Jw. Chandler et Je. Dale, NITROGEN DEFICIENCY AND FERTILIZATION EFFECTS ON NEEDLE GROWTH AND PHOTOSYNTHESIS IN SITKA SPRUCE (PICEA-SITCHENSIS), Tree physiology, 15(12), 1995, pp. 813-817
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.