高山松及其亲本种群在油松生境下的苗期性状

Seedling performance of Pinus densata and its parental population in the habitat of P. tab- uliformis

高山松(Pinus densata)是油松(P.tabuliformis)和云南松(P.yunnanensis)的天然二倍体杂交种,是为数不多的与亲本种没有严格生殖隔离的同倍体杂交种。为了检测3个种在油松生境下的苗期适应性和生长发育特点,为高山松成种机制提供数据,选取了代表高山松及其亲本种遗传多样性的25个种群,在油松生境下对比分析了苗期11个适应性指标和3个生长发育指标。结果表明,大部分适应性指标和生长发育指标在种间和种内群体间差异显著,主要变异存在于种间及种内群体间;出苗率、2011年11月和2012年10月的封顶率、二年生苗在2012年10月的保存率等指标的种间方差分量较大,种内变异较小,是体现种间苗期适应性和生长发育状况的重要指标。油松在大部分适应性指标和3个生长发育指标上均表现最好,总体适合度高于云南松和高山松;云南松在封顶率和保存率上都居于最低值,大部分一年生苗木到11月底仍未出现封顶现象且黄苗比例最高,二年生苗的存活率为0,表明云南松在油松生境下适合度最低;高山松除了在紫苗比例上表现出超亲优势外,大部分性状居于亲本种之间。此外,位于青藏高原东北部的高山松祖先种群在适应性上表现较好,具有在油松生境下发展的潜力;而位于青藏高原西部的高山松种群及东南部的康定种群对油松生境的适应性较差。研究揭示出生态选择在高山松的同倍性杂交物种形成中起到了关键作用。

Aims Pinus densata is the natural diploid hybrid of P. tabuliformis and P. yunnanensis, and is one of a few known examples of homoploid hybrid speciation. In order to describe the adaptive and growth characteristics among the three pine species at seedling stage and clarify the role of ecological selection in interspecific isolation between hybrid and parental species, we conducted a common garden comparative analysis of fitness traits at seedling stage in this species complex. Methods We investigated 14 adaptive and growth characters in seedlings from 25 representative populations of the three pine species in a typical habit of P. tabuliformis. The 14 traits are germination rate, seedling survival in Aug., Sept. and Nov. 2011, winter survival rate of one-year old seedlings, seedling survival rate in Oct. 2012, rates of bud-set in Nov. 2011 and Oct. 2012, the proportion of yellow, green and purple seedlings, seedling height, ground diameter and crown height of seedlings. Patterns of the variation of these characters were analyzed using multi-factor nested analysis of variance and correlated to geographical factors of each population. Important findings Most of the traits were significantly differentiated among species and among populations at seedling stage, and the large amount of variance were partitioned among species or among populations. Germina-tion rate, the rates of bud-set in two years, and the survival rate in Oct. 2012 of two-year old seedlings were the best indicators of among-species divergence. P. tabuliformis showed the highest values in most of the traits and appeared as more fit in its native habits than the other two pines. P. yunnanensis was at disadvantage in several critical traits, e.g. the survival rates of Aug., Sept., Nov. 2011 and rates of bud-set in two years. Most of one-year old seedlings of P. yunnanensis have not bud-set at the end of Nov. and the proportion of yellow seedlings were highest and its survival rate in Oct. 2012 was zero, which illustrates its low fitness in P. tabuliformis habitat. The hybrid pine, P. densata was intermediate between the parental species in most of traits except indice of the propor-tion of purple seedlings. The populations from the ancestry hybrid zone in the northeast of P. densata range coped with the test site environment better than the populations from the western range. Our study highlights the role of ecological selection in speciation of this homoploid hybrid pine.