Allelopathic effects of salicylic acid on activities of antioxidant enzymes of different allelopathic Chinese fir clones

Autotoxicity is one of the main reasons for land degradation and productivity decline in continuous-planting Chinese fir plantations, and salicylic acid (SA) is one of the Chinese fir autotoxins. In this study, the autotoxins-tolerant clone (No. 01) and autotoxins-sensitive clone (No. 02) of Chinese fir were used as the materials in the stress experiment. The allelopathic effects of SA on antioxidant enzymes of the two Chinese fir clones were analyzed to provide the biological strategies to solve the continuous-planting obstacle in pure Chinese fir forest. The results show that all SA levels promote SOD activity of two clones leaves at 10 d and 20 d, but inhibit it at 30 d. The differences of SA allelopathic effects on SOD activity between two clones become obvious from 20 d after stress. Improving effect of SA at the 20th day on No. 01 is more significant, and inhibiting effect at the 30th day is less significant than those on No. 02. All SA levels promote POD and AsA-POD activities of two clones leaves throughout the whole stress period. Stimulatory effect of SA on POD activity of No. 01 clone is greater than that of No. 02 clone at 10th and 20th days of stress. AsA-POD activity of No. 01 increases rapidly after SA stress and keeps higher after long time stress than that of No. 02. PPO activity of No. 01 clone is increased by all SA levels during the stress period, while that of No. 02 clone is decreased, then increased, and decreased finally with stress time.