Roots-Soil Interrelations And Eco-physiological Responses Of Manchurian Ash Seedlings Under Different Soil Water Potential

Based on the experiments of two-year-old Ash {Fraxinus mandshurica) seedlings which is the main kind on trees in the north part of China, relations between roots and soil on Ash {Fraxinus mandshurica) seedlings treated under 5 different osmotic irrigation conditions were study. In this paper, water absorption, nutrient absorption, photosynthesis of seedlings were analyzed. It was studied that moisture status, nutrient status, photosynthesis character and changes of soil nutrient content. The results are as follows:1. Multiplication of different parts of hydraulic resistance were severalfold or added with soil water potential decreased. Relative drought resulted in fall of fine water suction amount. In the sub-saturated (W1)and field capacity(W2)soil water conditions, Diurnal water suction patterns of Manchurian ash seedlings growing were single apexes. In the orderly increased stress states of soil water(W3~W5 treatments), which caused the consequent low water suction rate and low fluctuation levels of leaf water potential and transpiration was seriously restricted. Diurnal water suction patterns of Manchurian ash seedlings growing were double apexes, there were vales in the noon..2. The soil nutrient content was not more in the lower soil water potential condition(W3 ~W4) than other soil water potential conditions. Nutrient uptake was depressed conspicuously with the decline of the soil water potential. Fine root/leaf K content of Manchurian ash seedlings were decreased with the decrease of soil water potential. Relative drought resulted that growth of fine was seriously restricted, and nutrient efficient uptake is the most in W3 soil water condition.3. Photosynthetic potential of Manchurian ash seedlings were accordant in different soil water potential conditions. All the differently treated seedlings exhibited a maximal peak of net photosynthetic rate (Pn) in the early morning (approx. 6:00), there were no obvious differences in these seedlings. Obvious differences of photosynthesis were behaved after the morning, Diurnal photosynthetic accumulation of the leaves declined with the decrease of soil water potential, but water use efficiency was not heightened widely. Transpiration and photosynthesis were reduced because of low soil water potential, and In soil moisture condition which is lower than field capacity, the serious photosynthesis inhibition was examined to be predominated by nonstomatic limitations.4. In 0-160Kpa in the range, soil water potential influence Manchurian ash, including moisture status, nutrient status, photosynthesis characteristics. As a whole, the sub-saturated soil water condition (0~-40KPa) is the most feasible soil water condition. For the inherently shade-tolerant Manchuran ash seedlings, which grow under the whole light, the obvious water stress would be caused if the soil moisture was lower than the field.