What was done
Pine seedlings (Pinus radiata) were grown in open-top chambers near Bromley, Christchurch, New Zealand, for four years at atmospheric CO2 concentrations of 360 and 650 ppm.  After this time period, photosynthetic parameters were measured in current year and one-year-old needles of trees at each CO2 concentration to determine the effects of elevated CO2 and leaf age on photosynthesis.

What was learned
Elevated CO2 increased rates of photosynthesis by 63 and 31% in current and one-year-old needles, respectively, indicating that needle age is an important determinant of photosynthetic acclimation in this species.  Atmospheric CO2 enrichment did not induce changes in rubisco content or activity in current-year needles, but it did reduce rubisco content and activity by about 40% in one-year-old needles.  Thus, even after four years of CO2 enrichment, photosynthetic enhancement persisted in this species with partial down regulation exhibited only in one-year-old needles.

What it means
Pinus radiata will likely exhibit increased rates of photosynthesis as the CO2 content of the air steadily rises in the future. Even if acclimation occurs, it will not completely diminish enhanced rates of photosynthesis.  Thus, the resulting increase in carbohydrate production will likely be used to increase tree size and biomass, as the phenomenon of acclimation typically allows greater amounts of nitrogen to be mobilized away from photosynthesis and towards other processes, like structural growth, which are often limited by the availability of nitrogen.