太白红杉自然居群遗传多样性和遗传结构的研究

【作者】 赵利锋；

【导师】 赵桂仿；

【作者基本信息】 西北大学 ， 植物学， 2001， 硕士

【摘要】 太白红杉（Larix chinesis Beissn）为松科落叶松属的多年生木本植物，仅分布于秦岭山地海拔2800-3500m的山脊上，分布极其有限。现已被列为国家二级保护植物。太白红杉是秦岭森林最上线的唯一落叶针叶林树种和重要的水源涵养林，同时对保护高山地带水土流失、稳固山石、改善生态环境也有重要作用。另一方面，太白红杉的材质尚佳，是高山造林的优良树种，特别是它所生长的是其它树种不能生存的地方，更加显示出它在自然界中的作用和意义。因此，无论从自然物种的保存、科学研究，还是从生态效益和经济意义等各个方面，太白红杉都有重要的保护价值。本文以等位酶作为结构基因的分子标记，分析和检测太白红杉的居群遗传结构和遗传多样性，其结果可为预测太白红杉的遗传学命运，探讨致濒的可能原因，制定相应的保护对策提供有益的参考。 通过应用过氧化物酶、超氧化物歧化酶、苹果酸脱氢酶、莽草酸脱氢酶、谷氨酸脱氢酶、过氧化氢酶、苹果酸酶、淀粉酶等8种酶系统共编码15个基因位点，对太白红杉6个居群共120个个体进行等位酶分析，结果表明：多态位点的比率为66.7%，平均每个位点的等位基因数 A=1.7，平均每个位点的等位基因的有效数Ae=1.6。Shannon多样性指数为0.46。每个位点的平均观测杂合度Ho=0.33，每个位点的期望杂合度He=0.32。按照平均期望杂合度，6个居群遗传变异性的大致次序是太白山居群>光头山居群>玉皇山居群>牛背梁居群>朱雀居群>佛坪居群。F-统计分析显示，太白红杉居群总的固定指数FIT为-0.03；居群内的固定指数FIS为-0.07；居群间的固定指数FST为3.32%，即大约有96.68％的遗传变异存在于居群内，仅约有3.32％的遗传变异存在于居群间，说明居群间有很少遗传分化发生，这与太白红杉是一种风媒异花传粉植物相一致。基于FST，间接估计基因流（Nm）值约为7.3。Nm＞1，说明基因流足以抵制遗传漂变的作用，也同时防止了居群分化的发生。Nei（1978）的遗传距离和遗传一致度分析表明，太白红杉居群间的遗传一致度（I）很高，平均为0.99（变化范围：0.9510～1.00），遗传距离（D）平均值为0.01（变化范围：-0.0011～0.050），再次说明太白红杉居群间有很高的遗传相似性。利用Nei（1998）遗传距离，采用UPGMA法聚类分析，6个居群明显地被分为两支：佛坪居群和朱雀居群聚为一支，显示了两居群间有较高的相似性；其它4个居群聚成了另一个分支，其中，太白山居群与玉皇山居群在一级水平上聚在一起，太白山、玉皇山、光头山3个居群在二级水平上聚为一支，显示了它们之间具有较高的相似性；牛背梁居群具有相对的独立性。<WP=5>固定指数F值变化幅度较大，从-0.20 到-0.01，居群间平均约为-0.07。F值大多数是负值，与期望的随机交配相比，显示出居群有过多的杂合体，这可能与太白红杉以异交为主的繁殖方式有关。远交率t=1.1。t＞1，说明个体所接受来自各种基因型的花粉是随机的，暗示着太白红杉很可能是自交不亲和的。根据以上等位酶分析结果，与其它落叶松树植物相比较，太白红杉处于中等的遗传多样性水平。但是，太白红杉属于分布范围极其有限的珍稀濒危物种，已被列为国家二级保护植物。太白红杉分布范围狭窄的主要原因可能是其对秦岭高海拔生境的高度适应性。根据我们采样时的观察，自然状态下太白红杉的繁殖率很低，其自身也可能存在有性生殖障碍或衰退；此外，太白红杉在秦岭仅分布在为数不多的几个高海拔山头上，岛屿状间断的空间分布型式导致居群间的生殖隔离，小种群效应可能引起小的有效居群大小、遗传漂变效应以及近交衰退等等，进而导致遗传多样性水平降低，使太白红杉居群面临濒危的威胁。 在太白红杉的保护中应着重加强对太白山居群的就地保护。太白红杉林带一旦遭受破坏，就难以恢复更新，故做为一个群落类型应该妥加保护，禁止任意采伐。更多还原

