What was done
The authors grew fifteen-year-old Norway spruce (Picea abies L.) trees in open-top chambers maintained at atmospheric CO2 concentrations of 350 and 700 ppm for four years to study the long-term effects of elevated CO2 on photosynthetic acclimation.

What was learned
When measured at reciprocal growth CO2 concentrations, CO2-enriched shoots displayed an average reduction of 18% in net photosynthetic rate compared with that of ambiently-grown shoots, thus indicating the presence of CO2-induced photosynthetic acclimation.  Likewise, when analyzing photosynthetic pigments, the authors found the total amounts of chlorophylls and carotenoids in CO2-enriched needles to be 17 and 14% less, respectively, than the amounts found in needles of ambiently-grown trees.  When measured at growth CO2 concentrations, however, current-year CO2-enriched shoots still displayed rates of net photosynthesis that were 78% greater than those exhibited by shoots of trees grown in ambient air.

What it means
As the CO2 concentration of the air continues to increase, mature Norway spruce trees will likely exhibit some degree of photosynthetic acclimation.  Nevertheless, such trees should still maintain much greater rates of photosynthesis than they do under current ambient CO2 concentrations; and they will likely use the additional photosynthate thereby produced to increase their biomass.  Thus, carbon sequestration in forests and plantations dominated by Norway spruce will likely increase in the future.