Abstract:In order to understand the reason to growth stagnation of Glehnia littoralis in summer, the heat tolerance of leaf metabolic system was studied in comparison with a companion species Calystegia soldanella as reference. The results showed that both of the deactivation temperature of photosynthetic system and the half lethal temperature of cell membrane in G. littoralis were 5℃ lower than those in C. soldanella. In contrast, the activity of the respiration system in both plants were still very high even when the temperatures reached 50℃ with a decline of 10% and 24%, respectively, showing that the respiration system was apparently more heat-resistant than the photosynthetic and membrane systems. The Gaussian regression showed that the ratio of photosynthesis rate to respiration rate was persistently lower in G. littoralis than that in C. soldanella. Therefore, it was suggested that the excessive consumption of the photosynthetic assimilates could be the cause of the summer growth stagnation of G. littoralis. In addition, the overall lower heat-resistance of C. soldanella could also be associated with the summer growth stagnation in G. littoralis, while C. soldanella did not show growth stagnation in summer because of high heat resistance.