Fraser fir seedling gas exchange and growth in response to elevated CO 2

Abstract

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) CO 2 for 1 year (two artificial growing seasons) to determine the potential influence of a twice-ambient CO 2 concentration on this species. A subset of seedlings was transplanted from 172 cm 3 pots into 1000 cm 3 pots at 7 months to determine if CO 2 effects were dependent on rooting volume. At 5 and 12 months, net photosynthesis ( P net) and leaf conductance ( g l) were lower in elevated CO 2-grown seedlings grown in 172 cm 3 pots than in ambient CO 2-grown seedlings when measured at either 346 or 796 ppm CO 2. For 12-month-old seedlings grown in 1000 cm 3 pots, P net was reduced by an elevated CO 2 growth environment only when measured at 346 ppm CO 2, although g l was lower in these seedlings when measured at either CO 2 measurement level. Seedlings grown in both pot sizes and in elevated CO 2 for 1 year had greater height, diameter, and leaf, stem, root and total dry weights than seedlings grown in ambient CO 2. Specific leaf weight ( SLW) was greater in elevated than in ambient CO 2-grown needles only in the large pot size treatment. These results suggest that Fraser fir seedling growth will increase in a future elevated CO 2 environment despite changes in gas exchange characteristics.