Photosynthesis And Nutrient Supply In Needles Of Sitka Spruce [Picea-Sitchensis (Bong) Carr]

Growth and photosynthetic development were measured for currently developing needles of young trees of Sitka spruce [Picea sitchensis (Bong.) Carr.] throughout their fourth growth season. Treatments included trees that were fully fertilized (control), trees deficient in phosphorus (-P), or nitrogen (-N), and trees initially deficient but then supplied with phosphorus (-PR) or nitrogen (-NR). Growth was measured in terms of needle projected area, and the photosynthetic components measured were pigment concentration, net photosynthetic rate, (P(N)), activity of ribulose-1,5-bisphosphate carboxylase, (RuBPC), stomatal conductance to CO2, (G(S)), and the intercellular partial pressure of CO2, (C(i)). Needle growth was rapid, beginning in early May and being complete by the end of the month or early in June. Free growth occurred in the -NR treatment. Photosynthesis increased throughout the season, reaching a peak in August, with some variables subsequently showing a decrease in value. P(N) increased more rapidly during needle expansion than either chlorophyll concentration or RuBPC activity. Phosphorus deficiency led to a reduction in RuBPC activity, which was restored to the control value following refertilization with P. Nitrogen deficiency severely reduced values of all variables studied, except C(i), which was higher than for the controls. Refertilization of -N trees caused a very 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 with total chlorophyll concentration for all treatments, but P(N) was not correlated with G(s) or RuBPC activity.