title: Nitrogen and potassium effects on xylem cavitation and water-use efficiency in poplars.
abstract: Effects of N and K nutrition on drought and cavitation resistance were examined in six greenhouse-grown poplar clones: Populus trichocarpa (Torr. & Gray) and its hybrids with P. deltoides Bartr. and P. euramericana (Dole) Guinier, before and after preconditioning to water stress. Both tendency to cavitate and water-use efficiency (WUE) increased when N supply was increased, whereas K supply had little impact on cavitation. Mean xylem vessel diameters increased from 36.6 &mgr;m at low-N supply to 45.2 &mgr;m at high-N supply. Drought-hardy clones, which were relatively resistant to cavitation, had the smallest mean vessel diameters. Vulnerability to cavitation had a weakly positive relationship with vessel diameter, and a negative correlation with transpiration. Drought hardening offered no protection against cavitation in a subsequent drought. Under drought conditions, increasing N supply increased leaf loss and decreased water potentials, whereas increasing K supply decreased leaf loss. Drought-resistant clones exhibited similar WUE to drought-susceptible clones, but had smaller, more numerous stomata and greater leaf retention under drought conditions.
authors.affiliation: Centre for Forest Biology, University of Victoria, P.O. Box 1700, Victoria, B.C. V8W 2Y2, Canada.
authors.forename: H. P.
authors.initials: HP
authors.lastname: Harvey
authors.forename: R.
authors.initials: R
authors.lastname: Van Den Driessche