The Effects of Two Organic acids on physiology of Saraca dives Seedlings under Cadmium Stresses

To investigate the effects of exogenous organic acids (citric acid and malic acid) on the photosynthetic physiology of Saraca dives seedlings under different cadmium stresses, a two-factor completely randomized block design was used to set up five cadmium levels and three organic acids to analyze the physiological characteristics of S. seedlings under different treatments, using six-month-old S. seedlings as test materials. The results showed that different cadmium concentrations and organic acid treatments had significant effects on the photosynthetic and physiological indexes of S. seedlings. Cadmium stress significantly reduced the Chl a/b ratio, which tended to increase and then decrease when the cadmium concentration was higher than 50 mg/kg, and then increased with the addition of organic acids, Cadmium stress significantly reduced the Chl a/b ratio, which tended to increase and then decrease at cadmium concentrations higher than 50 mg/kg, and the Chl a/b ratio was elevated by the addition of organic acids, with the minimum values(Cd₁₅₀CA₄ and Cd₂₀₀MA₄ treatment groups) under citric and malic acid treatments increasing by 13.36 and 1.64%, respectively, compared with the same level of cadmium stressl; P_n, G_s, and T_r decreased with the increase of cadmium concentration, and the addition of organic acids significantly increased Pn, Gs, and Tr; Ci in each treatment group showed a first decrease and then an increase with the enhancement of Cd stress, and reached a peak at the Cd₂₀₀ level.; SS and SP content under Cd stress showed first increase and then decrease, in the Cd₅₀ treatment group all reached the peak, organic acid treatment significantly enhanced SS, and SP content, and the malic acid treatment effect is not as good as citric acid; Pro content increased with cadmium concentration, citric acid treatment in the Cd₁₀₀ when the maximum increase; cadmium stress to enhance the content of MDA, the imposition of organic acid was significantly reduced;The activities of SOD, POD and APX enzymes increased under Cd stress, and their activities were further enhanced by the application of organic acids, especially in the citric acid treatment group; in the analysis of the affiliation function, the Cd₁₀₀CA₄ treatment group had the best overall performance, followed by Cd₅₀CA₄.Therefore, in the Cd-contaminated environment, both organic acids were able to improve the photosynthetic physiological characteristics and stress tolerance of S. seedlings, and citric acid was more effective than malic acid.