Native plants have adaptations to their local environments and elucidation of these traits has implications in both agronomy and restoration ecology. Winterfat (Krascheninnikovia lanata (Pursh) A.D.J. Meeuse & Smit) is a native perennial shrub in North America capable of germinating at low temperatures. The effect of seed size on germination ability at low and subzero temperatures and the physiological mechanisms were investigated. Winterfat seeds achieved 50%–72% germination at –3 °C, a temperature slightly above the base temperature estimated using thermal time models. Small seeds required a longer time to reach 50% germination at subzero temperatures than large seeds. Large seeds maintained stable water uptake rate for both the seed and the embryo when temperatures decreased from 5 to –1 °C. In contrast, faster water uptake and greater relative K+ leakage in small seeds indicated possible damage to membrane integrity at subzero temperatures. Carbohydrate conversion efficiency (Rq/RCO2) of large seeds was significantly higher than that of small seeds at 10 °C but not at 20 °C. Higher cold resistance in large seeds was also correlated with higher concentrations of glucose, raffinose, and sucrose. This study revealed the potential basis of the low-temperature germination advantage of large seeds and provided the first direct evidence of germination under freezing temperatures in winterfat.

Keywords Calorimetry, Freezing tolerance, Potassium leakage, Seed size, soluble sugars, thermal time, winterfat (krascheninnikovia lanata).