【Abstract】 Larix Chinensis Beissn, the perennial and ligneous plant species, belongs to genus Larix mill and distributes only on the peak of Mt. Qinling with the limited altitude 2800-3500m, and it had been listed as second grade plant species of state in need of conservation. L. Chinensis, as the only deciduous and coniferous forest and important water-nurturing forest located on the top of other forest in Mt. Qinling, has important conservative and research value on the respect of species conservation, scientific research, ecology and economy. In the past, because the studies were limited in the area of surveying and morphological describing, and few researches were carried on conservative genetics, scientists knew very little about genetic structure and genetic diversity in natural populations of L. chinesis. This paper, using allozyme as the molecular mark, mainly deals with genetic structure and genetic diversity in natural populations of L. chinesis, foresee its genetic destiny and research its probably endemic reason, with the aim at providing beneficial reference for the protect of L. chinesis.Using 8 enzymes (Peroxidase, Superoxide dismutase, Malate dehydrogenase, Shikimate dehydrogenase, Glutamate dehydrogenase, Catalas, Malic enzyme, Amy) which result in 15 gene loci, 120 individuals from 6 populations were analyzed with allozyme, and the results indicate that percentage of polymorphic loci(P) is 66.7%; mean number of alleles per locus(A) is 1.71 (<WP=7> vary from 1.67 to 1.73 with population ) ; effective number of allele per locus, (Ae) is 1.63（range 1.47～1.68 ）；Shaanon index is 0.46(range 0.39 ～ 0.48); mean expected heterozygosity per locus (He) is 0.32（0.28 ～ 0.34）; mean observed heterozygosity per locus (Ho) is 0.3322( 0.32～0.34）. According to mean expected heterozygosity per locus, the sequence of genetic variation of six population is Taibaishan population > Guangtoushan population > Yuhuanshan population > Niubeiliang population > Zhuque population > Foping population. FIT= -0.03 (total population), FIS= -0.07 (in population), ratios of gene diversities of heterozygosities FST=3.32%(among population)，it is, approximately 96.8％genetic variability exists within populations and only about 3.32％ genetic variability lies among populations. They show that only a little genetic differentiation was found among population which correspond to wind-pollinate, outcrossing species of L. Chinesis. Based on FST , mean gene flow Nm is about 7. 3. Nm>1, it is enough to resist the effect of genetic drift and prevent population from subdivision. Analysis of Nei（1978）genetic identity and genetic distance show that genetic identity（I）among population of L. Chinesis is very high with a mean of 0.99（0.95～1.00）, and mean genetic distance (D) is 0.01（0.00～0.05）. Again, they show that high genetic similarity was found among population of L. ChinesisDendrogram resulting from UPGMA method clustering based on Nei （1978）genetic distance shows that the six population are divided into two branch: Foping and Zhuque population cluster into one branch showing the two population has high similarity. Other populations cluster into the other branch, of which, Taibaishan and Yuhuangshan population cluster on the first grade, Taibaishan, Yuhuangshan and Guangtoushan populations cluster on the second grade showing high similarity among them; Niubeiliang population is somewhat independent. <WP=8>Fixation indices (F value) change widely from -0.20to -0.01 with a mean of --0.07. For most of F values are negative, it means population was heterozygote excess compared to expected random mating, and this may be in relation with main reproductive mode of outcrossing in L. Chinesis. Outcrossing rate (t) is 1.1, more than 1, indicating that individual receiving different genotype pollen is randomly and imply that L. Chinesis may be self-incompatible. Based on the results of allozyme above and compared with other Larix species, L. chinesis is on the middle genetic diversity level. However, L. Chinesis belong更多还原