| With the increasing growth of the area of Acacia melanoxylon plantations in China, its development was limited due to the slow growth of the young plants caused by the seedling's easily falling off and limited knowledge on the nutrient demands. Two key cultivation techniques on stumping and fertilizing were chosen to explore the best stumping height and optimal fertilization. Four different stumping heights (5 cm,10 cm,15 cm, and 20 cm) were set to select the best stumping height by observing and analyzing their seedlings'growth, germination, root characteristics, nutrient uptake and photosynthesis characteristics. At the same time the treatments on different N (0～600 mg/seedling), P (0～200 mg/seedling), K (0～300 mg/seedling) fertilization and nutrient deficiency were taken on seedlings to explore different concentrations of fertilizer in the seedlings and fertilizer response mechanism by studying growth, root characteristics, nutrient uptake and photosynthesis characteristics. The study would provide a theoretical basis for silviculture of Acacia melanoxylon seedlings.The findings were as followings:(1) The sprouting of Acacia melanoxylon seedings could be hastened by stumping. The seedling diameter, root length, root average diameter, and root surface area increased rapidly after stumping. The net photosynthetic rates and contents of N, P, K were first increased and then decreased, and the values of stumped seedlings were higher than the control. The best stumping height was 10 cm, with the maximum photosynthetic rate (7.99μmol·m2·s-1) and maximum water use efficiency (2.51 umolCO2·mmol·H2O-1), and the contents of N (13.51 mg/plant), P (5.28 mg/plant), K (3.96 mg/plant), In the later period of the experiment, the diameter (5.23 mm), bud number (7.3), bud length (134.6 cm), root biomass (1.50 g), and root surface area (121.94 mm2) of the treatment with 10 cm stumping were significantly higher than those of the control.(2)The growth of Acacia melanoxylon seedings could be hastened significantly by exponential N fertilization. In the later period of the experiment, the diameter and height of seedlings were 2.43～2.98 mm and 26.42-32.10 mm. The biomass was 0.66-1.05 g, and root length, t root average diameter, root surface area and root volume were 01.22～343.34 cm,0.28～0.41 cm,13.44～26.29 cm2 and 0.19-0.35 cm3. The contents of N (19.70-43.53 mg/seedings), P (2.89-5.78 mg/seedings), and K (9.66～17.50 mg/seedings) of the whole plant increased significantly. The apparent quantum yields of seedlings (0.032～0.046), the maximum photosynthetic rate (7.95～9.19μmol·m-2·s-1), and the light saturation point (897-1140μmol·m-2·s-1) of different treatments showed significant difference with those of the control. The treatment with N-400 was best for Acacia melanoxylon's growth.(3) The growth of Acacia melanoxylon seedings could be hastened significantly by equally applying P fertilization. Especially after P-100 treatment, the seedlings showed higher growth quality than the other treatments. The diameter and the height were 2.30 mm and 36.20 cm, and the biomass of the upper part (stem, leaf) and underground part (root) were 1.23 g and 0.22 g. The root length, root average diameter, root surface area, and root volume were 417.09 cm,0.46 cm,35.16 cm2, and 0.48 cm3 separately The contents of N, P, K were 7.55 mg/seedling,1.39 mg/seedling and 3.98 mg/seedling. Thus, the fertilization with 100 mg P was best for plant growth, root system development, and nutrient absorption.(4) The growth of Acacia melanoxylon could be hastened significantly by equally applying K fertilization. Especially after the K-150 treatment, The seedlings showed higher growth quality than the other treatments. The diameter and height were 2.07 mm and 35.4 cm, and the biomass of the upper part (stem, leaf) and underground part (root) were 1.14 g and 0.19 g. The root length, root average diameter, root surface area, and root volume were 380.10 cm,0.35 cm,33.12 cm2, and 0.45 cm3 respectively. The contents of N, P, K were 7.01 mg/seedling,1.22 mg/seedling and 4.10 mg/seedling. Thus, the fertilization with 150 mg K was best for plant growth, root system development and nutrition absorption.(5) The lack of macronutrient elements could effect the Acacia melanoxylon's growth, biomass, root system morphological parameters, contents of nutrient elements and photosynthesis significantly. Lacking of N, P, and K led to the decrease of N amounts in leaf which decreased the contents of chlorophyll, weakened the assimilation and made the drought worse. The weaken of photosynthesis directly effected by the lack of N, P, and K, which would negatively effected carbohydrate feedback mechanism eventually. The contents of diastase were increased in three clones, and the contents of sugar increased in clone No.33. The drought caused by lacking of nutrient elements was the main reason of leaf dry weight droping. The root elongation of clone No.33 was limited by the lacking of N, but the root/canopy ratio was not affected by the elongation. According to the experiment, under the lack of nutrient elements (-N,-P,-K) conditions, the growth of clone No.33 were better than that of the clones No.4 and No.7. The results of this study would be beneficial for the development of more in-depth breeding on Acacia melanoxylon clones..
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