Drought is a key constraint on plant growth and development. Poplars and willows are dioecious plants, and sex-specific responses to drought differ across species. However, little is known about how xylem embolism drives sex-specific hydraulic failure. In this study, male and female Populus cathayana and Salix babylonica were used to investigate the role of embolism in sex-specific drought responses. Drought significantly reduced plant growth and photosynthetic capacity, increased membrane damage and reactive oxygen species accumulation, altered vessel structure and aggravated embolism. P. cathayana males maintained higher net photosynthetic rates than females, whereas S. babylonica females performed better than males under drought stress. P. cathayana males exhibited larger vessel area and diameter but lower density than females, while the opposite sex pattern was observed in S. babylonica. In terms of hydraulic function, male P. cathayana and female S. babylonica had lower embolism degrees, higher hydraulic conductivity and maintained more stable conductivity than their opposite sexes. Embolism degree was strongly correlated with both the standardized vessel structure index and the standardized photosynthetic index (R2 = 0.81 and 0.93 for P. cathayana; 0.78 and 0.91 for S. babylonica, respectively). Overall, male P. cathayana and female S. babylonica were more resistant to embolism, sustaining higher photosynthetic performance and growth. These findings suggest that drought alters xylem vessel structure, thereby inducing embolism and restricting growth, which forms the core mechanism underlying sex-specific drought responses in P. cathayana and S. babylonica.
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