Objective  Effect of aluminum (Al)-stress on organic acids in seedlings of Chinese fir, Cunninghamia lanceolata (Lamb.) Hook, was examined in a simulated study.

  Method   Nutrient culture solutions containing Al in varied concentrations were used to cultivate the seedlings. Organic acids in the plant tissues (i.e., needles and roots) and secreted from the root-tips of the seedlings grown in the media were determined to analyze the effect of Al-stress by a correlation analysis.

  Result   Six organic acids including oxalic acid, tartaric acid, L-malate, ascorbic acid, citric acid, and fumaric acid were found in the needles and roots of the Chinese fir seedlings. Among them, ascorbic acid had the highest content in the needles, while ascorbic acid and oxalic acid in the roots. Under Al-stress, tartaric acid, L-malate, ascorbic acid, citric acid, and fumaric acid increased initially and followed by a decline in the needles, but the oxalic acid on a constant increase trend. At Al concentration of 1 mmol·L⁻¹, L-malic acid and fumaric acid significantly increased, with no significant changes on the other acids, in the needles. The contents of the 6 organic acids in roots of the plants under varied Al-stresses were significantly lower than those of control. Aside from minute amounts of L-malate, ascorbic acid, and lactic acid, oxalic acid was the major organic acids found in the root-tip exudate. It was significantly reduced by the imposition of Al-stress.

  Conclusion  The responses of Chinese fir seedlings to the simulated Al-stress varied with respect to the organic acid contents in the needles or roots and the root-tip secretion. Significant effects were observed on L-malic acid and fumaric acid in the needles and on all 6 organic acids in the roots, as well as oxalic acid exudated from the root-tips. Al-stress appeared to exert greater harm to the roots than the needles on a fir plant.