Levels of Nonstructural Carbohydrate in Leaves and Roots and Some Characteristics of Chloroplasts after Application of Different Amounts of Nitrogen Fertilizer to Peach Seedlings

Abstract

The effects of different amounts of nitrogen, applied in the soil, on the accumulation of nonstructural carbohydrate in leaves and roots were determined as well as on some characteristics of chloroplasts in one-year-old peach trees (Prunus persica) grown in 500-ml pots. The amounts of nitrogen, applied as NH₄NO₃, were as follows : 0 mg/pot (N-0), 75 mg/pot (N-75), 150 mg/pot (N-150), 300 mg/pot (N-300), and 600 mg/pot (N-600). The weights of stems and leaves and shoot length were greatest in N-150 and N-300 trees, whereas root weights were heaviest in N-75 and N-150 trees. Shoot and root growth was significantly reduced in N-0 and N-600 trees. Leaf chlorophyll content (μg cm^-2), total soluble sugar (% dry weight), and nitrogen content (% dry weight) of leaves and roots increased with increased application of nitrogen, whereas starch content of leaves was inversely proportional to the amount of nitrogen administered. The amount of sorbitol (% fresh weight) in leaves was proportional to the growth rate of the trees. Chlorophyll was stained more heavily by 4', 6-diamidino-2-phenylindole in N-600 leaves than in N-0 leaves ; the staining concentrated at the periphery of chloroplasts, indicating an accumulation of starch. The level of the enzyme, ribulose-bisphosphate carboxylase-oxygenase (RuBisCO), increased with increased applied nitrogen, reaching maximum at N-300 and N-600. Total soluble sugar in roots was high in vigorous trees, where root starch content was inversely proportional to root growth.