Jw. Chandler et Je. Dale, PHOTOSYNTHESIS AND NUTRIENT SUPPLY IN NEEDLES OF SITKA SPRUCE [PICEA-SITCHENSIS (BONG) CARR], New phytologist, 125(1), 1993, pp. 101-111
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.