PHOTOSYNTHESIS AND NUTRIENT SUPPLY IN NEEDLES OF SITKA SPRUCE [PICEA-SITCHENSIS (BONG) CARR]

Growth and photosynthetic development were measured for currently deve loping needles of young trees of Sitka spruce [Picea sitchensis (Bong. ) Carr.] throughout their fourth growth season. Treatments included tr ees that were fully fertilized (control), trees deficient in phosphoru s (-P), or nitrogen (-N), and trees initially deficient but then suppl ied with phosphorus (-PR) or nitrogen (-NR). Growth was measured in te rms of needle projected area, and the photosynthetic components measur ed were pigment concentration, net photosynthetic rate, (P(N)), activi ty of ribulose-1,5-bisphosphate carboxylase, (RuBPC), stomatal conduct ance to CO2, (G(S)), and the intercellular partial pressure of CO2, (C (i)). Needle growth was rapid, beginning in early May and being comple te by the end of the month or early in June. Free growth occurred in t he -NR treatment. Photosynthesis increased throughout the season, reac hing a peak in August, with some variables subsequently showing a decr ease in value. P(N) increased more rapidly during needle expansion tha n either chlorophyll concentration or RuBPC activity. Phosphorus defic iency led to a reduction in RuBPC activity, which was restored to the control value following refertilization with P. Nitrogen deficiency se verely reduced values of all variables studied, except C(i), which was higher than for the controls. Refertilization of -N trees caused a ve ry rapid increase in values of all variables, with an increase in C(i) , representing a larger increase in mesophyll conductance to CO2, (G(M )), than G(S). P(N) and RuBPC activity were significantly correlated w ith total chlorophyll concentration for all treatments, but P(N) was n ot correlated with G(s) or RuBPC activity.