Starch Accumulation and Photosynthesis in Leaves of Young Peach Trees Grown under Different Levels of Nitrogen Application

Abstract

The effects of the different levels of nitrogen application on leaf characteristics including starch accumulation and photosynthesis were determined in two-year-old peach trees (Prunus persica (L.) Batsch. cv. Ohkubo). The nitrogen content on dry weight basis in the leaves was the lowest in the zero-nitrogen plot (N-0) : 2.5%, and increased with increasing the nitrogen application; 1.5 g plot (N-1.5), 2.9%; 3.0 g plot (N-3.0), 3.4%; and 6.0 g plot (N-6.0), 3.8%. Compared with those in higher nitrogen plots, the leaves on N-0 plot were thinner, smaller, and yellowish: chlorophyll content per unit leaf area was lower at decreasing levels of nitrogen application. The starch content in the chloroplasts of the leaves from the N-0 plot was higher than those from plots in which nitrogen was added. Amylase activity, which was the lowest in the leaves of N-0 plot, was in inverse proportion to the starch accumulation; amylase activity in leaves from the N-3.0 and N-6.0 plots, which contained less starch content, was higher. In the chloroplasts of the leaves from the N-0 plot, chloroplast nucleoids were localized at the periphery of the plastids, whereas they were evenly distributed in chloroplasts of leaves with higher nitrogen contents. The photosynthetic rate per unit leaf area was the lowest in N-0 plot, and increased with nitrogen application: the difference, however, between nitrogen plots was not significant.