Effect of freeze–thaw treatments with different conditions on frost fatigue in three diffuse-porous trees

Abstract In addition to inducing xylem embolism, freeze–thaw events can cause frost fatigue phenomena. Freezing temperature, freezing times, number of freeze–thaw cycles and frost drought can affect the level of freeze–thaw-induced embolism, but it is unknown whether there is an effect on frost fatigue. We assessed whether these frost-related factors changed frost fatigue in the three diffuse-porous species by simulating freeze–thaw treatments under different conditions. We also proposed a new metric, embolism area, in place of embolism resistance, to more accurately quantify the shift of the vulnerability curve after experiencing freeze–thaw-induced embolism and refilling. Frost fatigue caused vulnerability curves of all species to change from S-shaped to double S-shaped or even R-shaped curves. When exposed to a freeze–thaw event, Acer truncatum showed strong resistance to frost fatigue; in contrast, Populus (I-101 × 84 K) and Liriodendron chinense were more vulnerable. Changing freezing temperature and times did not impact the response to frost fatigue in the three species, but a greater number of freeze–thaw cycles and more severe frost drought significantly exacerbated their fatigue degree. Considering that frost fatigue may be a widespread phenomenon among temperate diffuse-porous species, more work is needed in the future to reveal the mechanisms of frost fatigue.