Abstract:
The effect of lifting date and root-pruning treatments on
water potential, root regeneration, and shoot growth of six-month-old
and three-year-old Douglas-fir seedlings bare-root transplanted
into a growth chamber, and sawdust bed, respectively, was studied.
Root growth in six-month-old and three-year-old seedlings was
highest in February and August respectively. Survival was highest
in November for seedlings of both ages. The time to first root growth,
water potential four weeks after transplanting, and survival were correlated.
The possibility that the maintenance of plant turgor
above the critical level necessary to allow root growth is important
for survival of an actively growing transplant is discussed. The
effect of root-pruning on transplant water potential, root growth
and survival varied with season.
In a second study six-month-old Douglas-fir seedlings were
subjected to eight drying cycles in which the seedlings were
allowed to dry to a -15 bar water potential before watering. Root
growth, water potential, and survival of transplants were measured
under stressed and control conditions. Water potential, soil
moisture content and survival of seedlings subjected to a prolonged
drying period were recorded. Preconditioning treatments were
effective in increasing drought resistance under stress conditions.
Reductions in shoot elongation, dry matter production, and early bud
set were noted. Though inadvertant watering of the transplants made
conclusions impossible, survival data and' data collected prior to
watering indicate that root growth and survival were improved by
the treatment.
