Seasonal changes in hydraulic functions of eight temperate tree species: divergent responses to freeze–thaw cycles in spring and autumn.

This article investigates seasonal changes in branch hydraulic functions and their responses to freeze–thaw cycles (FTCs) in eight temperate tree species representing three wood types: ring-porous, diffuse-porous, and tracheid. The study found that ring-porous trees exhibit consistently low hydraulic conductance and high hydraulic damage during non-growing seasons, recovering before the growing season by producing new xylem. Diffuse-porous and tracheid trees showed significant hydraulic damage after spring FTCs but not after autumn FTCs, with hydraulic functions recovering from winter to summer; this difference is attributed to the number of FTCs and tree vitality prior to freezing events. Additionally, wood density increased from summer to winter in diffuse-porous and tracheid trees, indicating higher carbon investment and hydraulic safety as adaptive strategies to freezing stress. These findings enhance understanding of how temperate trees’ hydraulic traits seasonally adjust and cope with different FTC types, informing models of plant growth and distribution under climate change.