Effects of Exogenous Phthalic Acid on Seed Germination, Root Physiological Characteristics, and Mineral Element Absorption of Watermelon

To understand the effect of exogenous PA on the watermelon root system, the watermelon variety ‘Zaojia 84–24’ was used as experimental material. This study investigated the effects of allelochemicals DIBP and DOP at varying different concentrations (0, 0.05, 0.1, 0.5, 1, and 4 mmol·L−1) on the physiological characteristics and mineral content of watermelon roots. The results revealed that proper PA treatment concentrations (0.05~0.1 mmol·L−1) promoted seed germination, increased the number of RBCs and the survival rate of RBCs, and enhanced the activities of PME and dehydrogenase in watermelon roots. In addition, proper PA treatment concentrations (0.05~0.1 mmol·L−1) promoted the activities of SOD, POD, CAT, and NR in watermelon roots. The contents of MDA and soluble protein were increased at 0.05~4 mmol·L−1 PA. In addition, proper PA treatment concentrations promoted the absorption and accumulation of P, K, Ca, Fe, Cu, and Zn elements in watermelon roots. These results indicate that PA at a concentration of 0.05~0.5 mmol·L−1 can promote watermelon seed germination, improve antioxidant enzyme activity of watermelon roots, and maintain normal physiological activities of watermelon by affecting absorption and accumulation of mineral elements in the root system.