RED SPRUCE SEEDLING GAS-EXCHANGE IN RESPONSE TO ELEVATED CO2, WATER-STRESS, AND SOIL FERTILITY TREATMENTS

The interactive influences of ambient (374 muL.L-1) or elevated (713 m uL.L-1) CO2, low or high soil fertility, well-watered or water-stresse d treatment, and rooting volume on gas exchange and growth were examin ed in red spruce (Picea rubens Sarg.) grown from seed through two grow ing seasons. Leaf gas exchange throughout two growing seasons and grow th after two growing seasons in response to elevated CO2 were independ ent of soil fertility and water-stress treatments, and rooting volume. During the first growing season, no reduction in leaf photosynthesis of seedlings grown in elevated CO2 compared with seedlings grown in am bient CO2 was observed when measured at the same CO2 concentration. Du ring the second growing season, net photosynthesis was up to 21% lower for elevated CO2-grown seedlings than for ambient CO2-grown seedlings when measured at 358 muL.L-1. Thus, photosynthetic acclimation to gro wth in elevated CO2 occurred gradually and was not a function of root- sink strength or soil-fertility treatment. However, net photosynthesis of seedlings grown and measured at an elevated CO2 concentration was still over 2 times greater than the photosynthesis of seedlings grown and measured at an ambient CO2 concentration. Growth enhancement by CO 2 was maintained, since seedlings grown in elevated CO2 were 40% large r in both size and weight after two growing seasons.