Abstract: The structure of secondary xylem and secondary phloem of Quercus liaotungensis grown under conditions of ambient (350 μl·L-1) and doubled CO2 concentration (700 μl·L-1) was investigated. Statistical analysis of results indicated that ring width increased significantly under the CO2-enriched environment, which was 300%–370% of those from plants grown under ambient CO2 environment (CK). In particular, latewood width was affected much more strongly by the treatment. Furthermore, vessel number per square millimeter and radial diameter of vessels of latewood as well as ratio of wood fibers also increased, 150%, 120% and 150% respectively of that observed under CK. Nevertheless, no dramatic change was observed in terms of mean length and tangential diameter of vessels, thickness of cell wall and length of fibers of secondary xylem. In the secondary phloem, mean length and number of phloem fibers and crystalliferous parenchyma cells per phloem fiber band increased in response to higher CO2(p≤0.05). In contrast, width and total cells of secondary phloem formed each year and diameter of sieve tubes were reduced to 82%, 80% and 87% of that of the CK grown plants respectively with increased CO2 concentration. It was concluded that secondary xylem responded positively, while the diameter of sieve tubes and the width of secondary phloem showed a negative response to CO2-enrichment during the experiment.

Key words: Quercus liaotungensis, Doubled CO2 concentration, Secondary xylem, Secondary phloem