| Being an excellent landscape and ornamental species in the world, Acer griseum (Franch.) Pax (Sapindaceae:Acer) is an endangered and endemic to China. It is distributed in Tsinling, Dabashan, Wuling and Zhongtiao mountains, which are located in one of high biodiversity regions in China, and also has experienced many significant geological events. The factors including habitat degradation, reproduction biological characteristics and artificial logging led A. griseum to the endangered state. It is urgent to take effective measures to conserve it’s genetic resources. Based on the analysis of rps16 sequence in cpDNA, phylogeographic study of Acer griseum was conducted on 11 natural populations in addition to the growth performance analysis of the natural populations. It is not only useful to comprehend genetic diversity and genetic structure of natural populations, but also can reveal the influence of the geological structure change and climate change on its geographical distribution pattern and provide theoretical basis for conservation of its genetic resources. The main results of the study are as follows:1. Growth performance of natural populations of A. griseumMost trees in the wild populations were small. According to the maximum value of DBH and ground diameter of each population, the 11 populations were grouped into central, transitional and marginal populations. The central populations were the populations with the maximum DBH larger than 40.00cm, The transitional populations were those populations with the maximum DBH from 28.00cm to 40.00cm, and the maximum ground diameter was 60.00cm. The marginal populations, with the maximum diameter smaller than 20.00 cm and the maximum ground diameter ranging from 24.00 to 44.00cm. In addition, most populations were damaged by human disturbance, resulting in slow-down of tree growth and decrease of population size of A. griseum.2. Haplotype geographical distribution of natural populations in A.griseum.Based on rps16 sequence analysis, a total of eight haplotypes were found in. A.griseum. H-1 was commonly and widely distributed with the maximum frequency, while H-5 was private haplotype only found in Chongqing population. H-1 was the ancient haplotype. Polymorphic haplotypes were concentrated in Chengkou and Neixiang populations, and monomorphic haplotype or less haplotypes were harbored in marginal populations of Zhongtiao and Wuling mountains.3. Genetic diversity Analysis of natural populations in A. griseumHaplotype diversity and nueleotide diversity of A. griseum were Hd= 0.662 and Pi= 0.662, respectively. There were great differences on genetic diversity among 11 populations. The genetic diversity of Dabashan and Qinling mountains were higher than the others and the genetic diversity of CHK was the higheset in 11 populations. High genetic diversity of A. griseum was not the reason leading to its endangered state.4. Genetic structure of natural populations in A. griseumAMOVA analysis results showed that the variance among the population (45.45%) was lower than the variation within the group (54.55%), the variation mainly exists in the community. Gst(0.567) of A.griseum was much lower than the average value of Gst (0.673) of the other angiosperm species. It indicated that relatively lower genetic differentiation existed among the populations. Nst (0.629) was slightly greater than Gst (0.567), which indicated that phylogeographical structure may excited but not distinctly in A griseum.5. History dynamic of A. griseumThe results of mismatch distribution analysis showed that the expansion curve was actually observed with a single peak curve, suggesting that A. griseum had undergone a rapid expansion event. And the above result was further supported by the significantly negative Fu’s Fs of Neutral test. Differentiation time speculated by molecular clock combined Orogeny time analysis, it was speculated that Aer griseum was initially concentrated origined with CHK population as the center of origin. Historically, there had been rapid population expansion, and the marginal distribution groups occurred founder effect. Additionally, mutations happened in the marginalized groups and they habored different haplotypes with those of original center.The significant decrease of genetic diversity and number of haplotypes of TBS and LC populations caused by Quaternary glaciers.The current fragmentatied distribution pattern of A. griseum might have been caused by Himalayan orogeny and theformation of moutains.6. Conservation strategy of genetic resources in A. griseumAccording to analysis of the growth performance, genetic structure and genetic diversity, the conservation strategy of of genetic resources in A. griseum were suggested in the following:(1) In situ conservation was considered primarily to set nature reserves in order to strengthen the protection of its habitat and avoid of the destruction of their original habitat. CHK and NX populations with the highest genetic diversity should be taken as prioritized conservation unit of genetic resources because they totally harhored 7 haplotypes.(2) Introduction and domestication of A. griseum should be strengthened and prioritized conservation populations should be collected to carry out ex situ conservation of genetic resources.(3) Central of China should be considered as prioritized biodiversity conservation unit for subtropical China. |
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