Effects of Leaf Nitrogen Content on Leaf Photosynthetic Characteristics of Sugar Cane (Saccharum spp.)

Abstract

Using eight varieties of Saccharum officinarum and one variety of S. sinense, effects of leaf nitrogen content on leaf photosynthetic characteristics were examined on the uppermost full expanded leaf. Four experimental blocks (nitrogen treatment, NT) were established under hydroponics using four nitrogen contents in culture solution. Factors of leaf photosynthesis characteristics investigated in this experiment were as follows; photosynthetic rate and water vapor exchange coefficient under 2000 μmol/m²/s and 240 μmol/m²/s of photosynthetically active radiation (P₂₀₀₀, D₂₀₀₀, P₂₄₀, and D₂₄₀, respectively), the contents of total nitrogen (N), soluble protein (SOLP), chlorophyll (CHL), and fraction 1 protein (F 1 P), and phosphoenolpyruvate carboxylase activity (PEPC). Significant differences among varieties were obtained in P₂₄₀, N, and F 1 P. All of leaf photosynthetic characteristics and related internal factors examined in this experiment showed significant difference of variance analysis in the nitrogen treatments (NT) and the interaction of NT and variety. On the statistical analysis with whole data in this experiment, P₂₀₀₀ showed highest relationship (r=0.747, P<0.01) to D₂₀₀₀. Correlation coefficients between P₂₀₀₀, and CHL, SOLP, and PEPC were 0.657, 0.648, and 0.556 with significant level at 1%, respectively. The ratio of F 1 P to SOLP was higher in the low leaf nitrogen content (block II) than in block I. The nitrogen use efficiency in photosynthesis of sugarcane was low as in a range of 2.5 to 3.7 mgCO₂/mgN/h.