The effects of exogenous malic acid in relieving aluminum toxicity in Pinus massoniana.

Two different genotypes of Pinus massoniana seedlings (aluminum-resistant FJ5 and aluminum-sensitive GD20) were used, the effects of different exogenous malic acid (0.00, 0.01, 0.02, 0.04, 0.08, 0.16 mmol·L^-1) on the growth attributes of P. massoniana seedlings treated by the Al³⁺ concentration of 0.8 mmol·L^-1 were studied, to provide a basis for the growth in acidified soil. In our experiment, the seedling growth was inhibited by Al³⁺ treatment. After treatment with a low concentration of exogenous malic acid, the activities of antioxidant enzymes in leaves were enhanced, the concentrations of hydrogen peroxide (H₂O₂), superoxide (O₂^-·), malondialdehyde (MDA) and osmotic adjustment substances were reduced accordingly. GD20 exhibited more severe changes compared with FJ5. The larger ones of the contribution rates of the indices in principal component analysis were H₂O₂, Glutathione Reductase (GR). These results indicated that Al³⁺ with high concentration inhibits the growth of P. massoniana. Malic acid could effectively alleviate the toxicity, and the mitigation effect on the aluminum-sensitive species, which genotype is more sensitive to the response of Al³⁺ toxicity, was more effective than that on the aluminum-resistant. How to select and cultivate more resistant species, by using the main parameter (H₂O₂ and GR), is worthy in further study.