Abstract:

【Objective】 Exponential fertilization is one of the nutrient loading methods, which adds the required nutrients into soil, according to the relative growth rate of seedlings. The effects of different fertilization methods and different nitrogen content on the growth, nutrient content and root morphology of seedlings were investigated in this study to reveal the regularity of the nitrogen absorption and the utilization ofTilia amurensis seedlings and provide scientific reference for cultivation of high quality seedlings. 【Method】 Under field conditions, nitrogen fertilization experiment was conducted with one-year-old seedlings of Tilia amurensis. Further, three treatments were applied: conventional fertilization (200 mg per seedling, CK), 1 time exponential fertilization (207.46 mg per seedling, No.E100), and 2 times exponential fertilization (414.92 mg per seedling, No.E200). The fertilization interval time was seven days, and nitrogen fertilizer was applied for 10 weeks until the end of the growing season. During the experimental period, the height and base diameter of seedlings were measured weekly after fertilization, and the data were used to plot the growth curve. When these seedlings were harvested, roots were separated from the plants for scanning and calculating their morphological indexes (root length, root surface area, root volume). After drying, the biomass, nitrogen content and nitrogen concentration of each plant organs were determined. 【Result】 Exponential fertilization significantly improved the height and base diameter growth ofT. amurensis seedlings compared with those by conventional fertilization. The seedling mean biomass of E100 and E200 treatments were 1.63 and 1.66 times higher than that of CK (P<0.05), respectively. The of shoot to root ratio was CK > E100 > E200 with increasing amount of nitrogen. The tendency of N content in roots, stems and leaves of seedlings was E200 > E100 > CK. The nitrogen content of the whole plant in E200 was 349.24 mg per seedling, whereas nitrogen contents of the whole plant in E100 and CK were 338.21 and 94.48 mg per seedling, respectively. The order of N concentration in roots, stems and leaves was E100 > E200 > CK. The root length, root surface area root volume, specific root length, specific root surface area, and root tissue density of the seedlings had the same trend which was expressed as E100 > E200 > CK. The nitrogen harvest index of seedlings showed E100 > E200 > CK (the index of E100 was 3.45 times of CK). The seedling quality index of E100 was 0.89 times higher than that of CK.【Conclusion】 Seedlings with nitrogen exponential fertilization have a better performance in growth, nutrient accumulation and root morphological characteristics than that of conventional fertilization, and the seedlings ofTilia amurensis treated with exponential fertilization at E100 (207.46 mg per seedling) grew best based on earlier measured indexes.

Key words: Tilia amurensis Rupr., exponential fertilization, seedling growth, root morphology, nitrogen utilization