7. Discussion
We tested three hypotheses to assess variability and coordination of key
plant hydraulic traits across ten deciduous forest stands. We found
little support that stand age and hydroclimate influenced relative xylem
vulnerability (hypothesis 1 & 2). While we detected some region and age
effects, variation in vulnerability to embolism was principally
determined by the large species effect. Additionally, we found little
support for hypothesis 3, which predicted stricter ΨLregulation would be associated more vulnerable xylem. Contrary to the
prevailing expectation, we found that the more anisohydric Q.
alba possessed stem tissues more vulnerable to embolism than their more
isohydric counterparts. Moreover, we found that Q. alba had small
or negative Ψsafety and a high degree of estimated
native embolism such that its loose regulation of ΨLlikely occurred with a substantial hydraulic cost.