야간 고온 조건에서 주간 온도가 포인세티아 ‘플레임’의 생육과 생리반응에 미치는 영향 = Growth and Physiological Responses of ‘Flame’ Poinsettia to Day Temperature under High Night Temperature Conditions

다국어 초록 (Multilingual Abstract)

This study aimed to propose a daytime temperature management strategy for poinsettia cultivation during high-temperature periods. To this end, high night temperature conditions were imposed with a constant night temperature of 26°C, and day temperatures of 30°C, 33°C, 36°C, and 39°C were applied for seven weeks. For comparison, a control treatment was maintained in a greenhouse at 27°C/20°C (day/night) during the same period. All plants in the 39°C/26°C treatment died within five days, and survival decreased to 60% under the 36°C/26°C treatment. Plant height, width, and branch number did not differ significantly between the 30°C/26°C and 33°C/26°C treatments; however, these parameters decreased by 29.5%, 30.9%, and 27.5%, respectively, at 36°C/26°C compared with 30°C/26°C. The number of newly formed leaves declined sharply with increasing day temperature, averaging only 2.3 leaves at 36°C/26°C, indicating minimal vegetative growth. Relative to the 27°C/20°C control, leaf length and width decreased by 20.3%–37.6% and 56.4%–57.1%, respectively, under high-temperature treatments, resulting in an increased leaf length-to-width ratio and narrower leaf morphology. The normalized difference vegetation index and maximum quantum yield of photosystem II (Fv/Fm) showed slight variation among treatments, whereas electrolyte leakage percentage increased markedly to 38% at 36°C/26°C. Net photosynthetic rate was highest at 27°C/20°C, remained similar between the 30°C/26°C and 33°C/26°C treatments, but declined to zero at 36°C/26°C even under a light intensity of 1,000 μmol·m-2·s-1. In addition, transpiration rate and intercellular CO2 concentration were significantly higher at 36°C/26°C. These results indicate that both physiological and morphological stress in poinsettia intensifies when daytime temperatures exceed 33°C. Therefore, maintaining daytime temperatures below 33°C is recommended for stable poinsettia production during high-temperature seasons.