| Joshua tree is a perennial monocot evergreen Liliaceae Yucca desert plant with long life, resistance to drought and barren, strong anti-jamming capability. If it can be introduced to China’s desertification area, can not only enrich the biodiversity of the area of desertification in China, but also will play a role in promoting the prevention and control of desertification in China. Joshua tree seedlings with different winter modes of wintering performance were studied, and cold resistance performance under low temperature stress. On the other hand, choice the sand habitat with different vegetation types on the southern margin of the horqin, transplant two years Joshua tree seedlings. By measuring the growth and photosynthetic physiological indexes explore the physiological and ecological response mechanism of Joshua tree seedlings to different of habitat, explore the suitable for habitat for Joshua tree in arid and semi-arid sand area in our country, to guide large-scale introduction of Joshua tree theoretical contribution, in order to make the theoretical contribution to the large-scale introduction of Joshua tree. The main results were as follows:1. As the increase of cold injury degree, the membrane permeability, free pro line and soluble sugar content of Joshua tree seedling with different ways of winter increased step by step, SPAD values decrease gradually. The severity of freeze injury of soil covering container seedlings is the most serious, the content of membrane permeability and the free proline and the soluble sugar is respectively74.8698%、3.5583mg/g、174.8864mg/g, the value of SPAD is28.5667, difference compared with the control reached a significant level; using principal component analysis, comprehensively evaluate the performance of Joshua tree seedlings which winter in three ways, effect of cold resistance and winter is best in cellar, understory seedlings and soil covering container seedlings are more serious freezing.2. With the loss of the temperature stress, membrane permeability and the soluble sugar content were significantly increased, when the processing time is24hours and the temperature was minus30℃, the membrane permeability was achieved97.77%, significantly higher than other processing temperature, soluble sugar content of the leaves reach2.6times of room temperature; Free proline content with the inflection point of-20℃showed a trend of decrease after the first rise, And at the same stress of temperature, stress increases with time gradually increased. The change trend of soluble protein content, CAT enzyme activity and chlorophyll were same, decreases with the decreasing of temperature.3. The semilethal low temperature (LT50) of Joshua tree seedlings is-18.92℃,-20℃is a turning point of the cell membrane relative permeability, MDA, free proline, soluble protein and activity of CAT, the physiological activities are limited Below this temperature. 4. From the perspective of the response of morphological structure of habitat, the plant height, ground diameter, leaf number, LMA and root-shoot ratio of the Joshua tree in bare sandy habitat were significantly higher than the other three woodland habitat, Bare sandy habitat is more suitable to Joshua tree growth and development of the habitat. The LMA and root-shoot ratio of Joshua tree in the woodland of Acer mono, were respectively4.74g·cm-2and2.03, the lower LMA make the dry weight of leaf surface area increase, so as to make the ability of dry weight of leaf surface area catching the light to be strengthened, this is the morphological structural adaptability of Joshua tree to weak light habitat of three woodland.5. The dominant environmental factor which affects the Joshua tree is PAR, the direct impact on the Pn of Joshua tree in bare sandy habitat and the woodland of Acer mono and Populuswere woodland is the largest, direct path coefficients were0.981,0.980and0.702respectively. Joshua tree in woodland habitat was sensitive to PAR, and had a higher water use efficiency, Joshua tree in the weak light environment using the limited water and photosynthetic radiation completed the photosynthesis, this is photosynthetic physiological adaptability performance to the low light environment of Joshua tree.6. The "midday depression of photosynthesis" of Joshua tree in the barely sandy habit is caused by the mesophyll cell activity decline of non-stomatal limiting factors. The PAR value of Joshua tree at the time of "midday depression of photosynthesis" and the turning point of Pn fo15:00were very close, which is1200μmol· m-2· s-1, that means it may be the Light saturation point of Joshua tree. |
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