Abstract
Acer tegmentosum, an indigenous medicinal plant under threat from overexploitation, is a deciduous tree species native to Northeast China, southern regions of the Russian Far East, and Korea. In this study, we analyzed the characteristics of samaras (single-seeded fruit) of A. tegmentosum to determine the type of seed dormancy as well as to identify the factors responsible for dormancy release. We identified the seed dormancy to be that of deep physiological dormancy (PD). PD can be combined with mechanical resistance of the seed coat, which limits the protrusion of the radicle during germination. We observed that mechanical resistance exhibited by the water-permeable testa is associated with PD of A. tegmentosum. This was previously attributed to seed dormancy in Acer as testa-imposed dormancy or embryo dormancy. In A. tegmentosum, PD and mechanical resistance of the testa were overcome through cold stratification treatment at 1 and 4 °C, which was similar to winter duration under natural conditions. The pericarp of samaras facilitated germination at an early spring temperature (15/6 °C) after cold stratification at 1 and 4 °C, enabling the seedling survival of A. tegmentosum. We concluded that the covering structures composed of testa and pericarp in A. tegmentosum play vital roles in dormancy release and subsequent seed germination; they respond to external environmental cues based on the climatic conditions of Northeast Asia. This adaptation probably determines their behavior at an early life stage in response to environmental factors.