Abstract: To clarify the effects of low temperature and weak light on photosynthetic characteristics and fluorescence parameters of chrysanthemum, a greenhouse experiment was carried out with chrysanthemum ‘Hongman’ as experimental material, following an orthogonal experiment design of L₁₆(2¹×4²). There were four levels of low temperature: 13 ℃ (day temperature)/3 ℃ (night temperature), 16 ℃/6 ℃, 19 ℃/9 ℃, 22 ℃/12 ℃, and two levels of low light: 200 and 400 μmol·m^-2·s^-1, with 28 ℃/18 ℃ and 800 μmol·m^-2·s^-1 as a control (CK). The duration was set up at 3, 6, 9, and 12 d. The cytochrome, photosynthetic parameters and chlorophyll fluorescence dynamic parameters of leaves with different treatments were measured. The results showed that the cytochrome content of leaves decreased with the intensity of low temperature and weak light stress and duration extension. The contents of chlorophyll a, chlorophyll b and carotenoid decreased by 23.17%, 42.39% and 47.04% in T₄ compared with CK, respectively. The maximum net photosynthetic rate (P_n max), light saturation point (LSP), and stomatal limit value (L_s) were decreased by 70.11%, 60.31% and 60.61% under T₄ treatment compared to the CK. With increasing intensity of low temperature and weak light stress and duration extension, light compensation point (LCP) and dark respiration rate (R_d) increased by 162.27% and 211.95% in T₄, compared to CK, respectively. With increasing intensity of low temperature and weak light stress and duration extension, maximum quantum efficiency (F_v/F_m), photochemical quenching coefficient (q_P) and PSⅡ actual photochemical efficiency (Φ_PSII) decreased significantly by 48.85%, 27.17% and 41.10%, respectively, compared with CK. The non-photochemical quenching coefficient (NPQ) increased by 88.77% compared with CK. The results indicated that the structure and function of photosystem were irreversibly damaged with increasing intensity of low temperature and weak light stress and duration extension. The low temperature and weak light stress index was established based on photosynthetic parameters, and the meteorological index of low temperature and weak light stress during the flowering period of chrysanthemum was determined. This study provides scientific basis for meteorological disaster prevention and facility environment optimization of chrysanthemum under low temperature and weak light.

Key words: chrysanthemum, low temperature and weak light, photosynthetic parameter, chlorophyll fluorescence parameter, meteorological disaster indicator.