Impact of Temperature on Growth, Photosynthetic Efficiency, Yield, and Functional Components of Bud-Leaves and Flowers in Edible Chrysanthemum (Chrysanthemum morifolium Ramat)

Edible chrysanthemum (Chrysanthemum morifolium Ramat.), widely consumed in Asia, is rich in bioactive compounds such as polyphenols, flavonoids, and amino acids. Optimizing cultivation temperature is critical for maximizing both yield and quality, especially under the challenges posed by climate change. This study evaluated the growth performance, photosynthetic characteristics, and metabolite accumulation of the ‘Taiwan Hangju No. 1’ variety under five day/night temperature regimes (15/13 °C, 20/15 °C, 25/20 °C, 30/25 °C, and 35/30 °C) over a 220-day period in an artificial climate greenhouse. The 25/20 °C regime promoted the best overall growth, with the highest yields of bud-leaves and flowers, and supported the highest net photosynthetic rate, indicating optimal carbon assimilation under moderate temperatures. In contrast, stomatal conductance, respiration rate, and transpiration rate increased with temperature, peaking at 35/30 °C. Water use efficiency was greatest at 15/13 °C. Bioactive compound accumulation exhibited complex and organ-specific responses to temperature. The concentration of polyphenols, luteolin, and caffeoylquinic acid derivatives (CQAs) increased with temperature in both bud-leaves and flowers, free amino acids decreased in bud-leaves with rising temperature, reaching a peak at 15/13 °C, and flavonoid concentration peaked at 35/30 °C. In flowers, free amino acids accumulated most at 20/15 °C, and flavonoids peaked at 25/20 °C. The differing yields of bud-leaves and flowers under various temperature conditions contributed to variation in the total content of functional compounds. Except for free amino acids, the total of other functional compounds in bud-leaves was highest at 30/25 °C. The total content of all functional compounds in flowers was highest at 25/20 °C. This study demonstrated that 25/20 °C provides the best balance between growth, photosynthetic efficiency, and accumulation of key bioactive compounds and is therefore recommended as the optimal cultivation temperature for ‘Taiwan Hangju No. 1’. These findings reveal temperature-dependent and organ-specific metabolic adjustments, suggesting that moderate warming may enhance crop quality if managed carefully. The results provide a scientific basis for climate-adaptive cultivation strategies of edible chrysanthemums in subtropical regions.