Complex Seed Dormancy in Parrotia subaequalis: Identification, Breaking Mechanisms, and Conservation Strategies for an Endangered Species in China

Parrotia subaequalis, an endangered plant unique to China, is highly valued for its significant ecological and ornamental value. The specific type of seed dormancy in this species has not been clearly reported, which limits its natural regeneration and artificial propagation, posing a challenge to its conservation and sustainable use. To address this, we conducted a comprehensive analysis of the seed dormancy mechanism of P. subaequalis and explored various methods to break dormancy, including cold and warm stratification, after-ripening, seed coat removal, and hormone soaking. Our analysis of the seeds' physical properties, water absorption patterns, seed coat structure, embryo development, and endogenous inhibitors revealed that P. subaequalis seeds exhibit complex characteristics of physical and non-deep physiological dormancy. Experimental results showed that soaking the seeds in gibberellin (GA₃) followed by seed coat removal effectively promoted germination. The optimal GA₃ concentration for germination was 800 mg·L^-1. Additionally, cold and warm stratification and after-ripening treatments significantly increased the germination percentage. These findings provide important technical support for dormancy release and seedling growth, which is crucial for the artificial propagation and population recovery of P. subaequalis.