Studies On Population Characteristics And Conservation Genetics Of Rhododendron Huadingense, A Rare Species Endemic To China

Rhododendron huadingense B. Y. Ding & Y. Y. Fang ex B. Y. Ding & X. F. Jin (Ericaceae), with great ornamental value, is a rare and remarkable species endemic to China. The individuals of R. huadingense are less than 300 in the type locality, Huading Mountain of Zhejiang Province, and the species was defined as’Small population’of the Enumeration of Rare and Endangered Plants in Zhejiang Province for conservation. Based on the field survey of ten sampled plots in the currently known distribution regions of R. huadingense (Dapan Mountain of Pan’an County: Q1-Q4; Huading Mountain of Tiantai County:Q5 and Q6; Siming Mountain of Yuyao County:Q7 and Q8; Gao’er Township of Pan’an County:Q9; Beishan Mountain of Jinhua County:Q10), the community characteristics, interspecific association and population age/size structure of R. huadingense were analyzed. Two cpDNA genes (trnL-F and atpB-rbcL) and one nrDNA gene (ITS) of 83 individuals from six populations were amplified, and the intraspecific genetic diversity and phylogeography were analyzed as well. The endangered mechanisms of R. huadingense were discussed and the strategy for efficient conservation was proposed. The results were mainly summarized as follows.1. Altitudes of plots--The altitudes of ten plots of Rhododendron huadingense ranged from 808m to 1145m. Among them, the altitudes of the plots Q1-Q4, Q9 and Q10 were all above 1000m, while the altitudes of the plots Q5 and Q6 ranged from 900m to 1000m, and the plots in Q7 and Q8 ranged from 800m to 900m.2. Community characteristics-- Rhododendron huadingense distributes in heterogenous habitats, and the communities showed low similarity between each other, with the similarity coefficient ranging 0.175 to 0.585 (average of 0.333). Due to its close geographical distance, the similarity coefficients between Q2, Q3 and Q4, and Q7 and Q8) were> 0.5, while the others were lower. There were 181 species of vascular plant totally in the ten plots, belonging to 119 genera of 58 families, which presented a trend of diversity. However, R. huadingense was only dominant in Q2, Q3 and Q8.3. Interspecific association-- Among the 507 species pairs (Importance Value> 0.05) in the tree layer and shrub layer in the communities of Rhododendron huadingense,183 pairs showed independent (PC:Percentage Co-occurrence=0) and most PC values of the others were lower than 0.6. Only 25 species pairs showed high associations (AC:Association Coefficient>0.6); The positive-negative ratios of Pearson and Spearman association coefficient ranged from 0.36 to 0.85, while the percentages of significant association ranged from 0.06 to 0.08. The analysis of interspecific association detected that the communities of R. huadingense were under unstable stages.3. Population age/size structure-- There were 451 individuals in 10 plots. The curves of size-classes of Rhododendron huadingense in ten plots showed that all the populations were at different levels of decline. There were lack of seedlings and saplings, while the proportions of mid-class and large-class trees were more than 50%. Meanwhile, the population size structures were fragmentary.4. Intraspecific genetic diversity and phylogeographic characteristics-- Based on the analysis of genetic diversity of Rhododendron huadingense, low levels of haplotypes diversity (Hd=0.4816) and nucleotide diversity (π=0.00024) were showed. Major genetic variation of R. huadingense was confined to within population (98.36%) rather than among populations (1.64%). Genetic differentiation coefficient was 0.0726, which detected the differentiation among populations was not significant and the mating system of R. huadingense was more close to mixed mating (outcrossing as the main way). The gene flow was 3.19, inhibiting diversification caused by genetic shift.In conclusion, there were several reasons promoting the reduction of R. huadingense:the narrow distribution regions especially the strict requirements on elevation, the unstable communities, the declining populations, the poor self-renewal capability and the low level of genetic diversity, etc. According to these status, few recommendations have been made for effective protective measures:(1) to establish nature reserves/plots in the concentrated distribution regions and carry out artificial assisted updation of seedlings; (2) transplant between different distribution regions to stimulate the genetic diversity and conduct artificial breeding reasonably.