Abstract:
In the Pacific north-west, the Cascade Mountain Range
blocks much of the precipitation and maritime influence
of the Pacific Ocean, resulting in distinct climates east and
west of the mountains. The current study aimed to investigate
relationships between water storage and transport
properties in populations of Douglas-fir (Pseudotsuga
menziesii) and ponderosa pine (Pinus ponderosa)
adapted to both climates. Sapwood thickness, capacitance,
vulnerability to embolism, and axial and radial conductivity
were measured on samples collected from trunks of
mature trees. The sapwood of ponderosa pine was three to
four times thicker than Douglas-fir. Radial conductivity
was higher in west-side populations of both species, but
axial conductivity was higher in the east-side populations
and in Douglas-fir. Eastern populations of both species
had sapwood that was more vulnerable to embolism than
west-side populations. Sapwood capacitance was similar
between species, but was about twice as great in east-side
populations (580 kg m⁻³ MPa⁻¹) as in west-side populations
(274 kg m⁻³ MPa⁻¹). Capacitance was positively correlated
with both mean embolism pressure and axial conductivity
across species and populations, suggesting that coordinated
adjustments in xylem efficiency, safety and water
storage capacity may serve to avoid embolism along a
gradient of increasing aridity.
