Whole-tree water relations of western gall rust infected lodgepole pine trees

Abstract

Lodgepole pine (Pinus contorta Dougl. ex Loud.) trees having galls resulting from infection by western gall rust (WGR; Endocronartium harknessii (J.P. Moore) Y. Hiratsuka) have a lower ability to conduct water than nongalled stems. Experiments were conducted to compare the leaf-specific hydraulic capacity (Q _L; g H₂O·cm⁻¹ ·MPa⁻¹) of galled and control trees. Specific objectives were to test the hypothesis that Q _L was reduced in galled trees, to determine which components of Q _L, if any, varied between galled and control trees, and to test the hypothesis that water stress would more negatively affect galled trees than control trees. Under well-watered conditions, galled trees had lower Q _L than control trees. This difference was associated with an increased water potential difference between the soil and leaves (ΔΨ MPa) rather than a change in transpiration per unit leaf area (E _L; g H₂O·cm⁻² A _L). Although water stress reduced Q _L, the effect was similar for galled and control trees, indicating that the former were no more vulnerable to xylem cavitation than the latter. The similarities in the short-term responses of galled and control trees under well-watered conditions are consistent with the observation that stem galls do not result in rapid tree mortality.

Keywords:

• western gall rust
• Endocronartium harknessii
• Pinus contorta
• leaf-specific hydraulic capacity
• transpiration