NITROGEN DEFICIENCY AND FERTILIZATION EFFECTS ON NEEDLE GROWTH AND PHOTOSYNTHESIS IN SITKA SPRUCE (PICEA-SITCHENSIS)

Two-year-old Sitka spruce (Picea sitchensis (Bong.) Carr.) seedlings w ere subjected to nitrogen (N) deficiency for 1 year and then treated t wice weekly with N fertilizer solutions (0 to 224 mg N l(-1)) for 20 w eeks. Needle growth in terms of projected area and cell number, and ph otosynthesis in terms of pigment concentration, net photosynthetic rat e (P-N), stomatal conductance to CO2 (G(S)) and intercellular partial pressure of CO2 (C-i) were measured. Nitrogen deficiency caused signif icant reductions in needle size and needle number per shoot. Refertili zation caused free growth, and increases in size and cell number of ne edles arising from primordia initiated during N deficiency. Nitrogen c oncentration did not affect mean cell size, indicating that N nutritio n determined needle size through cell division and not cell expansion, and that favorable N supply during needle expansion was more importan t in determining final needle size than limitations imposed on the pri mordia during the N deficiency pretreatment. Nitrogen deficiency cause d reductions in chlorophyll and carotenoid concentrations, P-N and G(S ), and an increase in C-i. 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 re sponse to the small amounts of added N suggest that young Sitka spruce trees respond positively to N supply and are tolerant of all but seve re N deficiency.