Objective To study the growth rhythm of Nuttall oak (Quercus nuttallii) seedlings under different light intensities, find out the appropriate light intensity and container size for seedling growth, and provide a theoretical basis and guidance for cultivation and management of container seedlings in the future.

Method Single factor experiments were used to study the effects of light intensities (50%, 75% and 100%)and container sizes(8 cm×10 cm, 10 cm×15 cm and 15 cm×20 cm)on seedling growth. Logistic equations were used to fit the growth of seedling height and ground diameter under different light intensities.

Result At the early stage of growth (before June 26), shading clearly promoted growth of seedling height. By the end of the growth season, the increments of seedling height were not significantly different among light treatments. Throughout the growth season, ground diameter was significantly enhanced by shading with the optimal light intensity being 75%. The growth rhythms of seedling height and ground diameter were generally consistent. Shading shifted the initial and final stages of linear growth of seedling height to earlier time. The linear growth days (LGD) of 50% light was 21 days shorter compared to 100% light, and the LGD of 75% and 100% light were not significantly different, while the LGD of ground diameter of 50% and 100% light were longer 19 days and 16 days than that of 75% light, respectively. LGD of seedlings height was substantially longer than that of ground diameter, indicating that when seedling height growth stopped, the ground diameter continued to grow. Container size significantly influenced seedling height, ground diameter and the ratio of height to diameter. Seedling height and ground diameter significantly increased by larger containers, and both were the highest (98.83 cm and 11.68 mm) in the 15 cm×20 cm container.

Conclusion Larger container (15 cm×20 cm) should be used to cultivate high quality seedlings of Q. nuttallii. Considering seedling height and ground diameter, we should use 50% light at the early stage of growth, then 75% light during the linear growth stage, and full light starting from Fall. At the late stage, ground diameter should be used as the index for detecting the ending of growth.