Lower Stem Freezing Point Tied to Greater Frost Embolism Vulnerability: A Comparison Between Ring‐ and Diffuse‐Porous Temperate Tree Species

Temperate ring‐porous tree species are more vulnerable to freezing‐induced embolism than their diffuse‐porous counterparts due to their large earlywood vessels. Although ring‐porous species can restore hydraulic function by forming earlywood vessels in early spring, they may face high risk of embolism during spring frosts. Here, we tested the hypothesis that ring‐porous temperate trees employ a strategy of enhanced freezing avoidance to protect their vulnerable earlywood vessels from the risk of freezing‐induced embolism. We quantified the degree of embolism in overwintering stems, ice nucleation temperature (INT xylem ), water content (WC xylem ), and non‐structural carbohydrate (NSC) concentrations in stem xylems of 20 temperate tree species (nine diffuse‐porous and 11 ring‐porous) grown in a common garden. Consistent with our hypothesis, ring‐porous species suffered severe embolism over the winter and exhibited stronger freezing avoidance during spring. While diffuse‐porous species rely on smaller vessels to resist freezing‐induced embolism, ring‐porous species showed stronger ability of freezing avoidance by lowering INT xylem via reduced WC xylem and higher NSC concentrations. This strategy likely protects their vulnerable, newly developed earlywood vessels from freezing‐induced hydraulic dysfunction. These findings reveal distinct strategies between temperate diffuse‐porous and ring‐porous species for coping with spring frost stress, providing insights into forest responses to climate change.