Genetic Diversity And Genetic Divergence Of Cunninghamia L Anceolata Hook Geographical Provenances

Cunninghamia lanceolata Hook is one of the most important merchantable timber species in South China,and it has a history of about 8000 years of deforestation and utilization and more than 2000 years of cultivation.There has always been different opinions and arguments aboutC.lanceolata natural forest existing or not for forestry researchers in China,and heretofore there was no effective and deep research.In addition,there has been controversy over the origin center,shelter and taxonomy ofCunninghamia,especially the taxonomic status of C.konishii and C.unicanaliculatathe problem about the origin center and shelter of C.lanceolataand taxonomy ofCunninghamia also existedcontroversy,especially the argument of the taxonomicstatusofC.konishiiand C.unicanaliculataon treating themas the species varieties or cultivated species.In order to further explore and answer aboved-mentioned questions,in this research,1352 individualsfrom 172 provenances and 185 individualsfrom 177 provenances of C.lanceolata planted before 1955 from Chinese Mainland and Taiwan province were selected using 8 SSR primers and 8 cpDNA fragments respectively to explore the level of genetic diversity and further analyse genetic structure of different geographical provenance and after that we could have definite answers about above questions.The main conclusions were as follows:（1）cpDNA diversity in C.lanceolata was very low（Pi=0.00002 and Hd=0.126）.We found 14 types of cpDNA haplotype,and Hap14 haplotype was shared among 170 individuals from 152 provenances.The lower diversityof C.lanceolata cpDNA was mainly ascribed to the strong conservative of chloroplast genome,and human continually felling and utilizing as well as selectingduring cultivation process were also important causes.（2）Nuclear gene genetic diversity and population genetic structure analysis results based on 8 SSR molecular markers on 172 C.lanceolata geographical provenancesshowed low genetic differentiation degree of different C.lanceolata geographical provenances(F_st was from 0.0085 to 0.0179),significantly lower than that of 20 published species of gymnospermspopulation genetic differentiation(F_st was from 0.027 to 0.280).AMOVA analysis indicated that the genetic variation within geographical provenance population accounted for 98.2%-99.16%of the total variation,only 0.84%-0.84%of the genetic variation among populations,which showed that genetic makeup among different geographical provenance populations has been basically consistent and genetic structure has been no obvious difference.The major reason for leading to low level of genetic differentiation between different geographical provenance groups was the high gene flow（N_mwas 2.689-6.328）.High level of gene flow was driven by large-scale long-distance artificial introduction and cultivation for more than 2000 years rather than nature.Therefore we proposed that forests of C.lanceolatainvestigated were artificial forest,and natural forest ofC.lanceolata had disappeared.（3）Natural forest of C.lanceolata was very wide distributed during Late Pleistoceneand Holoceneafter the analysis of sporopollen fossil and dark wood distribution records.And also,we found that there was C.lanceolatanatural forest distribution in the western Sichuan Basin and south of the Yangtze River Basin and its southern margin 2500-21300 years ago.By the comparison of the geographical distribution of natural C.lanceolata forest during geological history with the modern C.lanceolata region,we found that the modern C.lanceolata planting area distribution range was not beyond the possible natural forest distribution in the history except by the expansion fromto the north of Yangtze river.The expansion to the north is mainly the results of artificial introduction and cultivation activities from the tang dynasty（AD618）.We speculated that,after the Holocene,Yangtze river andits south area and the middle-south edge of western Sichuan basin wereC.lanceolata natural forest distribution area,the reason for this situation may be related to the little effect on the quaternary glaciation of south of Yangtze river and high genetic diversity（average N_A=24.5 and average H_E=0.751）strong adaptability of this species itself.So,we can determined that there were no single origin center or refuge for C.lanceolata.（4）The genetic structureof C.unicanaliculatawas differentfrom other geographical provenance of C.lanceolata.Given that C.lanceolatais endemic to the southwest edge of distribution area,geographic isolationwould reducedgene flow with other populations ofC.lanceolata.Thus,C.unicanaliculata might retain genetic structureof the early natural population.Consequently,it may be more appropriate for C.lanceolata classified as geographical race than as a species.In addition,the genetic evidence suggested that Cunninghamia konishiiarose through the long-distance seeds dispersal.However,there was no obvious difference in genetic diversity and genetic structure between geographical populations of Chinese mainland and C.konishii,so we inferred that C.konishii was likely to be the result of artificial introduction and cultivation across the strait,and it was a typical plantation community.Therefore,it was inappropriatefor C.konishii classified as a cultivar.Based on our molecular evidence,we determined only one species（C.lanceolata）in Cunninghamia.