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 diox ide concentration ([CO2]) and high and low nutrient supply rates on stem gr owth, annual ring structure and tracheid anatomy of Siberian larch (Larix s ibirica Ledeb.) seedlings over two growing seasons. Elevated [CO2] had no s ignificant effect on either stem height or diameter growth; however, both s tem height and diameter growth were enhanced by the high nutrient supply ra te, and these increases were stimulated by elevated [CO2]. Elevated [CO2] t ended to increase the width of the annual xylem ring, the number of cells i n 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 morph ology seemed to be dependent on changes in shoot elongation rates.