Abstract: Substrate culture was employed to study the effects of different nitrogen levels (i.e., 1, 3, 8, 16, 26mmol·L-1) and different ratios of nitrogen forms (i.e., NH+4-N to NO-3-N, 4∶0, 1∶3, 2∶2, 3∶1, 0∶4) on appearance quality, chlorophyll content and photosynthesis characters of chrysanthemum with small inflorescences. The results showed that 16 mmol·L-1 nitrogen was optimal for vegetative growth, and it increased plant height, canopy, fresh weight and leaf numbers of plant. On the other hand, 8 mmol·L-1 nitrogen was optimal for reproductive growth, and it increased flower numbers, flower dry weight and prolonged the period of blooming. The flower development and its blooming were inhibited at higher level of nitrogen, but the chlorophyll content, net photosynthetic rate (Pn), stomatal conductance(Gs) and transpiration rate (Tr) increased and the intercellular CO2 concentration(Ci) decreased. Plant height, canopy, leaf numbers, flowers numbers, flower dry weight were enhanced under NH₄⁺-N condition as compared to NO₃^--N. Furthermore, the chlorophyll content, net photosynthetic rate (Pn), transpiration rate (Tr) and stomatal conductance(Gs) increased, but the intercellular CO₂ concentration (Ci) obviously decreased during the late period of vegetative growth under NH₄⁺-N condition. However, nitrogen forms didn't affect the progress of flower development or the blooming period. It was found that a ratio of 3∶1 of NH₄⁺-N∶NO₃^--N was optimal for potted chrysanthemum with small inflorescences．

Key words: chrysanthemum with small inflorescences, nitrogen levels, nitrogen forms, photosynthesis character