Abstract: In order to explore the photosynthetic adaption mechanisms of kernel-used apricot under high temperature stress, gas exchange technique and chlorophyll fluorescence transient technique (JIP-test) were adopted to study the leaf photosynthetic characteristics and photosystemⅡ (PSⅡ) photochemical activity of 4 year-old ‘Chaoren’ (Armeniaca vulgaris × sibirica) growing on Horqin sandy land at 25 ℃, 30 ℃, 40 ℃, and 50 ℃. Within a definite temperature range, and as the temperature increased, the ‘Chaoren’ could enhance its leaf photosynthetic pigments content and ratio to maintain the light absorption, transfer, and conversion, and thereby, to ensure the function of photosynthetic apparatus. However, when the temperature exceeded the physiological adjustment threshold of leaves, the chlorophyll began to be decomposed, net photosynthetic rate (P_n) declined obviously, and intercellular CO₂ concentration (C_i) increased, indicating that the decline in photosynthesis was limited by mesophyll factor. At 40 ℃, the density of PSⅡ reaction centers per excited cross-section (RC/CS_o) dropped distinctly; and at 50 ℃, the K phase (W_k) and J phase (V_j) in the O-J-I-P chlorophyll fluorescence transients increased distinctly, indicating that high temperature damaged the oxygen-evolving complex (OEC), donor sides, and PSⅡ reaction centers. In addition, the minimum chlorophyll florescence (F_o) at 50 ℃ increased significantly by 1.26 times, compared with the control, and the maximum photochemical efficiency (F_v/F_m) and performance index (PI_ABS) reduced to 37.9% and 10.3% of the control, respectively. High temperature injured the function of the donor and acceptor sides in the PSⅡ of photosynthetic apparatus, leading to the decrease of photosynthetic efficiency, and being one of the main mechanisms for the damage of photosynthetic apparatus in kernel-used apricot leaves under high temperature stress.

Key words: kernel-used apricot, high temperature stress, photosynthetic characteristics, chlorophyll fluorescence, JIP test