Growth dynamics and water use of seedlings of Quercus alba L. in CO 2 ‐enriched atmospheres

summary White oak ( Quercus alba L.) seedlings were grown from a half‐sib collection of acorns in pots containing a nutrient‐Poor forest soil and maintained in controlled‐environment chambers having mean atmospheric CO 2 concentrations of 389, 496, and 793 cm 3 m −3 . Additions of nitrogen and phosphorus to the soil increased plant growth, indicating that the unfertilized plants were nutrient deficient. Despite the nutrient deficiency, the plants grown in elevated concentrations of CO., generally were larger than those in ambient CO 2 , but dry weight data from harvests at 5, 12, 24, and 36 weeks provided insufficient evidence of an effect of CO 2 because of the high variability associated with the recurrently‐Hushing habit of these seedlings. Mathematical growth analysis based on periodic non‐destructive measurements allowed comparisons of the continuous growth patterns of the plants and avoided the problems of ontogenetic variation. CO 2 , enrichment was thus shown to increase plant growth rate primarily through increased unit leaf rate rather than increased leaf area production. Unit leaf rate during the second half of the experiment was 22 and 27% higher in the medium and high concentrations of CO 2 compared with that in low CO 2 instantaneous measurements of foliar gas exchange also showed that CO 2 , assimilation increased with CO 2 , enrichment. The most pronounced effect of CO 2 , enrichment was increased water‐use efficiency, which was shown both through whole‐plant gravimetric analysis and instantaneous gas exchange measurements. Whole‐plant water‐use efficiency for the duration of the experiment was increased by 52 and 82% by the mdium and high concentrations of CO 2 . Limitations of resources, including water and nutrients, do not preclude plant growth responses to CO 2 enrichment of the atmosphere.