Relationships Between Xylem Strucrure And Drought Tolerance Of Drought Tolerant Tree Species

Xylem embolism vulnerability can be used as an indicator of drought resistance, the study of embolism has become a hot and key topic under global climate change. Drought tolerant tree species of Robinia pseudoacacia, Hippophae rhamnoides, Ulmus pumila, Corylus heterophylla, Salix matsudana, Acer truncatum were studied. Cochard cavitron centrifuge was used to establish embolism vulnerability curves and to calculate xylem vulnerability value, and staining as well as silicone injection techniques to measure vessel diameter, conduit wall span, number of vessels per unit area, contact faction, vessel length and wood density of drought tolerant tree species. The objective of the study was to probe into the relationship between xylem structure and embolism vulnerability, to distinguish the differences in resistance embolism of xylem in each species, and to establish drought tolerance indexes in xylem structure of six species. The main results are as follows:1. The vulnerability curves of six drought tolerant tree species were well fitted by single Weibull, the vulnerability curves of Robinia pseudoacacia, Hippophae rhamnoides, Ulmus pumila is “r” shape and “s” shape for Corylus heterophylla, Salix matsudana, Acer truncatum respectively.2. The sequence of the sensitivity of xylem embolism to water potentials of the drought tolerant tree species was Robinia pseudoacacia(-0.22±0.026MPa) >Ulmus pumila(-0.55±0.064MPa) >Hippophae rhamnoides(-1.31±0.183MPa) >Salix matsudana(-1.55± 0.103 MPa) > Acer truncatum(-2.64±0.214MPa) > Corylus heterophylla(-2.84±0.054MPa), the xylem vulnerability values extremely significantly difference in trees of “r” shape and “s” shape(p < 0.01), Corylus heterophylla was most resistant to embolism, Acer truncatum was the second and Salix matsudana was the last in vulnerability curves of “s” shape, Hippophae rhamnoides was the most resistant to embolism, Ulmus pumila was the second, and Robinia pseudoacacia was the last in vulnerability curves of “r” shape.3. The order of vessel diameter size of the six drought tolerant tree species was Robinia pseudoacacia> Ulmus pumila> Salix matsudana> Acer truncatum> Corylus heterophylla> Hippophae rhamnoides,vessel length: Robinia pseudoacacia> Ulmus pumila> Hippophae rhamnoides> Salix matsudana> Corylus heterophylla> Acer trunkatum,conduit wall span: Robinia pseudoacacia> Ulmus pumila> Hippophae rhamnoides> Salix matsudana> Acer truncatum> Corylus heterophylla, number of vessels per unit area: Salix matsudana> Corylus heterophylla> Hippophae rhamnoides> Acer truncatum> Ulmus pumila> Robinia pseudoacacia, contact fraction: Acer truncatum> Corylus heterophylla> Salix matsudana> Ulmus pumila> Hippophae rhamnoides> Robinia pseudoacacia, wood density: Hippophae rhamnoides> Salix matsudana> Acer truncatum> Robinia pseudoacacia= Ulmus pumila> Corylus heterophylla. Furthermore, linear analysis showed that the different effects between the xylem structure of the species was closely related to the vulnerability in the following order: the maximum effect was from wood density(t = 0.702), the medium effect was from vessel diameter(t = 0.532), and the minimum effect was from vessel length(t = 0.01).4. There was a relationship between xylem structure and vunerability.Regression analysis illustrated that there was a positive correlation between vessel diameter,vessel length,conduit wall span and vunerability(R2>0.70),and a negative correlation between number of vessels per unit area,contact fraction,wood density and vunerability(R2>0.60).