Phenotypic Plasticities Of Thellungiella Salsuginea And Allium Przewalskianum

Phenotypic plasticity, a common phenomenon, occurs in both plants and animals, that one species (or genotype) produces different phenotypes in response to environmental changes. Such phenotypic variations are adaptive, maladaptive and neutral plasticity for an individual's fitness. Adaptive plasticity not only can enhance the ability of organism to be adapted to a novel environment, but also can facilitate the innovative evolution of some traits in new environments. Phenotypic plasticity in certain traits can evolve independently from the others. Natural selection can lead to integrative evolution of diverse traits. Most previous studies of phenotypic plasticity have focused on adaptive evolution of single trait; however, little is studies of the integrative evolution of the diverse plastic traits. In this thesis, we studied phenotypic plasticities of Thellungiella salsuginea and Allium przewalskianum.1. T. salsuginea, a salt-tolerant plant, is widely distributed in northern China. Firstly, we examined variations and phenotypic integration in growth and ecophysiological traits of this species in response to salt stress. We found that ecophysiological traits were more plastic than growth traits, indicating that ecophysiological plasticity may allay the need for changes in growth. However, correlation coefficients under the salt stress changed greatly, indicting the integration of phenotypic traits in this species is relatively low. Secondly, we measured the growth and the morphological traits between populations collected from habitats with different temporal environmental variability in terms of salinity. All the populations showed a high degree of phenotypic plasticity in the leaf and root traits. In contrary to the initial expectations, across the spectrum of temporal variances involving habitat salinity, no clear trend was detected for the levels of plasticity of most traits, except the length of the expanded leaf, which showed a negative quadratic relationship with the heterogeneous environment.2. A. przewalskianum, a wild onion species growing at altitudes ranging from 1800 to 4500 m, has long been commonly used as an important vegetable and/or condiment by Tibetans, Indians, and Nepalese in the highlands of the Himalayas and adjacent regions. This species comprises both diploids and tetraploids. Tetraploid has very good adaptability, and can live in the high altitudinal regions with drought and changeful climate in the Tibetan plateau. However, the nutrition content and the variances between two cytotypes of this species have never been reported. In this study, we transplanted the bulbs of this species collected from 29 sites 9 diploids populations and 20 tetraploids in the Tibetan plateau with different altitudinal origins but cultivated in a common garden. We examined the nutritional content and biomass accumulation profiles between two cytotypes. On an average, this species has superior qualities in the minerals and amino acids compared to other edible congeners. When compared with the diploids, the tetraploids grew faster and accumulated more biomass; in addition, the tetraploids had higher values of moisture and energy, higher contents of cystine and P, but lower fiber levels. Moreover, the tetraploids from the higher altitudes had greater biomasses than the other tetraploids, in addition to having increased levels of proteins, fats, and the minerals Mg, Fe, Mn, and Cu. These results illustrate the large phenotypic variations in nutritional efficacy and growth within this single morphological species and provide critical information for its effective consumption in the future.