Xylem Structure And Embolism Vulnerability Of Populus Clones

Populus clones from Weihe Trail Base were studied. We used Cochard cavitroncentrifuge to determine embolism vulnerability(P₅₀), and staining as well as silicone injectiontechniques to measure vessel diameter, vessel lengths and pit area per vessel in six clones toreveal the differences among vulnerability curves of Populus clones. The aim is to probe intothe correlationship between embolism vulnerability and vessel structure to provide scientificbases for selecting embolism-resistant woody species, and for breeding and selectingdrought-resistant woody species in arid and semi-arid areas. The main results are as follows:（1）The sequence of the sensitivity of xylem embolism to water potentials of the sixclones was02-8-21>I-101>02-9-22>02-12-29>84K>Populus tomentosa30, and hybridprogeny02-9-22and02-12-29were more resistant to embolism than02-8-21. As droughttolerant tree species, Clones-30was the most resistant to embolism.（2）The order of vessel diameter size of the six clones was02-8-21>02-9-22>02-12-29>84K>P. tomentosa30>I-101, vessel length P. tomentosa30>02-8-21>02-9-22>02-12-29>I-101>84K, pit area per vessel02-8-21>02-9-22>02-12-29>P. tomentosa30>I-101>84K. This suggested that the vulnerability to embolismincreased with the vessel diameter and pit area per vessel.（3） Regression analysis illustrates that there was a strong positive correlation （R²>0.7）between the vessel diameter and the pit area per vessel, while weak correlation existedbetween the vessel length and embolism vulnerability （R²=0.066）. Except the02-9-22, thevessel lengths of other4clones （84K, I-101,02-8-21,02-12-29and Populus tomentosa30）were highly correlated to the value of P₅₀（R²=0.843）.（4） In the six clones, when they shared obvious disparities in vessel diameter and pit areaper vessel, their P₅₀values would have significant differences as well. So it can be concludedthat the level of differences of vulnerability of embolism was decided by the level ofdifferences in vessel diameter and pit area per vessel. There was no obvious relationshipbetween the differences of their P₅₀values and the significant differences of the vessel length, the vessel length only influenced on the P₅₀value.（5） Regression analysis illustrated that there was a strong positive correlation betweenthe pit fraction and the contact fraction（R²=0.988）, however, a weak correlation was foundbetween the pit fraction and pit field fraction（R²=0.265）. The contact fraction had strongerinfluence on the pit fraction.