Growth and annual ring structure of Larix sibirica grown at different carbon dioxide concentrations and nutrient supply rates

We compared effects of ambient (360 vpm) and elevated (720 vpm) carbon dioxide concentration (CO2]) and high and low nutrient supply rates on stem growth, annual ring structure and tracheid anatomy of Siberian larch (Larix sibirica Ledeb.) seedlings over two growing seasons. Elevated CO2] had no significant effect on either stem height or diameter growth; however, both stem height and diameter growth were enhanced by the high nutrient supply rate, and these increases were stimulated by elevated CO2]. Elevated CO2] tended to increase the width of the annual xylem ring, the number of cells in a radial file spanning the ring, and tracheid lumen diameter, whereas it tended to reduce cell wall thickness, although there were no statistically significant CO2 effects on tracheid anatomy. Changes in tracheid cell morphology seemed to be dependent on changes in shoot elongation rates.