Abstract:

【Objective】 This study compares the mitigating ability of oxalic acid, citric acid, and malic acid on Al toxicity in GD20 (Al-sensitive) genotypes of Pinus massoniana seedlings. It provides theoretical bases for the potential mechanisms through which organic acids mitigate Al tolerance. 【Method】 The effects of oxalic acid, citric acid and malic acid on the physiological indices related to growth, antioxidant system, and non-enzymatic substances of Al toxicity environment in Al³⁺ sensitive GD20 Pinus massoniana family lines were determined by hydroponics. Based on the growth, antioxidant system of root and leaf (SOD, POD, CAT, MDA), ROS of needles and leaves (H₂O₂, $\mathrm{O}_{2}^{-}$), non-enzymatic substances of root and leaf (soluble sugars, proline, protein) were classified for the determination indices. Using the principle of multi-factor integrated decision-making in fuzzy mathematics, the weighted average method and the maximum principle were applied to comprehensively evaluate the physiological indices affected by the external application of organic acids in the aluminum toxicity state of GD20. 【Result】The three organic acids effectively reduce the aluminum content in the root system and alleviate the inhibition of Al toxicity on the growth of horsetail pine. The application of these acids stimulates the antioxidant defense system, mitigating membrane lipid peroxidation and cellular damage caused by Al toxicity. They also maintain a stable metabolic environment by regulating the content of non-enzymatic substances in Pinus massoniana. In regulating the antioxidant system, oxalic acid (0.20 mmol/L) enhances the activities of SOD, POD, and CAT enzymes in the root system more effectively than malic acid (0.01 mmol/L) and citric acids(0.02 mmol/L); it also significantly reduces the accumulation of MDA in the root system due to aluminum toxicity. The comprehensive evaluation results, using the entropy weighting method, indicated that oxalic acid effectively regulates the antioxidant enzyme activities of P. massoniana seedlings under aluminum stress, achieving a scoring coefficient of 0.20 and a total score of 0.26, higher than those of citric acid and malic acid. 【Conclusion】 Citric acid, oxalic acid, and malic acid can jointly alleviate aluminum toxicity in horsetail pine seedlings. However, the detoxification effects of these acids vary, with oxalic acid demonstrating a superior ability to detoxify aluminum compared to citric acid and malic acid.

Key words: Pinus massoniana, organic acids, Al toxicity, antioxidant enzymes, non-enzymatic substances