FRASER FIR SEEDLING GAS-EXCHANGE AND GROWTH IN RESPONSE TO ELEVATED CO2

Growth and gas exchange characteristics were examined in Fraser fir (Abies fraseri (Pursh.) Poir.) seedlings grown from seed in elevated (713 ppm) or ambient (374 ppm) CO2 for 1 year (two artificial growing seasons) to determine the potential influence of a twice-ambient CO, concentration on this species. A subset of seedlings was transplanted from 172 cm3 pots into 1000 cm3 pots at 7 months to determine if CO2 effects were dependent on rooting volume. At 5 and 12 months, net photosynthesis (P(net)) and leaf conductance (g1) were lower in elevated CO2-grown seedlings grown in 172 cm3 pots than in ambient CO2-grown seedlings when measured at either 346 or 796 ppm CO2. For 12-month-old seedlings grown in 1000 cm3 pots, P(net) was reduced by an elevated CO2 growth environment only when measured at 346 ppm CO2, although g1 was lower in these seedlings when measured at either CO2 measurement level. Seedlings grown in both pot sizes and in elevated CO2 for 1 year had greater height, diameter, and leaf, stem, root and total dry weights than seedlings grown in ambient CO2. Specific leaf weight (SLW) was greater in elevated than in ambient CO2-grown needles only in the large pot size treatment. These results suggest that Fraser fir seedling growth will increase in a future elevated CO2 environment despite changes in gas exchange characteristics.