Climate reports released by the Intergovernmental Panel on Climate Change have predicted an increase in the mean annual air temperature of 2 to 4^°C and an increase in atmospheric CO₂ concentrations ([CO₂]) to 590 to 970 ppm by the year 2100.  Large shifts in precipitation are expected to accompany predicted increases in air temperature.  Previous studies have investigated the effect of increased temperature and/or increased [CO₂] on tree growth in one location.  We investigated the effect of increased temperature, increased [CO₂] and decreased precipitation on Pinus taeda growth at three locations along a longitudinal transect through its native range.  Treatment chambers were constructed in Blairsville, Athens and Tifton, GA.  At each location elevated temperature, elevated [CO₂] and water stress treatments were applied in combination.  Measurements of net photosynthesis (A_net), stomatal conductance (g_s), leaf water potential and fluorescence were made three times through the growing season (June, September and October).

Results/Conclusions

We observed a significant increase in A_net under elevated [CO₂] across all temperatures and sites during the June and September measurements.  Elevated temperature did not significantly affect A_net in saplings grown at any site or at any time throughout the season.  Water use efficiency (WUE) followed a similar trend as A_net, increasing in saplings grown under elevated [CO₂].  The water stress treatment significantly reduced A_net but increased WUE.  Temperature, [CO₂] and water treatment did not alter leaf water potential or fluorescence measurements throughout the season.  These results suggest that predicted changes in [CO₂] will significantly increase A_net in loblolly pine grown throughout its native range.  A decrease in precipitation, even under elevated [CO₂], will result in a decrease in A_net in loblolly pine grown throughout its native range.  However, predicted changes in temperature will have little impact on A_net.