Abstract: Taking one year-old Tripterygium wilfordii cutting seedlings as test materials, this paper studied the effects of foliar spraying 0, 5, 10, 15, 20, and 25 mg·L^-1 of abscisic acid (ABA) on the leaf photosynthesis and chlorophyll fluorescence characteristics of the seedlings under low temperature stress. Spraying 20 mg·L^-1of ABA increased the cold- resistance of the seedlings significantly, manifesting in the slowing down of the decrease amplitudes of leaf net photosynthetic rate (P_n), transpiration rate (T_r), stomatal conductance (g_s), and intercellular CO₂ concentration (C_i) and the increase of photosynthetic capacity. After 6 days exposure to low temperature, the initial fluorescence (F_o) decreased with increasing concentration of applied ABA, the maximum fluorescence (F_m) and maximal photochemical yield(F_v/F_m) increased, the actual photochemical efficiency of system Ⅱ (Φ_PSⅡ) and photochemical quenching coefficient (q_P) increased after an initial decrease,and the non-photochemical quenching coefficient (q_N) showed a ‘decreasing-increasing-decreasing’ trend. The P_n, g_s,q_P, F_m,and F_v/F_m reached their peak values at 20 mg·L^-1 of ABA. In all treatments, with the increase of photosynthetically active radiation (PAR), the relative electron transport rate (rETR) increased first and decreased then, reached the peak when the PAR was 395 μmol·m^-2·s^-1, and the peak value of the rETR in treatments 25 and 20 mg·L^-1of ABA was 17.1% and 5.2% higher than that of the control, respectively. The light response curves of the Φ_PSⅡdecreased with increasing PAR, whereas those of q_N performed in adverse.

Key words: Tripterygium wilfordii, low temperature, ABA, photosynthesis characteristic, chlorophyll fluorescence