K. Laitinen et al., Carbon assimilation and nitrogen in needles of fertilized and unfertilizedfield-grown Scots pine at natural and elevated concentrations of CO2, TREE PHYSL, 20(13), 2000, pp. 881-892
Effects of elevated CO2 concentration ([CO2]) on carbon assimilation and ne
edle biochemistry of fertilized and unfertilized 25-30-year-old Scots pine
(Pinus sylvestris L.) trees were studied in a branch bag experiment set up
in a naturally regenerated stand. In each tree, one branch was enclosed in
a bag supplied with ambient [CO2] (360 mu mol mol(-1)), a second branch was
enclosed in a bag supplied with elevated [CO2] (680 mu mol mol(-1)) and a
control branch was left unbagged. The CO2 treatments were applied from Apri
l 15 to September 15, starting in 1993 for unfertilized trees and in 1994 f
or fertilized trees, which were treated with N in June 1994. Net photosynth
esis, amount and activity of Rubisco, N, starch, C:N ratio and SLA of needl
es were measured during the growing season of 1995.
Light-saturated net photosynthetic rates of 1-year-old and current-year sho
ots measured at ambient [CO2] were not affected by growth [CO2] or N fertil
ization. Elevated [CO2] reduced the amount and activity of Rubisco, and the
relative proportion of Rubisco to soluble proteins and N in needles of unf
ertilized trees. Elevated [CO2] also reduced the chlorophyll concentration
(fresh weight basis) of needles of unfertilized trees. Soluble protein conc
entration of needles was not affected by growth [CO2]. Elevated [CO2] decre
ased the Rubisco:chlorophyll ratio in unfertilized and fertilized trees. St
arch concentration was significantly increased at elevated [CO2] only in 1-
year-old needles of fertilized trees. Elevated [CO2] reduced needle N conce
ntration on a dry weight or structural basis (dry weight minus starch) in u
nfertilized trees, resulting in an increase in needle C:N ratio. Fertilizat
ion had no effect on soluble protein, chlorophyll, Rubisco or N concentrati
on of needles. The decrease in the relative proportions of Rubisco and N co
ncentration in needles of unfertilized trees at elevated [CO2] indicates re
allocation of N resources away from Rubisco to nonphotosynthetic processes
in other plant parts. Acclimation occurred in a single branch exposed to hi
gh [CO2], despite the large sink of the tree. The responses 1-year-old and
current-year needles to elevation of growth [CO2] were similar.