Abstract: The effect of root temperature on growth, photosynthetic and other physiological characteristics of A. tricolor seedlings were studied in phytotron. The result showed that growth curve of A. tricolor seedling presented "S" shape, 30-day-old seedling grew fastest. Dry and fresh weight per a seedling was 0.45g and 6.79g respectively. The harmfulness of superoptimum root temperature to growth was bigger than that of suboptimum root temperature, 40℃ root temperature harmed growth and metabolism of root system of A. tricolor seriously. The variation of net photosynthetic rate (P_n), transpirat ion rate(T_r), stomatal conductance(C_s), and intercellular CO₂ partial pressure (P_i) with root temperature was similar in A. tricolor. C_s, P_i, P_n and T_r were higher at 20~25℃ root temperature. Suboptimum or superoptimum root temperature affected C_s, and caused decreasement of T_r and P_i, then affected P_n. Regressive analysis showed that P_n correlated with C_s and P_i positively, T_r and P_i correlated with C_s positively too. The main cause of the decreasement of P_n at suboptimum and superoptimum root temperature was the decreasement of C_s.

Key words: Amaranthus tricolor L., Root temperature, Grow th, Photosynthetic characteristics