原产地臭椿的分子系统地理学和入侵地臭椿的来源研究 英文标题:Molecular Phylogeography of Ailanthus Altissima in Source Area and the Provenances of Populations in Invasive Area

臭椿(Ailanthus altissima)隶属于苦木科(Simaroubaceae)臭椿属（Ailanthus)，是原产于中国的木本植物。臭椿在中国分布范围很广，南自广东、广西、云南，北至辽宁南部，以长江流域和黄河流域为分布中心。臭椿生长快速，25年能达到15米高，且寿命较短。臭椿的对生存环境的忍耐力和适应力非常强。臭椿能耐寒耐旱耐荫蔽，在微酸性、中性和石灰性土壤中都能适应；臭椿是深根性树种，根系发达，根蘖性强，繁殖容易，落叶量多，具有改良土壤的作用；对烟尘和二氧化硫抗性较强，是城市工业区绿化的重要树种。臭椿在18世纪传入欧洲和北美后，在欧美大陆迅速扩散蔓延，对当地生态环境造成了不小的冲击，成为令保护生物学家和生态学家头疼的入侵种。本研究采用叶绿体DNA(psbA-trnH、trnL-trnF、trnD-trnT)测序对中国臭椿的分子系统地理学和美国的臭椿来源进行研究，并用微卫星分子标记对美国臭椿的来源地进行详细地研究，通过上述方法来研究三个方面：(1)中国的臭椿遗传多样性，中国臭椿的种群历史动态;DNA单倍型的地理分布模式和现今谱系地理格局形成原因；冰期避难所及冰期后迁移路径的推测。(2)美国的臭椿遗传多样性水平，居群遗传结构以及居群内居群间分化差异如何，推测是否经历瓶颈效应和遗传多样性的降低原因。(3)推测美国的臭椿居群在中国的来源地，入侵地和原产地的亲缘关系，以及入侵后的适应性进化。中国的臭椿居群经过一系列的实验得到的主要结果如下：1.遗传多样性分析表明，臭椿种群内单倍型多样性π为0.0331±0.0162，单倍型多样性H为0.8457±0.0391，与其它木本植物相比，具有较高的遗传多样性水平。2.居群的空间遗传结构分析表明：尽管分布在同一地区的臭椿居群间的差异小于分布在不同地区的臭椿居群，然而臭椿居群间的遗传距离和地理距离之间并没有显著的相关性。3.种群历史动态分析(错配分析得到的失配曲线为多峰;Tajima’s D:-0.34456(P>0.10); Fu and Li’s D*test statistic:-0.32484(P>0.10); Fu and Li’s F*test statistic:-0.37459(P>0.10))，表明中国地区的臭椿的进化历史上没有发生明显的扩张。4.DNA单倍型的地理分布模式和现今谱系地理格局分析，12个叶绿体单倍型被分为3个支系，而连续种群扩张和异域片段化隔离是导致现今臭椿居群地理格局形成的原因。5.推测华东和华中地区是臭椿在冰期的避难所，而现今臭椿的地理分布很可能足最后一次冰期退却后形成。冰期后臭椿并没有经历一个快速的扩散过程，而人类活动在一定程度上导致了臭椿远距离的扩散。美国的臭椿居群经过一系列的实验得到的主要结果如下：1.美国的臭椿居群的遗传多样性显著低于其原产地中国的臭椿居群，可能足奠基者效应或遗传瓶颈的影响，也表明了植物具有低的遗传多样性并不影响其的入侵成功。2.错配分析的失配曲线为单峰，表明美国的臭椿居群经历了快速种群扩张，这体现了臭椿近三百年来在美国境内成功入侵，快速扩散。3.cpDNA单倍型和系统发育关系结果显示，美国境内分布最广的一个单倍型是来自中国，而这个单倍型在中国分布也较广。美国还具有两个独特的单倍型这可能与臭椿生活周期短，且具有对环境很强的适应能力有关，在入侵过程中快速进化产生新的基因型。4.美国居群与中国居群的分布比较结果显示，美国境内分布最广的单倍型占据了美国大部分地区，而这个单倍型来自两个源种群地，中国南京和中国安徽。这表明，臭椿是多次入侵，并来自原产地不同的源种群地。5.美国和中国两地臭椿基因组来源分析结果显示，美国居群的基因组组成与其源种群地并不相同，部分基因组的比例增长了。这表明，随着臭椿在美国成功入侵后，向新的地理区引入和扩散，基因组成上的调整来对新的非生物和生物环境条件的适应，产生了对生境条件的进化响应，这有利于植物快速进化调整。

Tree-of-heaven (Ailanthus altissima) belongs to the genus Ailanthus within the family Simaroubaceae, and it is a woody plant native to China. A. altissima has a wide distribution range in China, spanning from Guangdong, Guangxi, and Yunnan in the south to southern Liaoning in the north, with the Yangtze River and Yellow River basins as its core distribution areas. This species grows rapidly, reaching 15 meters in height within 25 years, and has a relatively short lifespan. It exhibits strong environmental tolerance and adaptability: it is cold-resistant, drought-tolerant, and shade-tolerant, and can adapt to slightly acidic, neutral, and calcareous soils. As a deep-rooted tree species with well-developed root systems and strong root sprouting ability, it is easy to propagate, produces large amounts of fallen leaves, and can improve soil quality. It also shows strong resistance to smoke and sulfur dioxide, making it an important tree species for greening in urban industrial zones.

