Abstract: Amaranth (Amaranthus tricolor L.) plants were exposed to several temperature levels (25, 30, 35, 40, and 45 ℃) for 1 h, and then, the characteristic parameters of chlorophyll fluorescence and the rapid light response curves of photosynthesis were measured, aimed to understand the effects of high temperature stress on the photosynthesis process of amaranth. High temperature stress (>40 ℃) decreased the maximum fluorescence (F_m), potential photochemical efficiency (F_v/F_o), and maximum photochemical efficiency of PSⅡ (F_v/F_m). Simultaneously, the electron transport rate (ETR), actual photochemical efficiency of PSⅡ (Yield), and photochemical quenching coefficient (q_P) also had some decrease. In contrast, the initial fluorescence (F_o) and nonphotochemical quenching coefficient (NPQ) were increased significantly. The initial slope rate (α), maximum apparent electron transport rates (ETR_max), and halfsaturation light intensity (Ik) under high temperature stress also had some decline. These results indicated that the photosynthesis of A. tricolor plants was very sensitive to high temperature stress. High temperature (>40 ℃) disturbed the A. tricolor plant’s light energy absorption and conversion, photosynthetic electron transport efficiency, and endurance against strong light.

Key words: heat island effect, energy balance function, spatiotemporal scale.