Abstract: In this paper, 4 Populus clones of 84K (Populus alba×P. glandulosa), I-101(Populus alba) and their hybrid progenies 02-8-21, 02-9-22 were studied. We used Cochard cavitron centrifuge to determine embolism vulnerability(P₅₀), and staining as well as silicone injection techniques to measure vessel diameter, vessel length and pit area per vessel of the four clones. The aim is to probe into the relationship between embolism vulnerability and vessel structure, and to establish xylem structure index system of poplar clones. The results showed that the sensitivity of xylem embolism to water potentials of the four clones was ranked as:02-8-21>I-101>02-9-22>84K, and hybrid progeny 02-9-22 was more resistant to embolism than 02-8-21. The order of vessel diameter size of the four clones was 02-8-21 > 02-9-22 > 84K > I-101, vessel length 02-9-22>02-8-21> I-101 > 84K, pit area per vessel 02-8-21 > 02-9-22 > I-101 > 84K. Regression analysis illustrated that with the vessel diameter and pit area per vessel increased, its embolism vulnerability also increased, indicating that there was a strong positive correlation (R²>0.7), while vessel length had weak correlation with embolism vulnerability (R²=0.019). Thus, vessel diameter size plays a decisive role on embolism vulnerability.

Key words: embolism vulnerability, vessel diameter, vessel length, pit area per vessel, Populus, xylem