To investigate the photosynthesis and growth of Cymbidium ‘Red Fire’ grown under different nitrogen fertilization and night-interruption (NI) illumination, we exposed plants to 9-h short days (SDs), SDs + 3 - 7 μmol·m-2·s-1 NI (low-light intensity of NI, LNI), or SDs + 120 μmol·m-2·s-1 NI (high-light intensity of NI, HNI) illumination with nitrogen supplemented at 0, 100, 200, or 400 mg·L-1. Cymbidium photosynthesized under 3 – 7 μmol·m-2·s-1 NI regardless of nitrogen treatment, promoting growth. HNI treatments and nitrogen supplements at 100 mg·L-1 increased the leaf chlorophyll concentration. LNI increased net CO2 assimilation (An), transpiration, and stomatal conductance. HNI without supplemental nitrogen reduced midday An. However, HNI with supplemental nitrogen increased midday An. Supplemental nitrogen should be provided to Cymbidium when high-irradiance NI is used to promote growth.

• Yoon Jin Kim(Department of Horticulture, Biotechnology and Landscape Architecture, Seoul Women’s University Department of Horticultural Science & Biotechnology, Seoul National University Research Institute for Agriculture and Life Sciences, Seoul National U)
• Ki Sun Kim(Department of Horticultural Science & Biotechnology, Seoul National University Research Institute for Agriculture and Life Sciences, Seoul National University) Corresponding author