© 1990 Heron Publishing—Victoria, Canada
Needle growth in Sitka spruce (Picea sitchensis): effects of nutrient deficiency and needle position within shoots
J. W. Chandler and J. E. Dale
Botany Department, University of Edinburgh, The King’s Buildings, Mayfield Road, Edinburgh EH9 3JH, Scotland / Received May 25, 1989
Summary
Needle development and shoot growth were studied in 14- and 20-year-old Sitka spruce (Picea sitchensis (Bong.) Carr.) planted on an oligotrophic peat and fertilized with N, P and K (control), N and P (–K), N and K (–P) or unfertilized
(–NPK). Shoot extension, needle number, and the size and number of needle cells were observed throughout the season. Beginning
with bud burst in early May, needle growth continued for nine weeks in the control treatment. Needle growth in the mineral
deficiency treatments terminated at the same time as in the controls, although it did not begin until up to three weeks later
than in the control trees. Needles developed acropetally along the shoot, with basal needles completing their development
first. Cell division in needles of control trees lasted about 3 weeks, with cell expansion continuing for a further 3 weeks.
Initial mean cell cycle times were shortest for proximal needles following bud burst, but lengthened as the season progressed.
Cell number increased from 6600 in the primordia to 200 000 in mature needles. Final needle dimensions and cell number varied
according to the position of the needle on the shoot. The largest needles with the most cells were near the middle of the
shoot. Relative to the controls, all mineral deficiency treatments reduced shoot length, bud and needle dimensions, and needle
cell number, particularly the –P treatment. Potassium and P deficiency treatments reduced primordial cell number by up to
42%, whereas final mean cell size was 30% greater in the –P treatment, 17% greater in the –NPK treatment, but 14% smaller
in the –K treatment. Mean cell size was constant for needles at all positions in any particular treatment at any time, so
that final needle size was determined by cell number alone. Needle dry weight/fresh weight ratio continued to increase until
early August, with significantly higher ratios in the –K and –P treatments than in the controls.
