Tissue chemistry and carbon allocation in seedlings of Pinus palustris subjected to elevated atmospheric CO2 and water stress

Longleaf pine (Pinus palustris Mill.) seedlings were grown in 45-1 pots and exposed to ambient or elevated (365 or 730 mu mol CO2 mol(-1)) CO2 concent ration in open-top chambers for 20 months. Two water-stress treatments (tar get values of -0.5 or -1.5 MPa xylem pressure potential) were imposed 19 we eks after initiation of the study. At harvest, tissues (needles, stems, tap roots, coarse roots, and fine roots) were analyzed for carbon (C), nitrogen (N), nonpolar extractives (fats, waxes, and oils), nonstructural carbohydr ates (sugars and starch), structural components (cellulose and lignin), and tannins. The greatest dry weights and lowest N concentrations occurred in tissues of plants grown at elevated CO2 or with adequate water. Although allocation of C fractions among tissues was generally unaffected b y treatments, concentrations of the analyzed compounds were influenced by t reatments in needles and taproots, but not in stems and lateral roots. Need les and taproots of plants exposed to elevated CO2 had increased concentrat ions of nonstructural carbohydrates. Among plant tissues, elevated CO2 caus ed reductions in structural C concentrations and foliar concentrations of f ats, waxes and oils.