Seedling Adaptability Of Populations In Pinus Densata And Its Parental Species In Different Niches

P. densata is a homoploid hybrid species between P. tabuliformis and P. yunnanensis, which has already confirmed by genetic methods. It occupies a high altitude niche which parental species are not distributed to, forms a significant geographical isolation with parental species. A large number of studies have shown that habitat differences played a crucial role in the process of sympatric species. However, there were no experiments of three species in transplanted niches for proving the variation of fitness bewteen them untill now. This study revealed the adaptive difference among the three pine species and populations within species on the basis of two-year field trials in transplanted niches, provide a reference for adaptive evolution mechanism of P. densata. The results as follows:(1) Three different test sites were significantly different from the selection intensity, Linzhi had strong selection pressure for the three species, both the three species showed low survival rates; Pingquan had strong selection for P. densata and P. yunnanensis, made their survival rates almost zero. Kunming had the weakest selection pressure for the three species, the survival rates of two-year old seedlings was high for the three species.(2) P. densata was more fit at seedling stage than its parental species in high-altitude habitat, and could evolved into a new species adaptively. Compared with the parental species P. tabuliformis, its outstanding adaptive advantage was the later timing of growth cessation, thus maintained its longer grwoth, and exhibited secondary growth obviously. While compared with the parental species P. yunnanensis, P. densata showed higer germination rate and survival rates.(3) The three pine species showed different fitness in distinct niches. The fitness of P. densata in the habitat of P. tabuliformis was poor, only the ancestral populations could survive. The fitness of P. densata in the habitat of P. yunnanensis was generally high. Parental species had a certain fitness in the habitat of P. densata. P. tabuliformis showed higher values in most of the traits and exhibited high fitness in the habitat of P. densata. The adaptability of P. yunnanensis in high altitude habitats relatively low. The different representative geographic populations of three pines showed difference in adaptability in distinct niches. For instance, the ancestral populations of P. densata was similar to local species P. tabuliformis in adaptability at seedling stage.(4) Temperature, moisture, photoperiod, soil conditions and other environmental factors affected the adaptability of interspecific or intraspecific in distinct niches. The major factors restrict the survive of P. yunnanensis in non-native habitats were low temperature, drought stress and photoperiod. Other than temperature and moisture, soil organic carbon, ground-forst frequence, soil pH and vapor pressure were also restricted the survive of P. densata in the habitat of P. tabuliformis. All of the three species in Kunming showed good adaptability.