© 1997 Heron Publishing—Victoria, Canada
Nutrition, xylem cavitation and drought resistance in hybrid poplar
H. P. Harvey and R. van den Driessche
B.C. Ministry of Forests Research Laboratory, 1320 Glyn Road, Victoria, BC V8W 3E7, Canada / Received November 20, 1996
Summary
Effects of mineral nutrition on susceptibility to cavitation were examined in four hybrid poplar clones. Two drought-sensitive
and two drought-resistant hybrid clones of black cottonwood (Populus trichocarpa Torr. & Gray) and eastern cottonwood (P. deltoides Bartr.) were grown at three concentrations of nitrogen (N) applied factorially with two concentrations of phosphorus (P)
in a greenhouse, and subjected to varying degrees of drought stress before measurement of cavitation and of anatomical features
that might affect cavitation. Mean vessel pit pore diameters were 0.132 µm at low P, and 0.074 µm at high P, but no other
significant effects of mineral nutrition on vessel dimensions were observed. Vessel diameter and specific conductivity were
greater in the drought-resistant clones than in the drought-susceptible clones. Drought-resistant clones did not reach such
low water potentials as drought-sensitive clones during the cavitation induction experiments, suggesting better stomatal and
cuticular control of water loss. Scanning electron microscope observations showed less damage to pit membranes, also suggesting
greater membrane strength in drought-resistant clones than in drought-sensitive clones. High concentrations of N increased
cavitation, whereas high concentrations of P decreased cavitation as measured by both hydraulic flow apparatus and dye perfusion
techniques. For one test, cavitation was 48% at high N and low P, but only 28% at high N and high P. We consider that N fertilization
may make poplars more susceptible to cavitation on dry sites, but P fertilization may reduce this effect.
Keywords:
cottonwood, embolism, hydraulic conductivity, nitrogen, phosphorus, Populus.
