Antagonistic and synergistic effects of main phenolic compounds present in continuously cropped sick cotton soil on its own seeds germination, seedling growth and antioxidant enzyme activities

Effects of 3-main phenolic compounds [p-hydroxybenzoic acid (p-HA, 22.5 mg/L), ferulic acid (FA, 6.6 mg/L) and vanillin (VA, 8.4 mg/L)], present in continuously cropped sick cotton soil and their combinations were studied on cotton seed germination and seedlings growth, root activity and antioxidant enzyme activities. Results showed that p-HA, VA, FA, p-HA+FA and VA+FA treatments stimulated the germination of cotton seeds. While the treatments VA, p-HA+VA, VA+FA and p-HA+VA+FA inhibited the seedlings growth. All phenolic compounds combinations inhibited the root activity of cotton seedlings. The VA, FA, p-HA+FA and VA+FA treatments reduced the malondialdehyde content. The superoxide dismutase activity was inhibited by p-HA, VA, VA+FA, p-HA+VA+FA, catalase activity was inhibited by VA, FA, VA+FA, p-HA+VA+FA and the peroxidase activity was stimulated by FA and p-HA+VA+FA. There were antagonistic effects between p-HA and VA on the cotton seeds germination. The antagonistic effects between p-HA and VA. However, there were significant synergistic effects between VA and FA.