Photosynthesis-related Ecophysiological Characteristics Of Tetraploid Allim Przewalskianum Regel To Adapt To(?)pine Habitats

Polyploidy is a major force of driving plant evolution, even about30%-70%of flowering plants have experienced one or more times polyploidization process in nature. Compared with their dioploid parents, due to the doubling of the gene, the polyploidy plants offen showed differences in the morphological and physiological characteristics, and occupied the different habitats. In order to study the ecophysiological mechanisms of photosynthesis in habitats’ differentiation of polyploid, we used the diploid and tetraploid Allium przewalskianum Regel which distributedin the Qinghai-Tibet Plateau as the test materials. Firstly, in order to study the morphological effects of gene doubling for A. przewalskianum, the growth and phenotypic characteristics of diploid and tetraploidy were measured; Then, the gas exchange parameters of tetraploid and diploid A. przewalskianum under different photosynthetic photon flux density, CO2concentration and temperature treatments were measured with the portable photosynthesis system(Li-6400) to investigate the differences of gas exchange characteristics between different ploidy of A. przewalskianum. Lastly, all the above goals were to clarify the photosynthesis-related ecophysiological characteristics of tetraploid A. przewalskianum to adapt to alpine harsh habitats, and provide a theoretical basis and/or data support for the habitat differentiation of polyploid in nature. The results of this thesis are as follows:(1) The data of morphological characteristics of diploid and tetraploid A. przewalskianum showed that the tetraploid leaf area per plant was significantly higher than its ancestral diploid, while its canopies and height of single plant were lower than its diploid. Therefore, there is no transgressive characteristics of tetraploid plants in phenotypic traits after gene doubling, which main reason may be the tetraploid distributed in high altitude areas of Qinghai-Tibet Plateau and resulted the plant in dwarf. Stomatal data showed that the stomatal sizes of tetraploid plant were greater than its diploid, which could be help to taking in more CO2in the low CO2partial pressure conditions. The volumes of single flower and in florescence of tetraploid plant were greater than its diploid, shown the advantage of gene doubling. However, the flowering length and seed setting rate were on the contrary, which showed there were the trade-offs among some reproductive traits in different ploidy plants.(2) There is no significant difference between the chlorophyll content of diploid and tetraploid plants, but the content of tetraploid flavonoids was higher than its diploid, these changes could help the tetraploid plants adapt to the strong ultraviolet radiation in high-altitude areas of the Qinghai-Tibet Plateau.(3) The response of net photosynthetic rate (Pn) to photosynthetic photon flux density (PAR) had no distinct differences in leaves of diploid and tetraploid A. przewalskianum. It may be because the chlorophyll content had no difference between diploid and tetraploid. Meanwhile, the response of photosynthetic rate (Pn) to intercellular CO2concentration (Ci) in leaves of diploid and tetraploid A.przewalskianum showed that the maximum net photosynthetic rate (Pmax), carboxylation efficiency (Vcmax), electron transport rate (Jmax) and triose phosphate utilization (TPU) of tetraploid plants were higher than its diploid. Then, high carbon dioxide utilization efficiency makes tetraploid plants adapt to the lower partial pressure of CO2. In addition, the responsive curves of photosynthetic rate (Pn) to different temperatures in A. przewalskianum indicated that the leaf gas exchange parameters of tetraploid plants were significantly higher than its diploid both at a specific temperature and in the same temperature fluctuation, then the sensitivity to temperature changes of tetraploid plants was lower than its diploid.In summary, we conclude that the tetraploid A. przewalskianum has obvious advantages both at the morphological and photosynthetic characteristics after gene doubling, which could help it adapt to the low temperature, lower partial pressure of CO2, and large unstable temperature habitats, contributing to its distribution, growth and survival in the high-altitude extreme environments.