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Two-year-old Sitka spruce (Picea sitchensis (Bong.) Carr.) seedlings were subjected to nitrogen (N) deficiency for 1 year and then treated twice weekly with N fertilizer solutions (0 to 224 mg N 1-1) for 20 weeks. Needle growth in terms of projected area and cell number, and photosynthesis in terms of pigment concentration, net photosynthetic rate (PN), stomatal conductance to CO2 (Gs) and intercellular partial pressure of CO2 (Ci) were measured. Nitrogen deficiency caused significant reductions in needle size and needle number per shoot. Refertilization caused free growth, and increases in size and cell number of needles arising from primordia initiated during N deficiency. Nitrogen concentration did not affect mean cell size, indicating that N nutrition determined needle size through cell division and not cell expansion, and that favorable N supply during needle expansion was more important in determining final needle size than limitations imposed on the primordia during the N deficiency pretreatment. Nitrogen deficiency caused reductions in chlorophyll and carotenoid concentrations, PN and Gs, and an increase in Ci. Refertilization caused a reversal of these changes, and the magnitude of the responses increased with increasing N supply. The large increases in many of the measured parameters in response to the small amounts of added N suggest that young Sitka spruce trees respond positively to N supply and are tolerant of all but severe N deficiency.

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.