Sonneratia Plants Distribution Characteristics And Population Development Research Of Sonneratia Hainanensis In Hainan Island

To investigate the distribution of Sonneratia species and endangered mechanisms for Sonneratia hainanensis in Qinglangang mangrove reserve in Hainan island, the community composition and distribution pattern of Sonneratia population were studied, as well as the breeding characteristics of the endangered species, Sonneratia hainanensis.Results concerning the community composition and distribution of Sonneratia population were as follows:Sonneratia plants usually grew on the coast near low-tide line, or extended to inland river and low tidal beach with low salinity. There were rich mangrove species including24true-mangrove and20semi-mangrove in Qinglan mangrove reserve. The forest community was dominated by Bruguiera sexangula and Sonneratia caseolaris. There were six species attributed to Sonneratia, including S. caseolaris, S. alba, S. apetala, S. ovata, S. paracaseolaris and S. hainanensis. There were three endangered Sonneratia species including S. ovata, S. paracaseolaris and S. hainanensis, with small number of individual tree, especially, S. hainanensis with only3individual trees in the fields.Results concerning breeding characteristics of the endangered species, Sonneratia hainanensis, were as follows:(1) Many factors of floral syndrome made an influence on staminode, which was negatively correlated with calyx diameter. Bagging test results showed that Sonneratia hainanensis was a cross-pollinated species without apomixis, which was partially self-compatible and needs pollinators like bat, bee and ants, etc.(2) Impacts of illumination time, temperature and water salinity on seed germination of mangrove tree, Sonneratia hainanensis, were explored through experiments in laboratory. Results showed that the empty grain rate for Sonneratia hainanensis was53.33%. The seeds did not germinate in the dark condition. The preferable temperature for the seed germination ranged from30to40℃with optimum temperature was35℃. Salinity between0and7.5%o was beneficial to germination. At2.5%o the germination rate, potential germination rate and radicle length were81.33%,72.67%and4.23cm. The results of correlation analysis showed that only salinity, respectively, was much negatively correlated with germination rate, potential germination rate and radicle length. Experiment results indicated that seeds were sensitive to water salinity, that low salinity promoted the seeds germinating while high salinity inhibited it.(3) Salinity between0and5%o was beneficial to seedling growth. Lower salinity was good at growth of lateral root while higher resulted in inhibition of root elongation.(4) The germination rate of Sonneratia hainanensis seeds in natural forest conditions was0, and the proportion of seeds eaten by animals was81.5%, with the seed moved18.5%. No seedlings were found near the parent trees through a field investigation. This probably indicates that the period from seed to seedling was a hard-growth time for Sonneratia hainanensis because of many barriers.According to the above results, it can be concluded that in Qinglan mangrove reserve, the forest is dominated by Sonneratia caseolaris and Bruguier sexangula. S. ovata, S. Paracaseolaris and S. hainanensis are all endangered species, especially there are only3individual trees for S. hainanensis in the study area. The reasons result in severe difficulty in natural regeneration for Sonneratia hainanensis are as follows:(1) light deficiency in understory caused inadequate temperature and higher salinity resulted in inhibition of seeds germinating and seedling growth;(2) there are high fruit-dropping rate and a certain number of stamen which degenerate in the flowering stage;(3) high percentage of empty grains contribute to low germination rate;(4) large amount of fruits and seeds were eaten by animals.Some measures can be done to effectively conserve the endangered plant S. hainanensis,(1) artificially cross pollination can be done to improve pollination rates for S. hainanensis;(2) small greenhouse can be built and natural forest conditions can be simulated to make seed germinate;(3) seedling population can be enlarged in greenhouse, and then trees are transplanted to the fields.