Abstract: Parrotia subaequalis, classified as a Grade I protected plant in China, exhibits low germination rate under natural conditions. To improve seed utilization efficiency, we explored the effects of gibberellic acid (GA₃) on seed germination and seedling growth of P. subaequalis using a soaking experiment with different GA₃ concentrations of 0, 600, 800, 1000, and 1200 mg·L^-1 for 48 h. We measured seed germination rate, germination potential, germination index, seedling rate, as well as indicators such as stem length, radicle length, lateral root number, leaf number, and fresh weight of seedlings at different stages. The results showed that applying GA₃ with an appropriate concentration enhanced germination rate, germination potential, germination index, and seedling rate of P. subaequalis seeds. The highest germination rate (81.1%) of P. subaequalis seeds was achieved at a GA₃ concentration of 800 mg·L^-1, with a corresponding seedling rate of 92.67%, a germination potential of 36.67%, and a germination index of 24.94. Under the conditions of soaking the seeds with a GA₃ concentration of 800 mg·L^-1, seedlings displayed optimal growth, showcasing an average stem length of 65.92 mm, radicle length of 44.84 mm, a root number of 11.6, leaf number of 4.2, and a fresh weight of 0.444 g after 90 d, signifying significant differences compared to the control group (P<0.05). In the artificial propagation of P. subaequalis, appropriate concentrations of GA₃ could be applied to enhance seed germination rates and shorten germination processes.

Key words: endangered plant, Parrotia subaequalis, seed germination, seedling growth, gibberellin