Effects of different nitrogen fertilizer on the morphological indexes and physiological characteristics of Dahlia pinnata

A pot experiment was carried out to determine the optimal nitrogen application rates (0, 0.15, 0.30 and 0.45 gkg-1) via performance of the morphological indexes and physiological characteristics of Dahlia pinnata. This study indicated that the stem diameter, leaf area, flower diameter, flowering stage and tuber weight of dahlia increased as the nitrogen application rate increased. The application of nitrogen fertilizer significantly increased the chlorophyll, soluble protein and proline contents, and the activities of nitrate reductase, superoxide dismutase, peroxidase (POD) and catalase (CAT), but significantly reduced the malondialdehyde content of D.pinnata plants, indicating that the application of nitrogen fertilizer enhanced the stability of plasma membrane, restrained the penetration of membrane, and strengthened the protective function of cell membrane of D.pinnata plants. Although the nitrate reductase activity of D.pinnata plants significantly increased as the nitrogen application rates increased, the excessive nitrogen application decreased the leaf area and proline content. These results showed that the moderate application of nitrogen fertilizer benefited the growth of D.pinnata plant, delayed its aging and improved ornamental value, while the excessive application of nitrogen fertilizer inhibited the growth of D.pinnata plant. This study suggested that the rational application of nitrogen fertilizer for pot D.pinnata was 0.30 gkg-1.