Effects of dormancy-breaking methods on germination of the water-impermeable seeds of Gleditsia caspica (Fabaceae) and seedling growth

Various treatments can be used to break physical dormancy (PY, i.e. water-impermeable seed coat) of legume species, but the effects of these treatments on seedling growth are of great importance in the success of afforestation projects. Our aims were to determine the effects of 20 PY-breaking treatments on (1) germination of Gleditsia caspica (Caspian locust) seeds and (2) seedling growth. Five germination and nine seedling growth and morphological traits were studied. Immersion in concentrated sulfuric acid (98%) for 60 minutes was optimal for all germination traits and for all seedling traits except root length. After seed coat removal or treatment with sulfuric acid (for 45 to 120 minutes), 99–100% of the seeds germinated, but seedling growth traits after 5 months were significantly lower in the former than in the latter treatment. Other treatments (e.g., different periods of exposure to cold water, boiling water, and KNO3) did not significantly increase germination or improve seedling growth. Thus, despite incurring adverse environmental impacts, sulfuric acid treatments have the best potential to break seed dormancy and produce high-quality seedlings (in terms of shoot length, root and shoot mass, root area, leaf number and area and collar diameter) of Caspian locust.