AN ABSTRACT OF THE THESIS OF
Mary Louise Duryea
for the degree of
Doctor of Philosophy
April 15, 1981
WATER RELATIONS, GROWTH AND SURVIVAL OF ROOT-WRENCHED
Abs tract Approved:
Denis P. Lavender
Growth and Survival of Root-Wrenched Douglas-fir Seedlings
Root wrenching of seedlings (severing the roots 15 cm below the
soil surface) was investigated as a nursery practice to improve growth
and survival of field-planted Douglas-fir from six local seed sources
in the Pacific Northwest.
At lifting, shoots of wrenched seedlings
were shorter, lighter, and had smaller diameters than those of
Among seedlings from four of the seed sources,
wrenching resulted in significantly lighter taproots but did not
significantly affect lateral root and total root weights.
no significant differences between these measurements among wrenched
and unwrenched seedlings from the other two sources. Mainly because
of lighter shoots, shoot-root ratios were smaller for wrenched than
for unwrenched seedlings.
In no case did root wrenching improve field
height growth or survival after one year, and among four of the sour-
ces shoot growth was significantly less than that of unwrenched
Water Relations of Root-wrenched Douglas-fir Seedlings
Root wrenching was investigated as a nursery practice to precon-
dition Douglas-fir seedlings to droughty field conditions.
shocked the seedlings while in the nursery, lowering plant water
potential and transpiration rate.
After planting, however, wrenched
and unwrenched seedlings transpired at equal rates when exposed to
stress with osmotic solutions of Polyethylene Glycol 1000 and under
field conditions. Throughout exposure in pots to a drought simulating
the Pacific Northwest summer drought, wrenched and unwrenched
seedlings did not differ in plant water potential, leaf relative water
content, or seedling condition. However, all wrenched seedlings of
four seed sources reflushed in