| Water and salt distribution of shallow soil were the main affecting factors of seedling growth. Taking soil columns planted with Tamarix chinensis Lour (3-year-old), a constructive species in the Yellow River Delta as the research object, we aimed at studying how the diving water level (DWL) affects the water and salt distribution. First, planting the Tamarix chinensis Lour soil column in the greenhouse, configuring the salt water which mineralization degree is 3 grams per liter with sea salt. And then setting up 6 kinds of diving water level which deeps respectively are 0.3m,0.6m,0.9m, 1.2m,1.5m and 1.8 m,and each processing settings 3 repeat. In the use of drying method and residue drying method, the relative water content(RWC), salt content, absolute concentration and eight soil salt ions at soil depths of 0-20 cm in a simulated device with DWL of 0.3m,0.6m,0.9m, 1.2m, 1.5m and 1.8m were measured. The study provided an important water level parameters for the planting and management of Tamarix chinensis, It is important for the improvement of saline alkali soil.The results showed that : 1 .Under the condition that the groundwater is brackish water,the maximum water level of soil water and salt can rise to the surface is 1.2m through capillary suction and atmospheric evaporation. Both the high soil salt content and the lack of soil moisture can affect plant growth, Therefore, according to the depth of different plant roots,choose the appropriate level of water to ensure the normal growth and development of plants.2. The soil cation content of Tamarix chinensis was Na+>Ca2+>Mg2+>K+at the phreatic water level 0.3-1.8m.There was a significant correlation between the total salt content and Na+?Ca2+ and Mg2+under the level of 0.05 of different phreatic water levels and have no significant correlation with K+. There was a significant difference in the total salt content and cation in soil, which were influenced by Na+ and Mg2+.The law of anion in 0.3m is Cl- >SO42->NO3->HCO3-,and show Cl->SO42->HCO3->NO3- at 0.6m-1.2m, but have no significant difference in 1.5-1.8m. Cl- and SO42- were the main anions in the salt ions in the experimental area. The ratio of Cl- and SO42- in the soil of Tamarix chinensis was higher than that of control group, and the ratio of Cl- and SO42- decreased with the increase of phreatic water level. Compared with the control group, the soil of Tamarix chinensis had a trend of desalination under different phreatic water levels.Under low water level, the soil is in a state of equilibrium,and keeping a stage of continuous desalination at high diving.3.The change of soil moisture in shallow soil increased in 6-8 months and decreased in 10-12. The minimum appeared in December and reached the maximum in August. The soil water content showed a downward trend with the increase of water level. Under the water level of 0.3-1.2m, the soil water content is high and fluctuates with time. Under the phreatic water level of 1.5-1.8m, the soil moisture content is low and fluctuates little with time. Soil salt content was closely related to soil water content. There were two peaks in October and April, and in 4 to 10 months, the accumulation in surface soil salinity was serious.4. Under the condition of brackish water, the content of Na+ in leaves of Tamarix is less than the control group, while the Na' content in stem was higher than the control group. It was indicated that the mechanism of salt tolerance for Tamarix is secreted the salt ions into the body through the leaves, in order to reduce the toxic effects of Na+ on plant cells.According to the analysis of the cation content in the stems and leaves of Tamarix under brackish water, we can find that ,for the willow, Na+ mainly inhibited Ca2+ in low water, and with the increase of phreatic water level, Na+ had a significant inhibitory effect on K+. For stems, Na+ was significantly inhibited in K+ and Ca2+ when the water level was low, and the influence weaken under a high water level.By correlation analysis, the phreatic water level is significantly related to soil salt content,soil water content and plant water content, but not to plant salinity. The content of water and salt in Tamarix chinensis is higher than that of soil under water. In Tamarix plants around,especially in the surface soil, Tamarix chinensis shoeed a certain concentration of soil water and salt,which is called "Salt island effect". When the groundwater is brackish water,the deeper the buried depth is, the more obvious the effect of salt island is. If the water is more than 1.2m, that effect is weakened, and Tamarix plant self desalinationeffect is enhanced.Therefore, we should consider the local diving water level should not be less than 1.2m in the cultivation of Tamarix chinensis, which can effectively improve the effect of Tamarix chinensis on saline alkali soil. |
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