Relationship of Sophora davidii seed size to germination, dormancy, and mortality under water stress

• The osmotic potential required for different size seeds germination was determined.
• Osmotic potential lead the fluctuation of seed germination, dormancy, and mortality.
• The response of different size seeds varied under water stress.
• Seed size significantly affected seed germination, dormancy, and mortality.

Sophora davidii is an important leguminous shrub that is widely used for revegetation in areas experiencing karst rocky desertification in southwest China. Seed size is a prominent life history trait affecting seed fate. Laboratory experiments were conducted to evaluate the effect of osmotic potential and seed size on germination, dormancy, and mortality. The osmotic potentials required for 50% inhibition of maximum germination of large, medium, and small size seeds were − 0.836, − 0.786, and − 0.812 MPa, respectively. The highest seed dormancy (70%) was observed in small seeds at − 1.0 MPa and the lowest seed mortality (6%) in large seeds at 0 MPa. Increasing osmotic potential caused a decrease in the germination of large and small seeds, but increased large seeds mortality. Under mild water stress, medium seed germination, large seed dormancy, and small seed mortality were higher, whereas medium and small seed dormancy was lower. Moreover, osmotic potential and seed size significantly affected seed germination, dormancy, and mortality, as well as the interactions between them. Our findings suggest that seed size plays an ecologically important role in the fate of S. davidii seeds by improving medium or small seed germination and reducing medium or small seed mortality in severe habitats of the karst rocky desertification region.