Me. Jach et R. Ceulemans, Effects of season, needle age and elevated atmospheric CO2 on photosynthesis in Scots pine (Pinus sylvestris), TREE PHYSL, 20(3), 2000, pp. 145-157
Five-year-old Scots pine (Pinus sylvestris L.) seedlings were grown in open
-top chambers at ambient and elevated (ambient + 400 mu mol mol(-1)) CO2 co
ncentrations. Net photosynthesis (A), specific leaf area (SLA) and concentr
ations of nitrogen (N), carbon (C), soluble sugars, starch and chlorophyll
were measured in current-year and 1-year-old needles during the second year
of CO2 enrichment. The elevated CO2 treatment stimulated photosynthetic ra
tes when measured at the growth CO2 concentration, but decreased photosynth
etic capacity compared with the ambient CO2 treatment. Acclimation to eleva
ted CO2 involved decreases in carboxylation efficiency and RuBP regeneratio
n capacity. Compared with the ambient CO2 treatment, elevated CO2 reduced l
ight-saturated photosynthesis (when measured at 350 mu mol mol(-1) in both
treatments) by 18 and 23% (averaged over the growing season) in current-yea
r and 1-year-old needles, respectively. We observed significant interactive
effects of CO2 treatment, needle age and time during the growing season on
photosynthesis. Large seasonal variations in photosynthetic parameters wer
e attributed to changes in needle chemistry, needle structure and feedbacks
governed by whole-plant growth dynamics. Down-regulation of photosynthesis
was probably a result of reduced N concentration on an area basis, althoug
h a downward shift in the relationship between photosynthetic parameters an
d N was also observed.