After being introduced to Europe and North America in the 18th century, A. altissima spread rapidly across the two continents, causing considerable impacts on local ecosystems and becoming an invasive species that poses a major headache for conservation biologists and ecologists.

In this study, chloroplast DNA (cpDNA) sequencing (psbA-trnH, trnL-trnF, trnD-trnT) was used to investigate the phylogeography of A. altissima in China and the source of A. altissima populations in the United States, while microsatellite molecular markers were applied to conduct a detailed analysis of the origin of US A. altissima populations. The following three aspects were explored using these methods:
(1) The genetic diversity of Chinese A. altissima populations, the demographic history of these populations, the geographic distribution patterns of DNA haplotypes and the causes of the current phylogeographic structure, as well as the inference of glacial refugia and post-glacial migration routes.
(2) The level of genetic diversity of US A. altissima populations, their population genetic structure, and the differentiation patterns within and among populations, as well as the inference of whether they have experienced bottleneck effects and the causes of reduced genetic diversity.
(3) The inference of the source regions of US A. altissima populations in China, the phylogenetic relationships between invasive and native populations, and adaptive evolution after invasion.

The main results from experiments on Chinese A. altissima populations are as follows:
1. Genetic diversity analysis showed that the haplotype diversity π was 0.0331 ± 0.0162, and the haplotype diversity H was 0.8457 ± 0.0391, indicating a relatively high level of genetic diversity compared to other woody plant species.
2. Analysis of spatial genetic structure revealed that although the genetic differentiation among populations in the same region was lower than that among populations from different regions, there was no significant correlation between genetic distance and geographic distance for A. altissima populations.
3. Analysis of population demographic history (the mismatch distribution curve obtained from mismatch distribution analysis was multi-peaked; Tajima’s D = -0.34456, P > 0.10; Fu and Li’s D* test statistic = -0.32484, P > 0.10; Fu and Li’s F* test statistic = -0.37459, P > 0.10) indicated that no obvious population expansion had occurred during the evolutionary history of A. altissima in China.
4. Analysis of the geographic distribution patterns of DNA haplotypes and the current phylogeographic structure showed that the 12 chloroplast haplotypes were divided into three clades, and continuous population expansion and allopatric fragmentation isolation were the main factors leading to the current geographic structure of A. altissima populations.
5. It was inferred that East and Central China were glacial refugia for A. altissima, and the current geographic distribution of the species most likely formed after the retreat of the Last Glacial Period. A. altissima did not experience rapid dispersal after the glacial period, while human activities have, to some extent, facilitated its long-distance dispersal.

The main results from experiments on US A. altissima populations are as follows:
1. The genetic diversity of US A. altissima populations was significantly lower than that of native Chinese populations, which may be attributed to founder effects or genetic bottlenecks, and this indicates that low genetic diversity does not hinder the successful invasion of plant species.
2. The mismatch distribution curve obtained from mismatch distribution analysis was single-peaked, indicating that US A. altissima populations have experienced rapid population expansion, reflecting the successful invasion and rapid spread of the species over the past 300 years in the United States.
3. The results of cpDNA haplotype and phylogenetic relationship analysis showed that the most widespread haplotype in the United States originated from China, and this haplotype also has a wide distribution in China. The United States also has two unique haplotypes, which may be related to the short life cycle of A. altissima and its strong environmental adaptability, as new genotypes were rapidly evolved during the invasion process.
4. A comparison between US and Chinese A. altissima populations showed that the most widespread haplotype in the United States occupied most regions of the country, and this haplotype originated from two source populations: Nanjing, China and Anhui, China. This indicates that A. altissima invaded the United States multiple times from different source populations in its native range.
5. Analysis of the genomic origins of A. altissima populations from both China and the United States showed that the genomic composition of US populations differed from their source populations, with the proportion of some genomic regions increased. This indicates that after the successful invasion of A. altissima in the United States, adjustments to its genomic composition occurred to adapt to new abiotic and biotic environmental conditions, producing evolutionary responses to habitat conditions that facilitate rapid evolutionary adjustments in the plant.