Effects of Atmospheric CO2 Enrichment on the Growth and Mineral Nutrition of Quercus alba Seedlings in Nutrient-Poor Soil

One-year-old dormant white oak (Quercus alba L.) seedlings were planted in a nutrient-deficient forest soil and grown for 40 weeks in growth chambers at ambient (362 microliters per liter) or elevated (690 microliters per liter) levels of CO(2). Although all of the seedlings became severely N deficient, CO(2) enrichment enhanced growth by 85%, with the greatest enhancement in root systems. The growth enhancement did not increase the total water use per plant, so water-use efficiency was significantly greater in elevated CO(2). Total uptake of N, S, and B was not affected by CO(2), therefore, tissue concentrations of these nutrients were significantly lower in elevated CO(2). An increase in nutrient-use efficiency with respect to N was apparent in that a greater proportion of the limited N pool in the CO(2)-enriched plants was in fine roots and leaves. The uptake of other nutrients increased with CO(2) concentration, and P and K uptake increased in proportion to growth. Increased uptake of P by plants in elevated CO(2) may have been a result of greater proliferation of fine roots and associated mycorrhizae and rhizosphere bacteria stimulating P mineralization. The results demonstrate that a growth response to CO(2) enrichment is possible in nutrient-limited systems, and that the mechanisms of response may include either increased nutrient supply or decreased physiological demand.