| 其他摘要 | Water is the most important resourse limiting crop production in arid and semi-arid area. Moreover, seedlings establishment period is one of the critical phase in the life cycle of seed plant. The seedlings are prone to be damaged since they are too young to endure these adverse conditions. The establishment and survival of seedling would be impaired; furtherly crop productivity was lowered greatly. In the practical theory of rain-fed agriculture, there are two significant points to ensure crop productivity: one is the physiological adaptive ability of crops; the other is water uptake ability of root. Therefore, corn seedlings were grown hydroponically, and drought stress simulated by PEG 6000 was imposed on these corn seedlings. The present study was mainly performed from those two aspects: response of corn to water stress during as its seedling stage; hydraulic properties of corn root under different water condition as well as techniques for hydraulic properties measuremens. The major results are as following: 1. During the period of corn seedlings establishment, different parts of young seedlings respond differently to water stress. Coleoptile development of seedlings were greatly impaired by water stress, while the adverse effects of water stress on mesocotyl is the least, compared to the other two parts (Coleoptile and root). It was notice-worthy that root developed better than control under mild water stress or under short duration of sever stress. It indicated that mesocotyl and root growth were ensure priorly, because mesocotyl elongation is the driving force of seedling establishment, and root is the prime organ obtaining water and nutrients. Nevertheless, seedling establishment required longer time underwater stress.2. Water content, osmolates accumulation, reactive oxygen species, membrane lipid peroxidation and oxygen radicals scavenging systems of four parts of corn seedlings were studied. The results showed water content of four parts declined, leaves water content decreased mostly under water stress; the content of proline, solubale sugar and soluble protein in all four parts increased remarkably; ROS accumulated in the four parts with different extent; the content of MDA and relative membrane permeability increased significantly, the increment of them were the greatest in leaves; protective enzyme activity and ROS scavenger content increased to prevent seedlings from the damage of excess ROS. Therefore, corn seedling leaves were the most susceptible to water stress, followed with root system, mesocotyl and stem.3. Corn young seedling stem is not appropriate to connect with RPP because air could not be completely removed from measurement system. Connecting RPP with mesocotyl of corn seedling can solve this problem. However, at least 2 cm mesocotyl is necessary to mount on RPP. Nevertheless, this method could not be used on corn seedlings that are older than three-four leaf stage, because the adventitious root will emerge on mesocotyl and the nodes between shoot and mesocotyl while plants grow. It indicated that hydraulic conductivity of root system of corn seedling could be measured by connecting mesocotyl with RPP. To some extent, it realizes the measurements of corn root system properties in situ, and provides technical promotion for further studying on gramineous plant relations at different levels. 4. Hydraulic conductivity for root systems of hydroponically corn seedlings with normal and drought conditions were measured using root pressure probe, high pressure flow meter, pressure chamber. The result showed drought simulated by PEG 6000 reduced hydraulic conductivity significantly. Moreover, three methods gave comparable results for those root systems of seedlings. Root pressure probe work best with such young seedlings before 2-3 leaf-stage grown hydroponically or grown in pots; the requirements of seedling age during measurements with pressure chamber was not strict, while HPFM can be used for plants at all age in the field 5. The hydraulic conductance, the morphological and physiological parameters of corn root system as well as photosynthetic parameters were investigated. The results showed under normal water condition root water uptake ability increased gradually as seedling aging. However, water stress hampered the increasing of it, and the water uptake ability decreased with duration of water stress. This was resulted from the change of root morphology, physiological metabolism and photosynthesis capacity. With correlation analysis, it is found the decrease of root water uptake ability was mainly resulted from root vigor, root active surface area and fresh weight. On the other hand, the correlation between hydraulic conductance and transpiration rate as well as stomatal conductance were not significant, it might be due to seedling was too young, and growing fast, as well as the measuring root system was exised from shoot.6. Hydraulic properties and solute transport parameters were studied at the level of individual root and whole root system by root pressure probe. It demonstrated water stress decreased root pressure, root hydrdaulic conductivity and solute permeability of whole root system, and the decrease aggravated with duration of wate stress. In general, water stress inhibited parameters mentioned above in whole root system more than individual root. |
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