Seed Rain,Soil Seed Bank and Quantitative Dynamics of Seedlings of Emmenopterys henryi Populations in Different Altitude Regions
GUO Lian-Jin, CAO Hao-Wei, XU Wei-Hong, TIAN Yu-Qing, XIAO Zhi-Peng
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Emmenopterys henryi Oliv., the only species of the genus Emmenopterys belonging to the family Rubiaceae, is one of the most rare trees endemic to China. The size of the wild population of E.henryi has been noted to be very small and to be endangered now. In Wuyishan Natural Reserve, the seed rain, seed banks and the dynamics of seedlings of E.henryi were observed continuously. We demonstrated the dynamic processes of natural regeneration of E.henryi populations to find out the most weak stages as well as their impacting factors, and ultimately to provide scientific basis for the recovery of E.henryi populations. Five E.henryi trees were selected and labeled as the research objects in each plot with different altitudes. In the directions of east, west, south and north of every E.henryi tree labeled, five sampling points was arranged, and on each point one 0.5 m×0.5 m×0.2 m collection box was set to estimate the seed rain, nine 0.5 m×0.5 m mini-plots were set to study the dynamic of the soil seed bank, and the seed germination and growth dynamic of seedlings were observed in each plot. The seed rain lasted for about two months, and the maximum intensity of seed rain emerged from the late November to mid of December, which was the peak of seed rain. With the altitude increasing, both of the total seed density and predated seed density were decreased significantly, by contrast, the thousand seed weight and intact seed density were both increased. The seed bank of E.henryi populations was transient soil seed bank. The seed densities on the southern and eastern sides of the mother tree were more than those of other directions, and most of the seeds were distributed in litter and moss layers. In March, the proportion of intact seeds in soil seed bank was only 1.80% of all dispersed seeds and the survival rate of one-year E.henryi seedlings was 6.18%. The loss of seeds in soil seed bank is the main reason resulting in the difficulty of the natural regeneration of E.henryi population. Different ground surface types had a significant effect on the survival of the seedlings, since the mortality rate of seedlings growing in litter and moss layers was 88%, which was significantly higher than that in soil(64%). The litter and moss layers in the forest should be cleared up to release more space for soil and also reduce the coverage of the herbaceous, thus the probability of the seeds to go bad or be destroyed decreased and therefore the radicle of the seedlings could be better reach the soil. The light condition should also be improved, and therefore the natural regeneration of E.henryi population could be improved.