ObjectiveThis paper aims to provide a scientific basis for endangered mechanism of Torreya fargesii by studying its photosynthetic characteristics at different tree ages and discussing the effects of light conditions on the photosynthetic characteristics of T. fargesii.

MethodThree well-growing 3-year-old and 15-year-old T. fargesii, each of which was randomly selected and marked for testing in secondary woodland in Zhoujiashijiao of Jinfo Mountains in Chongqing Nanchuan of southwestern China. The daily photosynthetic parameters, light response curve, carbon dioxide response curve and chlorophyll content were measured in the sample plot.

ResultThe results showed that the content of chlorophyll-a, chlorophyll-b and carotenoids of 15-year-old T. fargesii were higher than that of 3-year-old, and the difference of chlorophyll-a and chlorophyll-b was significant. The chlorophyll a/b of 3-year-old T. fargesii was higher than that of 15-year-old T. fargesii, with no significant difference.The mean daily values of P_n and T_r of 15-year-old T. fargesii were significantly higher than that of 3-year-old T. fargesii, and the daily average of intercellular CO₂ concentration was significantly lower than that of the 3-year-old T. fargesii. P_nmax of 15-year-old T. fargesii when light saturation was higher than that of 3-year-old T. fargesii, while AQY, R_d and light compensation point were less than that of 3-year-old T. fargesii. Light saturation point of 15-year-old T. fargesii was higher than that of 3-year-old T. fargesii. The P_nmax when CO₂ was saturated, CE, R_p, the CO₂ compensation points and the CO₂ saturation point of 15-year-old T. fargesii were higher than that of 3-year-old T. fargesii.

Conclusion3-year-old T. fargesii has a complete photosynthetic system and good photosynthetic capacity. In an environment with high temperature and high light intensity, the "photosynthetic midday depression phenomena" can be activated in time to protect the photosynthetic apparatus from being damaged. However, it is not suitable with strong light, and it can maintain high light energy by increasing the photorespiration rate and utilizing the weak light during the photosynthesis process. 15-year-old T. fargesii has a wider range in light and CO₂ utilization ability, especially in bright light. It can promptly start the "photosynthetic midday depression phenomena" to increase the transpiration rate to prevent the leaves from burning. In low light environments, it can also accumulate more organic matter by reducing the consumption of dark respiration, showing a greater adaptability to changes in the surrounding environment.