexual reproduction,two-years-old ramet cycle clone reproduction.In the canopy was significantly higher than that in other epiphytic locations(F=3.323,P=0.04<0.05).From the population number,the clone growth continues the individual life,maintains the population quantity but rarely increases the individual quantity.(5)In the whole life history stage of D.Sinense,the genet need to reach a certain threshold of individual size to carry out sexual reproduction,and the clone characteristics of D.Sinense play a role from the seedling start,according to the proportion of the biomass of the reproductive organs and the total biomass of the individual,the proportion of the resources devoted to reproduction has always been at about 27%,and the clonal reproduction occupies the dominant position of the two breeding ways.Second,clonal growth provides material energy preparation for sexual reproduction and creates multiple growth axes by enhancing branching strength to provide more breeding sites for sexual reproduction.However,there is a competitive relationship between the two modes of reproduction.